The objective of this assignment is to understand the
concept of C# interfaces while implementing a classical substitution cipher,
which reads and writes to files using streams. A cipher is used to encrypt and
decrypt information. Encryption refers to the process or algorithm that
converts plaintext into a coded or encrypted version, called cipher text.
Decryption refers to the conversion of cipher text to plaintext. For details on
what a cipher is, refer to this link on Wikipedia.