Codebook

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Codebook

In cryptography

Cryptography

Cryptography is the practice and study of hiding information. In modern times cryptography is considered a branch of both mathematics and computer science and is affiliated closely with information theory, computer security and engineering....
, a codebook is a document used for implementing a code

Code (cryptography)

In cryptography, a code is a method used to transform a message into an obscured form, preventing those who do not possess special information, or key , required to apply the transform from understanding what is actually transmitted....
. A codebook contains a lookup table

Lookup table

In computer science, a lookup table is a data structure, usually an array or associative array, often used to replace a runtime computation with a simpler array indexing operation....
for coding and decoding; each word or phrase has one or more strings which replace it. To decipher messages written in code, corresponding copies of the codebook must be available at either end.

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Encyclopedia

In cryptography

Cryptography

Code (cryptography)

Lookup table

Physical security

Physical security describes both measures that prevent or deter attackers from accessing a facility, resource, or information stored on physical media and guidance on how to design structures to resist various hostile acts....
of codebooks presents a special difficulty in the use of codes, compared to the secret information used in cipher

Cipher

In cryptography, a cipher is an algorithm for performing encryption and decryption — a series of well-defined steps that can be followed as a procedure....
s, the key, which is typically much shorter.

NSA

National Security Agency

The National Security Agency/Central Security Service is a Cryptology Intelligence agency of the Federal government of the United States, administered as part of the United States Department of Defense....
documents sometimes use codebook to refer to block cipher

Block cipher

In cryptography, a block cipher is a symmetric key algorithm cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation....
s; compare their use of combiner-type algorithm to refer to stream cipher

Stream cipher

In cryptography, a stream cipher is a symmetric key algorithm cipher where plaintext bits are combined with a pseudorandom cipher bit stream , typically by an exclusive-or operation....
s.

In social sciences

Social sciences

The social sciences comprise academic disciplines concerned with the study of the social life of human groups and individuals including anthropology, communication studies, economics, human geography, history, political science, psychology and sociology....
, a codebook is a document containing list of codes

Coding (social sciences)

Coding, the process of Statistical classification of information, is an important step in preparation of data for computer processing.Data which are coded usually come from questionnaires used in qualitative research in social sciences....
used in research.

Codebooks were also used in 19th- and 20th-century commercial code

Commercial code

In law, a Commercial code is a codification of private law relating to merchants, trade, business entities , commercial contracts and other matters such as negotiable instruments....
s for the non-cryptographic purpose of data compression

Data compression

In computer science and information theory, data compression or source coding is the process of encoding information using fewer bits than an code representation would use through use of specific encoding schemes....
.

A codebook is usually made in two parts, one part being for converting plaintext to ciphertext, the other for the opposite purpose. Both are usually organized similar to a standard dictionary, with plaintext words (in the first part) and ciphertext words (in the second part) presented like dictionary headwords.

An example of an algorithm using a codebook is the MacGuffin cipher

MacGuffin (cipher)

In cryptography, MacGuffin is a block cipher created in 1994 by Bruce Schneier and Matt Blaze at a Fast Software Encryption. It was intended as a catalyst for analysis of a new cipher structure, known as Generalized Unbalanced Feistel cipher ....
.