Cryptanalysis
Patterns and pairs
Also found as word patterns · word signatures · pair frequencies · contacts
A word signature records equality
Give the first new symbol 1, the next new symbol 2, and reuse a number whenever the same symbol returns. The signature keeps repeated positions while discarding the symbols themselves. A monoalphabetic substitution preserves it because equal plaintext letters still become equal ciphertext letters.Military Cryptanalytics, Part IGaines, Cryptanalysis
- MEET
1.2.2.3- NOON
1.2.2.1
The signature rules words out; it does not choose the remaining word for you.
Contacts keep the neighbourhood
A left contact is the unit immediately before a selected unit; a right contact is the unit immediately after it. Counts show common neighbours, while the number of distinct contacts shows variety. A reversal records that an ordered pair occurs in both directions, such as AB and BA.Gaines, CryptanalysisElements of Cryptanalysis
Decipher counts letter contacts inside letter runs. Spaces, apostrophes, and hyphens stop a run. They can remain visible in a word signature while still preventing a contact across the break.
Adjacent and aligned pairs answer different questions
| Pair | Built from | Example |
|---|---|---|
| Adjacent | neighbouring units in one sequence | ABABA gives AB, BA, AB, BA |
| Aligned | one unit from each of two sequences | ABCD against WXYZ at offset +1 gives BW, CX, DY |
Order always matters: AB and BA are different pairs. For aligned pairs, the signed offset decides which positions meet. A useful alignment is still only a comparison; it does not prove that the two sources share a cryptographic relation.
A displayed group may not be a word
Ciphertext is often grouped for readability. Five-letter groups, compact coordinate streams, and transposed text can hide or invent apparent word boundaries. Use word patterns only when the division has a reason to carry linguistic meaning.