What is Cryptography? Definition, Importance, Types | Fortinet
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What Is Cryptography?
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Cryptography Definition
Cryptography is the process of hiding or coding information so that only the person a message was intended for can read it. The art of cryptography has been used to code messages for thousands of years and continues to be used in bank cards, computer passwords, and ecommerce.
Modern cryptography techniques include algorithms and ciphers that enable the encryption and decryption of information, such as 128-bit and 256-bit encryption keys. Modern ciphers, such as the Advanced Encryption Standard (AES), are considered virtually unbreakable.
A common cryptography definition is the practice of coding information to ensure only the person that a message was written for can read and process the information. This cybersecurity practice, also known as cryptology, combines various disciplines like computer science, engineering, and mathematics to create complex codes that hide the true meaning of a message.
Cryptography can be traced all the way back to ancient Egyptian hieroglyphics but remains vital to securing communication and information in transit and preventing it from being read by untrusted parties. It uses algorithms and mathematical concepts to transform messages into difficult-to-decipher codes through techniques like cryptographic keys and digital signing to protect data privacy, credit card transactions, email, and web browsing.
The Importance of Cryptography
Cryptography remains important to protecting data and users, ensuring confidentiality, and preventing cyber criminals from intercepting sensitive corporate information. Common uses and examples of cryptography include the following:
Privacy and Confidentiality
Individuals and organizations use cryptography on a daily basis to protect their privacy and keep their conversations and data confidential. Cryptography ensures confidentiality by encrypting sent messages using an algorithm with a key only known to the sender and recipient. A common example of this is the messaging tool WhatsApp, which encrypts conversations between people to ensure they cannot be hacked or intercepted.
Cryptography also secures browsing, such as with virtual private networks (VPNs), which use encrypted tunnels, asymmetric encryption, and public and private shared keys.
Authentication
Integrity
Similar to how cryptography can confirm the authenticity of a message, it can also prove the integrity of the information being sent and received. Cryptography ensures information is not altered while in storage or during transit between the sender and the intended recipient. For example, digital signatures can detect forgery or tampering in software distribution and financial transactions.
Nonrepudiation
Cryptography confirms accountability and responsibility from the sender of a message, which means they cannot later deny their intentions when they created or transmitted information. Digital signatures are a good example of this, as they ensure a sender cannot claim a message, contract, or document they created to be fraudulent. Furthermore, in email nonrepudiation, email tracking makes sure the sender cannot deny sending a message and a recipient cannot deny receiving it.
Key Exchange
Key exchange is the method used to share cryptographic keys between a sender and their recipient.
Types of Cryptographic Algorithms
There are many types of cryptographic algorithms available. They vary in complexity and security, depending on the type of communication and the sensitivity of the information being shared.
Secret Key Cryptography
Secret key cryptography, also known as symmetric encryption, uses a single key to encrypt and decrypt a message. The sender encrypts the plaintext message using the key and sends it to the recipient who then uses the same key to decrypt it and unlock the original plaintext message.
Stream Ciphers
Stream ciphers work on a single bit or byte at any time and constantly change the key using feedback mechanisms. A self-synchronizing stream cipher ensures the decryption process stays in sync with the encryption process by recognizing where it sits in the bit keystream. A synchronous stream cipher generates the keystream independently of the message stream and generates the same keystream function at both the sender and the receiver.
Block Ciphers
Block ciphers encrypt one block of fixed-size data at a time. It will always encrypt a plaintext data block to the same ciphertext when the same key is used. A good example of this is the Feistel cipher, which uses elements of key expansion, permutation, and substitution to create vast confusion and diffusion in the cipher.
The stages of encryption and decryption are similar if not identical, which means reversing the key reduces the code size and circuitry required for implementing the cipher in a piece of software or hardware.
Public Key Cryptography
Public key cryptography (PKC), or asymmetric cryptography, uses mathematical functions to create codes that are exceptionally difficult to crack. It enables people to communicate securely over a nonsecure communications channel without the need for a secret key. For example, proxy reencryption enables a proxy entity to reencrypt data from one public key to another without requiring access to the plaintext or private keys.
A common PKC type is multiplication vs. factorization, which takes two large prime numbers and multiplies them to create a huge resulting number that makes deciphering difficult. Another form of PKC is exponentiation vs. logarithms such as 256-bit encryption, which increases protection to the point that even a computer capable of searching trillions of combinations per second cannot crack it.
Generic forms of PKC use two keys that are related mathematically but do not enable either to be determined. Put simply, a sender can encrypt their plaintext message using their private key, then the recipient decrypts the ciphertext using the sender’s public key.
Common PKC algorithms used for digital signatures and key exchanges include:
RSA
RSA was the first and remains the most common PKC implementation. The algorithm is named after its MIT mathematician developers, Ronald Rivest, Adi Shamir, and Leonard Adleman, and is used in data encryption, digital signatures, and key exchanges. It uses a large number that is the result of factoring two selected prime numbers. It is impossible for an attacker to work out the prime factors, which makes RSA especially secure.
Elliptic Curve Cryptography (ECC)
ECC is a PKC algorithm based on the use of elliptic curves in cryptography. It is designed for devices with limited computing power or memory to encrypt internet traffic. A common use of ECC is in embedded computers, smartphones, and cryptocurrency networks like bitcoin, which consumes around 10% of the storage space and bandwidth that RSA requires.
Digital Signature Algorithm (DSA)
DSA is a standard that enables digital signatures to be used in message authentication. It was introduced by the National Institute of Standards and Technology (NIST) in 1991 to ensure a better method for creating digital signatures.
Identity-based Encryption (IBE)
IBE is a PKC system that enables the public key to be calculated from unique information based on the user’s identity, such as their email address. A trusted third party or private key generator then uses a cryptographic algorithm to calculate a corresponding private key. This enables users to create their own private keys without worrying about distributing public keys.
Public Key Cryptography Standards (PKCS)
All PKC algorithms and usage are governed by a set of standards and guidelines designed by RSA Data Security. These are as follows:
PKCS #1 or RFC 8017: RSA Cryptography Standard
PKCS #3: Diffie-Hellman Key Agreement Standard
PKCS #5 and PKCS #5 v2.1 or RFC 8018: Password-Based Cryptography Standard
PKCS #6: Extended-Certificate Syntax Standard (being replaced by X.509v3)
PKCS #7 or RFC 2315: Cryptographic Message Syntax Standard
PKCS #8 or RFC 5958: Private Key Information Syntax Standard
PKCS #9 or RFC 2985: Selected Attribute Types
PKCS #10 or RFC 2986: Certification Request Syntax Standard
PKCS #11: Cryptographic Token Interface Standard
PKCS #12 or RFC 7292: Personal Information Exchange Syntax Standard
PKCS #13: Elliptic Curve Cryptography Standard
PKCS #14: Pseudorandom Number Generation Standard
PKCS #15: Cryptographic Token Information Format Standard
Diffie-Hellman and Key Exchange Algorithm (KEA)
The Diffie-Hellman algorithm was devised in 1976 by Stanford University professor Martin Hellman and his graduate student Whitfield Diffie, who are considered to be responsible for introducing PKC as a concept. It is used for secret key exchanges and requires two people to agree on a large prime number.
KEA is a variation of the Diffie-Hellman algorithm and was proposed as a method for key exchange in the NIST/National Security Agency’s (NSA) Capstone project, which developed cryptography standards for public and government use.
Hash Function
Hash functions ensure that data integrity is maintained in the encryption and decryption phases of cryptography. It is also used in databases so that items can be retrieved more quickly.
Hashing is the process of taking a key and mapping it to a specific value, which is the hash or hash value. A hash function transforms a key or digital signature, then the hash value and signature are sent to the receiver, who uses the hash function to generate the hash value and compare it with the one they received in the message.
A common hash function is folding, which takes a value and divides it into several parts, adds parts, and uses the last four remaining digits as the key or hashed value. Another is digit rearrangement, which takes specific digits in the original value, reverses them, and uses the remaining number as the hash value. Examples of hash function types include Secure Hash Algorithm 1 (SHA-1), SHA-2, and SHA-3.
What Are Cryptographic Key Attacks? What Are the Types?
Modern cryptographic key techniques are increasingly advanced and often even considered unbreakable. However, as more entities rely on cryptography to protect communications and data, it is vital to keep keys secure. One compromised key could result in regulatory action, fines and punishments, reputational damage, and the loss of customers and investors.
Potential key-based issues and attack types that could occur include:
Weak Keys
Keys are essentially random numbers that become more difficult to crack the longer the number is. Key strength and length need to be relative to the value of the data it protects and the length of time that data needs to be protected. Keys should be created with a high-quality, certified random number generator that collects entropy—the information density of a file in bits or characters—from suitable hardware noise sources.
Incorrect Use of Keys
When keys are used improperly or encoded poorly, it becomes easier for a hacker to crack what should have been a highly secure key.
Reuse of Keys
Every key should only be generated for a specific single-use encrypt/decrypt purpose, and use beyond that may not offer the level of protection required.
Non-rotation of Keys
Keys that are overused, such as encrypting too much data on a key, become vulnerable to attacks. This is particularly the case with older ciphers and could result in data being exposed. Keys need to be rotated, renewed, and updated when appropriate.
Inappropriate Storage of Keys
Storing keys alongside the information they have been created to protect increases their chances of being compromised. For example, keys stored on a database or server that gets breached could also be compromised when the data is exfiltrated.
Inadequate Protection of Keys
Huge cyberattacks like Meltdown/Spectre and Heartbleed have been capable of exposing cryptographic keys stored in server memory. Therefore, stored keys must be encrypted and only made available unencrypted when placed within secure, tamper-protected environments, or even kept offline.
Insecure Movement of Keys
Moving keys between systems should only occur when the key is encrypted or wrapped under an asymmetric or symmetric pre-shared transport key. If this is not possible, then the key must be split up into multiple parts that are kept separate, re-entered into the target system, then destroyed.
Insider Threats (User Authentication, Dual Control, and Segregation of Roles)
Insider threats are one of the most serious threats posed to any key. This is most likely to occur through a rogue employee having access to a key, then using it for malicious purposes or giving or selling it to a hacker or third party.
Lack of Resilience
Resilience is vital to protecting the availability, confidentiality, and integrity of keys. Any key that suffers a fault with no backup results in the data the key protects being lost or inaccessible.
Lack of Audit Logging
Key life cycles must be logged and recorded in full to ensure any compromise can be tracked and enable subsequent investigations to occur smoothly.
Manual Key Management Processes
Recording key management processes manually on paper or spreadsheets runs the risk of human error and makes the keys highly vulnerable to attack or theft.
How to Minimize the Risks Associated with Cryptography
Organizations and individuals can minimize and mitigate cryptography-related threats with a dedicated electronic key management system from a reputable provider. The solution must use a hardware security module to generate and protect keys, and underpin the entire system’s security.
It needs to include features like full key management life cycle, strong key generation, strict policy-based controls, swift compromise detection, secure key destruction, strong user authentication, secure workflow management, and a secure audit and usage log. This will protect the organization's keys, enhance efficiency, and ensure compliance with data and privacy regulations.
Another potential solution is cryptography quantum, whereby it is impossible to copy data encoded in a quantum state.
Frequently Asked Questions about Cryptography
What do you mean by cryptography?
In computer science, cryptography is the collection of secure information and communication techniques employing mathematical concepts and algorithms used to disguise the content of messages.
What are the three types of cryptography?
The three types of cryptography are:
Secret key cryptography
Public key cryptography
Hash function cryptography
What is an example of cryptography?
The Rivest-Shamir-Adleman (RSA) algorithm is widely used on the Internet. RSA uses a pair of keys to encrypt and decrypt information.
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Cryptography - Wikipedia
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1Terminology
2History
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2.1Classic cryptography
2.2Early computer-era cryptography
2.3Modern cryptography
3Modern cryptography
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3.1Symmetric-key cryptography
3.2Public-key cryptography
3.3Cryptographic hash functions
3.4Cryptanalysis
3.5Cryptographic primitives
3.6Cryptosystems
3.7Lightweight cryptography
4Applications
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4.1Cybersecurity
4.2Cryptocurrencies and cryptoeconomics
5Legal issues
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5.1Prohibitions
5.2Export controls
5.3NSA involvement
5.4Digital rights management
5.5Forced disclosure of encryption keys
6See also
7References
8Further reading
9External links
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Cryptography
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From Wikipedia, the free encyclopedia
This is the latest accepted revision, reviewed on 9 March 2024.
Practice and study of secure communication techniques
"Secret code" redirects here. For the Aya Kamiki album, see Secret Code.
"Cryptology" redirects here. For the David S. Ware album, see Cryptology (album).
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Lorenz cipher machine, used in World War II to encrypt communications of the German High Command
Cryptography, or cryptology (from Ancient Greek: κρυπτός, romanized: kryptós "hidden, secret"; and γράφειν graphein, "to write", or -λογία -logia, "study", respectively[1]), is the practice and study of techniques for secure communication in the presence of adversarial behavior.[2] More generally, cryptography is about constructing and analyzing protocols that prevent third parties or the public from reading private messages.[3] Modern cryptography exists at the intersection of the disciplines of mathematics, computer science, information security, electrical engineering, digital signal processing, physics, and others.[4] Core concepts related to information security (data confidentiality, data integrity, authentication, and non-repudiation) are also central to cryptography.[5] Practical applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.
Cryptography prior to the modern age was effectively synonymous with encryption, converting readable information (plaintext) to unintelligible nonsense text (ciphertext), which can only be read by reversing the process (decryption). The sender of an encrypted (coded) message shares the decryption (decoding) technique only with the intended recipients to preclude access from adversaries. The cryptography literature often uses the names "Alice" (or "A") for the sender, "Bob" (or "B") for the intended recipient, and "Eve" (or "E") for the eavesdropping adversary.[6] Since the development of rotor cipher machines in World War I and the advent of computers in World War II, cryptography methods have become increasingly complex and their applications more varied.
Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic algorithms are designed around computational hardness assumptions, making such algorithms hard to break in actual practice by any adversary. While it is theoretically possible to break into a well-designed system, it is infeasible in actual practice to do so. Such schemes, if well designed, are therefore termed "computationally secure". Theoretical advances (e.g., improvements in integer factorization algorithms) and faster computing technology require these designs to be continually reevaluated and, if necessary, adapted. Information-theoretically secure schemes that provably cannot be broken even with unlimited computing power, such as the one-time pad, are much more difficult to use in practice than the best theoretically breakable but computationally secure schemes.
The growth of cryptographic technology has raised a number of legal issues in the Information Age. Cryptography's potential for use as a tool for espionage and sedition has led many governments to classify it as a weapon and to limit or even prohibit its use and export.[7] In some jurisdictions where the use of cryptography is legal, laws permit investigators to compel the disclosure of encryption keys for documents relevant to an investigation.[8][9] Cryptography also plays a major role in digital rights management and copyright infringement disputes with regard to digital media.[10]
Terminology[edit]
Alphabet shift ciphers are believed to have been used by Julius Caesar over 2,000 years ago.[6] This is an example with k = 3. In other words, the letters in the alphabet are shifted three in one direction to encrypt and three in the other direction to decrypt.
The first use of the term "cryptograph" (as opposed to "cryptogram") dates back to the 19th century—originating from "The Gold-Bug", a story by Edgar Allan Poe.[11][12]
Until modern times, cryptography referred almost exclusively to "encryption", which is the process of converting ordinary information (called plaintext) into an unintelligible form (called ciphertext).[13] Decryption is the reverse, in other words, moving from the unintelligible ciphertext back to plaintext. A cipher (or cypher) is a pair of algorithms that carry out the encryption and the reversing decryption. The detailed operation of a cipher is controlled both by the algorithm and, in each instance, by a "key". The key is a secret (ideally known only to the communicants), usually a string of characters (ideally short so it can be remembered by the user), which is needed to decrypt the ciphertext. In formal mathematical terms, a "cryptosystem" is the ordered list of elements of finite possible plaintexts, finite possible cyphertexts, finite possible keys, and the encryption and decryption algorithms that correspond to each key. Keys are important both formally and in actual practice, as ciphers without variable keys can be trivially broken with only the knowledge of the cipher used and are therefore useless (or even counter-productive) for most purposes. Historically, ciphers were often used directly for encryption or decryption without additional procedures such as authentication or integrity checks.
There are two main types of cryptosystems: symmetric and asymmetric. In symmetric systems, the only ones known until the 1970s, the same secret key encrypts and decrypts a message. Data manipulation in symmetric systems is significantly faster than in asymmetric systems. Asymmetric systems use a "public key" to encrypt a message and a related "private key" to decrypt it. The advantage of asymmetric systems is that the public key can be freely published, allowing parties to establish secure communication without having a shared secret key. In practice, asymmetric systems are used to first exchange a secret key, and then secure communication proceeds via a more efficient symmetric system using that key.[14] Examples of asymmetric systems include Diffie–Hellman key exchange, RSA (Rivest–Shamir–Adleman), ECC (Elliptic Curve Cryptography), and Post-quantum cryptography. Secure symmetric algorithms include the commonly used AES (Advanced Encryption Standard) which replaced the older DES (Data Encryption Standard).[15] Insecure symmetric algorithms include children's language tangling schemes such as Pig Latin or other cant, and all historical cryptographic schemes, however seriously intended, prior to the invention of the one-time pad early in the 20th century.
In colloquial use, the term "code" is often used to mean any method of encryption or concealment of meaning. However, in cryptography, code has a more specific meaning: the replacement of a unit of plaintext (i.e., a meaningful word or phrase) with a code word (for example, "wallaby" replaces "attack at dawn"). A cypher, in contrast, is a scheme for changing or substituting an element below such a level (a letter, a syllable, or a pair of letters, etc.) in order to produce a cyphertext.
Cryptanalysis is the term used for the study of methods for obtaining the meaning of encrypted information without access to the key normally required to do so; i.e., it is the study of how to "crack" encryption algorithms or their implementations.
Some use the terms "cryptography" and "cryptology" interchangeably in English,[16] while others (including US military practice generally) use "cryptography" to refer specifically to the use and practice of cryptographic techniques and "cryptology" to refer to the combined study of cryptography and cryptanalysis.[17][18] English is more flexible than several other languages in which "cryptology" (done by cryptologists) is always used in the second sense above. RFC 2828 advises that steganography is sometimes included in cryptology.[19]
The study of characteristics of languages that have some application in cryptography or cryptology (e.g. frequency data, letter combinations, universal patterns, etc.) is called cryptolinguistics. Cryptolingusitics is especially used in military intelligence applications for deciphering foreign communications.[20][21]
History[edit]
Main article: History of cryptography
Before the modern era, cryptography focused on message confidentiality (i.e., encryption)—conversion of messages from a comprehensible form into an incomprehensible one and back again at the other end, rendering it unreadable by interceptors or eavesdroppers without secret knowledge (namely the key needed for decryption of that message). Encryption attempted to ensure secrecy in communications, such as those of spies, military leaders, and diplomats. In recent decades, the field has expanded beyond confidentiality concerns to include techniques for message integrity checking, sender/receiver identity authentication, digital signatures, interactive proofs and secure computation, among others.
Classic cryptography[edit]
Reconstructed ancient Greek scytale, an early cipher device
The main classical cipher types are transposition ciphers, which rearrange the order of letters in a message (e.g., 'hello world' becomes 'ehlol owrdl' in a trivially simple rearrangement scheme), and substitution ciphers, which systematically replace letters or groups of letters with other letters or groups of letters (e.g., 'fly at once' becomes 'gmz bu podf' by replacing each letter with the one following it in the Latin alphabet).[22] Simple versions of either have never offered much confidentiality from enterprising opponents. An early substitution cipher was the Caesar cipher, in which each letter in the plaintext was replaced by a letter some fixed number of positions further down the alphabet. Suetonius reports that Julius Caesar used it with a shift of three to communicate with his generals. Atbash is an example of an early Hebrew cipher. The earliest known use of cryptography is some carved ciphertext on stone in Egypt (c. 1900 BCE), but this may have been done for the amusement of literate observers rather than as a way of concealing information.
The Greeks of Classical times are said to have known of ciphers (e.g., the scytale transposition cipher claimed to have been used by the Spartan military).[23] Steganography (i.e., hiding even the existence of a message so as to keep it confidential) was also first developed in ancient times. An early example, from Herodotus, was a message tattooed on a slave's shaved head and concealed under the regrown hair.[13] Other steganography methods involve 'hiding in plain sight,' such as using a music cipher to disguise an encrypted message within a regular piece of sheet music. More modern examples of steganography include the use of invisible ink, microdots, and digital watermarks to conceal information.
In India, the 2000-year-old Kamasutra of Vātsyāyana speaks of two different kinds of ciphers called Kautiliyam and Mulavediya. In the Kautiliyam, the cipher letter substitutions are based on phonetic relations, such as vowels becoming consonants. In the Mulavediya, the cipher alphabet consists of pairing letters and using the reciprocal ones.[13]
In Sassanid Persia, there were two secret scripts, according to the Muslim author Ibn al-Nadim: the šāh-dabīrīya (literally "King's script") which was used for official correspondence, and the rāz-saharīya which was used to communicate secret messages with other countries.[24]
David Kahn notes in The Codebreakers that modern cryptology originated among the Arabs, the first people to systematically document cryptanalytic methods.[25] Al-Khalil (717–786) wrote the Book of Cryptographic Messages, which contains the first use of permutations and combinations to list all possible Arabic words with and without vowels.[26]
First page of a book by Al-Kindi which discusses encryption of messages
Ciphertexts produced by a classical cipher (and some modern ciphers) will reveal statistical information about the plaintext, and that information can often be used to break the cipher. After the discovery of frequency analysis, perhaps by the Arab mathematician and polymath Al-Kindi (also known as Alkindus) in the 9th century,[27] nearly all such ciphers could be broken by an informed attacker. Such classical ciphers still enjoy popularity today, though mostly as puzzles (see cryptogram). Al-Kindi wrote a book on cryptography entitled Risalah fi Istikhraj al-Mu'amma (Manuscript for the Deciphering Cryptographic Messages), which described the first known use of frequency analysis cryptanalysis techniques.[27][28]
16th-century book-shaped French cipher machine, with arms of Henri II of France
Enciphered letter from Gabriel de Luetz d'Aramon, French Ambassador to the Ottoman Empire, after 1546, with partial decipherment
Language letter frequencies may offer little help for some extended historical encryption techniques such as homophonic cipher that tend to flatten the frequency distribution. For those ciphers, language letter group (or n-gram) frequencies may provide an attack.
Essentially all ciphers remained vulnerable to cryptanalysis using the frequency analysis technique until the development of the polyalphabetic cipher, most clearly by Leon Battista Alberti around the year 1467, though there is some indication that it was already known to Al-Kindi.[28] Alberti's innovation was to use different ciphers (i.e., substitution alphabets) for various parts of a message (perhaps for each successive plaintext letter at the limit). He also invented what was probably the first automatic cipher device, a wheel that implemented a partial realization of his invention. In the Vigenère cipher, a polyalphabetic cipher, encryption uses a key word, which controls letter substitution depending on which letter of the key word is used. In the mid-19th century Charles Babbage showed that the Vigenère cipher was vulnerable to Kasiski examination, but this was first published about ten years later by Friedrich Kasiski.[29]
Although frequency analysis can be a powerful and general technique against many ciphers, encryption has still often been effective in practice, as many a would-be cryptanalyst was unaware of the technique. Breaking a message without using frequency analysis essentially required knowledge of the cipher used and perhaps of the key involved, thus making espionage, bribery, burglary, defection, etc., more attractive approaches to the cryptanalytically uninformed. It was finally explicitly recognized in the 19th century that secrecy of a cipher's algorithm is not a sensible nor practical safeguard of message security; in fact, it was further realized that any adequate cryptographic scheme (including ciphers) should remain secure even if the adversary fully understands the cipher algorithm itself. Security of the key used should alone be sufficient for a good cipher to maintain confidentiality under an attack. This fundamental principle was first explicitly stated in 1883 by Auguste Kerckhoffs and is generally called Kerckhoffs's Principle; alternatively and more bluntly, it was restated by Claude Shannon, the inventor of information theory and the fundamentals of theoretical cryptography, as Shannon's Maxim—'the enemy knows the system'.
Different physical devices and aids have been used to assist with ciphers. One of the earliest may have been the scytale of ancient Greece, a rod supposedly used by the Spartans as an aid for a transposition cipher. In medieval times, other aids were invented such as the cipher grille, which was also used for a kind of steganography. With the invention of polyalphabetic ciphers came more sophisticated aids such as Alberti's own cipher disk, Johannes Trithemius' tabula recta scheme, and Thomas Jefferson's wheel cypher (not publicly known, and reinvented independently by Bazeries around 1900). Many mechanical encryption/decryption devices were invented early in the 20th century, and several patented, among them rotor machines—famously including the Enigma machine used by the German government and military from the late 1920s and during World War II.[30] The ciphers implemented by better quality examples of these machine designs brought about a substantial increase in cryptanalytic difficulty after WWI.[31]
Early computer-era cryptography[edit]
Cryptanalysis of the new mechanical ciphering devices proved to be both difficult and laborious. In the United Kingdom, cryptanalytic efforts at Bletchley Park during WWII spurred the development of more efficient means for carrying out repetitive tasks, such as military code breaking (decryption). This culminated in the development of the Colossus, the world's first fully electronic, digital, programmable computer, which assisted in the decryption of ciphers generated by the German Army's Lorenz SZ40/42 machine.
Extensive open academic research into cryptography is relatively recent, beginning in the mid-1970s. In the early 1970s IBM personnel designed the Data Encryption Standard (DES) algorithm that became the first federal government cryptography standard in the United States.[32] In 1976 Whitfield Diffie and Martin Hellman published the Diffie–Hellman key exchange algorithm.[33] In 1977 the RSA algorithm was published in Martin Gardner's Scientific American column.[34] Since then, cryptography has become a widely used tool in communications, computer networks, and computer security generally.
Some modern cryptographic techniques can only keep their keys secret if certain mathematical problems are intractable, such as the integer factorization or the discrete logarithm problems, so there are deep connections with abstract mathematics. There are very few cryptosystems that are proven to be unconditionally secure. The one-time pad is one, and was proven to be so by Claude Shannon. There are a few important algorithms that have been proven secure under certain assumptions. For example, the infeasibility of factoring extremely large integers is the basis for believing that RSA is secure, and some other systems, but even so, proof of unbreakability is unavailable since the underlying mathematical problem remains open. In practice, these are widely used, and are believed unbreakable in practice by most competent observers. There are systems similar to RSA, such as one by Michael O. Rabin that are provably secure provided factoring n = pq is impossible; it is quite unusable in practice. The discrete logarithm problem is the basis for believing some other cryptosystems are secure, and again, there are related, less practical systems that are provably secure relative to the solvability or insolvability discrete log problem.[35]
As well as being aware of cryptographic history, cryptographic algorithm and system designers must also sensibly consider probable future developments while working on their designs. For instance, continuous improvements in computer processing power have increased the scope of brute-force attacks, so when specifying key lengths, the required key lengths are similarly advancing.[36] The potential impact of quantum computing are already being considered by some cryptographic system designers developing post-quantum cryptography.[when?] The announced imminence of small implementations of these machines may be making the need for preemptive caution rather more than merely speculative.[5]
Modern cryptography[edit]
Prior to the early 20th century, cryptography was mainly concerned with linguistic and lexicographic patterns. Since then cryptography has broadened in scope, and now makes extensive use of mathematical subdisciplines, including information theory, computational complexity, statistics, combinatorics, abstract algebra, number theory, and finite mathematics.[37] Cryptography is also a branch of engineering, but an unusual one since it deals with active, intelligent, and malevolent opposition; other kinds of engineering (e.g., civil or chemical engineering) need deal only with neutral natural forces. There is also active research examining the relationship between cryptographic problems and quantum physics.
Just as the development of digital computers and electronics helped in cryptanalysis, it made possible much more complex ciphers. Furthermore, computers allowed for the encryption of any kind of data representable in any binary format, unlike classical ciphers which only encrypted written language texts; this was new and significant. Computer use has thus supplanted linguistic cryptography, both for cipher design and cryptanalysis. Many computer ciphers can be characterized by their operation on binary bit sequences (sometimes in groups or blocks), unlike classical and mechanical schemes, which generally manipulate traditional characters (i.e., letters and digits) directly. However, computers have also assisted cryptanalysis, which has compensated to some extent for increased cipher complexity. Nonetheless, good modern ciphers have stayed ahead of cryptanalysis; it is typically the case that use of a quality cipher is very efficient (i.e., fast and requiring few resources, such as memory or CPU capability), while breaking it requires an effort many orders of magnitude larger, and vastly larger than that required for any classical cipher, making cryptanalysis so inefficient and impractical as to be effectively impossible.
Modern cryptography[edit]
Symmetric-key cryptography[edit]
Main article: Symmetric-key algorithm
Symmetric-key cryptography, where a single key is used for encryption and decryption
Symmetric-key cryptography refers to encryption methods in which both the sender and receiver share the same key (or, less commonly, in which their keys are different, but related in an easily computable way). This was the only kind of encryption publicly known until June 1976.[33]
One round (out of 8.5) of the IDEA cipher, used in most versions of PGP and OpenPGP compatible software for time-efficient encryption of messages
Symmetric key ciphers are implemented as either block ciphers or stream ciphers. A block cipher enciphers input in blocks of plaintext as opposed to individual characters, the input form used by a stream cipher.
The Data Encryption Standard (DES) and the Advanced Encryption Standard (AES) are block cipher designs that have been designated cryptography standards by the US government (though DES's designation was finally withdrawn after the AES was adopted).[38] Despite its deprecation as an official standard, DES (especially its still-approved and much more secure triple-DES variant) remains quite popular; it is used across a wide range of applications, from ATM encryption[39] to e-mail privacy[40] and secure remote access.[41] Many other block ciphers have been designed and released, with considerable variation in quality. Many, even some designed by capable practitioners, have been thoroughly broken, such as FEAL.[5][42]
Stream ciphers, in contrast to the 'block' type, create an arbitrarily long stream of key material, which is combined with the plaintext bit-by-bit or character-by-character, somewhat like the one-time pad. In a stream cipher, the output stream is created based on a hidden internal state that changes as the cipher operates. That internal state is initially set up using the secret key material. RC4 is a widely used stream cipher.[5] Block ciphers can be used as stream ciphers by generating blocks of a keystream (in place of a Pseudorandom number generator) and applying an XOR operation to each bit of the plaintext with each bit of the keystream.[43]
Message authentication codes (MACs) are much like cryptographic hash functions, except that a secret key can be used to authenticate the hash value upon receipt;[5][44] this additional complication blocks an attack scheme against bare digest algorithms, and so has been thought worth the effort. Cryptographic hash functions are a third type of cryptographic algorithm. They take a message of any length as input, and output a short, fixed-length hash, which can be used in (for example) a digital signature. For good hash functions, an attacker cannot find two messages that produce the same hash. MD4 is a long-used hash function that is now broken; MD5, a strengthened variant of MD4, is also widely used but broken in practice. The US National Security Agency developed the Secure Hash Algorithm series of MD5-like hash functions: SHA-0 was a flawed algorithm that the agency withdrew; SHA-1 is widely deployed and more secure than MD5, but cryptanalysts have identified attacks against it; the SHA-2 family improves on SHA-1, but is vulnerable to clashes as of 2011; and the US standards authority thought it "prudent" from a security perspective to develop a new standard to "significantly improve the robustness of NIST's overall hash algorithm toolkit."[45] Thus, a hash function design competition was meant to select a new U.S. national standard, to be called SHA-3, by 2012. The competition ended on October 2, 2012, when the NIST announced that Keccak would be the new SHA-3 hash algorithm.[46] Unlike block and stream ciphers that are invertible, cryptographic hash functions produce a hashed output that cannot be used to retrieve the original input data. Cryptographic hash functions are used to verify the authenticity of data retrieved from an untrusted source or to add a layer of security.
Public-key cryptography[edit]
Main article: Public-key cryptography
Public-key cryptography, where different keys are used for encryption and decryption.
Symmetric-key cryptosystems use the same key for encryption and decryption of a message, although a message or group of messages can have a different key than others. A significant disadvantage of symmetric ciphers is the key management necessary to use them securely. Each distinct pair of communicating parties must, ideally, share a different key, and perhaps for each ciphertext exchanged as well. The number of keys required increases as the square of the number of network members, which very quickly requires complex key management schemes to keep them all consistent and secret.
Whitfield Diffie and Martin Hellman, authors of the first published paper on public-key cryptography.
In a groundbreaking 1976 paper, Whitfield Diffie and Martin Hellman proposed the notion of public-key (also, more generally, called asymmetric key) cryptography in which two different but mathematically related keys are used—a public key and a private key.[47] A public key system is so constructed that calculation of one key (the 'private key') is computationally infeasible from the other (the 'public key'), even though they are necessarily related. Instead, both keys are generated secretly, as an interrelated pair.[48] The historian David Kahn described public-key cryptography as "the most revolutionary new concept in the field since polyalphabetic substitution emerged in the Renaissance".[49]
In public-key cryptosystems, the public key may be freely distributed, while its paired private key must remain secret. In a public-key encryption system, the public key is used for encryption, while the private or secret key is used for decryption. While Diffie and Hellman could not find such a system, they showed that public-key cryptography was indeed possible by presenting the Diffie–Hellman key exchange protocol, a solution that is now widely used in secure communications to allow two parties to secretly agree on a shared encryption key.[33]
The X.509 standard defines the most commonly used format for public key certificates.[50]
Diffie and Hellman's publication sparked widespread academic efforts in finding a practical public-key encryption system. This race was finally won in 1978 by Ronald Rivest, Adi Shamir, and Len Adleman, whose solution has since become known as the RSA algorithm.[51]
The Diffie–Hellman and RSA algorithms, in addition to being the first publicly known examples of high-quality public-key algorithms, have been among the most widely used. Other asymmetric-key algorithms include the Cramer–Shoup cryptosystem, ElGamal encryption, and various elliptic curve techniques.[citation needed]
A document published in 1997 by the Government Communications Headquarters (GCHQ), a British intelligence organization, revealed that cryptographers at GCHQ had anticipated several academic developments.[52] Reportedly, around 1970, James H. Ellis had conceived the principles of asymmetric key cryptography. In 1973, Clifford Cocks invented a solution that was very similar in design rationale to RSA.[52][53] In 1974, Malcolm J. Williamson is claimed to have developed the Diffie–Hellman key exchange.[54]
In this example the message is only signed and not encrypted. 1) Alice signs a message with her private key. 2) Bob can verify that Alice sent the message and that the message has not been modified.
Public-key cryptography is also used for implementing digital signature schemes. A digital signature is reminiscent of an ordinary signature; they both have the characteristic of being easy for a user to produce, but difficult for anyone else to forge. Digital signatures can also be permanently tied to the content of the message being signed; they cannot then be 'moved' from one document to another, for any attempt will be detectable. In digital signature schemes, there are two algorithms: one for signing, in which a secret key is used to process the message (or a hash of the message, or both), and one for verification, in which the matching public key is used with the message to check the validity of the signature. RSA and DSA are two of the most popular digital signature schemes. Digital signatures are central to the operation of public key infrastructures and many network security schemes (e.g., SSL/TLS, many VPNs, etc.).[42]
Public-key algorithms are most often based on the computational complexity of "hard" problems, often from number theory. For example, the hardness of RSA is related to the integer factorization problem, while Diffie–Hellman and DSA are related to the discrete logarithm problem. The security of elliptic curve cryptography is based on number theoretic problems involving elliptic curves. Because of the difficulty of the underlying problems, most public-key algorithms involve operations such as modular multiplication and exponentiation, which are much more computationally expensive than the techniques used in most block ciphers, especially with typical key sizes. As a result, public-key cryptosystems are commonly hybrid cryptosystems, in which a fast high-quality symmetric-key encryption algorithm is used for the message itself, while the relevant symmetric key is sent with the message, but encrypted using a public-key algorithm. Similarly, hybrid signature schemes are often used, in which a cryptographic hash function is computed, and only the resulting hash is digitally signed.[5]
Cryptographic hash functions[edit]
Cryptographic hash functions are functions that take a variable-length input and return a fixed-length output, which can be used in, for example, a digital signature. For a hash function to be secure, it must be difficult to compute two inputs that hash to the same value (collision resistance) and to compute an input that hashes to a given output (preimage resistance). MD4 is a long-used hash function that is now broken; MD5, a strengthened variant of MD4, is also widely used but broken in practice. The US National Security Agency developed the Secure Hash Algorithm series of MD5-like hash functions: SHA-0 was a flawed algorithm that the agency withdrew; SHA-1 is widely deployed and more secure than MD5, but cryptanalysts have identified attacks against it; the SHA-2 family improves on SHA-1, but is vulnerable to clashes as of 2011; and the US standards authority thought it "prudent" from a security perspective to develop a new standard to "significantly improve the robustness of NIST's overall hash algorithm toolkit."[45] Thus, a hash function design competition was meant to select a new U.S. national standard, to be called SHA-3, by 2012. The competition ended on October 2, 2012, when the NIST announced that Keccak would be the new SHA-3 hash algorithm.[46] Unlike block and stream ciphers that are invertible, cryptographic hash functions produce a hashed output that cannot be used to retrieve the original input data. Cryptographic hash functions are used to verify the authenticity of data retrieved from an untrusted source or to add a layer of security.
Cryptanalysis[edit]
Main article: Cryptanalysis
Variants of the Enigma machine, used by Germany's military and civil authorities from the late 1920s through World War II, implemented a complex electro-mechanical polyalphabetic cipher. Breaking and reading of the Enigma cipher at Poland's Cipher Bureau, for 7 years before the war, and subsequent decryption at Bletchley Park, was important to Allied victory.[13]
The goal of cryptanalysis is to find some weakness or insecurity in a cryptographic scheme, thus permitting its subversion or evasion.
It is a common misconception that every encryption method can be broken. In connection with his WWII work at Bell Labs, Claude Shannon proved that the one-time pad cipher is unbreakable, provided the key material is truly random, never reused, kept secret from all possible attackers, and of equal or greater length than the message.[55] Most ciphers, apart from the one-time pad, can be broken with enough computational effort by brute force attack, but the amount of effort needed may be exponentially dependent on the key size, as compared to the effort needed to make use of the cipher. In such cases, effective security could be achieved if it is proven that the effort required (i.e., "work factor", in Shannon's terms) is beyond the ability of any adversary. This means it must be shown that no efficient method (as opposed to the time-consuming brute force method) can be found to break the cipher. Since no such proof has been found to date, the one-time-pad remains the only theoretically unbreakable cipher. Although well-implemented one-time-pad encryption cannot be broken, traffic analysis is still possible.
There are a wide variety of cryptanalytic attacks, and they can be classified in any of several ways. A common distinction turns on what Eve (an attacker) knows and what capabilities are available. In a ciphertext-only attack, Eve has access only to the ciphertext (good modern cryptosystems are usually effectively immune to ciphertext-only attacks). In a known-plaintext attack, Eve has access to a ciphertext and its corresponding plaintext (or to many such pairs). In a chosen-plaintext attack, Eve may choose a plaintext and learn its corresponding ciphertext (perhaps many times); an example is gardening, used by the British during WWII. In a chosen-ciphertext attack, Eve may be able to choose ciphertexts and learn their corresponding plaintexts.[5] Finally in a man-in-the-middle attack Eve gets in between Alice (the sender) and Bob (the recipient), accesses and modifies the traffic and then forwards it to the recipient.[56] Also important, often overwhelmingly so, are mistakes (generally in the design or use of one of the protocols involved).
Poznań monument (center) to Polish cryptanalysts whose breaking of Germany's Enigma machine ciphers, beginning in 1932, altered the course of World War II
Cryptanalysis of symmetric-key ciphers typically involves looking for attacks against the block ciphers or stream ciphers that are more efficient than any attack that could be against a perfect cipher. For example, a simple brute force attack against DES requires one known plaintext and 255 decryptions, trying approximately half of the possible keys, to reach a point at which chances are better than even that the key sought will have been found. But this may not be enough assurance; a linear cryptanalysis attack against DES requires 243 known plaintexts (with their corresponding ciphertexts) and approximately 243 DES operations.[57] This is a considerable improvement over brute force attacks.
Public-key algorithms are based on the computational difficulty of various problems. The most famous of these are the difficulty of integer factorization of semiprimes and the difficulty of calculating discrete logarithms, both of which are not yet proven to be solvable in polynomial time (P) using only a classical Turing-complete computer. Much public-key cryptanalysis concerns designing algorithms in P that can solve these problems, or using other technologies, such as quantum computers. For instance, the best-known algorithms for solving the elliptic curve-based version of discrete logarithm are much more time-consuming than the best-known algorithms for factoring, at least for problems of more or less equivalent size. Thus, to achieve an equivalent strength of encryption, techniques that depend upon the difficulty of factoring large composite numbers, such as the RSA cryptosystem, require larger keys than elliptic curve techniques. For this reason, public-key cryptosystems based on elliptic curves have become popular since their invention in the mid-1990s.
While pure cryptanalysis uses weaknesses in the algorithms themselves, other attacks on cryptosystems are based on actual use of the algorithms in real devices, and are called side-channel attacks. If a cryptanalyst has access to, for example, the amount of time the device took to encrypt a number of plaintexts or report an error in a password or PIN character, they may be able to use a timing attack to break a cipher that is otherwise resistant to analysis. An attacker might also study the pattern and length of messages to derive valuable information; this is known as traffic analysis[58] and can be quite useful to an alert adversary. Poor administration of a cryptosystem, such as permitting too short keys, will make any system vulnerable, regardless of other virtues. Social engineering and other attacks against humans (e.g., bribery, extortion, blackmail, espionage, rubber-hose cryptanalysis or torture) are usually employed due to being more cost-effective and feasible to perform in a reasonable amount of time compared to pure cryptanalysis by a high margin.
Cryptographic primitives[edit]
Much of the theoretical work in cryptography concerns cryptographic primitives—algorithms with basic cryptographic properties—and their relationship to other cryptographic problems. More complicated cryptographic tools are then built from these basic primitives. These primitives provide fundamental properties, which are used to develop more complex tools called cryptosystems or cryptographic protocols, which guarantee one or more high-level security properties. Note, however, that the distinction between cryptographic primitives and cryptosystems, is quite arbitrary; for example, the RSA algorithm is sometimes considered a cryptosystem, and sometimes a primitive. Typical examples of cryptographic primitives include pseudorandom functions, one-way functions, etc.
Cryptosystems[edit]
Main article: List of cryptosystems
One or more cryptographic primitives are often used to develop a more complex algorithm, called a cryptographic system, or cryptosystem. Cryptosystems (e.g., El-Gamal encryption) are designed to provide particular functionality (e.g., public key encryption) while guaranteeing certain security properties (e.g., chosen-plaintext attack (CPA) security in the random oracle model). Cryptosystems use the properties of the underlying cryptographic primitives to support the system's security properties. As the distinction between primitives and cryptosystems is somewhat arbitrary, a sophisticated cryptosystem can be derived from a combination of several more primitive cryptosystems. In many cases, the cryptosystem's structure involves back and forth communication among two or more parties in space (e.g., between the sender of a secure message and its receiver) or across time (e.g., cryptographically protected backup data). Such cryptosystems are sometimes called cryptographic protocols.
Some widely known cryptosystems include RSA, Schnorr signature, ElGamal encryption, and Pretty Good Privacy (PGP). More complex cryptosystems include electronic cash[59] systems, signcryption systems, etc. Some more 'theoretical'[clarification needed] cryptosystems include interactive proof systems,[60] (like zero-knowledge proofs)[61] and systems for secret sharing,[62][63].
Lightweight cryptography[edit]
Lightweight cryptography (LWC) concerns cryptographic algorithms developed for a strictly constrained environment. The growth of Internet of Things (IoT) has spiked research into the development of lightweight algorithms that are better suited for the environment. An IoT environment requires strict constraints on power consumption, processing power, and security.[64] Algorithms such as PRESENT, AES, and SPECK are examples of the many LWC algorithms that have been developed to achieve the standard set by the National Institute of Standards and Technology.[65]
Applications[edit]
This section needs expansion. You can help by adding to it. (December 2021)
Main category: Applications of cryptography
Cryptography is widely used on the internet to help protect user-data and prevent eavesdropping. To ensure secrecy during transmission, many systems use private key cryptography to protect transmitted information. With public-key systems, one can maintain secrecy without a master key or a large number of keys.[66] But, some algorithms like Bitlocker and Veracrypt are generally not private-public key cryptography. For example, Veracrypt uses a password hash to generate the single private key. However, it can be configured to run in public-private key systems. The C++ opensource encryption library OpenSSL provides free and opensource encryption software and tools. The most commonly used encryption cipher suit is AES,[67] as it has hardware acceleration for all x86 based processors that has AES-NI. A close contender is ChaCha20-Poly1305, which is a stream cipher, however it is commonly used for mobile devices as they are ARM based which does not feature AES-NI instruction set extension.
Cybersecurity[edit]
Cryptography can be used to secure communications by encrypting them. Websites use encryption via HTTPS.[68] "End-to-end" encryption, where only sender and receiver can read messages, is implemented for email in Pretty Good Privacy and for secure messaging in general in WhatsApp, Signal and Telegram.[68]
Operating systems use encryption to keep passwords secret, conceal parts of the system, and ensure that software updates are truly from the system maker.[68] Instead of storing plaintext passwords, computer systems store hashes thereof; then, when a user logs in, the system passes the given password through a cryptographic hash function and compares it to the hashed value on file. In this manner, neither the system nor an attacker has at any point access to the password in plaintext.[68]
Encryption is sometimes used to encrypt one's entire drive. For example, University College London has implemented BitLocker (a program by Microsoft) to render drive data opaque without users logging in.[68]
Cryptocurrencies and cryptoeconomics[edit]
Cryptographic techniques enable cryptocurrency technologies, such as distributed ledger technologies (e.g., blockchains), which finance cryptoeconomics applications such as decentralized finance (DeFi). Key cryptographic techniques that enable cryptocurrencies and cryptoeconomics include, but are not limited to: cryptographic keys, cryptographic hash function, asymmetric (public key) encryption, Multi-Factor Authentication (MFA), End-to-End Encryption (E2EE), and Zero Knowledge Proofs (ZKP).
Legal issues[edit]
See also: Cryptography laws in different nations
Prohibitions[edit]
Cryptography has long been of interest to intelligence gathering and law enforcement agencies.[9] Secret communications may be criminal or even treasonous.[citation needed] Because of its facilitation of privacy, and the diminution of privacy attendant on its prohibition, cryptography is also of considerable interest to civil rights supporters. Accordingly, there has been a history of controversial legal issues surrounding cryptography, especially since the advent of inexpensive computers has made widespread access to high-quality cryptography possible.
In some countries, even the domestic use of cryptography is, or has been, restricted. Until 1999, France significantly restricted the use of cryptography domestically, though it has since relaxed many of these rules. In China and Iran, a license is still required to use cryptography.[7] Many countries have tight restrictions on the use of cryptography. Among the more restrictive are laws in Belarus, Kazakhstan, Mongolia, Pakistan, Singapore, Tunisia, and Vietnam.[69]
In the United States, cryptography is legal for domestic use, but there has been much conflict over legal issues related to cryptography.[9] One particularly important issue has been the export of cryptography and cryptographic software and hardware. Probably because of the importance of cryptanalysis in World War II and an expectation that cryptography would continue to be important for national security, many Western governments have, at some point, strictly regulated export of cryptography. After World War II, it was illegal in the US to sell or distribute encryption technology overseas; in fact, encryption was designated as auxiliary military equipment and put on the United States Munitions List.[70] Until the development of the personal computer, asymmetric key algorithms (i.e., public key techniques), and the Internet, this was not especially problematic. However, as the Internet grew and computers became more widely available, high-quality encryption techniques became well known around the globe.
Export controls[edit]
Main article: Export of cryptography
In the 1990s, there were several challenges to US export regulation of cryptography. After the source code for Philip Zimmermann's Pretty Good Privacy (PGP) encryption program found its way onto the Internet in June 1991, a complaint by RSA Security (then called RSA Data Security, Inc.) resulted in a lengthy criminal investigation of Zimmermann by the US Customs Service and the FBI, though no charges were ever filed.[71][72] Daniel J. Bernstein, then a graduate student at UC Berkeley, brought a lawsuit against the US government challenging some aspects of the restrictions based on free speech grounds. The 1995 case Bernstein v. United States ultimately resulted in a 1999 decision that printed source code for cryptographic algorithms and systems was protected as free speech by the United States Constitution.[73]
In 1996, thirty-nine countries signed the Wassenaar Arrangement, an arms control treaty that deals with the export of arms and "dual-use" technologies such as cryptography. The treaty stipulated that the use of cryptography with short key-lengths (56-bit for symmetric encryption, 512-bit for RSA) would no longer be export-controlled.[74] Cryptography exports from the US became less strictly regulated as a consequence of a major relaxation in 2000;[75] there are no longer very many restrictions on key sizes in US-exported mass-market software. Since this relaxation in US export restrictions, and because most personal computers connected to the Internet include US-sourced web browsers such as Firefox or Internet Explorer, almost every Internet user worldwide has potential access to quality cryptography via their browsers (e.g., via Transport Layer Security). The Mozilla Thunderbird and Microsoft Outlook E-mail client programs similarly can transmit and receive emails via TLS, and can send and receive email encrypted with S/MIME. Many Internet users do not realize that their basic application software contains such extensive cryptosystems. These browsers and email programs are so ubiquitous that even governments whose intent is to regulate civilian use of cryptography generally do not find it practical to do much to control distribution or use of cryptography of this quality, so even when such laws are in force, actual enforcement is often effectively impossible.[citation needed]
NSA involvement[edit]
NSA headquarters in Fort Meade, Maryland
See also: Clipper chip
Another contentious issue connected to cryptography in the United States is the influence of the National Security Agency on cipher development and policy.[9] The NSA was involved with the design of DES during its development at IBM and its consideration by the National Bureau of Standards as a possible Federal Standard for cryptography.[76] DES was designed to be resistant to differential cryptanalysis,[77] a powerful and general cryptanalytic technique known to the NSA and IBM, that became publicly known only when it was rediscovered in the late 1980s.[78] According to Steven Levy, IBM discovered differential cryptanalysis,[72] but kept the technique secret at the NSA's request. The technique became publicly known only when Biham and Shamir re-discovered and announced it some years later. The entire affair illustrates the difficulty of determining what resources and knowledge an attacker might actually have.
Another instance of the NSA's involvement was the 1993 Clipper chip affair, an encryption microchip intended to be part of the Capstone cryptography-control initiative. Clipper was widely criticized by cryptographers for two reasons. The cipher algorithm (called Skipjack) was then classified (declassified in 1998, long after the Clipper initiative lapsed). The classified cipher caused concerns that the NSA had deliberately made the cipher weak in order to assist its intelligence efforts. The whole initiative was also criticized based on its violation of Kerckhoffs's Principle, as the scheme included a special escrow key held by the government for use by law enforcement (i.e. wiretapping).[72]
Digital rights management[edit]
Main article: Digital rights management
Cryptography is central to digital rights management (DRM), a group of techniques for technologically controlling use of copyrighted material, being widely implemented and deployed at the behest of some copyright holders. In 1998, U.S. President Bill Clinton signed the Digital Millennium Copyright Act (DMCA), which criminalized all production, dissemination, and use of certain cryptanalytic techniques and technology (now known or later discovered); specifically, those that could be used to circumvent DRM technological schemes.[79] This had a noticeable impact on the cryptography research community since an argument can be made that any cryptanalytic research violated the DMCA. Similar statutes have since been enacted in several countries and regions, including the implementation in the EU Copyright Directive. Similar restrictions are called for by treaties signed by World Intellectual Property Organization member-states.
The United States Department of Justice and FBI have not enforced the DMCA as rigorously as had been feared by some, but the law, nonetheless, remains a controversial one. Niels Ferguson, a well-respected cryptography researcher, has publicly stated that he will not release some of his research into an Intel security design for fear of prosecution under the DMCA.[80] Cryptologist Bruce Schneier has argued that the DMCA encourages vendor lock-in, while inhibiting actual measures toward cyber-security.[81] Both Alan Cox (longtime Linux kernel developer) and Edward Felten (and some of his students at Princeton) have encountered problems related to the Act. Dmitry Sklyarov was arrested during a visit to the US from Russia, and jailed for five months pending trial for alleged violations of the DMCA arising from work he had done in Russia, where the work was legal. In 2007, the cryptographic keys responsible for Blu-ray and HD DVD content scrambling were discovered and released onto the Internet. In both cases, the Motion Picture Association of America sent out numerous DMCA takedown notices, and there was a massive Internet backlash[10] triggered by the perceived impact of such notices on fair use and free speech.
Forced disclosure of encryption keys[edit]
Main article: Key disclosure law
In the United Kingdom, the Regulation of Investigatory Powers Act gives UK police the powers to force suspects to decrypt files or hand over passwords that protect encryption keys. Failure to comply is an offense in its own right, punishable on conviction by a two-year jail sentence or up to five years in cases involving national security.[8] Successful prosecutions have occurred under the Act; the first, in 2009,[82] resulted in a term of 13 months' imprisonment.[83] Similar forced disclosure laws in Australia, Finland, France, and India compel individual suspects under investigation to hand over encryption keys or passwords during a criminal investigation.
In the United States, the federal criminal case of United States v. Fricosu addressed whether a search warrant can compel a person to reveal an encryption passphrase or password.[84] The Electronic Frontier Foundation (EFF) argued that this is a violation of the protection from self-incrimination given by the Fifth Amendment.[85] In 2012, the court ruled that under the All Writs Act, the defendant was required to produce an unencrypted hard drive for the court.[86]
In many jurisdictions, the legal status of forced disclosure remains unclear.
The 2016 FBI–Apple encryption dispute concerns the ability of courts in the United States to compel manufacturers' assistance in unlocking cell phones whose contents are cryptographically protected.
As a potential counter-measure to forced disclosure some cryptographic software supports plausible deniability, where the encrypted data is indistinguishable from unused random data (for example such as that of a drive which has been securely wiped).
See also[edit]
Collision attack
Comparison of cryptography libraries
Crypto Wars – Attempts to limit access to strong cryptography
Encyclopedia of Cryptography and Security – Book by Technische Universiteit Eindhoven
Global surveillance – Mass surveillance across national borders
Indistinguishability obfuscation – Type of cryptographic software obfuscation
Information theory – Scientific study of digital information
Outline of cryptography – Overview of and topical guide to cryptography
List of cryptographers
List of important publications in cryptography
List of multiple discoveries
List of unsolved problems in computer science – List of unsolved computational problems
Secure cryptoprocessor
Strong cryptography – Term applied to cryptographic systems that are highly resistant to cryptanalysis
Syllabical and Steganographical Table – Eighteenth-century work believed to be the first cryptography chart – first cryptography chart
World Wide Web Consortium's Web Cryptography API – World Wide Web Consortium cryptography standard
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^ "6.5.1 What Are the Cryptographic Policies of Some Countries?". RSA Laboratories. Archived from the original on 16 April 2015. Retrieved 26 March 2015.
^ Rosenoer, Jonathan (1995). "Cryptography & Speech". CyberLaw."Archived copy". Archived from the original on 1 December 2005. Retrieved 23 June 2006.{{cite web}}: CS1 maint: archived copy as title (link)
^ "Case Closed on Zimmermann PGP Investigation". IEEE Computer Society's Technical Committee on Security and Privacy. 14 February 1996. Archived from the original on 11 June 2010. Retrieved 26 March 2015.
^ a b c Levy, Steven (2001). Crypto: How the Code Rebels Beat the Government – Saving Privacy in the Digital Age. Penguin Books. p. 56. ISBN 978-0-14-024432-8. OCLC 244148644.
^ "Bernstein v USDOJ". Electronic Privacy Information Center. United States Court of Appeals for the Ninth Circuit. 6 May 1999. Archived from the original on 13 August 2009. Retrieved 26 March 2015.
^ "Dual-use List – Category 5 – Part 2 – "Information Security"" (PDF). Wassenaar Arrangement. Archived from the original on 26 September 2018. Retrieved 26 March 2015.
^ ".4 United States Cryptography Export/Import Laws". RSA Laboratories. Archived from the original on 31 March 2015. Retrieved 26 March 2015.
^ Schneier, Bruce (15 June 2000). "The Data Encryption Standard (DES)". Crypto-Gram. Archived from the original on 2 January 2010. Retrieved 26 March 2015.
^ Coppersmith, D. (May 1994). "The Data Encryption Standard (DES) and its strength against attacks" (PDF). IBM Journal of Research and Development. 38 (3): 243–250. doi:10.1147/rd.383.0243. Archived from the original on 4 March 2016. Retrieved 26 March 2015.
^ Biham, E.; Shamir, A. (1991). "Differential cryptanalysis of DES-like cryptosystems". Journal of Cryptology. 4 (1): 3–72. doi:10.1007/bf00630563. S2CID 206783462.
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^ Ferguson, Niels (15 August 2001). "Censorship in action: why I don't publish my HDCP results". Archived from the original on 1 December 2001. Retrieved 16 February 2009.
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^ "Order Granting Application under the All Writs Act Requiring Defendant Fricosu to Assist in the Execution of Previously Issued Search Warrants" (PDF). United States District Court for the District of Colorado. Archived (PDF) from the original on 9 June 2021. Retrieved 26 March 2015.
Further reading[edit]
Further information: Books on cryptography
Arbib, Jonathan; Dwyer, John (2011). Discrete Mathematics for Cryptography. Algana Publishing. ISBN 978-1-907934-01-8.
Becket, B (1988). Introduction to Cryptology. Blackwell Scientific Publications. ISBN 978-0-632-01836-9. OCLC 16832704. Excellent coverage of many classical ciphers and cryptography concepts and of the "modern" DES and RSA systems.
Cryptography and Mathematics by Bernhard Esslinger, 200 pages, part of the free open-source package CrypTool, "PDF download" (PDF). Archived from the original on 22 July 2011. Retrieved 23 December 2013.{{cite web}}: CS1 maint: bot: original URL status unknown (link). CrypTool is the most widespread e-learning program about cryptography and cryptanalysis, open source.
In Code: A Mathematical Journey by Sarah Flannery (with David Flannery). Popular account of Sarah's award-winning project on public-key cryptography, co-written with her father.
James Gannon, Stealing Secrets, Telling Lies: How Spies and Codebreakers Helped Shape the Twentieth Century, Washington, D.C., Brassey's, 2001, ISBN 1-57488-367-4.
Oded Goldreich, Foundations of Cryptography Archived 9 August 2016 at the Wayback Machine, in two volumes, Cambridge University Press, 2001 and 2004.
Alvin's Secret Code by Clifford B. Hicks (children's novel that introduces some basic cryptography and cryptanalysis).
Introduction to Modern Cryptography Archived 16 October 2009 at the Wayback Machine by Jonathan Katz and Yehuda Lindell.
Ibrahim A. Al-Kadi, "The Origins of Cryptology: the Arab Contributions," Cryptologia, vol. 16, no. 2 (April 1992), pp. 97–126.
Christof Paar, Jan Pelzl, Understanding Cryptography, A Textbook for Students and Practitioners. Archived 31 October 2020 at the Wayback Machine Springer, 2009. (Slides, online cryptography lectures and other information are available on the companion web site.) Very accessible introduction to practical cryptography for non-mathematicians.
"Max Planck Encyclopedia of Public International Law". Archived from the original on 1 May 2018. Retrieved 15 December 2021., giving an overview of international law issues regarding cryptography.
Introduction to Modern Cryptography by Phillip Rogaway and Mihir Bellare, a mathematical introduction to theoretical cryptography including reduction-based security proofs. PDF download Archived 24 September 2009 at the Wayback Machine.
Stallings, William (2013). Cryptography and Network Security: Principles and Practice (6th ed.). Prentice Hall. ISBN 978-0-13-335469-0.
Tenzer, Theo (2021): Super Secreto – The Third Epoch of Cryptography: Multiple, exponential, quantum-secure and above all, simple and practical Encryption for Everyone, Norderstedt, ISBN 978-3755761174.
Johann-Christoph Woltag, 'Coded Communications (Encryption)' in Rüdiger Wolfrum (ed) Max Planck Encyclopedia of Public International Law (Oxford University Press 2009).
External links[edit]
Wikiquote has quotations related to Cryptography.
Wikibooks has more on the topic of: Cryptography
At Wikiversity, you can learn more and teach others about Cryptography at the Department of Cryptography
Wikisource has the text of the 1911 Encyclopædia Britannica article "Cryptography".
Library resources about Cryptography
Online books
Resources in your library
Resources in other libraries
The dictionary definition of cryptography at Wiktionary
Media related to Cryptography at Wikimedia Commons
Cryptography on In Our Time at the BBC
Crypto Glossary and Dictionary of Technical Cryptography Archived 4 July 2022 at the Wayback Machine
A Course in Cryptography by Raphael Pass & Abhi Shelat – offered at Cornell in the form of lecture notes.
For more on the use of cryptographic elements in fiction, see: Dooley, John F., William and Marilyn Ingersoll Professor of Computer Science, Knox College (23 August 2012). "Cryptology in Fiction". Archived from the original on 29 July 2020. Retrieved 20 February 2015.{{cite web}}: CS1 maint: multiple names: authors list (link)
The George Fabyan Collection at the Library of Congress has early editions of works of seventeenth-century English literature, publications relating to cryptography.
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What is cryptography? | IBM
What is cryptography? | IBM
What is cryptography?
Explore IBM cryptography solutions
What is cryptography?
Cryptography is the practice of developing and using coded algorithms to protect and obscure transmitted information so that it may only be read by those with the permission and ability to decrypt it. Put differently, cryptography obscures communications so that unauthorized parties are unable to access them.
In our modern digital age, cryptography has become an essential cybersecurity tool for protecting sensitive information from hackers and other cybercriminals.
Derived from the Greek word “kryptos,” meaning hidden, cryptography literally translates to “hidden writing.” Of course, it can be used to obscure any form of digital communication, including text, images, video or audio. In practice, cryptography is mainly used to transform messages into an unreadable format (known as ciphertext) that can only be decrypted into a readable format (known as plaintext) by the authorized intended recipient through the use of a specific secret key.
Cryptology, which encompasses both cryptography and cryptanalysis, is deeply rooted in computer science and advanced mathematics. The history of cryptography dates back to ancient times when Julius Caesar created the Caesar cipher to obscure the content of his messages from the messengers who carried them in the first century B.C. Today, organizations like the National Institute of Standards and Technology (NIST) continue to develop cryptographic standards for data security.
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Core tenets of modern cryptography
Modern cryptography has grown significantly more advanced over time. However, the general idea remains the same and has coalesced around four main principles.
Confidentiality: Encrypted information can only be accessed by the person for whom it is intended and no one else.
Integrity: Encrypted information cannot be modified in storage or in transit between the sender and the intended receiver without any alterations being detected.
Non-repudiation: The creator/sender of encrypted information cannot deny their intention to send the information.
Authentication: The identities of the sender and receiver, as well as the origin and destination of the information are confirmed.
Why cryptography is important
In today’s digital landscape, cryptography plays a vital role in our daily lives, ensuring that sensitive data like credit card numbers, e-commerce transactions and even WhatsApp messages remain confidential and secure.
On a macro level, advanced cryptography is crucial for maintaining national security, safeguarding classified information from potential threat actors and adversaries.
Common uses for cryptography
The following are some of the most common use cases for cryptography.
Passwords
Cryptography is frequently used to validate password authenticity while also obscuring stored passwords. In this way, services can authenticate passwords without the need to keep a plaintext database of all passwords which might be vulnerable to hackers.
Cryptocurrency
Cryptocurrencies like Bitcoin and Ethereum are built on complex data encryptions that require significant amounts of computational power to decrypt. Through these decryption processes, new coins are “minted” and enter circulation. Cryptocurrencies also rely on advanced cryptography to safeguard crypto wallets, verify transactions and prevent fraud.
Secure web browsing
When browsing secure websites, cryptography protects users from eavesdropping and man-in-the-middle (MitM) attacks. The Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols rely on public key cryptography to protect data sent between the web server and client and establish secure communications channels.
Electronic signatures
Electronic signatures, or e-signatures, are used to sign important documents online and are frequently enforceable by law. Electronic signatures created with cryptography can be validated to prevent fraud and forgeries.
Authentication
In situations where identity authentication is necessary, such as logging into an online bank account or accessing a secure network, cryptography can help confirm a verify a user’s identity and authenticate their access privileges.
Secure communications
Whether sharing classified state secrets or simply having a private conversation, end-to-end encryption is used for message authentication and to protect two-way communications like video conversations, instant messages and email. End-to-end encryption provides a high level of security and privacy for users and is widely used in communication apps like WhatsApp and Signal.
Types of cryptography
There are two main types of encryption in use today: symmetric cryptography and asymmetric cryptography. Both types use keys to encrypt and decrypt data sent and received. There are also hybrid cryptosystems that combine both.
A cryptosystem is considered symmetrical if each party—sender and receiver—uses the same key to encrypt and decrypt data. Algorithms such as the Advanced Encryption Standard (AES) and Data Encryption Standard(DES) are symmetric systems.
Asymmetric cryptography uses multiple keys—some shared and some private. In this way, the sender and receiver of an encrypted message have asymmetrical keys, and the system is asymmetrical. RSA—named after its progenitors Rivest, Shamir and Adleman—is one of the most common public key encryption algorithms.
While asymmetric systems are often considered to be more secure due to their use of private keys, the true measure of a system’s strength is more dependent on key length and complexity.
Symmetric cryptography
Symmetric key cryptography uses a shared single key for both encryption and decryption. In symmetric cryptography, both the sender and receiver of an encrypted message will have access to the same secret key.
Caesar’s cipher is an early example of a single key system. This primitive cipher worked by transposing each letter of a message forward by three letters, which would turn the word “cat” into “fdw” (although Caesar would have probably used the Latin word “cattus”). Since Caesar’s generals knew the key, they would be able to unscramble the message by simply reversing the transposition. In this way, symmetrical cryptosystems require that each party have access to the secret key prior to the encrypting, sending and decrypting of any information.
Some of the main attributes of symmetric encryption include the following:
Speed: The encryption process is comparatively fast.
Efficiency: Single key encryption is well suited for large amounts of data and requires fewer resources.
Confidential: Symmetrical encryption effectively secures data and prevents anyone without the key from decrypting the information.
Asymmetric cryptography
Asymmetric cryptography (also referred to as public key cryptography) uses one private key and one public key. Data that is encrypted with a public and private key requires both the public key and the recipient’s private key to be decrypted.
Public key cryptography enables secure key exchange over an insecure medium without the need to share a secret decryption key because the public key is only used in the encryption, but not the decryption process. In this way, asymmetric encryption adds an additional layer of security because an individual’s private key is never shared.
Some of the main attributes of symmetric encryption include the following:
Security: Asymmetric encryption is generally considered more secure.
Robust: Public key cryptography offers additional benefits, providing confidentially, authenticity and non-repudiation.
Resource intensive: Unlike single key encryption, asymmetrical encryption is slow and requires greater resources, which can be prohibitively expensive in some cases.
Cryptographic keys and key management
Cryptographic keys are essential for the secure use of encryption algorithms. Key management is a complex aspect of cryptography involving the generation, exchange, storage, use, destruction and replacement of keys. The Diffie-Hellman key exchange algorithm is a method used to securely exchange cryptographic keys over a public channel. Asymmetric key cryptography is a critical component in key exchange protocols.
Unlike Caesar’s cipher, which used a shifted Roman alphabet as a key, modern keys are far more complex and typically contain 128, 256 or 2,048 bits of information. Advanced cryptographic algorithms use these bits to rearrange and scramble the plaintext data into ciphertext. As the number of bits increases, the number of total possible arrangements of the data rises exponentially. Caesar’s cipher uses very few bits and would be very easy for a computer to decrypt (even without the secret key) by simple trying all the possible arrangements of the scrambled ciphertext until the entire message was transformed into readable plaintext. Hackers call this technic a brute force attack.
Adding more bits makes brute force attacks prohibitively difficult to compute. While a 56-bit system can be brute forced in 399 seconds by today’s most powerful computers, a 128-bit key would require 1.872 x 1037 years. A 256-bit system would take 3.31 x 1056 years. For reference, the entire universe is believed to have existed for only 13.7 billion years, which is less than a percent of a percent of the time it would take to brute force either a 128-bit or 256-bit cryptosystem.
Cryptographic algorithms and encryption methods
An encryption algorithm is a component of a cryptosystem that performs the transformation of data into ciphertext. Block ciphers like AES operate on fixed-size blocks of data, using a symmetric key for encryption and decryption. Stream ciphers, conversely, encrypt data one bit at a time.
Digital signatures and hash functions
Digital signatures and hash functions are used for authentication and ensuring data integrity. A digital signature created with cryptography provides a means of non-repudiation, ensuring that a message's sender cannot deny the authenticity of their signature on a document.
Hash functions, like the Secure Hash Algorithm 1 (SHA-1), can transform an input into a string of characters of a fixed-length, which is unique to the original data. This hash value helps in verifying the integrity of data by making it computationally infeasible to find two different inputs that could produce the same output hash.
The future of cryptography
In keeping pace with advancing technology and increasingly more sophisticated cyberattacks, the field of cryptography continues to evolve. Next-generation advanced protocols like quantum cryptography and elliptic curve cryptography (ECC) represent the cutting edge of cryptographic techniques.
Elliptical curve cryptography
Considered to be one of the main focal points of the next generation, elliptic curve cryptography (ECC) is a public key encryption technique based on elliptic curve theory that can create faster, smaller and more efficient cryptographic keys.
Traditional asymmetric cryptosystems, while secure, are difficult to scale. They require a lot of resources and become very slow as they are applied to larger amounts of data. Furthermore, attempts to improve the security of public key cryptosystems to evade increasingly powerful attacks would require increasing the bit length of the public and private keys, which would significantly slow the encryption and decryption process.
First-generation public key cryptosystems are built on the mathematic functions of multiplication and factoring, in which public and private keys reveal the specific mathematical functions necessary to both encrypt plaintext and decrypt ciphertext. These keys are made by multiplying prime numbers. ECC uses elliptical curves—equations that can be represented as curved lines on a graph—to generate public and private keys based on different points on the line graph.
In a world where we are increasingly reliant on devices with less computing power, such as mobile phones, ECC provides an elegant solution based on the obscure mathematics of elliptical curves to generate smaller keys that are more difficult to crack.
The advantages of ECC over previous public key cryptosystems are undisputed, and it is already being used by the U.S. government, Bitcoin and Apple’s iMessage service. While first-generation systems like RSA are still effective for most settings, ECC is poised to become the new standard for privacy and security online—especially as the tremendous potential of quantum computing looms over the horizon. While quantum computers are still in their infancy and difficult to build, program and maintain, the potential increase in computation power would render all known public key encryption systems insecure, since a quantum machine could theoretically achieve a brute force attack significantly faster than classical computers.
Quantum cryptography
Quantum cryptography uses the principles of quantum mechanics to secure data in a way that is immune to many of the vulnerabilities of traditional cryptosystems. Unlike other types of encryption that rely on mathematic principles, quantum cryptography is based on physics to secure data in a way that is theoretically completely immune to hackers. Because it is impossible for a quantum state to be observed without it being changed, any attempts to covertly access quantum encoded data would be immediately identified.
Originally theorized in 1984, quantum encryption functions by using photon light particles sent across a fiberoptic cable to share a private key between the sender and receiver. This stream of photons travel in a single direction and each one represents a single bit of data, either 0 or 1. A polarized filter on the sender’s side changes the physical orientation of each photon to a specific position, and the receiver uses two available beam splitters to read the position of each photon. The sender and receiver compare the sent photon positions to the decoded positions, and the set that matches is the key.
Quantum cryptography provides many benefits over traditional cryptography because it does not rely on potentially solvable math equations to secure encrypted data. It also prevents eavesdropping since quantum data cannot be read without also being changed, and quantum cryptography can also integrate well with other types of encryption protocols. This type of cryptography enables users to digitally share a private encryption key that cannot be copied during transit. Once this key is shared, it can be used to encrypt and decrypt further messages in a way that has almost no risk of being compromised.
However, quantum cryptography also faces many challenges and limitations that have yet to be solved and currently prevent practical use of quantum cryptography. As quantum computing has yet to crossover from proofs of concept into practical application, quantum cryptography remains prone to error due to unintended changes in proton polarization. Quantum cryptography also requires specific infrastructure. Fiber optic lines are necessary for transferring protons and have a limited range of typically about 248 to 310 miles, which computer science researchers are working to extend. Additionally, quantum cryptography systems are limited by the number of destinations where they can send data. Since these types of systems rely on the specific orientation of unique photons, they are incapable of sending a signal to more than one intended recipient at any given time.
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What is cryptography?
Tagged as Information technology
As a child, you may recall using symbols to write coded messages to your classmates that no one else could understand. More seriously, codes and ciphers are used for information security in computer systems and networks to protect sensitive and commercial information from unauthorized access when it is at rest or in transit. Uses include anything from keeping military secrets to transmitting financial data safely across the Internet.
Cryptography is an important computer security tool that deals with techniques to store and transmit information in ways that prevent unauthorized access or interference.
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How cryptography keeps communication secret and safe
The cryptographic process of scrambling text from a readable form to an unintelligible form – known as cipher text – is called encryption. Sending secret or private messages as cipher text is a typical use of cryptography. Once the cipher text is received, it is descrambled by the authorized recipient back to its readable form. The descrambling (or decryption) is performed with the use of an encryption key, which serves to prevent third parties from reading these messages.
Encryption methods have been used by many civilizations throughout history to prevent non-authorized people from understanding messages. Julius Caesar is credited for one of the earliest forms of cipher – the “Caesar Cipher” – to convey messages to his generals. With increasing sophistication, cryptography now plays a vital role in ensuring the privacy, data confidentiality, data integrity and authentication in computer systems and networks. In today’s world, where the majority of our personal and professional communications and transactions are conducted online, cryptography is more important than ever.
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To learn how your data will be used, please see our privacy notice.Types of cryptography systems
Cryptography refers to the techniques and algorithms that are used today for secure communication and data in storage. It incorporates mathematics, computer science, electronics and digital signal processing. Broadly speaking, there are four types of cryptography systems:
Symmetric-key cryptography (or “secret key”): In this type of system, both the sender and the receiver share the same key, which is used to encrypt and decrypt the message.
Asymmetric-key cryptography (or “public key”): In this type of cryptography system, there are two keys – one public and one private; these form a pair and are related mathematically. To apply asymmetric cryptography, the sender uses the public key of the intended recipient to encode the message, and then sends it on its way. When the message arrives, only the recipient’s private key can be used to decode it, meaning that a stolen message is of no use to the thief without the corresponding private key. Encryption mechanisms are the focus of ISO/IEC 18033, a suite of International Standards that specifies a number of asymmetric ciphers. The multipart series includes identity-based ciphers, block ciphers, stream ciphers, and homomorphic encryption.
Cryptographic key management: This type of system is crucial for protecting the keys used in both symmetric and asymmetric cryptography. It includes a set of processes covering the entire “life cycle” of a key, including its generation, exchange and distribution, storage, use, safe destruction and replacement. If the key management is weak, then the protection of encrypted data is weak. There are a number of International Standards relating to key management (e.g. ISO/IEC 11770) and key generation (e.g. ISO/IEC 18031 and ISO/IEC 18032).
Cryptographic hash function: This is a technique that converts a string of data of any length into a hashed output (a digest of the input) of fixed length. Hash functions have many applications such as in digital signatures, MACs (message authentication codes), and checksums (to check data corruption). International Standards that specify hash functions include ISO/IEC 9797-2, ISO/IEC 9797-3 and ISO/IEC 10118.
Information security principles and uses of cryptography
The key principles of information security are confidentiality, integrity and availability. Cryptography is an important tool that helps to preserve two of these principles:
Data confidentiality ensures that data is not disclosed to unauthorized parties. Cryptographic techniques such as encryption can be used to protect the confidentiality of data by making it unreadable to those who don’t have the proper decryption key.
Data integrity ensures that data has not been modified or corrupted. One example for International Standards on data integrity is ISO/IEC 9797, which specifies algorithms for calculating message authentication codes.
In addition to these key information security objectives, cryptography is used to achieve:
Entity authentication
By checking knowledge of a secret, entity authentication verifies the identity of the sender. Various crypto-based mechanisms and protocols can be used to achieve this, such as symmetric systems, digital signatures, zero-knowledge techniques and checksums. ISO/IEC 9798 is a series of standards that specifies entity authentication protocols and techniques.
Digital signatures
Used to verify the authenticity of data, digital signatures confirm that the data originated from the signer and has not been changed. They are used, for example, in email messages, electronic documents and online payments. International Standards that specify digital signature schemes include ISO/IEC 9796, ISO/IEC 14888, ISO/IEC 18370 and ISO/IEC 20008.
Non-repudiation
Cryptographic techniques such as digital signatures can be used to provide non-repudiation by ensuring that the sender and receiver of a message cannot deny that they, respectively, sent or received the message. The standard ISO/IEC 13888 describes techniques (symmetric and asymmetric) for the provision of non-repudiation services.
Lightweight cryptography
Lightweight cryptography is used in applications and technologies that are constrained in computational complexity: limiting factors can be memory, power and computing resources. The need for lightweight cryptography is expanding in our modern digital world. Constrained devices – for example IoT (Internet of Things) sensors or actuators like the ones switching on appliances in a so-called smart home – use lightweight symmetric cryptography. ISO/IEC 29192 is an eight-part standard that specifies various cryptographic techniques for lightweight applications.
Digital rights management
Digital rights management (DRM) protects the copyright of your digital content. DRM uses cryptographic software to ensure that only authorized users can have access to the material, modify or distribute it.
Electronic commerce and online shopping
Secure e-commerce is made possible by the use of asymmetric-key encryption. Cryptography plays an important role in online shopping as it protects credit card information and related personal details, as well as customers’ purchasing history and transactions.
Cryptocurrencies and blockchain
A cryptocurrency is a digital currency that uses cryptographic techniques to secure transactions. Each cryptocurrency coin is validated via distributed ledger technologies (e.g. blockchain). A ledger, in this case, is a continuously growing list of records – known as blocks – that are linked together using cryptography. What are cryptographic algorithms?
A cryptographic algorithm is a math-based process for encoding text and making it unreadable. Cryptographic algorithms are used to provide data confidentiality, data integrity and authentication, as well as for digital signatures and other security purposes.
Both DES (Data Encryption Standard) and AES (Advanced Encryption Standard) are popular examples of symmetric-key algorithms, while prominent asymmetric-key algorithms include RSA (Rivest-Shamir-Adleman) and ECC (elliptic curve cryptography).
Elliptic curve cryptography (ECC)
ECC is an asymmetric-key technique based on the use of elliptic curves, which has applications in encryption and digital signatures, for example. ECC technology can be used to create faster, smaller and more efficient cryptographic keys. Elliptic curve techniques are covered in the multipart standard ISO/IEC 15946.
Standards for cryptography
Cryptography has been the subject of intense standardization efforts resulting in a range of International Standards that encapsulate the knowledge and best practice of leading experts in the field. Internationally agreed ways of working make technology more secure and interoperable. By using cryptography standards, developers can rely on common definitions, as well as proven methods and techniques. Future-proofing cryptography
Today, we are on the edge of a quantum revolution. The advent of quantum computing in the coming years will provide mankind with processing powers on a scale that traditional computers can never hope to match. While this offers countless possibilities for complex problem-solving, it also comes with corresponding security threats. That very same power could undermine much of today’s cybersecurity – including established cryptographic practices.
Quantum cryptography is a method of encryption that applies the principles of quantum mechanics to provide secure communication. It uses quantum entanglement to generate a secret key to encrypt a message in two separate places, making it (almost) impossible for an eavesdropper to intercept without altering its contents. Hailed as the next big revolution in secure communication systems, quantum cryptography has the potential to be a real breakthrough for data that needs to stay private far into the future.
The new dawn of encryption is looking bright!
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What is cryptography?
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As the world becomes increasingly digital, the need for security has become ever more imperative. That’s where cryptography and its applications to cybersecurity come in.
Essentially, the word refers to the study of secure communications techniques, but cryptography is closely associated with encryption, or the act of scrambling ordinary text into what’s known as ciphertext—and then back again into ordinary text (called
plaintext) when it arrives at its destination. Several historical figures have been credited with creating and using cryptography through the centuries, from Greek historian Polybios and French diplomat Blaise de Vigenère to Roman Emperor Julius Caesar—who
is credited with using one of the first modern ciphers—and Arthur Scherbius, who created the Enigma code-breaking machine during World War Two. Likely, none of them would recognize the ciphers of the 21st century. But exactly what is cryptography?
And, how does it work?
Cryptography Definition
Cryptography is the technique of obfuscating or coding data, ensuring that only the person who is meant to see the information–and has the key to break the code–can read it. The word is a hybrid of two Greek words: “kryptós”, which means hidden, and “graphein”,
which means to write. Literally, the word cryptography translates to hidden writing, but in reality, the practice involves the secure transmission of information.
The use of cryptography can be traced to the ancient Egyptians and their creative use of hieroglyphics. But, the art of coding has seen great strides over the millennia, and modern cryptography combines advanced computer technology, engineering, and maths—among
other disciplines—to create highly sophisticated and secure algorithms and ciphers to protect sensitive data in the digital era.
For example, cryptography is used to create various types of encryption protocols that are regularly used to protect data. These include 128-bit or 256-bit encryption, Secure Sockets Layer (SSL), and Transport Layer Security (TLS). These encryption protocols
protect all manner of digital information and data, from passwords and emails to ecommerce and banking transactions.
There are different cryptographic types, which are useful for different purposes. For example, the simplest is symmetric key cryptography. Here, data is encrypted using a secret key, and then both the encoded message and the secret key are sent to the
recipient for decryption. Of course, the problem here is that if the message is intercepted, the third party can easily decode the message and steal the information.
To create a more secure system of encoding, cryptologists devised asymmetric cryptography, which is sometimes known as the “public key” system. In this instance, all users have two keys: one public and one private. When creating a coded message, the sender
will request the recipient’s public key to encode the message. This way, only the intended recipient’s private key will decode it. This way, even if the message is intercepted, a third party cannot decode it.
Why is cryptography important?
Cryptography is an essential cybersecurity tool. Its use means that data and users have an additional layer of security that ensures privacy and confidentiality and helps keep data from being stolen by cybercriminals. In practice, cryptography has many
applications:
Confidentiality: Only the intended recipient can access and read the information, so conversations and data remain private.
Integrity of data: Cryptography ensures that the encoded data cannot be modified or tampered with enroute from the sender to the receiver without leaving traceable marks— an example of this is digital signatures.
Authentication: Identities and destinations (or origins) are verified.
Non-repudiation: Senders become accountable for their messages since they cannot later deny that the message was transmitted—digital signatures and email tracking are examples of this.
What is cryptography in cybersecurity?
Interest in the use of cryptography grew with the development of computers and their connections over an open network. Over time, it became obvious that there was a need to protect information from being intercepted or manipulated while being transmitted
over this network. IBM was an early pioneer in this field, releasing its “Lucifer” encryption in the 1960s—this eventually became the first Data Encryption Standard (DES).
As our lives become increasingly digital, the need for cryptography to secure massive amounts of sensitive information has become even more imperative. Now, there are many ways in which cryptography is crucial in the online space. Encryption is an essential
part of being online, since so much sensitive data is transmitted everyday. Here are a few real-life applications:
Using virtual private networks (VPNs) or protocols such as SSL to browse the internet safely and securely.
Creating limited access controls so that only individuals with the correct permissions can carry out certain actions or functions, or access particular things.
Securing different types of online communication, including emails, login credentials, and even text messages—such as with WhatsApp or Signal—through end-to-end encryption.
Protecting users from various types of cyberattacks, such as man-in-the-middle attacks.
Allowing companies to meet legal requirements, such as the data protections set out in the General Data Protection Regulation (GDPR).
Creating and verifying login credentials, especially passwords.
Allowing the secure management and transaction of cryptocurrencies.
Enabling digital signatures to securely sign online documents and contracts.
Verifying identities when logging into online accounts.
What are the types of cryptography?
Cryptography definitions are, understandably, quite broad. This is because the term covers a wide range of different processes. As such, there are many different types of cryptographic algorithms, each one offering varying levels of security, depending
on the type of information being transmitted. Below are the three main cryptographic types:
Symmetric Key Cryptography: This simpler form of cryptography takes its name from the fact that both the sender and receiver share one key to encrypt and decrypt information. Some examples of this are the Data Encryption Standard (DES) and Advanced
Encryption Standard (AES). The main difficulty here is finding a way to securely share the key between the sender and receiver.
Asymmetric Key Cryptography: A more secure type of cryptography, this involves both the sender and receiver having two keys: one public and one private. During the process, the sender will use the receiver’s public key to encrypt the message, while
the receiver will use their private key to decrypt it. The two keys are different, and since only the receiver will have the private key, they will be the only ones able to read the information. The RSA algorithm is the most popular form of asymmetric
cryptography.
Hash Functions: These are types of cryptographic algorithms that do not involve the use of keys. Instead, a hash value—a number of fixed lengths that acts as a unique data identifier—is created based on the length of the plain text information and
used to encrypt the data. This is commonly used by various operating systems to protect passwords, for example.
From the above, it is clear that the main difference in symmetric and asymmetric encryption in cryptography is that the first only involves one key while the second requires two.
Types of symmetric cryptography
Symmetric encryption is sometimes called secret key cryptography because one single—purportedly—secret key is used to encrypt and decrypt information. There are several forms of this type of cryptography, including:
Stream ciphers: These work on a single byte of data at a time and regularly change the encryption key. In this process, the keystream can be in tandem with—or independent of the message stream. This is called self-synchronizing or synchronous, respectively.
Block ciphers: This type of cryptography—which includes the Feistel cipher—codes and decodes one block of data at a time.
Forms of asymmetric key cryptography
Asymmetric cryptography—sometimes referred to as public-key encryption—hinges on the fact that the receiver has two keys in play: a public one and a private one. The first is used by the sender to encode the information, while the receiver uses the latter—which
only they have—to securely decrypt the message.
Asymmetric key cryptography encrypts and decrypts messages using algorithms. These are based on various mathematical principles, such as multiplication or factorization—multiplying two big prime numbers to generate one massive, random number which is
incredibly tricky to crack—or exponentiation and logarithms, which create exceptionally complex numbers that are nearly impossible to decrypt, such as in 256-bit encryption. There are different types of asymmetric key algorithms, such as:
RSA: The first type of asymmetric cryptography to be created, RSA is the basis of digital signatures and key exchanges, among other things. The algorithm is based on the principle of factorization.
Elliptic Curve Cryptography (ECC): Often found in smartphones and on cryptocurrency exchanges, ECC employs the algebraic structure of elliptic curves to build complex algorithms. Significantly, it does not require much storage memory or usage bandwidth,
making it especially useful for electronic devices with limited computing power.
Digital Signature Algorithm (DSA): Built on the principles of modular exponentiations, DSA is the gold standard for verifying electronic signatures and was created by the National Institute of Standards and Technologies.
Identity-based Encryption (IBE): This unique algorithm negates the need for a message recipient to provide their public key to the sender. Instead, a known unique identifier—such as an email address—is used by the sender to generate a public key to
encode the message. A trusted third-party server then generates a corresponding private key that the receiver can access to decrypt the information.
Cryptographic attacks
As with most technologies, cryptography has become increasingly sophisticated. But that does not mean that these encryptions cannot be broken. If the keys are compromised, it is possible for an external party to crack the coding and read the protected
data. Here are a few potential issues to watch for:
Weak keys: Keys are a collection of random numbers used with an encryption algorithm to alter and disguise data so that it is incomprehensible to others. Longer keys involve more numbers, making them much trickier to crack—and therefore, better for
protecting data.
Using keys incorrectly: Keys need to be used correctly—if they are not, hackers can easily crack them to access the data they are supposed to protect.
Reusing keys for different purposes: Like passwords, each key should be unique—using the same key across different systems weakens the ability of cryptography to protect data.
Not changing keys: Cryptographic keys can quickly become out of date, which is why it is important to regularly update them to keep data secure.
Not storing keys carefully: Ensure that keys are kept in a secure place where they cannot easily be found, otherwise they can be stolen to compromise the data they protect.
Insider attacks: Keys can be compromised by individuals who legitimately have access to them—such as an employee— and who them sells them on for nefarious purposes.
Forgetting the backup: Keys should have a backup because if they suddenly become faulty, the data they protect could become inaccessible.
Recording keys incorrectly: Manually entering keys into a spreadsheet or writing them down on paper may appear to be a logical choice, but it is also one that is prone to error and theft.
There are also specific cryptography attacks designed to break through encryptions by finding the right key. Here are some of the common:
Brute force attacks: Broad attacks that try to randomly guess private keys using the known algorithm.
Ciphertext-only attacks: These attacks involve a third party intercepting the encrypted message—not the plaintext—and trying to work out the key to decrypt the information, and later, the plaintext.
Chosen ciphertext attack: The opposite of a chosen plaintext attack, here, the attacker analyses a section of ciphertext against its corresponding plaintext to discover the key.
Chosen plaintext attack: Here, the third party chooses the plaintext for a corresponding ciphertext to begin working out the encryption key.
Known plaintext attack: In this case, the attacker randomly accesses part of the plaintext and part of the ciphertext and begins to figure out the encryption key. This is less useful for modern cryptography as it works best with simple ciphers.
Algorithm attack: In these attacks, the cybercriminal analyses the algorithm to try and work out the encryption key.
Is it possible to mitigate the threat of cryptography attacks?
There are a few ways in which individuals and organizations can try and lower the possibility of a cryptographic attack. Essentially, this involves ensuring the proper management of keys so that they are less likely to be intercepted by a third party,
or useable even if they do. Here are a few suggestions:
Use one key for each specific purpose—for example, use unique keys for authentication and digital signatures .
Protect cryptographic keys with stronger Key-encryption-keys (KEKs).
Use hardware security modules to manage and protect keys—these function like regular password managers.
Ensure that keys and algorithms are regularly updated.
Encrypt all sensitive data.
Create strong, unique keys for each encryption purpose.
Store keys securely so they cannot be easily accessed by third parties.
Ensure the correct implementation of the cryptographic system.
Include cryptography in security awareness training for employees.
The need for cryptography
Most people will not need to have more than a basic understanding of what cryptography is. But learning the cryptography definition, how the process works, and its applications to cybersecurity, can be useful in being more mindful about managing day-to-day
digital interactions. This can help most people keep their emails, passwords, online purchases, and online banking transactions—all of which use cryptography in their security features—more secure.
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What is cryptography?
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What is the difference between symmetric and asymmetric cryptography?
What problems does cryptography solve?
What are the principles?
What to read next
Definition
Cryptography provides for secure communication in the presence of malicious third-parties—known as adversaries. Encryption uses an algorithm and a key to transform an input (i.e., plaintext) into an encrypted output (i.e., ciphertext). A given algorithm will always transform the same plaintext into the same ciphertext if the same key is used. Algorithms are considered secure if an attacker cannot determine any properties of the plaintext or key, given the ciphertext. An attacker should not be able to determine anything about a key given a large number of plaintext/ciphertext combinations which used the key.
What is the difference between symmetric and asymmetric cryptography?
With symmetric cryptography, the same key is used for both encryption and decryption. A sender and a recipient must already have a shared key that is known to both. Key distribution is a tricky problem and was the impetus for developing asymmetric cryptography.
With asymmetric crypto, two different keys are used for encryption and decryption. Every user in an asymmetric cryptosystem has both a public key and a private key. The private key is kept secret at all times, but the public key may be freely distributed.
Data encrypted with a public key may only be decrypted with the corresponding private key. So, sending a message to John requires encrypting that message with John’s public key. Only John can decrypt the message, as only John has his private key. Any data encrypted with a private key can only be decrypted with the corresponding public key. Similarly, Jane could digitally sign a message with her private key, and anyone with Jane’s public key could decrypt the signed message and verify that it was in fact Jane who sent it.
Symmetric is generally very fast and ideal for encrypting large amounts of data (e.g., an entire disk partition or database). Asymmetric is much slower and can only encrypt pieces of data that are smaller than the key size (typically 2048 bits or smaller). Thus, asymmetric crypto is generally used to encrypt symmetric encryption keys which are then used to encrypt much larger blocks of data. For digital signatures, asymmetric crypto is generally used to encrypt the hashes of messages rather than entire messages.
A cryptosystem provides for managing cryptographic keys including generation, exchange, storage, use, revocation, and replacement of the keys.
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What problems does cryptography solve?
A secure system should provide several assurances such as confidentiality, integrity, and availability of data as well as authenticity and non-repudiation. When used correctly, crypto helps to provide these assurances. Cryptography can ensure the confidentiality and integrity of both data in transit as well as data at rest. It can also authenticate senders and recipients to one another and protect against repudiation.
Software systems often have multiple endpoints, typically multiple clients, and one or more back-end servers. These client/server communications take place over networks that cannot be trusted. Communication occurs over open, public networks such as the Internet, or private networks which may be compromised by external attackers or malicious insiders.
It can protect communications that traverse untrusted networks. There are two main types of attacks that an adversary may attempt to carry out on a network. Passive attacks involve an attacker simply listening on a network segment and attempting to read sensitive information as it travels. Passive attacks may be online (in which an attacker reads traffic in real-time) or offline (in which an attacker simply captures traffic in real-time and views it later—perhaps after spending some time decrypting it). Active attacks involve an attacker impersonating a client or server, intercepting communications in transit, and viewing and/or modifying the contents before passing them on to their intended destination (or dropping them entirely).
The confidentiality and integrity protections offered by cryptographic protocols such as SSL/TLS can protect communications from malicious eavesdropping and tampering. Authenticity protections provide assurance that users are actually communicating with the systems as intended. For example, are you sending your online banking password to your bank or someone else?
It can also be used to protect data at rest. Data on a removable disk or in a database can be encrypted to prevent disclosure of sensitive data should the physical media be lost or stolen. In addition, it can also provide integrity protection of data at rest to detect malicious tampering.
What are the principles?
The most important principle to keep in mind is that you should never attempt to design your own cryptosystem. The world’s most brilliant cryptographers (including Phil Zimmerman and Ron Rivest) routinely create cryptosystems with serious security flaws in them. In order for a cryptosystem to be deemed “secure,” it must face intense scrutiny from the security community. Never rely on security through obscurity, or the fact that attackers may not have knowledge of your system. Remember that malicious insiders and determined attackers will attempt to attack your system.
The only things that should be “secret” when it comes to a secure cryptosystem are the keys themselves. Be sure to take appropriate steps to protect any keys that your systems use. Never store encryption keys in clear text along with the data that they protect. This is akin to locking your front door and placing the key under the doormat. It is the first place an attacker will look. Here are three common methods for protecting keys (from least secure to most secure):
Store keys in a filesystem and protect them with strong access control lists (ACLs). Remember to adhere to the principal of least privilege.
Encrypt your data encryption keys (DEKs) with a second key encrypting key (KEK). The KEK should be generated using password-based encryption (PBE). A password known to a minimal number of administrators can be used to generate a key using an algorithm such as bcrypt, scrypt, or PBKDF2 and used to bootstrap the cryptosystem. This removes the need to ever store the key unencrypted anywhere.
A hardware security module (HSM) is a tamper-resistant hardware appliance that can be used to store keys securely. Code can make API calls to an HSM to provide keys when needed or to perform decryption of data on the HSM itself.
Make sure that you only use algorithms, key strengths, and modes of operation that conform to industry best practices. Advanced encryption standard (AES) (with 128, 192, or 256-bit keys) is the standard for symmetric encryption. RSA and elliptical curve cryptography (ECC) with at least 2048-bit keys are the standard for asymmetric encryption. Be sure to avoid insecure modes of operation such as AES in Electronic Codebook (ECB) mode or RSA with no padding.
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Cryptography
Overview
Cryptography uses mathematical techniques to transform data and prevent it from being read or tampered with by unauthorized parties. That enables exchanging secure messages even in the presence of adversaries. Cryptography is a continually evolving field that drives research and innovation. The Data Encryption Standard (DES), published by NIST in 1977 as a Federal Information Processing Standard (FIPS), was groundbreaking for its time but would fall far short of the levels of protection needed today.
As our electronic networks grow increasingly open and interconnected, it is crucial to have strong, trusted cryptographic standards and guidelines, algorithms and encryption methods that provide a foundation for e-commerce transactions, mobile device conversations and other exchanges of data. NIST has fostered the development of cryptographic techniques and technology for 50 years through an open process which brings together industry, government, and academia to develop workable approaches to cryptographic protection that enable practical security.
Our work in cryptography has continually evolved to meet the needs of the changing IT landscape. Today, NIST cryptographic solutions are used in commercial applications from tablets and cellphones to ATMs, to secure global eCommcerce, to protect US federal information and even in securing top-secret federal data. NIST looks to the future to make sure we have the right cryptographic tools ready as new technologies are brought from research into operation. For example, NIST is now working on a process to develop new kinds of cryptography to protect our data when quantum computing becomes a reality. At the other end of the spectrum, we are advancing so-called lightweight cryptography to balance security needs for circuits smaller than were dreamed of just a few years ago.
In addition to standardizing and testing cryptographic algorithms used to create virtual locks and keys, NIST also assists in their use. NIST’s validation of strong algorithms and implementations builds confidence in cryptography—increasing its use to protect the privacy and well-being of individuals and businesses.
NIST continues to lead public collaborations for developing modern cryptography, including:
Block ciphers, which encrypt data in block-sized chunks (rather than one bit at a time) and are useful in encrypting large amounts of data.
Cryptographic hash algorithms, which create short digests, or hashes, of the information being protected. These digests find use in many security applications including digital signatures (the development of which NIST also leads).
Key establishment, employed in public-key cryptography to establish the data protection keys used by the communicating parties.
Post-quantum cryptography, intended to be secure against both quantum and classical computers and deployable without drastic changes to existing communication protocols and networks.
Lightweight cryptography, which could be used in small devices such as Internet of Things (IoT) devices and other resource-limited platforms that would be overtaxed by current cryptographic algorithms.
Privacy-enhancing cryptography, intended to allow research on private data without revealing aspects of the data that could be used to identify its owner.
Digital Signatures, which is an electronic analogue of a written signature that provides assurance that the claimed signatory signed, and the information was not modified after signature generation.
Random Bit Generation, which is a device or algorithm that can produce a sequence of bits that appear to be both statistically independent and unbiased.
NIST also promotes the use of validated cryptographic modules and provides Federal agencies with a security metric to use in procuring equipment containing validated cryptographic modules through other efforts including: FIPS 140, Cryptographic Programs and Laboratory Accreditation Cryptographic Module Validation Program (CMVP), Cryptographic Algorithm Validation Program (CAVP), and Applied Cryptography at NIST's National Cybersecurity Center of Excellence (NCCoE).
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NIST Role and Activities Relative to the Post Quantum Cryptography White House …
Cryptography Resources
Migration to Post-Quantum Cryptography
Applied Cryptography
Post Quantum Encryption
Post-Quantum Cryptography: the Good, the Bad, and the Powerful
In an animated story featuring NIST’s Matthew Scholl, this video emphasizes how NIST is working with the brightest minds in government, academia, and industry from around the world to develop a new set of encryption standards that will work with our current classical computers—while being resistant to the quantum machines of the future. Quantum computers will be incredibly powerful and will have the potential to provide tremendous societal benefits; however, there are concerns related to how quantum computers could be used by our adversaries, competitors, or criminals. This video explores these scenarios and explains how we are staying ahead of this potential cybersecurity threat.
To learn more about NIST’s cryptography work, please visit our main cryptography page: https://www.nist.gov/cryptography.
To learn about a specific project, Crypto Agility: Considerations for Migrating to Post-Quantum Cryptographic Algorithms, please visit this page: https://www.nccoe.nist.gov/projects/building-blocks/post-quantum-cryptography.
News
Post-Quantum Cryptography: A Q&A With NIST’s Matt Scholl
Quantum computing algorithms seek to use quantum phenomena to perform certain types of calculations much more efficiently than today’s classical, binary, transistor-based computers can. If and when a powerful enough quantum computer is built, it could run algorithms that would break many of the encryption codes we use to protect our data. In this interview with Taking Measure, Matt Scholl, chief
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NIST to Standardize Encryption Algorithms That Can Resist Attack by Quantum Computers
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NIST Selects ‘Lightweight Cryptography’ Algorithms to Protect Small Devices
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NIST Retires SHA-1 Cryptographic Algorithm
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What is Cryptography? Definition from SearchSecurity
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cryptography
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By
Kathleen Richards
What is cryptography?
Cryptography is a method of protecting information and communications through the use of codes, so that only those for whom the information is intended can read and process it.
In computer science, cryptography refers to secure information and communication techniques derived from mathematical concepts and a set of rule-based calculations called algorithms, to transform messages in ways that are hard to decipher. These deterministic algorithms are used for cryptographic key generation, digital signing, verification to protect data privacy, web browsing on the internet and confidential communications such as credit card transactions and email.
Cryptography techniques
Cryptography is closely related to the disciplines of cryptology and cryptanalysis. It includes techniques such as microdots, merging words with images and other ways to hide information in storage or transit. However, in today's computer-centric world, cryptography is most often associated with scrambling plaintext (ordinary text, sometimes referred to as cleartext) into ciphertext (a process called encryption), then back again (known as decryption). Individuals who practice this field are known as cryptographers.
Modern cryptography concerns itself with the following four objectives:
Confidentiality. The information cannot be understood by anyone for whom it was unintended.
Integrity.The information cannot be altered in storage or transit between sender and intended receiver without the alteration being detected.
Non-repudiation. The creator/sender of the information cannot deny at a later stage their intentions in the creation or transmission of the information.
Authentication. The sender and receiver can confirm each other's identity and the origin/destination of the information.
Procedures and protocols that meet some or all of the above criteria are known as cryptosystems. Cryptosystems are often thought to refer only to mathematical procedures and computer programs; however, they also include the regulation of human behavior, such as choosing hard-to-guess passwords, logging off unused systems and not discussing sensitive procedures with outsiders.
Cryptography is the process of encrypting and decrypting data.
Cryptographic algorithms
Cryptosystems use a set of procedures known as cryptographic algorithms, or ciphers, to encrypt and decrypt messages to secure communications among computer systems, devices and applications.
A cipher suite uses one algorithm for encryption, another algorithm for message authentication and another for key exchange. This process, embedded in protocols and written in software that runs on operating systems (OSes) and networked computer systems, involves:
public and private key generation for data encryption/decryption
digital signing and verification for message authentication
key exchange
Types of cryptography
Single-key or symmetric-key encryption algorithms create a fixed length of bits known as a block cipher with a secret key that the creator/sender uses to encipher data (encryption) and the receiver uses to decipher it. One example of symmetric-key cryptography is the Advanced Encryption Standard (AES). AES is a specification established in November 2001 by the National Institute of Standards and Technology (NIST) as a Federal Information Processing Standard (FIPS 197) to protect sensitive information. The standard is mandated by the U.S. government and widely used in the private sector.
In June 2003, AES was approved by the U.S. government for classified information. It is a royalty-free specification implemented in software and hardware worldwide. AES is the successor to the Data Encryption Standard (DES) and DES3. It uses longer key lengths -- 128-bit, 192-bit, 256-bit -- to prevent brute force and other attacks.
Symmetric cryptography uses a single key while asymmetric cryptography uses a key pair to encrypt and decrypt data.
Public-key or asymmetric-key encryption algorithms use a pair of keys, a public key associated with the creator/sender for encrypting messages and a private key that only the originator knows (unless it is exposed or they decide to share it) for decrypting that information.
Examples of public-key cryptography include:
RSA, used widely on the internet
Elliptic Curve Digital Signature Algorithm (ECDSA) used by Bitcoin
Digital Signature Algorithm (DSA) adopted as a Federal Information Processing Standard for digital signatures by NIST in FIPS 186-4
Diffie-Hellman key exchange
To maintain data integrity in cryptography, hash functions, which return a deterministic output from an input value, are used to map data to a fixed data size. Types of cryptographic hash functions include SHA-1 (Secure Hash Algorithm 1), SHA-2 and SHA-3.
Cryptography concerns
Attackers can bypass cryptography, hack into computers that are responsible for data encryption and decryption, and exploit weak implementations, such as the use of default keys. However, cryptography makes it harder for attackers to access messages and data protected by encryption algorithms.
Growing concerns about the processing power of quantum computing to break current cryptography encryption standards led NIST to put out a call for papers among the mathematical and science community in 2016 for new public key cryptography standards.
Unlike today's computer systems, quantum computing uses quantum bits (qubits) that can represent both 0s and 1s, and therefore perform two calculations at once. While a large-scale quantum computer may not be built in the next decade, the existing infrastructure requires standardization of publicly known and understood algorithms that offer a secure approach, according to NIST. The deadline for submissions was in November 2017, analysis of the proposals is expected to take three to five years.
History of cryptography
The word "cryptography" is derived from the Greek kryptos, meaning hidden.
The prefix "crypt-" means "hidden" or "vault," and the suffix "-graphy" stands for "writing."
The origin of cryptography is usually dated from about 2000 B.C., with the Egyptian practice of hieroglyphics. These consisted of complex pictograms, the full meaning of which was only known to an elite few.
The first known use of a modern cipher was by Julius Caesar (100 B.C. to 44 B.C.), who did not trust his messengers when communicating with his governors and officers. For this reason, he created a system in which each character in his messages was replaced by a character three positions ahead of it in the Roman alphabet.
In recent times, cryptography has turned into a battleground of some of the world's best mathematicians and computer scientists. The ability to securely store and transfer sensitive information has proved a critical factor in success in war and business.
Because governments do not want certain entities in and out of their countries to have access to ways to receive and send hidden information that may be a threat to national interests, cryptography has been subject to various restrictions in many countries, ranging from limitations of the usage and export of software to the public dissemination of mathematical concepts that could be used to develop cryptosystems.
However, the internet has allowed the spread of powerful programs and, more importantly, the underlying techniques of cryptography, so that today many of the most advanced cryptosystems and ideas are now in the public domain.
This was last updated in September 2021
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Identity 101
What Is Cryptography? Definition & How It Works
What Is Cryptography? Definition & How It Works
Learn how Adaptive Multi-Factor Authentication combats data breaches, weak passwords, and phishing attacks.
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Okta
Updated: 04/21/2022 - 12:27
Time to read: 9 minutes
Modern cryptography is a method of sending and receiving messages that only the intended receiver and sender can read — to prevent third-party access. It often involves encryption of electronic data, which commonly creates ciphertext by scrambling regular text. Then, it uses a decryption key of some form to return it to readable format on the receiving end. Cryptography can involve either a symmetric key system, which is the simplest, or an asymmetric key system, which is typically more secure. Cryptography provides methods for secure communication and electronic data that malicious adversaries cannot read, interpret, or access.
What is cryptography?
Cryptography is used to keep messages and data secure from being accessible to anyone other than the sender and the intended recipient. It is the study of communications and a form of security for messaging. Ultimately, cryptography can keep data from being altered or stolen. It can also be used to authenticate users. Cryptography often uses encryption and an algorithm to keep electronic data and messages secure and only readable by the intended parties. Cryptography has been around for centuries. The term itself comes from the Greek word kryptos, which translates to hidden. Today, cryptography is based on computer science practices and mathematical theory.
Types of cryptography
There are two main types of cryptography used for digital data and secure messages today: symmetric cryptography and asymmetric cryptography. Hash functions, a third type, doesn’t involve use of a key.
Symmetric cryptography: This is one of the most commonly used and simplest forms of encrypting and decrypting electronic data. It is also called secret-key or private-key cryptography. With symmetric cryptography, both the sender and the recipient will have the same key. This key is used to encrypt messages and data on one end and then decrypt it on the other end. Before communications begin, both parties must have the same secret key. Symmetric cryptography is fast, easy to use, and best suited for transmitting large amounts of data or for bulk encryption. The issue with this form of cryptography is that if a third party gets the secret key, they too can read and decrypt the data or messages. There are two main forms of symmetric encryption algorithms: stream and block algorithms.
Stream algorithm: This type encrypts the data while it is being streamed; therefore, it is not stored in the system’s memory. One of the most popular stream ciphers is the RC4 (Rivest Cipher 4), which encrypts messages one byte at a time.
Block algorithms: This type encrypts specific lengths of bits in blocks of data using the secret key. The data is held within the system’s memory while blocks are completed. The Advanced Encryption Standard (AES) is the most commonly used symmetric algorithm. Blocks of 128-bit data are encrypted and decrypted using cryptographic keys of 128, 192, and 256 bits. The AES is FIPS (Federal Information Processing Standards) approved under guidance from NIST (National Institute of Standards and Technology).
Asymmetric cryptography: This is also called public-key cryptography, and it involves the use of two different keys. A public key is distributed widely to everyone to encrypt data. This key is required to send messages and encrypt them. A sender can request the public key for the recipient to encrypt the data. Then, it will require the private key, which is kept secret, to decrypt the message. The key pair of the private and public key are mathematically related. Both keys are needed to perform operations, send and receive encrypted data and messages, and access sensitive data. Asymmetric cryptography needs higher processing and longer keys, with pieces of data that are smaller than the key; therefore, is often used on a smaller scale. Asymmetric and symmetric cryptography can be used together in a cryptosystem. Asymmetric cryptography can be used to encrypt symmetric keys, for example, while the symmetric cryptography is used to transmit or encrypt larger amounts of data.
Hash functions: This is a third type of cryptography that does not use a key. It uses a fixed length hash value based on the plain text message. This can then be used to ensure that the message has not been altered or compromised. Hash functions add an extra layer of security, as the hashed output can’t be reversed to reveal the data that was originally input.
What is cryptography used for?
The intention of cryptography is to keep data and messages secure and inaccessible to potential threats or bad actors. It is often working behind the scenes to encrypt and decrypt data you are sending through social media, applications, interactions on websites, and email. Symmetric cryptography can be used for these purposes:
Card transactions and payment applications
Random number generation
Signature verification to ensure the sender is who they claim to be
Asymmetric cryptography can be used for the following purposes:
Email messages
SIM card authentication
Web security
Exchange of private keys
Key principles of cryptography
Cryptography strives for private communications and data security to protect digital information from being altered, accessed, or read by anyone other than those with legitimate access. These are key principles of cryptography:
Confidentiality: The basis of cryptography relies on the information being kept private and confidential from third-party or malicious adversaries. Confidentiality agreements contain specific guidelines and rules that are meant to ensure that information is restricted, secure, and only accessible to certain people or within certain arenas.
Encryption: Encryption is what converts readable data into an unreadable form to protect the privacy as messages or data are sent between a sender and a receiver. This is typically done using an algorithm.
Decryption: The reverse of encryption is decryption, and this is returning the data to its original and readable form. Typically, this is performed using a specific key, which can be the same for encryption and decryption or require two different keys.
Data integrity: Data needs to stay consistent and accurate over its entire lifestyle, and data integrity can help to maintain this accuracy. Data cannot be altered anywhere in the communication path. It all needs to remain intact between the sender and the receiver.
Authentication: This is to determine that the message or data received is sent from the actual originator of the message. The sender is often required to verify that they are indeed the originator of the message received by the recipient.
Non-repudiation: This is the ability to ensure that the originator of a message or piece of data is unable to deny the authenticity of their signature. The use of digital signatures can prevent the originator or sender from denying their communication.
Best practices
Messages and data should always be encrypted to ensure privacy and security. The best practices for cryptography include using an entire cryptographic system, or cryptosystem, that regularly uses multiple forms of encryption to keep data and communications safe and secure. This system should have an easy-to-use interface along with strong cryptographic algorithms that conform to the industry’s best practices. For symmetric encryption, this means using AES with 128, 192, or 256-bit keys. For asymmetric encryption standards, it should include elliptical curve cryptography (ECC) and RSA. These are examples of files and data that should be encrypted and protected with cryptography:
Email and messages
Critical and sensitive files
Company data
Payment information
Personal identification details
Cryptographic methods need to be effective, but also user-friendly to ensure that they are actually going to be used as intended. Using encryption functions can also help to prevent the loss or theft of data even if the hardware itself is stolen or compromised. A strong cryptosystem should be able to hold up to the security community and not rely on security through obscurity. Instead, the system should be known, and the only thing kept secret and private are the actual keys. The public key can be publicized, but the secret or private key should be protected. These are methods for keeping your keys secure:
Do not store your encryption keys in clear text or along with the data that is encrypted.
Store your keys in a file system protected with strong access control lists (ACLs) while adhering to the principle of least privilege — access only to those who need it.
Use a second encryption key to encrypt your data encryption keys, generated using password-based encryption (PBE). A small number of administrators can use a password to generate a key to avoid storing the key in an unencrypted form within the system.
Use a tamper-resistant hardware appliance called a hardware security model (HSM) that can securely store keys. When data is needed to be decrypted, code can make an application programming interface (API) call to the HSM.
Key takeaways
Cryptography is a necessary form of cybersecurity that uses encryption methods to keep digital data and communications secure and out of the hands of potential threats or bad actors. Data protection is highly important in this digital era where so much information is stored on computers, in the cloud, and on the internet. Data security is important to businesses, industries, companies, and individuals alike. Cryptography is a form of securing digital data and messages often using special keys that only the sender and recipient have access to. Cryptography uses mathematical systems and algorithms to encrypt and decrypt data. Symmetrical cryptography uses the same key for both encryption and decryption. It can quickly encrypt and decrypt data, and it is easy to use. It can also be compromised if a third party gains access to the key, however. It is important to keep your data encryption keys safe and secure. Sending your encryption key in a plain text form along with your encrypted message, for example, is similar to leaving your front door key in plain sight in front of your locked door. Keep your keys safe to keep your data safe. Asymmetrical cryptography is a step further than symmetrical cryptography, using different keys for encryption and decryption. The encryption key is “public,” and everyone has access to it. The decryption key is kept “private,” and only intended recipients can have access to this secret key. While this adds an extra layer of security, it can also take longer to encrypt and decrypt data, so it is regularly used for smaller bits of data. A strong cryptosystem often uses multiple forms of encryption and cryptographic methods to keep digital data private and secure from adversaries. Cryptography is a vital component of digital security.
References
Definition of ‘Cryptography.’ (January 2022). The Economic Times.
Security Component Fundamentals for Assessment. (2020). Security Controls Evaluation, Testing, and Assessment Handbook (Second Edition).
Advanced Encryption Standard (AES). (2001). National Institute of Standards and Technology (NIST).
Compliance FAQs: Federal Information Processing Standards (FIPS). (November 2019). National Institute of Standards and Technology (NIST).
Security and Privacy in the Internet of Things. (2016). Internet of Things.
Elliptical Curve Cryptography ECC. (June 2020). National Institute of Standards and Technology (NIST).
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