Cryptanalysis Assignments

You have been emailed a personalized directory name that contains your cryptanalysis assignments. To access your personalized assignments directory append your directory name to the URL of this directory. For example, supposing your passwords was zeph then the resulting URL would be:

Inside there are four files:

• substitution.txt - encrypted using webcrypt's Substitution cipher. This is similar to Stinson's substitution on p. 7, except that passwords are used to generate permutations as on p. 13 of Singh.
• 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.

For the files you cryptanalyze, the goal is to recover the secret key. Partial credit is given for recovery or the plain-text, or portions of the plain-text without recovery of the key.

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