Provide an example of non-reciprocal cipher

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].

Citations:
[1] https://en.wikipedia.org/wiki/Symmetric-key_algorithm
[2] https://en.wikipedia.org/wiki/One-way_compression_function
[3] https://www.geeksforgeeks.org/caesar-cipher-in-cryptography/
[4] https://www.slideserve.com/smattingly/cryptanalysis-of-the-affine-cipher-powerpoint-ppt-presentation
[5] https://www.bbc.co.uk/bitesize/guides/znxxh39/revision/2
[6] https://www.thesslstore.com/blog/difference-encryption-hash...