35 lines
592 B
C++
35 lines
592 B
C++
|
// 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
|