DH itself is a trivial algorithm. All you need is a decent multiple precsion math package. I think all it takes is -- random numbers -- primality test -- gcd -- raise-to-power-modulo-some-number One more thing -- you want the base for the exponentiations to be a generator of the subgroup. Also, ideally the modulus should be a prime of the form kp+1, where p is also a prime and k is a small integer. Your DH toolkit should include routines to generate the base and modulus according to those criteria. BTW, schneier is literally a FAQ for cypherpunks. Fantastic book. Cough up the money for it... Indeed, though I've only seen some drafts; my copy of the book itself hasn't arrived yet.