Affine cipher
Affine ciphers is a special case of the more general substitution ciphers.
In affine ciphers the encryption function for a letter is  (mod m) where,
- a and m are relatively prime.
- a and b are integers between 0 and m.
- m is the size of the alphabet.
The decryption function is  (mod m) where  is the inverse of a in the group Zm
This cipher is less secure then a substitution cipher as it is vulnerable to all of the attacks that work against substitution ciphers as well as other attacks. The cipher's primary weakness comes from the fact that if the cryptanalyst can discover (by means of frequency analysis, brute force, guessing or otherwise) the plaintext of two ciphertext characters then the key can be obtained by solving a simultaneous equations. As we know a and m are relatively prime this can be used to rapidly discard many "false" keys in an automated system.
See also: Topics in cryptography, affine functions.
Referenced By
Affine | Topics in cryptography
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