The Matasano Crypto Challenges

Maciej runs Pinboard, and is extremely down to earth about tech... plus he writes in a direct good fashion. His insights around security are interesting.

I mentioned earlier that I thought every web programmer should try their hand at these. It is very illuminating to look at your own web app from the vantage point of an attacker actually writing code. At the very least, you will never be confused about cipher block modes again, or have to worry that someone will ask you to explain how a public key works in an interview. And there is a whole slew of dumb mistakes you will now avoid (replacing them with smarter mistakes that will become the subject matter of challenges 48-96)