Suggest an easy to read book for first reading for nonnerds. Applied Cryptography, Protocols, Algorithms, and Source Code in C, second edition by Bruce Schneier. Most of the popular encrytion systems are public keys systems based on the difficulty of factoring large composites into two primes of nearly equal magnitudes. Difficulty in prime factorisation is only an assumption without mathematical basis. Let's face it.
Cryptology is almost like witch-craft.
Even cryptologists themselves do not know how secure their inventions are and that is why there are all these RSA and DES challenges offered.