# Cryptology/Related Articles

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*See also changes related to Cryptology, or pages that link to Cryptology or to this page or whose text contains "Cryptology".*

## Parent topics

- Information security [r]: The set of policies and protective measures used to ensure appropriate confidentiality, integrity and availability to information; usually assumed to be information in a computer or telecommunications network but the principles extend to people and the physical world
^{[e]} - Signals intelligence [r]: the practice of acquiring information through monitoring the electromagnetic signals deliberately trasmitted by an opponent, including communications (COMINT) and non-communications electronics such as radar (ELINT).
^{[e]}

## Subtopics

- Cryptography [r]: A field at the intersection of mathematics and computer science that is concerned with the security of information, typically the confidentiality, integrity and authenticity of some message.
^{[e]} - Cryptanalysis [r]: The sub-field of cryptology which deals with breaking into existing codes and ciphers.
^{[e]} - Symmetric key cryptography [r]: A cryptographic system in which there is only one key; the same secret key is used for encryption and decryption.
^{[e]} - Asymmetric key cryptography [r]: A category of cryptographic techniques, which greatly simplify key management, which are based on mathematically related key pairs, such that the "public" key can be used to encrypt and be freely available, and only the holder of the "private" key can decrypt the message
^{[e]} - Steganography [r]: The study of techniques for hiding a secret message within an apparently innocent message.
^{[e]}

## Main techniques

- Cipher [r]: A means of combining plaintext (of letters or numbers, or bits), using an algorithm that mathematically manipulates the individual elements of plaintext, into ciphertext, a form unintelligible to any recipient that does not know both the algorithm and a randomizing factor called a cryptographic key
^{[e]} - Block cipher [r]: A symmetric cipher that operates on fixed-size blocks of plaintext, giving a block of ciphertext for each
^{[e]} - Stream cipher [r]: A cipher that encrypts data by mixing it with the output of a pseudorandom number generator controlled by a key; to decrypt, run the same generator with the same key to get the same pseudorandom data, then reverse the mixing step.
^{[e]} - Hybrid cryptosystem [r]: A system that combines public key with secret key methods; usually with a cryptographic hash for authentication as well.
^{[e]} - One-time pad [r]: A cipher system in which the cryptographic key, i.e. the secret used to encrypt and decrypt messages, is a sequence of random values, each one of which is only ever used once, and only to encrypt one particular letter or word.
^{[e]} - Random number generator [r]: A member of a sequence of which the successive values cannot be predicted, produced by measurement of physical phenomena, appropriate algorithms, or a combination of the two
^{[e]} - Hash (cryptography) [r]: An algorithm that produces a fixed-size digest from an input of essentially arbitrary size.
^{[e]} - Code (cryptography) [r]: A means of substituting, for the linguistically meaningful symbols of plaintext composed of words or other symbols meaningful to humans, into inherently meaningless numbers, letters, or words that make no sense to a recipient who is not in possession of a codebook or other means of reversing the substitution of symbols
^{[e]} - Cryptographic key [r]: Value used by a computer together with a complex algorithm to encrypt and decrypt messages.
^{[e]}

## Well-known instances

- Data Encryption Standard [r]: A block cipher specification issued by the U.S. government in 1976, intended for sensitive but unclassified data. It is now obsolescent, succeeded by the Advanced Encryption Standard, but still used in commercial systems.
^{[e]} - Advanced Encryption Standard [r]: A US government standard issued in 2002 for a stronger block cipher to succeed the earlier Data Encryption Standard.
^{[e]} - RSA algorithm [r]: A widely used public key encryption algorithm whose strength depends on the difficulty of integer factorisation.
^{[e]} - Diffie-Hellman [r]: A technique that allows two parties to safely establish a shared secret for use as a cryptographic key, even if someone is eavesdropping on their interaction. It requires that the parties have some means of authentication to be sure they are talking to the right person.
^{[e]} - Enigma machine [r]: The primary high-security cryptographic communications security machine of Nazi Germany. Unknown to the Germans, it had been substantially cryptanalyzed by the British Government Code and Cipher School, with French, Polish, and U.S. help.
^{[e]} - PURPLE machine [r]: WWII Japanese cipher machine used for diplomatic communications; system broken by U.S. and made available to U.K. in exchange for ULTRA communications intelligence on Germany
^{[e]} - Pretty Good Privacy [r]: E-mail encryption package created by Phillip Zimmerman.
^{[e]} - IPsec [r]:
*Add brief definition or description*

## Famous cryptologists

The AES competition article has a list of well-known players involved in that.

- William Friedman [r]:
*Add brief definition or description* - Auguste Kerckhoffs [r]:
*Add brief definition or description* - Alan Turing [r]:
*Add brief definition or description* - Claude Shannon [r]:
*Add brief definition or description* - Sir Francis Walsingham [r]:
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## Government cryptology

- Communications intelligence [r]:
*Add brief definition or description* - Signals intelligence [r]: the practice of acquiring information through monitoring the electromagnetic signals deliberately trasmitted by an opponent, including communications (COMINT) and non-communications electronics such as radar (ELINT).
^{[e]} - Radiofrequency MASINT [r]:
*Add brief definition or description* - Communications Security Establishment [r]:
*Add brief definition or description* - Government Communications Headquarters [r]:
*Add brief definition or description* - Government Communications Security Bureau [r]:
*Add brief definition or description* - National Security Agency [r]:
*Add brief definition or description* - FAPSI [r]:
*Add brief definition or description* - Foreign Intelligence Surveillance Act [r]:
*Add brief definition or description*

- Wiretapping [r]:
*Add brief definition or description* - Communication [r]:
*Add brief definition or description* - Computer network [r]:
*Add brief definition or description* - Convergence of communications [r]:
*Add brief definition or description* - Information theory [r]:
*Add brief definition or description* - Linguistics [r]:
*Add brief definition or description* - Mathematics [r]:
*Add brief definition or description* - Statistics [r]:
*Add brief definition or description* - Telecommunications [r]:
*Add brief definition or description*