RSA encryption algorithm in Java: no BigIntegers

Question

I need to implement RSA algorithm in Java. I've found the best solution using BigIntegers, problem is that I need to work only with ints or longs. The encrypting is done like this: M[i]^e mod n where M[i] is an input char and e is a key value. I tried using the ASCII codes of chars, and with codes such as 115 and 116 I quickly get out of range. How can I solve the problem? Thanks in advance.

Answer 1

You may have a look at modular exponentiation. This way you overcome most of the overflows in your calculations.