# Cryptology/Related Articles

From Citizendium, the Citizens' Compendium

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

## Contents

## 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]:
**I**nternet**P**rotocl**sec**urity is a set of protocols for providing encryption and/or authentication services for Internet packets.^{[e]}

## Famous cryptologists

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

- William Friedman [r]: Possibly the greatest cryptologist in history, he pioneered the application of mathematics to cryptanalysis and built the U.S. Army Signal Intelligence Service technical base.
^{[e]} - Auguste Kerckhoffs [r]: A 19th Century French writer, famous for giving some axioms for cryptography.
^{[e]} - Alan Turing [r]: British mathematician, code breaker and computer pioneer.
^{[e]} - Claude Shannon [r]: (1916-2001) A theoretical mathematician and electrical engineer, one of the foundational researchers in computer and communications design.
^{[e]} - Sir Francis Walsingham [r]:
*Add brief definition or description*

## Government cryptology

- Communications intelligence [r]: The subset of SIGINT concerned with signals intended to be intelligible to human beings, in the form of voice, messages, or images.
^{[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]} - Radiofrequency MASINT [r]: Collection and processing of intelligence information derived from unintentional electromagnetic radiation from targets of interest
^{[e]} - Communications Security Establishment [r]: The Canadian government organization responsible for communications security and signals intelligence
^{[e]} - Government Communications Headquarters [r]: The British government agency responsible for signals intelligence and information assurance
^{[e]} - Government Communications Security Bureau [r]: The organization, in the government of New Zealand, which has responsibility for information security and signals intelligence
^{[e]} - National Security Agency [r]: An organization within the United States Department of Defense, with the dual roles of the principal signals intelligence agency in the United States intelligence community, but also having the responsibility for information assurance of military, diplomatic, and other critical communications.
^{[e]} - FAPSI [r]: A communications intelligence and information security organization in Russia, which became independent of the KGB at the end of the Soviet Union, but now has been absorbed back into the FSB
^{[e]} - Foreign Intelligence Surveillance Act [r]:
*Add brief definition or description*

- Wiretapping [r]:
*Add brief definition or description* - Communication [r]: The set of interactive processes that create shared meaning.
^{[e]} - Computer network [r]: A collection of computers or digital devices ("nodes") connected by communication links.
^{[e]} - Convergence of communications [r]: Technical specifications and infrastructure to allow all types of communications (e.g., telephone, web, television) to interface over a common set of information transfer technologies
^{[e]} - Information theory [r]: Theory of the probability of transmission of messages with specified accuracy when the bits of information constituting the messages are subject, with certain probabilities, to transmission failure, distortion, and accidental additions.
^{[e]} - Linguistics [r]: The scientific study of language.
^{[e]} - Mathematics [r]: The study of quantities, structures, their relations, and changes thereof.
^{[e]} - Statistics [r]: A branch of mathematics that specializes in enumeration, or counted, data and their relation to measured data.
^{[e]} - Telecommunications [r]:
*Add brief definition or description*

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