Computer Security and Cryptography

6.5 ANALYSIS OF A 1-ROTOR SYSTEM: CIPHERTEXT ONLY

Example 6.1

The ciphertext that follows contains eight rows, each containing 78 letters and a final ninth row of 26 letters. We begin the cryptanalysis by writing the ciphertext in Table 6.3 in columns of 26 letters. Denote by N(i) the length of the ith column and N_t(i) the number of times the letter t appears in the ith column.

______________________________________________________________________________
                                  cipherEx6.1
______________________________________________________________________________
rblfogzbkgcwuqfydkibkrfolsfjmyxvlhdwfeyuiwhguybqsrhhbolkagixxkritjwdhrqcwrkdae
pcdyfrekdxwwuovrarqxihbrintjrrryhdfcwsmkicnnidgoxdhniwlbytelcqbmoxpwmsdszeglae
ffqpyltbmkrwookdq jodlwbkuakoapeeobehtvoocnkrrpvllliqbgyijzyzqkrgsgmrsdcbielyvz
agpetywbgpeijuicgvwczqtbchzfwvozhdibshmmnhtjdufabtsszflhhvjdrqembkphelvhfyjdkx
rirmjmlcnvwgtsfvisgpfrgojrwistjzzxubpwlhwetjncbjwdlmpxlhtzjnmaxmmkeemxlegzldxw
coslyehxjnchjscwquemqejlinzzcxzwojiqgvcnicdwrdrmibdoxyrvajhcixgwuzohtrwgqsaxqn
ozsjzzrlnhunekpooaqxihlavycciphbobqhwbpdmcnkwcfyjrgekclyfvoljslxohfemkizfyjfvl
xuiyfgrfiqiltkqqhkcpiklavcxpzaduwpisutlxpyuxusfrdmmabhxdzxxbujjgaqfydkoejuktgj
ptfpzjybeotomkplyvrstrnbaq
______________________________________________________________________________

If t is the correct plaintext value for ciphertext s in the 0th column, then t – i will be the correct plaintext value for ciphertext s – i in the ith column for every i with 0 ≤ i < 26. It follows from the law ...