1 // GoGOST -- Pure Go GOST cryptographic functions library
2 // Copyright (C) 2015-2023 Sergey Matveev <stargrave@stargrave.org>
4 // This program is free software: you can redistribute it and/or modify
5 // it under the terms of the GNU General Public License as published by
6 // the Free Software Foundation, version 3 of the License.
8 // This program is distributed in the hope that it will be useful,
9 // but WITHOUT ANY WARRANTY; without even the implied warranty of
10 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 // GNU General Public License for more details.
13 // You should have received a copy of the GNU General Public License
14 // along with this program. If not, see <http://www.gnu.org/licenses/>.
18 import "encoding/binary"
20 type mul128 struct{ buf [16]byte }
22 func newMul128() *mul128 {
26 func gf128half(n int, t, x0, x1, z0, z1 uint64) (uint64, uint64, uint64, uint64, uint64) {
28 for i := 0; i < n; i++ {
34 x1 = (x1 << 1) ^ (x0 >> 63)
40 return t, x0, x1, z0, z1
43 func (mul *mul128) Mul(x, y []byte) []byte {
44 x1 := binary.BigEndian.Uint64(x[:8])
45 x0 := binary.BigEndian.Uint64(x[8:])
46 y1 := binary.BigEndian.Uint64(y[:8])
47 y0 := binary.BigEndian.Uint64(y[8:])
49 _, x0, x1, z0, z1 := gf128half(64, y0, x0, x1, 0, 0)
50 t, x0, x1, z0, z1 = gf128half(63, y1, x0, x1, z0, z1)
54 binary.BigEndian.PutUint64(mul.buf[:8], z1)
55 binary.BigEndian.PutUint64(mul.buf[8:], z0)