Obfuscation

The M-209 cipher is a mechanical rotor-based cipher device developed by the American engineer Boris Hagelin and adopted by the U.S. military in 1941. It was a portable, hand-operated machine designed for tactical battlefield communications, encrypting messages character by character using a combination of rotors, a rotating drum with movable pins, and a set of lugs to generate a polyalphabetic substitution.

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 Keyed Caesar cipher is a variation of the classical Caesar cipher, adapted to increase security by combining a keyword with a shift-based substitution. The original Caesar cipher, attributed to Julius Caesar around 58–50 BCE, shifts each letter of the alphabet by a fixed number of positions. In the Keyed Caesar cipher, a keyword is first used to create a modified alphabet: the letters of the keyword are placed at the start of the alphabet (omitting duplicates), followed by the remaining unused letters in standard order.

The Kangaroo cipher, sometimes referred to as a jumping key cipher, is a classical polyalphabetic cipher whose exact origins are uncertain, but which appeared in cryptographic literature and practice in the late 19th century to early 20th century. Unlike fixed-key polyalphabetic systems such as the Vigenère cipher, the defining feature of the Kangaroo cipher is that the key does not advance in a simple, linear fashion. Instead, it “jumps” through the key according to a predefined rule, much like a kangaroo hopping unevenly forward.

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 Base64 cipher is an encoding scheme developed in 1993 as part of the MIME (Multipurpose Internet Mail Extensions) standard by a group including Philippe J. Flajolet and other contributors to internet protocols. Unlike classical ciphers, Base64 is not used for cryptographic secrecy but for converting binary data into ASCII text to ensure safe transmission over systems that handle text poorly.