Cryptanalysis Exercises

The following directory contains the cryptanalysis examples used in a webcrypt cryptanalysis lecture (PDF slides):

cryptanalysis examples directory

• substitution.txt - encrypted using webcrypt's Substitution cipher which employs the monoalphabetic substitution This is similar to Stinson's substitution on p. 7, except that passwords are used to generate permutations as on p. 13 of Singh. For example the keyword "CAPTAINAHAB" is truncated to the non-redundant "CAPTINHB" which generates the plaintext to cipher text mapping: "abcdefghijklmnopqrstuvwxyz" → "CAPTINHBDEFGJKLMOQRSUVWXYZ".
• vigenere.txt - encrypted using webcrypt's Vigenere cipher which is similar to Stinson's Vigenere on p. 12, except that keys are written as words which are then re-interpreted as sequences of base-26 numbers.
• hill.txt - encrypted using webcrypt's Hill cipher. This is similar to Stinson's Hill on pp. 13-18 except for the following:
  1. Each plain-text block is converted to a column vector v, as opposed to a row vector so that the matrix key K is used to multiply from the left obtaining cipher-text blocks K.v.
  2. The key is given as word which is reinterpreted as a sequence of base-26 numbers. These numbers are put in order into the matrix key K starting at the upper-left corner and going column by column.
  3. Keys are inputted in the form "number_word". For example the key "3_albatross" generates the following matrix key K:

     	      A A O    0  0 14
     	 K =  L T S = 11 19 18 
     	      B R S    1 17 18
       

• enigma.txt - encrypted using webcrypt's Enigma cipher. You may assume three rotors and 5 plug-board settings. Keys are inputted in the form "rotor1rotor2rotor3_cable1_cable2_cable3_cable4_cable5". For example, the key "ADZ_AB_CD_EF_GH_IJ" represents setting the first rotor to A, the second to D, and the third to Z, plugging A to B, plugging C to D, plugging E to F, plugging G to H, and plugging I to J.

All plaintexts are random segments of about 1000 letters taken from Moby Dick by Herman Melville. You may find the following statistical files useful (best viewed in the web-browser under "fixed width" fonts).

• Monograph frequencies in Moby Dick
• Digraph frequencies in Moby Dick
• Trigraph frequencies in Moby Dick