gf256.cpp

// gf256.cpp - originally 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