1// gf256.cpp - written and placed in the public domain by Wei Dai
2
3#include "pch.h"
4#include "gf256.h"
5
6NAMESPACE_BEGIN(CryptoPP)
7
8GF256::Element GF256::Multiply(Element a, Element b) const
9{
10	word result = 0, t = b;
11
12	for (unsigned int i=0; i<8; i++)
13	{
14		result <<= 1;
15		if (result & 0x100)
16			result ^= m_modulus;
17
18		t <<= 1;
19		if (t & 0x100)
20			result ^= a;
21	}
22
23	return (GF256::Element) result;
24}
25
26GF256::Element GF256::MultiplicativeInverse(Element a) const
27{
28	Element result = a;
29	for (int i=1; i<7; i++)
30		result = Multiply(Square(result), a);
31	return Square(result);
32}
33
34NAMESPACE_END
35