Question

I want to calculate the RSA algorithm by myself . I need to calculate the modulus of a number at a certain power. The thing is that that number at that certain power can get quite big.

Here is what i want :

x = pow(n, p) % q

How can I efficiently determine x?

Answer 1

If you’re using .NET 4, I suggest you look at BigInteger, which even provides the ModPow method to do it all in a single operation 🙂

BigInteger n = ...;
BigInteger p = ...;
BigInteger q = ...;
BigInteger x = BigInteger.ModPow(n, p, q);