Readings:

For this phase of the final project please read pages 35-38 (until example 1.22) in Lewand.

Key Concepts:

Up until now we have only discussed how to decode message when we have the key. But what if we don't? This is obviously the more realistic and also more interesting case. This is the cryptanalysis part of the cryptology. The reading for this phase of the final project will show you one technique called \textit{frequency analysis} that suggests how to go about decrypting messages when we do not have the key. So by the end of this phase you should be familiar with frequency analysis and how it can help in decoding the three ciphers we have been using this term.

Cryptology Program:

Add a decode_rand() function to your Add_Cipher.cpp program that takes a pointer to a string as a parameter and decodes that string (though the returns type as with our other encode and decode functions should be void). A few things to keep in mind before you get started: