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Encyclopedia > Encryption

In cryptography, encryption is the process of transforming information (referred to as plaintext) to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information (in cryptography, referred to as ciphertext). In many contexts, the word encryption also implicitly refers to the reverse process, decryption (e.g. “software for encryption” can typically also perform decryption), to make the encrypted information readable again (i.e. to make it unencrypted). Encrypt is a television movie, and premiered June 14, 2003, on the Sci-Fi Channel. ... Look up cipher in Wiktionary, the free dictionary. ... The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and the verb γράφω gráfo write or λεγειν legein to speak) is the study of message secrecy. ... The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and the verb γράφω gráfo write or λεγειν legein to speak) is the study of message secrecy. ... The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ... In cryptography, plaintext is information used as input to an encryption algorithm; the output is termed ciphertext. ... A key is a piece of information that controls the operation of a cryptography algorithm. ... Encryption software is software whose main task is encryption and decryption of data, usually in the form of files on hard drives and removable media, email messages, or in the form of packets sent over computer networks. ...


Encryption has long been used by militaries and governments to facilitate secret communication. Encryption is now used in protecting information within many kinds of civilian systems, such as computers, networks (e.g. the Internet e-commerce), mobile telephones, wireless microphones, wireless intercom systems, Bluetooth devices and bank automatic teller machines. Encryption is also used in digital rights management to restrict the use of copyrighted material and in software copy protection to protect against reverse engineering and software piracy. This article is about the machine. ... Computer networks may be classified according to the network layer at which they operate according to some basic reference models that are considered to be standards in the industry such as the seven layer OSI reference model and the four layer Internet Protocol Suite model. ... Electronic commerce, EC, e-commerce or ecommerce consists primarily of the distributing, buying, selling, marketing, and servicing of products or services over electronic systems such as the Internet and other computer networks. ... Cellular redirects here. ... A wireless microphone, as the name implies, is a microphone without a physical cable connecting it directly to the sound recording or amplifying equipment with which it is associated. ... A wireless intercom is an electronic device that enables room-to-room or building-to-building voice communication. ... Bluetooth logo This article is about the electronic protocol named after Harald Bluetooth Gormson. ... Outdoor ATMs may be free-standing, like this kiosk, or built into the side of banks or other buildings An automatic teller machine, automated teller machine (ATM) or cash machine is an electronic device that allows a banks customers to make cash withdrawals and check their account balances without... Digital rights management (DRM) is an umbrella term that refers to access control technologies used by publishers and other copyright holders to limit usage of digital media or devices. ... Copy prevention, also known as copy protection, is any technical measure designed to prevent duplication of information. ... Reverse engineering (RE) is the process of taking something (a device, an electrical component, a software program, etc. ... This article is about maritime piracy. ...


Encryption, by itself, can protect the confidentiality of messages, but other techniques are still needed to verify the integrity and authenticity of a message; for example, a message authentication code (MAC) or digital signatures. Standards and cryptographic software and hardware to perform encryption are widely available, but successfully using encryption to ensure security is a challenging problem. A single slip-up in system design or execution can allow successful attacks. Sometimes an adversary can obtain unencrypted information without directly undoing the encryption. See traffic analysis, TEMPEST. A cryptographic message authentication code (MAC) is a short piece of information used to authenticate a message. ... In cryptography, a digital signature or digital signature scheme is a type of asymmetric cryptography used to simulate the security properties of a signature in digital, rather than written, form. ... Wikipedia does not yet have an article with this exact name. ... Traffic analysis is the process of intercepting and examining messages in order to deduce information from patterns in communication. ... í For other uses, see Tempest. ...

Contents

History

Main article: History of cryptography

Encryption has been used to protect communications since ancient times, but only organizations and individuals with extraordinary need for confidentiality had bothered to exert the effort required to implement it. Encryption, and successful attacks on it, played a vital role in World War II. Many of the encryption techniques developed then were closely-guarded secrets (Kahn). In the mid-1970s, with the introduction of the U.S. Data Encryption Standard and public key cryptography, strong encryption emerged from the preserve of secretive government agencies into the public domain. The history of cryptography begins thousands of years ago. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... The Data Encryption Standard (DES) is a cipher (a method for encrypting information) selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976, and which has subsequently enjoyed widespread use internationally. ... Public key cryptography is a form of cryptography which generally allows users to communicate securely without having prior access to a shared secret key, by using a pair of cryptographic keys, designated as public key and private key, which are related mathematically. ...


Ciphers

In cryptography, a cipher (or cypher) is an algorithm for performing encryption and decryption — a series of well-defined steps that can be followed as a procedure. An alternative term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts are distinct in cryptography. In classical cryptography, ciphers were distinguished from codes. Codes operated by substituting according to a large codebook which linked a random string of characters or numbers to a word or phrase. For example, “UQJHSE” could be the code for “Proceed to the following coordinates”. The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and the verb γράφω gráfo write or λεγειν legein to speak) is the study of message secrecy. ... In mathematics, computing, linguistics, and related disciplines, an algorithm is a finite list of well-defined instructions for accomplishing some task that, given an initial state, will terminate in a defined end-state. ... This article is about algorithms for encryption and decryption. ... In the context of cryptography, a code is a method used to transform a message into an obscured form, preventing those not in on the secret from understanding what is actually transmitted. ... In cryptography, a classical cipher is a type of cipher used historically but which now have fallen, for the most part, into disuse. ... Categories: Cryptography stubs | Cryptography ...


The original information is known as plaintext, and the encrypted form as ciphertext. The ciphertext message contains all the information of the plaintext message, but is not in a format readable by a human or computer without the proper mechanism to decrypt it; it should resemble random gibberish to those not intended to read it. In cryptography, plaintext is information used as input to an encryption algorithm; the output is termed ciphertext. ...


The operation of a cipher usually depends on a piece of auxiliary information, called a key or, in traditional NSA parlance, a cryptovariable. The encrypting procedure is varied depending on the key, which changes the detailed operation of the algorithm. A key must be selected before using a cipher to encrypt a message. Without knowledge of the key, it should be difficult, if not nearly impossible, to decrypt the resulting cipher into readable plaintext. A key is a piece of information that controls the operation of a cryptography algorithm. ... NSA can stand for: National Security Agency of the USA The British Librarys National Sound Archive This page concerning a three-letter acronym or abbreviation is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...


Most modern ciphers can be categorized in several ways:

  • By whether they work on blocks of symbols usually of a fixed size (block ciphers), or on a continuous stream of symbols (stream ciphers).
  • By whether the same key is used for both encryption and decryption (symmetric key algorithms), or if a different key is used for each (asymmetric key algorithms). If the algorithm is symmetric, the key must be known to the recipient and to no one else. If the algorithm is an asymmetric one, the encyphering key is different from, but closely related to, the decyphering key. If one key cannot be deduced from the other, the asymmetric key algorithm has the public/private key property and one of the keys may be made public without loss of confidentiality. The Feistel cipher uses a combination of substitution and transposition techniques. Most (block ciphers) algorithms are based on this structure.

Encryption Decryption In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... The operation of the keystream generator in A5/1, a LFSR-based stream cipher used to encrypt mobile phone conversations. ... Symmetric-key algorithms are a class of algorithms for cryptography that use trivially related cryptographic keys for both decryption and encryption. ... In cryptography, an asymmetric key algorithm uses a pair of cryptographic keys to encrypt and decrypt. ... In cryptography, a Feistel cipher is a block cipher with a symmetric structure, named after IBM cryptographer Horst Feistel; it is also commonly known as a Feistel network. ... Encryption Decryption In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ...

Etymology of “Cipher”

“Cipher” is alternatively spelled “cypher” (however, this variant is now uncommon and therefore often incorrectly considered an error by native speakers); similarly “ciphertext” and “cyphertext”, and so forth. It also got into Middle French as cifre and Medieval Latin as cifra, from the Arabic sifr (zero). This article is about algorithms for encryption and decryption. ... This article is about algorithms for encryption and decryption. ...


The word “cipher” in former times meant “zero” and had the same origin (see Zero — Etymology), and later was used for any decimal digit, even any number. There are these theories about how the word “cipher” may have come to mean encoding: For other senses of this word, see zero or 0. ...

  • Encoding often involved numbers.
  • Conservative Catholic opponents of the Arabic numerals equated it with any “dark secret”.[citation needed]
  • The Roman number system was very cumbersome because there was no concept of zero (or empty space). The concept of zero (which was also called “cipher”), which we all now think of as natural, was very alien in medieval Europe, so confusing and ambiguous to common Europeans that in arguments people would say “talk clearly and not so far fetched as a cipher”. Cipher came to mean concealment of clear messages or encryption.
    • The French formed the word “chiffre” and adopted the Italian word “zero”.
    • The English used “zero” for “0”, and “cipher” from the word “ciphering” as a means of computing.
    • The Germans used the words “Ziffer” (number, “Zahl”) and “Chiffre”.

Dr. Al-Kadi (ref-3) concluded that the Arabic word sifr, for the digit zero, developed into the European technical term for encryption. For other uses, see Arabic numerals (disambiguation). ... Roman numerals are a numeral system originating in ancient Rome, adapted from Etruscan numerals. ... Ibrahim A. Al-Kadi, Ph. ...


Ciphers versus codes

Main article: Code (cryptography)

In non-technical usage, a “(secret) code” typically means a “cipher”. Within technical discussions, however, the words “code” and “cipher” refer to two different concepts. Codes work at the level of meaning — that is, words or phrases are converted into something else and this chunking generally shortens the message. Ciphers, on the other hand, work at a lower level: the level of individual letters, small groups of letters, or, in modern schemes, individual bits. Some systems used both codes and ciphers in one system, using superencipherment to increase the security. In some cases the terms codes and ciphers are also used synonym to substitution and transposition. In the context of cryptography, a code is a method used to transform a message into an obscured form, preventing those not in on the secret from understanding what is actually transmitted. ... In the context of cryptography, a code is a method used to transform a message into an obscured form, preventing those not in on the secret from understanding what is actually transmitted. ... Superencipherment is the practice of encrypting a message using two or more ciphering schemes in sequence. ...


Historically, cryptography was split into a dichotomy of codes and ciphers, and coding had its own terminology, analogous to that for ciphers: “encoding, codetext, decoding” and so on.


However, codes have a variety of drawbacks, including susceptibility to cryptanalysis and the difficulty of managing a cumbersome codebook. Because of this, codes have fallen into disuse in modern cryptography, and ciphers are the dominant technique. Cryptanalysis (from the Greek kryptós, hidden, and analýein, to loosen or to untie) is the study of methods for obtaining the meaning of encrypted information, without access to the secret information which is normally required to do so. ... Categories: Cryptography stubs | Cryptography ...


=Types of Cipher

There are a variety of different types of encryption. Algorithms used earlier in the history of cryptography are substantially different from modern methods, and modern ciphers can be classified according to how they operate and whether they use one or two keys. The history of cryptography begins thousands of years ago. ...


Historical pen and paper ciphers used in the past are sometimes known as classical ciphers. They include simple substitution ciphers and transposition ciphers. For example “GOOD DOG” can be encrypted as “PLLX XLP” where “L” substitutes for “O”, “P” for “G”, and “X” for “D” in the message. Transposition of the letters “GOOD DOG” can result in “DGOGDOO”. These simple ciphers and examples are easy to crack, even without plaintext-ciphertext pairs. In cryptography, a classical cipher is a type of cipher used historically but which now have fallen, for the most part, into disuse. ... In cryptography, a substitution cipher is a method of encryption by which units of plaintext are substituted with ciphertext according to a regular system; the units may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. ... In classical cryptography, a transposition cipher changes one character from the plaintext to another (to decrypt the reverse is done). ...


Simple ciphers were replaced by polyalphabetic substitution ciphers which changed the substitution alphabet for every letter. For example “GOOD DOG” can be encrypted as “PLSX TWF” where “L”, “S”, and “W” substitute for “O”. With even a small amount of known or estimated plaintext, simple polyalphabetic substitution ciphers and letter transposition ciphers designed for pen and paper encryption are easy to crack. A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. ...


During the early twentieth century, electro-mechanical machines were invented to do encryption and decryption using transposition, polyalphabetic substitution, and a kind of “additive” substitution. In rotor machines, several rotor disks provided polyalphabetic substitution, while plug boards provided another substitution. Keys were easily changed by changing the rotor disks and the plugboard wires. Although these encryption methods were more complex than previous schemes and required machines to encrypt and decrypt, other machines such as the British Bombe were invented to crack these encryption methods. A series of three rotors from an Enigma machine, used by Germany during World War II In cryptography, a rotor machine is an electro-mechanical device used for encrypting and decrypting secret messages. ... The Bombe replicated the action of several Enigma machines wired together. ...


Modern encryption methods can be divided into symmetric key algorithms (Private-key cryptography) and asymmetric key algorithms (Public-key cryptography). In a symmetric key algorithm (e.g., DES and AES), the sender and receiver must have a shared key set up in advance and kept secret from all other parties; the sender uses this key for encryption, and the receiver uses the same key for decryption. In an asymmetric key algorithm (e.g., RSA), there are two separate keys: a public key is published and enables any sender to perform encryption, while a private key is kept secret by the receiver and enables only him to perform correct decryption. Symmetric-key algorithms are a class of algorithms for cryptography that use trivially related cryptographic keys for both decryption and encryption. ... Symmetric-key algorithms are a class of algorithms for cryptography that use trivially related cryptographic keys for both decryption and encryption. ... In cryptography, an asymmetric key algorithm uses a pair of cryptographic keys to encrypt and decrypt. ... A big random number is used to make a public-key pair. ... The Data Encryption Standard (DES) is a cipher (a method for encrypting information) selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976, and which has subsequently enjoyed widespread use internationally. ... In cryptography, the Advanced Encryption Standard (AES), also known as Rijndael, is a block cipher adopted as an encryption standard by the U.S. government. ... This article is about an algorithm for public-key encryption. ...


Symmetric key ciphers can be distinguished into two types, depending on whether they work on blocks of symbols of fixed size (block ciphers), or on a continuous stream of symbols (stream ciphers). Encryption Decryption In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... The operation of the keystream generator in A5/1, a LFSR-based stream cipher used to encrypt mobile phone conversations. ...

Image File history File links This is a lossless scalable vector image. ...

Key Size and Vulnerability

In a pure mathematical attack (i.e., lacking any other information to help break a cypher), three factors above all, count:

  • Mathematical advances that allow new attacks or weaknesses to be discovered and exploited.
  • Computational power available, i.e. the computing power which can be brought to bear on the problem. It is important to note that average performance/capacity of a single computer is not the only factor to consider. An adversary can use multiple computers at once, for instance, to increase the speed of exhaustive search for a key (i.e. “brute force” attack) substantially.
  • Key size, i.e., the size of key used to encrypt a message. As the key size increases, so does the complexity of exhaustive search to the point where it becomes infeasible to crack encryption directly.

Since the desired effect is computational difficulty, in theory one would choose an algorithm and desired difficulty level, thus decide the key length accordingly. In computer science, brute-force search is a trivial but very general problem-solving technique, that consists of systematically enumerating all possible candidates for the solution and checking whether each candidate satisfies the problems statement. ... In cryptography, the key size (alternatively key length) is the size of the digits used to create an encrypted text; it is therefore also a measure of the number of possible keys which can be used in a cipher, and the number of keys which must be tested to break... In computer science, brute-force search is a trivial but very general problem-solving technique, that consists of systematically enumerating all possible candidates for the solution and checking whether each candidate satisfies the problems statement. ...


An example of this process can be found at Key Length which uses multiple reports to suggest that a symmetric cypher with 128 bits, an asymmetric cypher with 3072 bit keys, and an elliptic curve cypher with 512 bits, all have similar difficulty at present. This article is about the unit of information, see Bit (disambiguation) for other meanings. ...


Claude Shannon proved, using information theory considerations, that any theoretically unbreakable cipher must have keys which are at least as long as the plaintext, and used only once: one-time pad. Claude Shannon Claude Elwood Shannon (April 30, 1916 – February 24, 2001), an American electrical engineer and mathematician, has been called the father of information theory,[1] and was the founder of practical digital circuit design theory. ... Excerpt from a one-time pad. ...


References

  • Helen Fouché Gaines, “Cryptanalysis”, 1939, Dover. ISBN 0-486-20097-3
  • Ibrahim A. Al-Kadi, “The origins of cryptology: The Arab contributions”, Cryptologia, 16(2) (April 1992) pp. 97–126.
  • Ibrahim A. Al-Kadi, “Cryptography and Data Security: Cryptographic Properties of Arabic”, proceedings of the Third Saudi Engineering Conference. Riyadh, Saudi Arabia: Nov 24-27, Vol 2:910-921., 1991.
  • David Kahn, The Codebreakers - The Story of Secret Writing (ISBN 0-684-83130-9) (1967)
  • Abraham Sinkov, Elementary Cryptanalysis: A Mathematical Approach, Mathematical Association of America, 1966. ISBN 0-88385-622-0

Ibrahim A. Al-Kadi, Ph. ... Cryptology is an umbrella term for cryptography and cryptanalysis. ... Cryptologia is a journal in cryptography published quarterly since 1977. ... Ibrahim A. Al-Kadi, Ph. ... David Kahn is a US historian, journalist and writer. ... Dr. Abraham Sinkov (1907-1998) was a US cryptanalyst. ...

See also

The German Lorenz cipher machine, used in World War II for encryption of very high-level general staff messages Cryptography (or cryptology; derived from Greek κρυπτός kryptós hidden, and the verb γράφω gráfo write or λεγειν legein to speak) is the study of message secrecy. ... Encryption software is software whose main task is encryption and decryption of data, usually in the form of files on hard drives and removable media, email messages, or in the form of packets sent over computer networks. ... Some famous ciphertexts (or cryptograms) are: The Zimmermann Telegram The Magic Words are Squeamish Ossifrage The cryptogram in The Gold Bug Beale ciphers Voynich Manuscript Dorabella Cipher Kryptos Zodiac Killer ciphers DAgapeyeff cipher Chaocipher The Shugborough House inscription See also: Topics in cryptography External links Famous Unsolved Codes and... Symmetric-key algorithms are a class of algorithms for cryptography that use trivially related cryptographic keys for both decryption and encryption. ... A big random number is used to make a public-key pair. ... In cryptography, a classical cipher is a type of cipher used historically but which now have fallen, for the most part, into disuse. ... In cryptography, a substitution cipher is a method of encryption by which units of plaintext are substituted with ciphertext according to a regular system; the units may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. ... In classical cryptography, a transposition cipher changes one character from the plaintext to another (to decrypt the reverse is done). ... A series of three rotors from an Enigma machine, used by Germany during World War II In cryptography, a rotor machine is an electro-mechanical device used for encrypting and decrypting secret messages. ... The operation of the keystream generator in A5/1, a LFSR-based stream cipher used to encrypt mobile phone conversations. ... Encryption Decryption In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. ... Pretty Good Privacy is a computer program that provides cryptographic privacy and authentication. ... Steganography is the art and science of writing hidden messages in such a way that no one apart from the intended recipient knows of the existence of the message; this is in contrast to cryptography, where the existence of the message itself is not disguised, but the content is obscured. ... A hash function is a reproducible method of turning some kind of data into a (relatively) small number that may serve as a digital fingerprint of the data. ...

External links

Look up encryption in Wiktionary, the free dictionary.
  • SecurityDocs Resource for encryption whitepapers
  • Accumulative archive of various cryptography mailing lists. Includes Cryptography list at metzdowd and SecurityFocus Crypto list.

  Results from FactBites:
 
Washingtonpost.com: Encryption Special Report (1561 words)
Encryption has become one of the hottest hi-tech issues on Capitol Hill, as Congress debates whether the government should step in and limit the strength of encryption products to maintain law enforcement's historical ability to eavesdrop electronically on anyone it wants.
Modern encryption is achieved with algorithms that use a "key" to encrypt and decrypt messages by turning text or other data into digital gibberish and then by restoring it to its original form.
In 1996, the Clinton relaxed its stand somewhat, declaring that encryption software would no longer be considered a munition, unless it was created specifically for military purposes, and allowing manufacturers to incorporate stronger encryption into their products as long as they committed to systems that allow the government to recover keys.
Encryption - Wikipedia, the free encyclopedia (993 words)
In the mid-1970s, strong encryption emerged from the sole preserve of secretive government agencies into the public domain, and is now employed in protecting widely-used systems, such as Internet e-commerce, mobile telephone networks and bank automatic teller machines.
Encryption can be used to ensure secrecy, but other techniques are still needed to make communications secure, particularly to verify the integrity and authenticity of a message; for example, a message authentication code (MAC) or digital signatures.
Encryption or software code obfuscation is also used in software copy protection against reverse engineering, unauthorized application analysis, cracks and software piracy used in different encryption or obfuscating software
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