Bifid cipher decoder and encoder

The Bifid cipher was invented by the French amateur cryptographer Félix Delastelle around 1901. It is a fractionating transposition cipher, and was considered as a system of importance in cryptology. The Bifid cipher uses a Polybius square to achieve the fractionation. Each character depends on two plaintext characters, so it is a digraphic cipher.

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Bifid cipher tool

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Polybius square



  • The Bifid cipher is an example of a digraphic cipher. Each crypto letter depends on two letters in the plaintext.
  • It is simple enough to be possible to carry out by hand.
  • It can encrypt 25 characters. Because the alphabet has 26 letters, one letter has to be replaced by another (for example replacing j by i).
  • 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 odd, it will be hardest to break the crypto.

Sample text


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