Symmetric

The Knapsack cipher, also known as the Merkle–Hellman knapsack cryptosystem, is an early public-key cryptosystem introduced by Ralph Merkle and Martin Hellman in 1978. It is based on the subset-sum problem, where the goal is to select numbers from a set that sum to a target value. The cipher uses a private superincreasing sequence, then applies a multiplier m and a modulus n to produce a public key.

The Kama-Sutra cipher, also known as the Kamasutra cipher, is a classical substitution cipher originating in ancient India and described in the Kama Sutra, traditionally attributed to Vātsyāyana around 300 CE to 400 CE. Despite its modern name association, the cipher itself is not related to sexuality; it appears in a section on secret writing as a practical method for discreet communication. The cipher is a simple monoalphabetic substitution system based on paired letters rather than a full substitution table.

The Blowfish cipher is a symmetric-key block cipher designed by Bruce Schneier in 1993 as a fast, secure alternative to existing encryption algorithms like DES. It operates on 64-bit blocks of plaintext and uses variable-length keys ranging from 32 to 448 bits. Blowfish employs a Feistel network structure consisting of 16 rounds of substitution and permutation.

The Baconian cipher is a substitution cipher devised by the English philosopher and statesman Francis Bacon in 1605. It represents one of the earliest examples of a binary-style encryption system, where each letter of the plaintext is encoded into a sequence of five symbols. Bacon originally used the letters A and B as the building blocks of his system, creating a simple yet ingenious method to conceal textual information within seemingly ordinary text.

The XOR Cipher is a symmetric key cipher that uses the logical XOR (exclusive or) operation for encryption and decryption. It gained prominence in computer science and cryptography for its simplicity and efficiency. The origins of the XOR Cipher are not attributed to a single creator or a specific date; rather, it has been known since the early days of binary computing, particularly during the 1960s.

The Vigenère cipher is a classical polyalphabetic substitution cipher developed in its modern form by the French cryptographer Blaise de Vigenère in 1586, although its conceptual origins trace back to Giovan Battista Bellaso in 1553. It encrypts text by shifting each letter of the plaintext according to the corresponding letter in a repeating keyword, effectively using multiple Caesar ciphers in sequence.

The Vernam cipher is a symmetric stream cipher invented by the American engineer Gilbert S. Vernam in 1917. It represents a foundational development in modern cryptography because it introduced the concept of combining plaintext with a random key using the bitwise XOR operation, which became the basis for the one-time pad. Vernam’s design originally targeted teleprinter communication systems, using a punched paper tape to supply the key stream.

The Transposition cipher is a classical encryption method that conceals a message by rearranging the positions of its letters rather than changing the letters themselves. It is one of the oldest families of ciphers, with documented use dating back to ancient civilizations, including examples attributed to Spartan military practices such as the scytale around 5th century BCE. Unlike substitution-based systems, a Transposition cipher preserves the original characters of the plaintext but alters their order according to a specific rule or key.

The Templar Cipher is a cryptographic method associated with the Knights Templar, a medieval Christian military order founded during the Crusades. It is one of the many historical ciphers that have been attributed to the Knights Templar, although the exact cipher they used remains a subject of debate and speculation.

The Spiral cipher is a classical transposition cipher that arranges plaintext letters into a grid or spiral pattern, then reads them off in a predetermined order to produce ciphertext. It is a variant of route ciphers, where the sequence of reading the letters is the key. While the exact origin is unclear, spiral and route-based ciphers were explored in Europe during the 16th and 17th centuries for military and diplomatic correspondence, combining simple letter rearrangement with a concealed reading path.