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Cryptology/Citable Version

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Version 1, 25 August 2013‎

Cryptology (the science of secrets, from Greek) is the general term that encompasses both cryptography (the study of techniques for keeping secrets) and cryptanalysis (codebreaking, acquiring secrets without authorisation). The field has a long and interesting history, see History of cryptology.

Cryptology provides the scientific background for a broad range of activities in signals intelligence and information security.

Based on Claude Shannon's definition of Information theory as the study of "communication in the presence of noise", Ron Rivest wrote: "Cryptology is about communication in the presence of adversaries" [1].

Related articles

Parent topics


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

Famous cryptologists

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

Government cryptology

Other related topics


  1. Ronald Rivest, Cryptology (1990)