Cryptology Terminology

This page is a synopsis of definitions and terms used in cryptology. It is neither complete or definitive. Minor variances are omitted to allow the non specialist to use the list. Any glaring errors or omissions can be reported on by using the comments button at the bottom of the page.

Cipher

A mapping algorithm that is applied to a fixed number of characters at a time with an intent of concealing the contents of the message.

Code

A mapping algorithm that is applied to a vaiable number of characters (according to linguistic entities) at a time with an intent of concealing the contents of the message.

Commercial Code

A code used in business primarily to reduce cost by shortening messages. It involves no secrecy. The prime example is the 'Philips' Code.

Cryptanalysis

The study of methods of reading enciphered and encoded messages without original knowledge of the cipher method used or the current keys.

Cryptography

The study of methods of enciphering and deciphering messages to conceal the contents of a message.

Cryptology

The study of both cryptography (enciphering and deciphering) and cryptanalysis (breaking or cracking a code system or individual messages).

Deciphering

The procedure of turning enciphered text into plain text with prior knowledge of the algorithms or keys involved. This is what the intended message receiver does.

Decryption

The science of turning enciphered text into plain text without prior knowledge of the algorithms or keys involved. This is what the interceptor or 'cracker' does.

Digraphs

A plaintext character pairing technique that prevents frequency analysis of commonly occuring pairs such as 'qu'. Note that trigraphs (three characters at a time) is an extension of the theme.

Homophones

Several replacement letters for the same letter in plaintext

Key

A word or phrase that modifies the enciphering/deciphering process in such a way that knowledge of the algorithm alone is insufficient to decipher an enciphered message.

Monoalphabet

A single mapping of plaintext letters to ciphertext letters.

Nomenclator

Half code and half cipher, it was a list of word/syllable substitutions and cipher alphabet with homophones.

Nulls

Meaningless letters used to confuse by modifying frequency distributions or predictability. Sometimes used to fill a message to a specific length.

Plaintext

The original message to be encoded or enciphered

Polyalphabet

A method where several mappings of plaintext letters to ciphertext letters occur in a message.

Public Key Cryptosystem

A system where a pair of keys are used, one freely distributed and the other known only to the recipient.

Steganography

The art of concealing a message's existance. One example would be through the use of photographic microdots.

Substitution

Enciphering by replacing one letter by another.

Symmetric Key Cryptosystem

A system where both sender and receiver use the same key for enciphering and deciphering.

Transmission Security

The art of concealing an electrically transmitted message through burst encoding or spread spectrum methods.

Transposition

Enciphering by shuffling the order of letters.