Symmetric

The M-94 Cipher is a mechanical cipher system developed by the U.S. Army in 1922, using 25 rotating disks, each engraved with a scrambled alphabet. Messages are encoded by arranging the disks in a predetermined order and reading the ciphertext from a selected row. Each disk acts as a simple substitution cipher, but the combination of multiple disks creates a polyalphabetic substitution.

The Jefferson Disk Cipher, invented by Thomas Jefferson in the late 18th century, is a polyalphabetic substitution cipher that uses a set of rotating disks, each marked with a scrambled alphabet. Each disk represents a cipher alphabet, and by aligning the disks in a chosen sequence, the plaintext is encoded by selecting a row from the disks. This system effectively produces a complex, polyalphabetic cipher resistant to simple frequency analysis.

Morse Code is a communication system that encodes letters, numbers, and punctuation into sequences of short and long signals, known as dits (·) and dahs (–). Developed by Samuel Morse and Alfred Vail in the 1830s–1840s, it was originally used for telegraph transmission but has since become a standard for signaling across many media. Each character in the plaintext is represented by a unique pattern of dots and dashes.

The Columnar Transposition Cipher is a classical transposition method that encrypts a message by rearranging entire columns of text according to a keyword. Unlike substitution systems such as the Caesar Cipher, the letters themselves are not altered — only their positions are changed.

It expands upon the simpler Columnar Cipher by explicitly reordering columns based on the alphabetical ranking of the keyword. This column permutation is the defining feature of the cipher.

The Cadenus–Gronsfeld Cipher is a variation of the Gronsfeld Cipher, itself a numeric version of the Caesar Cipher. It operates on alphabetic text by shifting each letter according to a repeating numeric key, but with the added twist that the key may include a reversible sequence or "cadenus" pattern, providing irregularity in the shifts. This makes it a hybrid between classical polyalphabetic ciphers and simple numeric substitution, increasing resistance to frequency analysis.

The Autokey Vigenère Cipher is an advanced polyalphabetic cipher that builds upon the classic Vigenère Cipher by incorporating an autokey mechanism. Instead of repeating a short keyword cyclically, the key is extended by appending the plaintext itself after the initial keyword. This produces a variable-length key, reducing repeating patterns in ciphertext and making frequency analysis considerably more difficult than in the standard Vigenère system.

The Trithemius Cipher is a polyalphabetic substitution cipher that shifts the alphabet progressively for each letter of the message. Instead of using a fixed shift like the Caesar Cipher, the shift increases step by step as the message is encoded.

The cipher was introduced by Johannes Trithemius in 1508. It works by applying a sequence of Caesar shifts to each letter of the plaintext. The first letter is shifted by 0, the second by 1, the third by 2, and so on. This changing shift produces a new substitution alphabet for every letter in the message.

The Porta Cipher is a classical polyalphabetic substitution cipher named after the Italian scholar Giambattista della Porta, who described it in the 16th century. It is a variant of the polyalphabetic cipher family, similar in principle to the Vigenère Cipher, but with a reciprocal structure that makes encoding and decoding symmetrical—using the same process in reverse produces the original text.

The M‑209 Cipher is a portable mechanical encryption device used by the U.S. Army during World War II for tactical field communications. It employs six rotating key wheels, each with a different number of pins, and a set of lugs connecting pairs of wheels. When a letter is entered, the current wheel positions and lug connections generate a polyalphabetic shift. Each subsequent letter causes the wheels to step, producing a dynamic substitution pattern.

The Lorenz Cipher is a machine-based stream cipher developed by the German Army during World War II, primarily for high-level communications such as messages between headquarters. Unlike the Enigma Cipher, which was used for tactical messages, the Lorenz system encrypted teleprinter (teletype) transmissions and relied on a series of twelve rotors to generate pseudo-random key streams for each character.