Trifid

Explanation

The trifid cipher is a polygraphic substitution cipher and is an extension of the Bifid cipher.

To encode, a key matrix is generated, typically a permutation of the alphabet plus some additional symbols. Each letter of the plaintext is converted into its corresponding coordinates in the 3x3x3 grid. For example, if the letter is 'A', it could be represented as (1,1,1).

The coordinates are then rearranged according to the key matrix and the plaintext coordinate is (1,1,1), it might be rearranged to 2,3,1 based on the position of 'A' in the key matrix. The rearranged coordinates are converted back into letters.

The process is reversed. The ciphertext is first converted into coordinates, rearranged back using the key matrix, and then converted back into plaintext.

The Trifid cipher provides a higher degree of security compared to simpler ciphers like Caesar or Atbash, but it's still vulnerable to cryptanalysis, especially with modern computational methods. Despite its age, it remains an interesting historical cipher and is occasionally used in puzzles and cryptography challenges.

Facts

It was invented by Felix Delastelle in 1901.

It was used by the French during World War I.

Its name, 'Trifid', comes from the Latin word 'trifidus', meaning 'divided into three parts.'