A non-reciprocal cipher is one where the encryption and decryption processes are not identical and require different transformations or keys. An example of a non-reciprocal cipher is the Affine Cipher.
In the Affine Cipher, encryption and decryption are performed using different mathematical operations. The encryption function is given by:
E(x) = (ax + b) \mod m
where $$ a $$ and $$ b $$ are keys, $$ x $$ is the plaintext character, and $$ m $$ is the size of the alphabet.
The decryption function, on the other hand, is:
D(y) = a^{-1}(y - b) \mod m
where $$ a^{-1} $$ is the modular multiplicative inverse of $$ a $$ modulo $$ m $$, and $$ y $$ is the ciphertext character.
This difference in the encryption and decryption processes makes the Affine Cipher a non-reciprocal cipher[4].
