Trifid cipher decoder and encoder

The Trifid cipher was invented by the French amateur cryptographer Félix Delastelle and described in 1902. It is an extension of the bifid cipher, from the same inventor. The Trifid cipher uses three tables to fractionate letters into trigrams, mixes the parts of the trigrams and then uses the table to convert the trigrams back to letters again.

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Trifid cipher tool


Polybius squares



  • The Trifid cipher is an example of a trigraphic cipher. Each crypto letter depends on three letters in the plaintext.
  • It is probably the first practical trigraphic cipher to be possible to carry out by hand.
  • It can encrypt 27 characters. Because the alphabet has 26 letters, one extra symbol has to be added to the alphabet (for instance a plus-sign).
  • The larger number of symbols than monoalphabetic ciphers produce makes it much more resistant to frequency analysis.
  • Longer messages are often broken into smaller groups and then each group is encrypted by itself. If the length of each group is not divisible by 3, it will be hardest to break the crypto.

Sample text


The ciphertext above represents "FELIX DELASTELLE" encrypted using the key CRYPTOGRAPHY.