Negative exponents using the BigInteger class

Question

I'm doing some maths using the Java BigInteger class but getting an error when I'm trying to use a negative number as an exponent. Am I right in thinking that you can rearrange:

b · φ(N)^−1 mod N

as:

      b
------------
φ(N)^1 mod N

If not how can I rearrange the expression as to not get a negative exponent error in my Java code?

Answer 1

BigInteger can't have negative exponents, because that would make it a fraction (1 over something), which is not an "integer".

Try using BigDecimal instead.

As for your rearrangement of the expression, it should be rearranged like this:

      b
------------  mod N
   φ(N)^1