http://www.meetup.com/Technarium/events/234151752/

If you’re curious how the real world cryptography works and how it is being broken, join us in solving the Matasano Crypto challenge exercise set 1. We’ll restart where we left during the last time at ex.7.

All you need is a basic familiarity with at least one programming language, 9th grade math knowledge and a laptop.
More info: http://cryptopals.com/
https://blog.pinboard.in/2013/04/the_matasano_crypto_challenges/