The *Oxford Dictionary of English Etymology* gives *to steal* and *to pilfer* as definitions of the Shakespearian verb *to crib*. The term *cribbing* in cryptography refers to the process of inferring key and plaintext from ciphertext based on partial knowledge of the plaintext. A *crib* is a word or phrase *w* = (*w*_{0}, *w*_{1}, …, *w*_{M−1}) known (or assumed) to appear in the plaintext. Partial knowledge of the plaintext is a reasonable assumption:

- Letters usually contain stereotyped beginnings and/or endings: Dear …, Sincerely yours, Att:, Senator …;
- Message transmitted over a network have special formats; and
- Files are often highly structured, records divided into fields containing data with known characteristics.

When the crib *w* = (*w*_{0}, *w*_{1}, …, *w*_{M − l}) occurs in the plaintext *x*, certain strings of letters derived from *w* will also occur in the ciphertext *y* = *T _{N, τ}*(

If *N* ≥ *M*, then *w* determines *N subcribs*, which are all the *maximal length* strings ≡ {*S*_{0}, *S*_{1}, …, *S*_{n−1}} formed by the letters in *w*, which are pairwise-separated by exactly *N* positions.

where *s _{i}* will denote the length of

The cryptanalysis of columnar transposition by cribbing is based on the following result.

**Proposition 2.1:** If *x* → *y* = *T _{N, τ}* (

2.1a |
Pairs of letters (x_{t}, x_{t+N}) in the plaintext separated by N places ... |

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