simple substitution cipher Algorithm

In cryptanalysis, a substitution cipher is a method of encryption by which units of plaintext are replaced with ciphertext, according to a fixed system; the" units" may be individual letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth. A monoalphabetic cipher uses fixed substitution over the entire message, whereas a polyalphabetic cipher uses a number of substitutions at different positions in the message, where a unit from the plaintext is mapped to one of several possibility in the ciphertext and vice versa.

simple substitution cipher source code, pseudocode and analysis