Matasano Crypto Challenges

Anyone done these before? Looks like fun, just sent the request e-mail. I'll try to report back!

We've built a collection of 48 exercises that demonstrate attacks on real-world crypto.

This is a different way to learn about crypto than taking a class or reading a book. We give you problems to solve. They're derived from weaknesses in real-world systems and modern cryptographic constructions. We give you enough info to learn about the underlying crypto concepts yourself. When you're finished, you'll not only have learned a good deal about how cryptosystems are built, but you'll also understand how they're attacked.
http://www.matasano.com/articles/crypto-challenges/

>>22

do bi-direction correctly

My bad, autofill put it there.

file(), od()

I'm not entirely sure what you mean. My problem is that I need to determine if a string has been properly decoded by only looking at every n^th character.

For example I'm trying to find out if "Some sort of programming BBS" has been decoded with the right key by only looking at "Seo oai S", "o ropgmnB", and "mstfrrmgB"