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6 - Codes

Published online by Cambridge University Press:  13 August 2009

R. F. Churchhouse
Affiliation:
Cardiff University
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Summary

Characteristics of codes

As was mentioned in Chapter 1, the distinction between codes and ciphers is not always clear, but one might reasonably say that whereas most codes tend to be static most ciphers are dynamic. That is to say that a letter or phrase enciphered simply by means of a code will produce the same cipher each time the code is used, whereas a letter or phrase enciphered by a cipher system will generally produce different cipher text at different times. This is because most cipher systems involve one or more parameters, such as keywords or, as we shall see later, wheel settings, which are changed at regular or irregular intervals and so cause the cipher outputs from the same plaintext to be different. The basic mechanism, or algorithm, for generating the cipher doesn't change, but the parameters do. In general, a code has no such parameters though the entire code may itself be changed, in which case it becomes a different code. In practice this is achieved by issuing a new code-book every now and then. Using this criterion the Julius Caesar cipher would be classed as a code, because the encipherment of a fixed letter across many messages is invariably the same.

Type
Chapter
Information
Codes and Ciphers
Julius Caesar, the Enigma, and the Internet
, pp. 64 - 71
Publisher: Cambridge University Press
Print publication year: 2001

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  • Codes
  • R. F. Churchhouse, Cardiff University
  • Book: Codes and Ciphers
  • Online publication: 13 August 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511542978.007
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  • Codes
  • R. F. Churchhouse, Cardiff University
  • Book: Codes and Ciphers
  • Online publication: 13 August 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511542978.007
Available formats
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To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Codes
  • R. F. Churchhouse, Cardiff University
  • Book: Codes and Ciphers
  • Online publication: 13 August 2009
  • Chapter DOI: https://doi.org/10.1017/CBO9780511542978.007
Available formats
×