Cryptography/Breaking transposition ciphers

From Wikibooks, open books for an open world
Jump to: navigation, search

Earlier, we discussed how Permutation cipher and Transposition ciphers work for people who know the secret key. Next, we'll discuss how, in some cases, it is possible for a person who only has the ciphertext -- who doesn't know the secret key -- to recover the plaintext.

The frequency distribution of the letters in any transposition or permutation ciphertext is the same as the frequency distribution for plaintext.

breaking columnar transposition ciphers[edit]

The frequency distribution of digrams can be used to help break columnar transposition ciphers. [1]

breaking double columnar transposition ciphers[edit]

breaking turning grille ciphers[edit]

Turning grilles, also called Fleissner grilles, ...

A guess at some sequence of two or more consecutive holes of the grill in one position of the grill (by a "known word" or an expected common digraph) can be "checked" by seeing if those holes, after the grill is rotated a half-turn, produce reasonable digraph.[2][3]


breaking other grille ciphers[edit]

Further reading[edit]

  1. Prof. H. Williams. "Transposition Ciphers". section "Analysis of columnar transposition ciphers". Retrieved 2014-05-01.
  2. Helen Fouché Gaines. "Cryptanalysis: A Study of Ciphers and Their Solution". 1956. section "The Turning Grille". p. 29 to 36.
  3. "Elementary Course in Cryptanalysis: Assignment 9: Grille Transposition Ciphers".