Symmetric

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.

The Knapsack Cipher is a public-key cryptosystem based on the mathematical problem of the subset sum, also known as the "knapsack problem." It was one of the first attempts at a public-key encryption scheme, proposed by Ralph Merkle and Martin Hellman in 1978. The cipher transforms a plaintext message into a binary representation and encodes it as a sum of elements from a specially chosen sequence, making decryption without the private key computationally difficult.

The Kama-Sutra Cipher is a classical substitution cipher that encodes letters in pairs, based on a fixed alphabetic mapping. Each letter in a pair is replaced with its corresponding partner, making it a simple but effective polyalphabetic-style substitution. It is often used as an educational example of fractionating substitution systems, similar in concept to the Atbash Cipher but with paired letter substitution.

The Blowfish Cipher is a symmetric-key block cipher designed by Bruce Schneier in 1993. It was created as a fast, free alternative to older encryption standards and operates on 64-bit blocks using variable key lengths ranging from 32 bits to 448 bits. Blowfish is known for its speed in software implementations and its flexible key size, making it widely adopted in secure applications for many years.

The Baconian Cipher, created by Francis Bacon in the early 17th century, is a method of steganographic substitution rather than traditional cryptography. It encodes each letter of the alphabet into a unique sequence of five characters, typically A and B. This allows messages to be hidden in plain sight by representing letters as patterns within other text, fonts, or visual symbols. For example, under the variant mapping used here, the plaintext "H" is encoded as AABBB and "E" as AABAA.

The XOR Cipher is a symmetric encryption technique that operates at the bit level, combining each bit of the plaintext with a corresponding bit from a secret key using the exclusive OR (XOR) operation. It is simple but effective for situations where the key is as long as the message, forming the basis of the one-time pad. Its strength comes from the reversibility of the XOR operation: applying the same key twice restores the original plaintext.

The Vigenère Cipher is a classical polyalphabetic substitution cipher that uses a repeating keyword to determine shifting values for each letter in a message. Unlike the Caesar Cipher, which applies a single fixed shift, the Vigenère Cipher changes the shift for every letter based on the key. This shifting pattern significantly reduces simple frequency analysis.

It can be viewed as a systematic expansion of the Trithemius Cipher, which uses a progressive shifting pattern instead of a repeating keyword.

The Vernam Cipher is a symmetric encryption technique that combines each letter of the plaintext with a corresponding character from a secret key using modular addition on their alphabetical indices. Developed by Gilbert Vernam in 1917, it is the foundation of the one-time pad when the key is truly random and used only once. Its main strength lies in producing ciphertext that is theoretically unbreakable if the key is never reused.

The Transposition Cipher is a classical cipher technique that rearranges the letters of the plaintext according to a defined system, without changing the letters themselves. Unlike substitution ciphers, where letters are replaced with other letters or symbols, transposition ciphers preserve the original letters but change their positions to create the ciphertext.