Cryptography

Cryptography is an interdisciplinary subject, drawing from several fields. Older forms of cryptography were chiefly concerned with patterns in language. More recently, the emphasis has shifted, and cryptography makes extensive use of mathematics, particularly discrete mathematics, including topics from number theory, information theory, computational complexity, statistics and combinatorics. Cryptography is also considered a branch of engineering, but it is considered to be an unusual one as it deals with active, intelligent and malevolent opposition (see cryptographic engineering and security engineering). Cryptography is a tool used within computer and network security.

Terminology

The study of how to circumvent the use of cryptography is called cryptanalysis, or codebreaking. Cryptography and cryptanalysis are sometimes grouped together under the umbrella term cryptology, encompassing the entire subject. In practice, the term cryptography (from the Greek kryptós, "hidden", and gráphein, "to write") is often used to refer to the field as a whole; crypto is an informal abbreviation. The first recorded usage of the word 'cryptography' occurs in Sir Thomas Browne's Discourse of 1658 entitled The Garden of Cyrus: "the strange Cryptography of Gaffarel in his Starrie Booke of Heaven".

Related Topics:
Cryptanalysis - Greek - Thomas Browne - 1658 - The Garden of Cyrus - Gaffarel

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Encryption (or enciphering) is the process of converting ordinary information (plaintext) into an unreadable form, termed ciphertext, or a cryptogram.

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Decryption, or deciphering, is the reverse process, recovering the plaintext back from the ciphertext. A cipher (sometimes spelt cypher) is an algorithm for encryption and decryption. The exact operation of a cipher is normally controlled by a key — some secret piece of information that customizes how the ciphertext is produced. Cryptographic protocols specify the details of how ciphers (and other cryptographic primitives) are to be used to achieve specific tasks. A suite of protocols, ciphers, key management, user-prescribed actions implemented together as a system constitute a cryptosystem.

Related Topics:
Decryption - Algorithm - Key - Cryptographic protocol - Cryptosystem

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In ordinary parlance, a (secret) "code" is often used synonymously with "cipher". In cryptography, however, the term has a specialised technical meaning: Codes are a historical method which involves substituting larger units of text, typically words or phrases (for example, "apple pie" replaces "attack at dawn"). In contrast, classical ciphers usually substitute or rearrange individual letters (or small groups of letters) — for example, "attack at dawn" becomes "buubdl bu ebxo" by substitution.

Related Topics:
Code - Code

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