Symmetric

The Autokey Cipher is a polyalphabetic substitution cipher designed to reduce the repetition vulnerabilities found in simpler systems such as the Caesar Cipher. Instead of using a short, repeating key, the Autokey Cipher extends the key by appending the plaintext itself after an initial keyword. This produces a variable-length key that is as long as the message, effectively minimizing repeated patterns and increasing resistance to frequency analysis.

The Atbash Cipher is a classical monoalphabetic substitution cipher that works by reversing the standard alphabet. In its simplest form, A is replaced by Z, B by Y, C by X, and so on, effectively mirroring the alphabet around its midpoint. This simple inversion makes it a symmetric cipher: encryption and decryption are identical operations. The Atbash Cipher has roots in ancient Hebrew cryptography but has been adapted for use with the Latin alphabet and other scripts.

The Affine Cipher is a type of monoalphabetic substitution cipher that combines multiplication and addition operations to transform plaintext letters into ciphertext. Each letter x in the plaintext is first converted to a numeric value, typically A=0 through Z=25, and then encrypted using the function E(x) = (ax + b) mod 26, where a and b are keys chosen such that a is coprime with 26.

The A1Z26 Cipher is a straightforward substitution cipher in which each letter of the alphabet is replaced by its corresponding numerical position. Specifically, A=1, B=2, C=3, continuing through Z=26. This simple mapping transforms plaintext into a sequence of numbers, creating a numeric representation of the original message while maintaining a direct, one-to-one correspondence between letters and values.