Editing Transposition cipher (section)

=== History ===

In the middle of the 17th century, [[Samuel Morland]] introduced an early form of columnar transposition. {{Citation needed|date=May 2025}} The technique was developed further over the next two centuries and became widely used in the late 19th and 20th centuries, notably by French military services, Japanese diplomats, and Soviet intelligence agencies.

John Falconer's ''[[Cryptomenysis Patefacta]]'' (1685) contains one of the earliest known English-language explanations of a keyed columnar transposition. Falconer gives no account of the cipher's origin, but he does explain how to write the plaintext into a rectangular grid, pad the final row with null letters, and extract the columns in a secret order determined by a keyword.<ref name="Falconer1685">{{cite book |last=Falconer |first=John |title=Cryptomenysis Patefacta; or, ''The Art of Secret Information Disclosed Without a Key'' |location=London |publisher=Daniel Brown|year=1685 |url=https://archive.org/details/cryptomenysispat00falc/page/62/mode/2up |page=62}}</ref>

Even more importantly, Falconer offers a worked method of cryptanalysis. He shows that an analyst can test different grid heights and reorder the columns by trial and error until readable text emerges, noting that the cipher preserves normal letters frequencies and is therefore susceptible to detection. He indicates that such letter frequencies can be used to detect the likely language of the text, even without knowing its contents, as letter frequencies differ between languages. Falconer does not discuss double transposition or how to solve ciphers where nulls are not provided in the final column, which suggests these were not widespread at the time.

Columnar transposition was subsequently incorporated into more elaborate systems—most famously the double transposition used by French military and diplomatic services, Japanese and German ciphers of the First and Second World Wars, and Soviet agents—remaining in serious use into the 1950s.  Falconer’s analysis anticipates many of the systematic attacks later refined against those double-stage versions, making ''Cryptomenysis Patefacta'' a landmark in the early literature of cryptanalysis.