The 1944 Bletchley Park Cryptographic Dictionary

- 83 -

SUBSCRIBER :

An official or authorised user of a particular cipher or code.

SUBSTITUTION :

Process or action of putting one letter, figure, or other symbol or group of such, in place of any other unit or group. Systematic substitution is the basis of all codes and all ciphers except trans- position ciphers.

SUBTRACTOR

1. A series of figures or letters (or a group or single unit of such) which is added non-carrying figure by figure or letter by letter to the figures or letters of code groups in the process of reciphering or to the letters of plain language in the process of enciphering, and subtracted from the cipher in the processes of stripping and deciphering; an adder or additive.

2. A series of figures or letters (or a group or single unit of such) from which the figures or letters of code-groups are subtracted non-carrying figure by figure or letter by letter in the process of reciphering or from which the letters of plain language are similarly subtracted in the process of enciphering, and from which the figures or letters of the cipher text are subtracted in the processes of stripping and deciphering; properly a Beaufort subtractor, type one. cf. Minuend.

3. A series of figures or letters(or a group or single unit of such) which is subtracted non-carrying figure by figure or letter by letter from the figures or letters of code groups in the process of reciphering or from the letters of plain language in the process of enciphering, and added to the cipher in the processes of stripping and deciphering; properly a Beaufort subtractor, type two.

Note: all three types are also variously termed, recipher, recipher key, key, etc., as well as adder, additive key, subtractor. This inconsistency in nomenclature is inevitable as reciphered codes can in fact be stripped and broken and made wholly readable without knowing which of the above types of recipher is used, unless some limitation, or other feature, or accident, reveals the true figures.

4. Short for "subtractor cipher", i.e. a reciphered code.

SUMBOOK :

A book containing in numerical order the sums of every pair of a convenient number of good groups in a code-book (including the sum of each group and itself) together with the two good groups which each sum represents, designed to assist key-breaking with subtractor tables having as the second half of each table the groups which are the reciprocals of the groups in the first half in the same order.

| previous page | next page | index page |