Keyword Ciphers

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Keyword ciphers are substitution ciphers that use a key to determine what to substitute for each letter of the message.

• rather than shifting all letters by the same number:
  • shift each letter to match the corresponding letter in the keyword
• E.g.
  • choose a keyword, take those letters out of the alphabet and put it in front of the alphabet to spell the word, then keep the remaining letters in order
  • align to the regular alphabet

Vulnerable to frequency analysis, which means you can make guess about what the message contents might be based on the frequency of characters used, where those characters appear in words, and when they’re repeated.

• fixed by one-time pad