C-source for diffie-hellman?

I was just talking with a friend, and I think it would be pretty good for medium-level security on irc to hack up something do that /dcc does diffie-hellman key exchange, and maybe triple-des or something. Is there some available C-source which would help? (I guess I should get the Schneier book.. But urgh! $50 on a "starving-student" budget is quite a bit.)