start with simple crypto algorithms and start playing with prime numbers. lots of information on google groups. mostly high end calc. (quantum computing destroys all or crytography )

Interestingly enough, I was recently working with someone who was developing quantum cryptography. Not only was it strong encryption, but you would be able to tell if someone had decrypted the message in transit.

That's cool - when it was decrypted, was a series of bits changed to reflect the numbers of times that it was put through a decryption sequence?

It uses the fact that in quantum machanics, you cannot observe a particle (in this case a photon) without changing it. Most quantum cryptography devices use polarization to encode the data, and there are three different polarization states for each photon. If you read one, the others change.