Vigenere Cipher Breaker

Usage

vcb  [flags]  trigram-stat-file  cipher-text-file

Tries to decrypt the vigenere cipher encrypted cipher-text-file. It will only break keys of length up to and including 12. The program works reliable for text length of 150 characters and bigger. Lengthy texts slow the program down, though.

The key using the encoding below and the most likely plaintext are printed to stdout.

Flags

-d: Print debugging information
-l linelength: Specify the approximate length of a line of plain text on your display (default: 75); Print debugging information
-p penalty: Specify a penalty for illegal trigrams (default: -1000) We recommend to use the negative frequency of the trigram: "the" "penalty" is used by the trigram scorer

Encoding

space a b c d e f g h i  j  k  l  m  n  o  p  q  r  s  t  u  v  w  x  y  z
0     1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

The trigram-stat-file

The trigram-stat-file is an ascii file that has been generated by the statistic tool .

The cipher-text-file

The ciphertext-file is an ascii file. Only lowercase letters, space, and newline may used. Newlines are ignored, though. It is expected that words are separated by a word separator character that might be different from space.

Last Update: 15.04.96 (Format: DD.MM.YY)