codebook

From code +‎ book.

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codebook (plural codebooks)

1. (cryptography) A book, table, database, or other object that stores the mapping between plaintext words or phrases and their equivalents in a code.
   • 2011 July 25, John Markoff, “Codebook Shows an Encryption Form Dates Back to Telegraphs”, in The New York Times‎:

     In the 19th century codebooks were used not so much for secrecy as for compression, to bring down the prohibitive cost of telegraph communication. […] But when Dr. Bellovin hunted though the card catalog, his interest was piqued by an 1882 codebook whose title included the word “secrecy.”

2. (computer science) A lookup table.
   • 2013, Kazuhiro Kondo, Multimedia Information Hiding Technologies and Methodologies for Controlling Data, Hershey, P.A.: Information Science Reference, →ISBN, page 226, column 2:

     We assume that DWT coefficients belong to a codeblock that is divided by its quantization step size in advance and the two codebooks, ${\displaystyle C^{0}}$ and ${\displaystyle C^{1}}$, for the two quantizers can be defined as […]

   • 2016 July 26, Pam Belluck, “W.H.O. Weighs Dropping Transgender Identity From List of Mental Disorders”, in The New York Times‎:

     The change, which has so far been approved by each committee that has considered it, is under review for the next edition of the W.H.O. codebook, which classifies diseases and influences the treatment of patients worldwide.