Calculating pow(a,b) mod n

Question

I want to calculate a^b mod n for use in RSA decryption. My code (below) returns incorrect answers. What is wrong with it?

unsigned long i         


        

Answer 1

int's are generally not enough for RSA (unless you are dealing with small simplified examples)

you need a data type that can store integers up to 2²⁵⁶ (for 256-bit RSA keys) or 2⁵¹² for 512-bit keys, etc