Objective: This homework covers Abstract Data Types $($ADTs$).$ In particular, it uses an abstraction of an encryption$/$decryption mechanism for transforming text into an unreadable form $($and then recovering the original$).$

Background

In the field of cryptography, encryption mechanisms are used to secure sensitive information from unauthorized access. In this homework, you will be writing a program that provides both the interface and various implementations for encryption mechanisms that mutate an entire string by repeatedly calling a single character mutation method. Thanks to the power of ADTs in Java, one can begin by specifying abstractly the general methods that are involved in every encryption technique, thereby separating the specification from the actual implementation details $($i$.$e$.,$ the magic trick behind the encryption$/$decryption$).$ This is actually a very important and canonical example of why abstract data types are crucial $$ the client $($who will be provided public access to the encryption object$)$ can only use it to encrypt or decrypt data based on a key, but will not be able to tell how, because if they did, the encryption loses its purpose all$-$together! In a sense, we want