gf256 operator*(gf256 a, gf256 b)
{
unsigned raw_a = a.to_byte();
unsigned raw_b = b.to_byte();
if (raw_a == 0 || raw_b == 0) {
return gf256::zero();
} else {
auto& t = get_tables();
return gf256(t.exp[(t.log[raw_a] + t.log[raw_b]) % 255]);
}
}
gf256 operator/(gf256 a, gf256 b)
{
unsigned raw_a = a.to_byte();
unsigned raw_b = b.to_byte();
if (raw_a == 0) {
return gf256::zero();
} else if (raw_b == 0) {
throw std::domain_error("division by zero");
} else {
auto& t = get_tables();
return gf256(t.exp[(t.log[raw_a] + 255 - t.log[raw_b]) % 255]);
}
}
static word64 SHARKTransform(word64 a)
{
static const byte iG[8][8] = {
0xe7, 0x30, 0x90, 0x85, 0xd0, 0x4b, 0x91, 0x41,
0x53, 0x95, 0x9b, 0xa5, 0x96, 0xbc, 0xa1, 0x68,
0x02, 0x45, 0xf7, 0x65, 0x5c, 0x1f, 0xb6, 0x52,
0xa2, 0xca, 0x22, 0x94, 0x44, 0x63, 0x2a, 0xa2,
0xfc, 0x67, 0x8e, 0x10, 0x29, 0x75, 0x85, 0x71,
0x24, 0x45, 0xa2, 0xcf, 0x2f, 0x22, 0xc1, 0x0e,
0xa1, 0xf1, 0x71, 0x40, 0x91, 0x27, 0x18, 0xa5,
0x56, 0xf4, 0xaf, 0x32, 0xd2, 0xa4, 0xdc, 0x71,
};
word64 result=0;
GF256 gf256(0xf5);
for (unsigned int i=0; i<8; i++)
for(unsigned int j=0; j<8; j++)
result ^= word64(gf256.Multiply(iG[i][j], a>>(56-8*j))) << (56-8*i);
return result;
}
// apply theta to a roundkey
static void SquareTransform (word32 in[4], word32 out[4])
{
static const byte G[4][4] =
{
0x02U, 0x01U, 0x01U, 0x03U,
0x03U, 0x02U, 0x01U, 0x01U,
0x01U, 0x03U, 0x02U, 0x01U,
0x01U, 0x01U, 0x03U, 0x02U
};
GF256 gf256(0xf5);
for (int i = 0; i < 4; i++)
{
word32 temp = 0;
for (int j = 0; j < 4; j++)
for (int k = 0; k < 4; k++)
temp ^= (word32)gf256.Multiply(GETBYTE(in[i], 3-k), G[k][j]) << ((3-j)*8);
out[i] = temp;
}
}
gf256 gf256::exp(unsigned p)
{
return gf256(get_tables().exp[p % 255]);
}