[unknownAttacker]

about theory: I think the best way to learn theory is to also learn history: start at simple transposition and monoalphabetic substitution ciphers, then go all the way to modern encryption. writing encryption/decryption software is not hard when you know both theory and programming. cracking is difficult as you need to know a lot about cryptanalysis and a lot of math. also, using encryption everyday doesn't require more than a basic theory and good software (TrueCrypt and PGP should be enough)