Codebook

From CryptoDox, The Online Encyclopedia on Cryptography and Information Security

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, corresponding 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.

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

In social sciences, a codebook is a document containing list of codes used in research.

In telegraphy, a codebook is a book (similar to a nomenclator) that converts common phrases and sentences used in business into (typically) 5-letter code groups before transmitting, and (at the other side of the ocean) converts back into the original phrases and sentences. This could save a lot of money when telegrams cost $25 per word. ^{[1] [2] [3]}

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1. ↑ "Ordered codes"
2. ↑ "Commercial Telegraphic Code Books"
3. ↑ "telegraphic codes and message practice, 1870-1945"

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