Glossary for Historical Cryptology

This site contains definition of terms related to historical cryptology, including terminology for codes and nomenclators. Terms related to modern cryptology are not covered.

Certain terms, through long usage, have become more or less standard and generally acceptable while other terms hold different meanings in different areas. The lack of standardization has resulted, at times, in confusion and misunderstanding.

Ralph J. Canine in Basic Cryptologic Glossary (REF ID:A64719)


ADFGVX system
A German high-command cipher system used in World War I. Essentially, a biliteral substitution system employing a 6 x 6 square, to which a columnar transposition was subsequently applied.

Alternate horizontal route transposition
Row transposition in which the route followed is alternately from left to right and from right to left in successive rows.
Other terms with the same meaning: boustrophedon.

Alternate vertical route transposition
Columnar transposition in which the route followed is alternately up and down in successive columns.
Other terms with the same meaning: boustrophedon.

Plain language reconstructed from a transposition cipher by restoring the letters of the cipher text to their original order.

Autokey system
An aperiodic substitution system in which the key, following the application of a previously arranged initial key, is generated from elements of the plain or cipher text of the message.

Baconian cipher
A multiliteral cipher system invented by Sir Francis Bacon (1561-1626) in which the cipher units are composed of arrangements of five elements, each of which may be chosen from one of two categories.

Beaufort system
A polyalphabetic substitution system employing a key word in connection with a Vigenere square, but differing from the normal Vigenere method in its rules for application of the key.

Begin spell
The plain equivalent of a code group indicating that the groups immediately following represent elements taken from the syllabary or other special list.
Other terms with the same meaning: switch group.

Bipartite alphabet
A multiliteral alphabet in which the cipher units may be divided into two separate parts whose functions are clearly defined, e. g., row indicators and column indicators of a matrix.

Bipartite system
A substitution system involving the use of a bipartite alphabet.

Blocked code
A form of modified one-part code in which the code groups and their corresponding plaintext values are arranged in one-part order within blocks which themselves are scattered in two-part order within the code.
When these reshuffled blocks are consistently of the same length as a page, the system is called a repaginated code.

Book cipher
A cipher system, utilizing any agreed-upon book, in which the cipher identifies a plain element present in the book.

Caesar's cipher
An ancient form of simple substitution cipher in which each plaintext letter was replaced by the letter three places to the right of it in the normal alphabet; attributed to Julius Caesar.

I. A cipher system.
II. A cryptogram produced by a cipher system (use cryptogram instead).

Cipher alphabet
An ordered arrangement of the letters (or other conventional signs, or both) or a written language and of the characters which replace them in a cryptographic process of substitution.

Cipher device
A relatively simple mechanical contrivance for encipherment and decipherment, usually hand-operated or manipulated by the fingers, such as sliding strips or rotating disks.

Cipher disk
A cipher device consisting of two or more concentric disks, each hearing on its periphery one component of a cipher alphabet.

Cipher machine
A relatively complex apparatus or mechanism for encipherment and decipherment, usually equipped with a keyboard and often requiring an external power source.

Cipher system
Any cryptosystem in which cryptographic treatment is applied to plaintext units of regular length.

Cipher text
The text of a cryptogram which has been produced by means of a cipher system. Of or pertaining to the encrypted text produced by a cipher system or to the elements which comprise such text; as the ciphertext distribution.
Often shortened to cipher.

l. A code system.
II. A code book.
III. A system of signals used in electrical or electronic communication.

Code book
A book or document used in a code system, arranged in systematic form, containing units of plain text of varying length (letters, syllables, words, phrases, or sentences) -each accompanied by one or more arbitrary groups of symbols used as equivalents in messages.

Code group
A group of letters or numbers, or a combination of both, assigned (in a code system) to represent a plaintext element.
Letter / Syllable / Phrase/ Word - group: Code group that refers to letter / syllable / phrase / word.

Code system
A cryptosystem in which arbitrary groups of symbols represent plaintext units of varying length, usually syllables, whole words, phrases, and sentences.

Code table
A short code in tabular form.

Code text
The text of a cryptogram which has been produced by means of a code system.

A word which conveys an agreed upon meaning rather than its conventional meaning. A cover name.

Columnar transposition
A method uf transposition in which the ciphertext is obtained by inscribing the plain text into a matrix in any way except vertically and then transcribing the columns of the matrix.

Cover name
An arbitrary word used, for security reasons, to indicate a specific meaning such as a device, program, place, or unit and which specifically has no semantic connection with its meaning.

I. Plain text assumed or known to be present in a cryptogram.
II. Keys known or assumed to have been used in a cryptogram.

The analysis of encrypted messages; the steps or processes involved in converting encrypted messages into plain text without initial knowledge of the key employed in the encryption.

A person versed in the art of cryptanalysis.

A communication in visible writing which conveys no intelligible meaning in any known language, or which conveys some meaning other than the real meaning.
Other terms with the same meaning: encrypted message.

All documents, devices, and machines employed in encrypting and decrypting messages.

The associated items of cryptomaterial and the methods and rules by which these items are used as a unit to provide a single means of encryption and decryption. A cryptosystem embraces the general cryptosystem and the specific keys essential to the employment of the general cryptosystem.

To convert an enciphered message into its equivalent plain text by a reversal of the cryptographic process used in the encipherment.
(This does not include solution by cryptanalysis.)

A decrypted, but not translated, message. To transform an encrypted communication into an intelligible one by a reversal of the cryptographic process used in encryption.
(This does not include solution by cryptanalysis.)

Digraphic substitution
Encipherment by substitution methods in which the plaintext units are pairs of characters and their cipher equivalents usually consist of two characters.

Double transposition
A cryptosystem in which the characters of a first or primary transposition are subjected to a second transposition.

To convert a plaintext message into unintelligible language or signals by means of a cipher system.

To convert a plaintext message into unintelligible language or signals by means of a cryptosystem.

Encrypted text
The text produced by the application of a cryptosystem to a plaintext message.

Equivalent key
A specific key that produces the same cryptographic results as a different specific key.

Friedman square
A cipher square in which all the diagonals reading in one direction contain the same sequence; in machine cipher solution, the square represents the substitution effected by rotating a single rotor through all possible positions.
Other terms with the same meaning: rod square.

I. A sheet of paper, cardboard, thin metal, plastic, or like material in which perforations have been made for the uncovering of spaces in which textual units or key may be written or read on a grid.
II. A matrix in which certain squares are blocked out or otherwise marked so as not to be used. Also called a stencil.

Gronsfeld system
A polyalphabetic substitution system employing the first 10 alphabets of a direct standard Vigenere table in conjunction with a numerical key. The cipher equivalent of a given plaintext letter is found by counting down the normal sequence the number of positions indicated by the numerical key.

Different cipher text elements that maps to the same plain text element - having the same meaning (by definition there are always at least two homophones).

Initial key
The key used in starting an encipherment; especially, the short key used to begin an autokey encipherment.
Other terms with the same meaning: preliminary key or priming key.

I. In a transposition system, the process of writing a message into a matrix.
II. The process of writing a series of numbers, letters, or coded meanings into a code chart or table.

Jefferson cipher
A polyalphabetic substitution system invented by Thomas Jefferson and independently at a later date by the French cryptographer Bazeries. It provided for encipherment by means of a manually operated device involving a number of revolvable disks, each bearing a mixed alphabet on its periphery.

In cryptography, a symbol or sequence of symbols applied to successive textual elements of a message to control their encryption or decryption.

Key word
An arbitrarily selected word used as a key per se, or from which a key is derived.

Latin square
A cipher square in which no row or column contains a repeated symbol.

Any thought or idea expressed in plain or secret language, prepared in a form suitable for transmission by any means of communication.

Mnemonic key
A key so constructed as to he easily remembered.

Monoalphabetic substitution
A type of substitution employing a single cipher alphabet by means of which each cipher equivalent, composed of one or more elements, invariably represents one particular plaintext unit, wherever it occurs throughout any given message.

Multiliteral cipher alphabet
A cipher alphabet in which one plaintext letter is represented by cipher units of two or more elements.

Multiliteral system
A substitution system involving one or more multiliteral cipher alphabets.

Multipartite alphabet
A multiliteral alphabet in which each letter of plain text is represented by a cipher unit of two or more characters whose functions are clearly defined.

Multiple-alphabet system
A type of substitution in which successive lengthy portions of a message are each monoalphabetically enciphered by a different alphabet; monoalphabetic encipherment by sections.

Encryption method that contains elements of both a code and a cipher; this usually means that frequent words, names and locations have their own code groups, while other words are encrypted letter-wise.
Commonly used as a combination of a monoalphabetic/homophonic substitution, digraphic/trightraphic substitution, codes and nulls;

Normal alphabet
The conventional sequence of letters which form the elements of written language and are used to represent approximately the sounds of the spoken language. The direct standard alphabet beginning with "A" and ending with "Z".

Code group that has no meaning.

Code group that makes another codegroup meaningless.
Prefix nullifier / postfix nullifier / embraced nullifier / embracing nullifier: Nullifier that makes the following / the previous / both / the embraced code group(s) meaningless; expressions like “3-prefix nullifier”, “2-postfix nullifier”, or “2-3-embraced nullifier” may be used if several code groups are made meaningless.

One-part code
A code in which the plaintext clements arc arranged in alphabetical, numerical, or other systematic order accompanied by their code groups also arranged in alphabetical, numerical, or other systematic order.

Nomenclator, in which the plaintext units and the codegroups are sorted analogously.

One-time pad
A form of key honk used in a one-time system, so designed as to permit the destruction of each page of key as soon as it has been used.

One-time system
A cryptosystem in which the key, normally of a random nature, is used only once.

Open code
A system of disguised secret writing in which units of plain text are used as the code equivalents for letters, numbers, words, phrases, or sentences. The code equivalents themselves, usually words or phrases, can be combined to form the intelligible text of apparently innocent messages.

Extraneous text added to a message for the purpose of concealing its length and beginning or ending or both.

Partially-polygraphic system
Any polygraphic substitution system in which the encipherment of certain members of the polygraphs show group relationships; small matrix systems, such as the four-square, two-square and Playfair systems involve such group relationships and are considered to be partially-digraphic systems.

A plaintext or cipher sequence which contains or shows a pattern in its construction as regards the number and positions of repeated elements.
Other terms with the same meaning: idiomorph.

Periodic substitution
Periodic polyalphabetic substitution. A method of encipherment involving the cyclic use of two or more alphabets.
Other terms with the same meaning: repeating key method.

Periodic system
A system in which the enciphering process is repetitive in character and which usually results in the production of cyclic phenomena in the cryptographic text.

Plain code
Unenciphered code.

Plain text
I. Normal text or language which, with no hidden or secret meaning, conveys knowledge.
II. The intelligible text underlying a cryptogram.
Other terms with the same meaning: clear text, text in claris.

Of or pertaining to that which conveys an intelligible meaning in the language in which it is written with no hidden meaning; as the plaintext equivalents.
Often shortened to plain.

Playfair system
A type of digraphic substitution using a single matrix normally of 25 cells.

Polyalphabetic substitution
A type of substitution in which the successive plaintext elements of a message, usually single letters, are enciphered by a succession of different alphabets.

Polygraphic substitution
Encipherment by substitution methods in which the plaintext units are regular length groupings of more than one element.

Cipher text element having several meanings. Cipher text element in a polyalphabetic system.

Porta system
A forerunner of the Vigenere system of polyalphabetic substitution, this system employs 13 alphabets formed by sliding the second half of the normal alphabet against the first half. Each alphabet may be identified by either of two key letters.

One of the components contained in the heading of a message whose elements include the degree of precedence, the date-time-group, and message instructions.

Probable word
A word assumed or known to be present in the underlying plain text of a cryptogram. A crib.

Pseudo-polygraphic system
A polygraphic substitution system in which at least one of the letters in each polygraph is enciphered monoalphabetically.

Q code and Q signal
Q code - A code adopted by the International Telecommunications Conference at Cairo, 1938.
Q signal - In joint and combined usage, a trigraph beginning with "Q" used to facilitate the handling of traffic, to direct net operation, or to convey certain originator's instructions in a message.

Random text
Text which appears to have been produced by chance or accident, having no discernible patterns or limitations.

To solve; to reconstruct (e. g., cryptographic data or plain text.)

Recovered code
A codebook whose groups have been identified by cryptanalysis.

Repaginated code
A code in which the pages of the code book have been assigned a new sequence of identifying symbols.

Revolving grille
A type of grille in which the apertures are so distributed that when the grille is turned successively through four angles of 90 degrees and set in position on the grid, all the cells on the grid are disclosed only once.
Other terms with the same meaning: rotating grille.

A movable metal collar bearing symbols, usually the letters of the alphabet, on a rotor.

A disk designed to rotate within a cipher machine and which controls the action of some other machine component or produces a variation in some textual or keying element. Other terms with the same meaning: wheel.

Route transposition
A method of transposition in which the cipher-text equivalent of a message is obtained by transcribing, according to any prearranged route, the letters inscribed in the cells of a matrix into which the message was inscribed earlier according to some prearranged route.

Running key
In polyalphahetic ciphers, a non-periodic key arbitrarily prepared or obtained from a book or any continuous text.

Simple substitution
Monoalphahetic uniliteral substitution.

In its cryptanalytic application, the process or result of solving a cryptogram or cryptosystem by cryptanalysis.

To cryptanalyze. To find the plain text of encrypted communications by cryptanalytic processes, or to recover by analysis the keys and the principles of their application.

A stationary element in a cipher machine, (e. g., an endplate, a separator or a rotor), that does not move during the operation of the machine.

Substitution cipher
I. A cipher system in which the elements of the plain text are replaced by other elements.
II. A cryptogram produced by enciphering a plaintext message with a substitution system.

In a code hook, a list of individual letters, combination of letters, or syllables, accompanied by their equivalent code groups, usually provided for spelling out words or proper names not present in the vocabulary of a code; a spelling table.

I. In a transposition system, the process of removing the text from a matrix or grid by a method or route different from that used in the inscription.
II. A written copy of a previously recorded radio transmission; also the process of preparing such copy from tapes or records.

Transposition cipher
I. A transposition system.
II. A cryptogram produced by enciphering a message with a transposition system.

Transposition system
A cryptosystem in which the elements of plain text, whether individual letters, groups of letters, syllables, words, phrases, sentences or code groups or their components undergo some change in their relative positions without a change in their identities.

Trigraphic substitution system
A substitution system in which the plaintext units are composed of three elements.

Two-part code
A randomized code, consisting of an encoding section in which the plaintext groups are arranged in an alphabetical or other systematic order accompanied by their code groups arranged in a non-alphabetical or random order; and a decoding section, in which the code groups are arranged in alphabetical or numerical order and are accompanied by their meanings as given in the encoding section.

Two-part nomenclator
Nomenclator, in which the plaintext units and the codegroups are sorted not analogously.

Of, or pertaining only to cryptosystems, cipher alphabets and frequency distributions which involve cipher units of single letters or characters.

Uniliteral substitution
A cryptographic process in which the individual letters or a message text are replaced by single-letter cipher equivalents.

Weather code
A code used for the transmission of weather data.

Wheatstone cipher device
A cipher device consisting essentially of two rings mounted concentrically in a single plane, the outer (IUld larger) ring being the plain component of the device and comprising 27 equisized divisions, the inner (and smaller) ring being the-cipher component, comprising 26 smaller divisions. The device incorporates two hands (similar to those on a clock) pivoted at the center or the device-the larger hand serving the outer ring and the smaller hand the inner-so geared together that for each complete revolution of the larger, the smaller turns through one complete revolution plus one twenty-sixth.