(and the recent past, too).
Cryptography, in some aspects, has been used since antiquity, although the methods were far less refined (basic substitution, Vigenere, and so on) as compared to today. In this day and age, it's fairly useful to get a good amount of number theory and discrete mathematics in order before setting off in in-depth analysis of how cryptographic algorithms are created and what makes them secure. It's also helpful to know the mathematical nuts and bolts when creating cryptosystems, but simple prudence and the correct use of known-secure algorithms as recommended and documented is a very good initial start.
