Substitution

The Pollux Cipher is a classical encryption technique that blends keyed substitution with positional manipulation to provide polyalphabetic behavior. It utilizes a keyword to generate a keyed alphabet and can optionally apply padding to ensure the plaintext aligns with the cipher’s structural rules.

The Slidefair Cipher is a classical cipher that combines keyed substitution with a sliding mechanism to diffuse plaintext characters. It relies on a keyword to generate a keyed alphabet, and uses numeric or positional shifts to rearrange letters, introducing both substitution and transposition characteristics in a single step.

The Quagmire IV Cipher is the most advanced member of the classical Quagmire cipher family, combining multiple keyed alphabets with a dynamic indicator system. It extends the ideas of Quagmire I, II, and III by using a fully keyed plaintext alphabet, a fully keyed cipher alphabet, and a repeating indicator key derived from the keyword itself. This results in a highly complex polyalphabetic substitution system.

The Quagmire III Cipher is a classical polyalphabetic substitution cipher that extends the Quagmire family by using two keyed alphabets along with a repeating indicator keyword. Unlike Quagmire I and Quagmire II, which only key one side of the substitution, the Quagmire III Cipher uses a keyed plaintext alphabet and a keyed cipher alphabet, significantly increasing complexity and resistance to analysis.

The Quagmire II Cipher is a polyalphabetic substitution cipher that builds upon the foundation of the Quagmire I Cipher but introduces a variation in how the cipher alphabet is generated. Unlike Quagmire I, where the first keyword defines the base alphabet in standard order, Quagmire II uses the first keyword to create a mixed cipher alphabet, while the second keyword continues to control the dynamic shifts for each plaintext letter. Padding characters like X are used to fill incomplete blocks if needed.

The Quagmire I Cipher is a polyalphabetic substitution cipher designed to increase the security of classical ciphers by introducing a mixed alphabet keyed on a second keyword. It builds upon the Caesar Cipher concept, but instead of a fixed shift, each plaintext letter is encrypted using a shifting alphabet determined by a primary key (the first keyword) and a secondary key (the second keyword), which rotates the cipher alphabet for each letter. Padding characters like X are used to complete plaintext blocks when necessary.

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.