Cryptography

I am currently listening (for free, on iTunes - search on "math 55") to Professor James Demmel's Discrete Mathematics series of lectures at University of California, Berkeley - highly recommended (so far). Anyway, Lecture 18 audio is relevant to today's post, which is on public-key cryptography, and, specifically RSA. The reason cryptography is involved is because RSA relies on the difficulty of factoring large semiprimes for keeping encoded messages secret. Some links:
http://en.wikipedia.org/wiki/Public-key_cryptography
http://en.wikipedia.org/wiki/Rsa
http://www.cs.berkeley.edu/~demmel/ma55_Fall07/LectureNotes/Lecture_15_Oct_03.txt