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A codebook is a type of document used for gathering and storing
cryptography code In cryptology, a code is a method used to encrypt a message that operates at the level of meaning; that is, words or phrases are converted into something else. A code might transform "change" into "CVGDK" or "cocktail lounge". The U.S. Nat ...
s. Originally codebooks were often literally books, but today codebook is a byword for the complete record of a series of codes, regardless of physical format.


Cryptography

In
cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...
, a codebook is a document used for implementing a
code In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communication ...
. A codebook contains a
lookup table In computer science, a lookup table (LUT) is an array that replaces runtime computation with a simpler array indexing operation. The process is termed as "direct addressing" and LUTs differ from hash tables in a way that, to retrieve a value v wi ...
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 Physical security describes security measures that are designed to deny unauthorized access to facilities, equipment and resources and to protect personnel and property from damage or harm (such as espionage, theft, or terrorist attacks). Physica ...
of codebooks presents a special difficulty in the use of codes, compared to the secret information used in
cipher In cryptography, a cipher (or cypher) is an algorithm for performing encryption or decryption—a series of well-defined steps that can be followed as a procedure. An alternative, less common term is ''encipherment''. To encipher or encode i ...
s, the
key Key or The Key may refer to: Common meanings * Key (cryptography), a piece of information that controls the operation of a cryptography algorithm * Key (lock), device used to control access to places or facilities restricted by a lock * Key (map ...
, which is typically much shorter. The United States
National Security Agency The National Security Agency (NSA) is a national-level intelligence agency of the United States Department of Defense, under the authority of the Director of National Intelligence (DNI). The NSA is responsible for global monitoring, collecti ...
documents sometimes use ''codebook'' to refer to
block cipher In cryptography, a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called ''blocks''. Block ciphers are specified cryptographic primitive, elementary components in the design of many cryptographic protocols and ...
s; compare their use of ''combiner-type algorithm'' to refer to
stream cipher stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (keystream). In a stream cipher, each plaintext digit is encrypted one at a time with the corresponding digit of the keystream ...
s. Codebook come in two forms, one-part or two-part: * In one part codes, the plain text words and phrases and the corresponding code words are in the same alphabetical order. They are organized similar to a standard dictionary. Such codes are half the size of two-part codes but are more vulnerable since an attacker who recovers some code word meanings can often infer the meaning of nearby code words. One part codes may be used simply to shorten messages for transmission or have their security enhanced with
superencryption Multiple encryption is the process of encryption, encrypting an already encrypted message one or more times, either using the same or a different algorithm. It is also known as cascade encryption, cascade ciphering, multiple encryption, and superen ...
methods, such as adding a secret number to numeric code words. * In two part codes, one part is for converting plaintext to ciphertext, the other for the opposite purpose. They are usually organized similar to a language translation dictionary, with plaintext words (in the first part) and ciphertext words (in the second part) presented like dictionary headwords. The earliest known use of a codebook system was by Gabriele de Lavinde in 1379 working for the
Antipope Clement VII Robert of Geneva, (french: Robert de Genève; 1342 – 16 September 1394) elected to the papacy as Clement VII (french: Clément VII) by the cardinals who opposed Pope Urban VI, was the first antipope residing in Avignon, France. His election l ...
. Klaus Pommerening
"Codebooks"
Two-part codebooks go back as least as far as
Antoine Rossignol The Rossignols, a family of French cryptographers and cryptanalysts, included Antoine Rossignol (1600–1682), Bonaventure Rossignol and Antoine-Bonaventure Rossignol. The family name means "nightingale" in French. As early as 1406, the word ' ...
in the 1800s. From the 15th century until the middle of the 19th century, nomenclators (named after
nomenclator Nomenclator may refer to: *''Nomenclator omnium rerum propria nomina variis linguis explicata indicans'', 16th century book written by Hadrianus Junius *Nomenclator, in cryptography, a kind of substitution cypher *Nomenclator (nomenclature) as ...
) were the most used cryptographic method. Chris Christensen
"Codes and Nomenclators"
p. 4
Codebook with superencryption was the most used cryptographic method of World War I. The
JN-25 The vulnerability of Japanese naval codes and ciphers was crucial to the conduct of World War II, and had an important influence on foreign relations between Japan and the west in the years leading up to the war as well. Every Japanese code was e ...
code used in World War II used a code book of 30,000 code groups superencrypted with 30,000 random additives. The book used in a
book cipher A book cipher, or Ottendorf cipher, is a cipher in which the key is some aspect of a book or other piece of text. Books, being common and widely available in modern times, are more convenient for this use than objects made specifically for crypto ...
or the book used in a
running key cipher In classical cryptography, the running key cipher is a type of polyalphabetic substitution cipher in which a text, typically from a book, is used to provide a very long keystream. Usually, the book to be used would be agreed ahead of time, while ...
can be any book shared by sender and receiver and is different from a cryptographic codebook.


Social sciences

In social sciences, a codebook is a document containing a list of the codes used in a set of data to refer to variables and their values, for example locations, occupations, or clinical diagnoses.


Data compression

Codebooks were also used in 19th- and 20th-century commercial codes for the non-cryptographic purpose of data compression. Codebooks are used in relation to
precoding Precoding is a generalization of beamforming to support multi-stream (or multi-layer) transmission in multi-antenna wireless communications. In conventional single-stream beamforming, the same signal is emitted from each of the transmit antennas ...
and
beamforming Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in an antenna array in such a way that signals at particular angles e ...
in mobile networks such as 5G and LTE. The usage is standardized by 3GPP, for example in the documen
TS 38.331
NR; Radio Resource Control (RRC); Protocol specification.


See also

*
Block cipher modes of operation In cryptography, a block cipher mode of operation is an algorithm that uses a block cipher to provide information security such as confidentiality or authenticity. A block cipher by itself is only suitable for the secure cryptographic transforma ...
*
The Code Book ''The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography'' is a book by Simon Singh, published in 1999 by Fourth Estate and Doubleday. ''The Code Book'' describes some illustrative highlights in the history of cryptog ...


References

{{Reflist Cryptography Social research