The Bifid Cipher is a Fractionating Transposition cryptographic technique that was invented by the French amateur cryptographer Félix Delastelle in 1901. It is a fractionating transposition cipher that combines elements of both substitution and transposition methods.
The Bifid Cipher operates on a square grid known as the Polybius square or Polybius checkerboard. This square consists of a 5x5 grid containing the letters of the alphabet (usually excluding the letter 'J').
The encryption process in the Bifid Cipher involves the following steps: