1. Learner Objectives:

At the conclusion of this programming assignment, participants should be able to:

Design, implement and test classes in C++ Apply and implement ? overloaded? operators and functions Design and implement classes using inheritance

II. Prerequisites:

Before starting this programming assignment, participants should be able to:

?Analyze a basic set of requirements for a problem

?Compose basic C++ language programs

?Create basic test cases for a program

?Apply arrays, strings, and pointers

?Declare and define ? constructors

?Declare and define ? destructors

?Compare and contrast ? public? and ? private? access specifiers in C++

?Describe what is an ? attribute? or data member of a class

?Describe what is a ? method? of a class

? Apply and implement ? overloaded? functions

?Distinguish between pass-by-? value? and pass-by-? reference

?Discuss ? classes? versus ? objects

III. Overview & Requirements:

NOTE:? Parts of this assignment are courtesy of Jack Hagemeister.

Security and secrecy are popular topics in computer science. Every nation in the world has struggled with the task of communicating important information to its allies and armies at the same time trying to keep that information secret from others. In this assignment, you will be implementing some simple ciphers from history and look at ways to "decode" them.

You will find that the use of modern computers makes decoding of some of these very easy.

You should first review some information about ciphers. Start at the following web site, Codes, Ciphers, & Codebreaking? . It has an excellent introduction into the classic / historical Ciphers. You will need to read at least the first section, but I recommend reading sections 2 and 3 as well. These sections include: "1.0: Introduction to Codes, Ciphers, & Codebreaking", "2.0: Refining the Art", and "3.0 The Rise of Field Ciphers".

You will design objects for each of the two encryption techniques required. Each object should hold a message that is either "clear text" or "encrypted". You should be able to create any object around a string of text and an indicator of its status. You should have methods to retrieve the clear text or encrypted message from the object no matter how it is stored. Ok, so there are some other issues. If you have an encoded message and do not know the key in the Caesar Cipher or the substitution cipher you need methods to interact with the message to try and determine the key. For the Caesar Cipher this is simply being able to test each key number from 1 through 25. You probably do not even have to do anything special except in the calling program. For the substitution cipher, you will have to have a method that does frequency analysis, and gives you a best guess. You may want to be able to put in substitutions as well to correct any problems that you find in the analysis.

0.? ? Build a basic cipher base class that may be derived from for the ciphers described below.

1.? ? Encode a text message using the Caesar Cipher, a mono-alphabetic substitution cipher. You will need to input the KEY number from 1 to 25. Do not encode special characters or white space. All encoded text should be upper case only. You should be able to save an encoded message to a file.

2.? ? Decode a Caesar Cipher text. You will have two cases:

a.? ? You are given the KEY.

b.? ? You have to break the KEY by brute force trial and error.

3.? ? Build a randomly generated simple substitution cipher and use it to encode messages. Again the encoded messages will be in all upper case letters only. Only encode the letters.

4.? ? Build a method for performing frequency analysis to decode a substitution cipher. Your system should determine the frequency of characters in the

5.? ? Build a standard text-based wrapper/class for the application.