Trevanion Cipher

The Trevanion code is a method of steganography that involves concealing a message by using the position of punctuation marks within a text.

Each punctuation mark serves as a marker to extract a letter from the hidden message located at a position determined by a rule (defined between the communicating parties).

Trevanion's method of encryption/steganography involves writing a base text by precisely placing punctuation marks. After each mark (comma, period, semicolon, exclamation mark, question mark, etc.), a fixed number of letters are counted (for example, 3 letters). The letter in that position corresponds to a letter in the hidden message.

Decryption requires knowing the shift N used during encoding.

To find the hidden message, scan the text and identify each punctuation mark defined as a trigger.

After each one, count N letters (according to the chosen rule) to extract one letter from the plaintext.

A message using the Trevanion code is difficult to recognize if the underlying text is natural and the punctuation appears consistent.

However, excessively frequent or artificial punctuation can raise suspicions. Therefore, the method is not inherently undetectable, but relies on the discretion and plausibility of the text.

Without knowing the parameters (value of N, trigger characters, counting method), decryption relies on assumptions and brute-force attacks.

dCode can automatically test the most common combinations, varying the shifts and counting methods, to identify plausible messages.

It is possible to set the trigger characters, eg. to use characters other than the classical punctuation.

The method for calculating the offset may be different for each person, some will count for all characters, others will treat only letters.

17th century but the author is probably not John Trevanion. The name of this code was given in honor of John Trevanion, an Englishman, a prisoner who received a letter from a friend using this principle. But historians have found inconsistencies in this story and its authenticity is called into question.