Encrypts or decrypts texts with the affine cipher. The affine cipher is a simple substitution cipher which shifts each letter using the formula (a*c + b) mod 26 for a letter c and integer values a and b.
Drop the header into your program folder and #include in your program.
The following functions are provided:
affine: Encrypt a single letter or character ordinal, or string or array of ordinals.
affine_in_place: Encrypt a string or array of ordinals into an existing object.
all_affines: Encrypt a string or array of ordinals with all invertible values of a and all values of b, both variables between 0 to 25.
decrypt_affine: Decrypt a single letter or character ordinal, or string or array of ordinals.
decrypt_affine_in_place: Decrypt a string or array of ordinals into an existing object.
decrypt_all_affines: Decrypt a string or array of ordinals with all the coprimes of the invertible values of a and all values of b, both variables between 0 to 25.
Pass the standard alphabet into all_affines or decrypt_all_affines to get a lookup table for every valid combination of settings and letters. However, I tested the performance of using a lookup table to encrypt a string millions of times vs regenerating the encryptions every time, and the running time was identical on my machine (Core i7-6500u, 2.50GHz, 16GB DDR3). Thus, I did not include any lookup tables or retrieval algorithms in the library.
Copyright (c) 2020 Mike Castillo under the MIT License. See LICENSE for the full terms.