Polygraphic

The T9 / Phone Code Cipher is based on the multi-tap input method used on traditional numeric keypads. Each digit key corresponds to multiple letters, and the number of presses determines which letter is selected. Spaces between words are preserved.

The Tap Code Cipher is a substitution cipher that encodes letters based on their position in a 5x5 Polybius square, typically combining the letters I and J. Each letter is represented by two numbers: the row and column where it appears in the square. These numbers are then expressed as a series of taps, with the number of taps indicating the row and column.

The Nihilist Cipher is a polygraphic substitution cipher that combines the principles of the Polybius Square with a numeric key to produce a series of ciphertext numbers. It was developed in the 19th century by Russian nihilists to securely transmit messages, hence its name. Each letter is first converted into a pair of digits using a Polybius grid, then combined with corresponding digits from a numeric key by addition, resulting in ciphertext that appears as a sequence of numbers.

The Bifid–Bacon Hybrid Cipher is a creative fusion of the Bifid Cipher and the Baconian Cipher. It combines polygraphic transposition with dual-character substitution to create a cipher that spreads each plaintext letter across multiple symbols while encoding them into A and B sequences. This hybrid approach increases diffusion and adds a layer of steganography, making it more resistant to frequency analysis than either cipher alone.

The Straddling Checkerboard Cipher is a substitution cipher that encodes letters into digits using a numeric grid with main rows and offset rows. Common letters are assigned a single digit in the main rows, while less frequent letters use one of the offset rows as a prefix to create a two-digit code. This method compresses messages and provides a simple layer of obfuscation.