gf256.cpp

// gf256.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"
#include "gf256.h"

NAMESPACE_BEGIN(CryptoPP)

GF256::Element GF256::Multiply(Element a, Element b) const
{
        word result = 0, t = b;

        for (unsigned int i=0; i<8; i++)
        {
                result <<= 1;
                if (result & 0x100)
                        result ^= m_modulus;

                t <<= 1;
                if (t & 0x100)
                        result ^= a;
        }

        return (GF256::Element) result;
}

GF256::Element GF256::MultiplicativeInverse(Element a) const
{
        Element result = a;
        for (int i=1; i<7; i++)
                result = Multiply(Square(result), a);
        return Square(result);
}

NAMESPACE_END

---