Codebook

In cryptography, a codebook is a document used for implementing a code. A codebook contains a lookup table for coding and decoding; each word or phrase has (one or more) strings which replace it. To decipher messages written in code, identical copies of the codebook must be available at either end. The distribution and physical security of codebooks presents a special difficulty in the use of codes, compared to the secret information used in ciphers, the key, which is typically much shorter.

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NSA documents sometimes use "codebook" to mean 'block cipher'; compare their use of "combiner-type algorithm" to mean 'stream cipher'.

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Cryptography: Cryptography is the field concerned with linguistic and mathematical techniques for securing information, particularly in communications. Historically, cryptography was concerned solely with encryption; that is, means of converting information from its normal, comprehensible form into an incomprehen...

Code: :For other senses of the word "code", see code (disambiguation)....

Lookup table: In computer science, a lookup table is a data structure, usually an array or associative array, used to replace a runtime computation with a simpler lookup operation. The speed gain can be significant, since retrieving a value from memory is often faster than undergoing an expensive computation....