Homework 6, You can't break me!

Short Description:

This assignment is worth 100 points.

Goals

• Developed your ability to use two dimensional arrays.
• Developed your ability to create code in multiple files.

Formal Description

• Caesar cipher
• VIC cipher
• Playfair cipher
• Vigenere cipher

For the Vigenere cipher, you are REQUIRED to create and use a Vigenere square or Vigenere table.

You should produce five programs: Caesar, VIC, Playfair, Vignere, CodeBench. Each of these programs should be interactive and user friendly.

• Caesar: The user is asked for an offset and a text, the encrypted (or decrypted) text is printed. Non-alphabetic characters are printed as is.

  Example:

  Caesar Cypher Program:
  Enter the shift amount: -3
  Enter the text: Qeb Nrfzh Yoltk Clu Grjmp Lsbo Qeb Ixwv Ald
  The encrypted text is: The Quick Brown Fox Jumps Over The Lazy Dog
      

• VIC: The user is asked for an encryption key, if they are encrypting or decrypting the message, and the message. Non-alphabetic characters are printed as is.

  Example:

  Vigenere Cipher Program:
  Enter the encryption key: LEMON
  Are you encrypting (e) or decrypting (d) the message? : d
  Enter the text: Lxfopv ef rnhr
  The decrypted text is:  Attack at dawn
      

• Playfair: The user is asked for an encryption key and the message and if they are encrypting or decrypting. Non-alphabetic characters are printed as is.

  Example:

  Playfair Cipher Program:
  Enter the encryption key: Playfair example
  Are you encrypting (e) or decrypting (d) the message? : d
  Enter the Phrase: Bmod zbx dnab ek udm uiexm ouvif
  The decrypted text is: Hide the gold in the tree stump.
      

• Vic: The user is asked for an encryption key, the message and if they are encrypting or decrypting. Non-alphabetic characters are printed as is.

  Example:

  VIC Cipher Program:
  Enter the encryption key: ET AON RIS
  Are you encrypting (e) or decrypting (d) the message? : e
  Enter the Phrase: Attack at dawn.
  The encrypted text is: 31132127 31 223655.
      

• CodeBench: This program is a combination of the first four. The user should be presented with a menu, which includes a choice for the above listed ciphers and a quit option. After the user selects a cipher method, the dialog should be similar to that above. The program should allow the user to encrypt/decrypt many messages with many different ciphers.

You should also create library of utility functions, which are common to two or more ciphers. This library might contain, for example, the following functions:

• void MakeUppercase(string text); : translate all of the letters in the text to upper case.
• string UniqueLetters(string text); : return a list of all of the unique letters in a given string.
• int PositionInAlphabet(char letter); : return the position of a letter in the alphabet (a=0, b=1 ...)
• char LetterFromPosition(int position); : return the letter at a given position (opposite of PositionInAlphabet).

Discussion

• Whenever possible, eliminate repeated code by building subroutines. If you find you are repeating code, pull it out and put it into a subroutine.
• You should probably write some experimental code, and then revise your design.
• You should create a sub-directory and perform all work for this project within this directory.
• If you need help, you should ask.
• Please do not put this work off until the weekend before it is due.
• If you require help with the Makefile, or creating the tar file, please ask for assistance.

Required Files

A tar file is a file which compresses many files and folders into a single file. TAR stands for Tape ARchive, and is a utility which has existed for most of the history of UNIX. It maintains dates, permissions and ownership of the file. It is a POSIX standard.

To create a tar file:

These instructions assume all of your work is in a folder called program5. Following these instructions you will produce a file called submission.tgz.

1. Remove all object files and executable files from the folder.
2. In the folder containing program5 (not in the program5 folder, but its parent) issue the command

   tar cvzf submission.tgz program5
       

3. This will create a file called submission.tgz
   • You may call it anything you wish. This example the name was submission but any name will do. The convention is to call the tar file for the directory program5
   • The extension .tgz stands for compressed tar file, and should be used.
4. You should submit this file.
5. If you wish, you may look at the contents of this file with the command

   tar tzf submission.tgz
       

   tar xvzf submission.tgz
       

   You should probably do this in another directory. This will create a new folder called program5 and extract all of the files in the tar file into it.

Submission