Negative Exponents

[SkyRat23@aol.com]

Hello.  I have been recently working on the Hughes variant of the Diffie-Hellman key exchange and it requires me to compute y^-1 and use this as the exponent, k=X^(y^(-1))  (y being a large randomly generated number).  Anyway, I cannot seem to find anything in the GMP library that will allow me to do this.  I am using gmzs for everything else and investigated the other types but found that gmf and gmqs would not allow me to do many of the other steps.  I assume that many on this list would be familiar with encryption/key-exchange algorithms and therefore may have dealt/come across this issue before.  How do I get around this?

Thanks guys.

David Swiston