2.1-2.2, and 2.4, due September 7

Shift ciphers and substitution ciphers were simple enough to understand, but I had never encountered an affine cipher before.  The principle behind it seems simple enough, but I think I'll just need to work out a few examples to better understand the way to encrypt and decrypt it, as well as how to attack it.  These are really simple methods of encryption that are really easy to break now, but they're interesting to me in a historical sense, since these seem to be some of the oldest methods of encryption.  This is evidenced, for instance, by the fact that Julius Caesar was purported to have used the shift cipher.