128 bit RSA implementation on nios2

Hi there,

I hope some one has an idea how this can be done.

I am trying to implement a 128 RSA encryption on my nios2 cyclone development board. The problem is that, when I try a modular exponentiation on nios2 its seems to truncate my result to 2^32 that is:

If I try the following operation. 5^15mod77(read 5 to the power 15 and then modulus 77) it does not give the correct answer. but if I try a lower value(say 5^13mod77) it works and give me the correct value.

It seems to me that the processor can only do 32 bit operations more than that the performance is not garrateed.

My nios is version 6.

If any one has any idea how I can solve the problem up to 128 bit, your assistance will be much appreciated.

Thanks in advance