The poem code is a simple, and insecure,
cryptographic method which was used during World War II by the British
Special Operations Executive
The Special Operations Executive (SOE) was a secret British World War II organisation. It was officially formed on 22 July 1940 under Minister of Economic Warfare Hugh Dalton, from the amalgamation of three existing secret organisations. Its pu ...
(SOE) to communicate with their agents in Nazi-occupied Europe.
The method works by the sender and receiver pre-arranging a
poem
Poetry (derived from the Greek '' poiesis'', "making"), also called verse, is a form of literature that uses aesthetic and often rhythmic qualities of language − such as phonaesthetics, sound symbolism, and metre − to evoke meanings ...
to use. The sender chooses a set number of words at random from the poem and gives each letter in the chosen words a number. The numbers are then used as a
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 (ma ...
for a
transposition cipher
In cryptography, a transposition cipher is a method of encryption which scrambles the positions of characters (''transposition'') without changing the characters themselves. Transposition ciphers reorder units of plaintext (typically characters o ...
to conceal the
plaintext
In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted.
Overview
With the advent of com ...
of the message. The cipher used was often double
transposition. To indicate to the receiver which words had been chosen, an indicator group of letters is sent at the start of the message.
Description
To encrypt a message, the agent would select words from the poem as the key. Every poem code message commenced with an indicator group of five letters, whose position in the alphabet indicated which five words of an agent's poem would be used to encrypt the message. For instance, suppose the poem is the first stanza of
Jabberwocky
"Jabberwocky" is a nonsense poem written by Lewis Carroll about the killing of a creature named "the Jabberwock". It was included in his 1871 novel '' Through the Looking-Glass'', the sequel to ''Alice's Adventures in Wonderland'' (1865). The ...
:
''’Twas brillig, and the slithy toves''
'' Did gyre and gimble in the wabe:''
''All mimsy were the borogoves,''
'' And the mome raths outgrabe.''
We could select the five words THE WABE TOVES TWAS MOME, which are at