Kiss (cryptanalysis)

In cryptanalysis, a kiss was a term used at Bletchley Park during World War II for occasions when the enemy sent an identical message twice, once in a breakable cipher and again in an unbroken cipher. A deciphered message in the breakable system provided a "crib" (piece of known plaintext) which could then be used to read the unbroken messages. One example was where messages read in a German meteorological cipher could be used to provide cribs for reading the difficult 4-wheel Naval Enigma cipher.

cribs from re-encipherments .... were known as 'kisses' in Bletchley Park parlance because the relevant signals were marked with 'xx'

See also

• Cryptanalysis of the Enigma
• Known-plaintext attack

References

• Smith, Michael and Erskine, Ralph (editors): Action this Day (2001, Bantam London) ISBN 0-593-04910-1