How to find d, given p, q, and e in RSA?

Question

I know I need to use the extended euclidean algorithm, but I\'m not sure exactly what calculations I need to do. I have huge numbers. Thanks

Answer 1

Well, d is chosen such that d * e == 1 modulo (p-1)(q-1), so you could use the Euclidean algorithm for that (finding the modular multiplicative inverse).

If you are not interested in understanding the algorithm, you can just call BigInteger#modInverse directly.

 d = e.modInverse(p_1.multiply(q_1))