Polygraphic

The Nihilist Substitution Cipher is a classical encryption method that combines a Polybius square with a numeric additive key to produce a numeric ciphertext. It was historically used for its simplicity in encoding messages into numbers while maintaining a level of secrecy. Each letter of the plaintext is converted into a two-digit number via a Polybius square and then offset by a numeric key to generate the final ciphertext.

The Checkerboard Cipher, also known as the Polybius Checkerboard Cipher, is a classical substitution cipher that converts letters into numeric pairs or digits using a keyword-based grid. Each letter is assigned a coordinate in a 5x5 or 6x5 checkerboard matrix, with the keyword determining the arrangement of letters. This approach allows letters to be represented as one or two digits, providing a compact numeric encoding while introducing a keyed substitution system.

The Tri-Square Cipher is a polygraphic substitution cipher that operates on digraphs (pairs of letters) using three separate keyed 5×5 squares. Each square contains a unique permutation of the alphabet, often constructed from a keyword, with the letter J typically combined with I to fit the 25-cell square. By using three squares simultaneously, the cipher increases complexity and resists frequency analysis more effectively than simpler digraphic systems like the Playfair Cipher or Digrafid Cipher.

The Portax Cipher is a classical polygraphic substitution cipher that combines elements of the Porta Cipher with structured digraph processing. It operates on pairs of letters and uses a repeating keyword to control how each pair is transformed. Unlike simple substitution ciphers, the Portax Cipher modifies both letters in a pair simultaneously, increasing diffusion and reducing recognizable patterns.

The Bazeries Cipher is a classical encryption method that combines substitution and transposition techniques into a multi-stage process. It was developed by Étienne Bazeries, a French cryptographer, and is known for blending a keyed substitution alphabet (similar to the Playfair Cipher) with a numeric or keyword-driven transposition. This layered design makes it more complex than simple substitution or transposition ciphers alone.

The Nicodemus Cipher is a classical polygraphic transposition cipher designed to encrypt messages using a keyword-driven arrangement of letter pairs. Named after cryptographer Nicodemus, this cipher extends the principles of traditional substitution and transposition by working on multiple letters at a time, often in digraphs or trigraphs, and incorporating padding to maintain regular block sizes. It provides a higher level of complexity than simple monoalphabetic or basic polyalphabetic ciphers.

The Swagman Cipher is a classical polyalphabetic substitution cipher that encrypts plaintext using a repeating keyword to control shifts across letters. It operates similarly to a modified Vigenère cipher, but incorporates unique internal rules for letter substitution that can vary based on the implementation. The cipher aims to increase security over simple monoalphabetic systems by making each letter’s encoding dependent on its position and the keyword.

The Three Square Cipher is a classical polygraphic substitution cipher that encrypts pairs of letters using three separate keyed squares. It is closely related to the Playfair Cipher and the Two-Square Cipher, but increases complexity by introducing a third square, which enhances diffusion and reduces recognizable patterns in the ciphertext.

The Digrafid Cipher is a classical digraphic substitution cipher that encrypts plaintext in pairs of letters, also known as digraphs. It uses a keyword to create a 5x5 (or 6x6 for extended alphabets) grid, similar in concept to the Playfair Cipher, but with modifications that enhance diffusion and obfuscation. Each digraph is mapped to another digraph according to the grid rules, producing ciphertext that appears less patterned than simple substitution ciphers.

The Myszkowski Transposition Cipher is a variation of the classical columnar transposition cipher that introduces a unique handling of repeated letters in the key. Named after its Polish origin, this cipher modifies the standard columnar approach by allowing duplicate key letters to share the same column rank, resulting in a more nuanced and less predictable rearrangement of the plaintext.