go.cypherpunks.ru namespace usage

[gogost.git] / gost3410 / vko.go

diff --git a/gost3410/vko.go b/gost3410/vko.go
new file mode 100644 (file)
index 0000000..bb10f94
--- /dev/null
+++ b/gost3410/vko.go
@@ -0,0 +1,35 @@
+// GoGOST -- Pure Go GOST cryptographic functions library
+// Copyright (C) 2015-2019 Sergey Matveev <stargrave@stargrave.org>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, version 3 of the License.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package gost3410
+
+import (
+       "math/big"
+)
+
+func (prv *PrivateKey) KEK(pub *PublicKey, ukm *big.Int) ([]byte, error) {
+       keyX, keyY, err := prv.C.Exp(prv.Key, pub.X, pub.Y)
+       if err != nil {
+               return nil, err
+       }
+       if ukm.Cmp(bigInt1) != 0 {
+               keyX, keyY, err = prv.C.Exp(ukm, keyX, keyY)
+               if err != nil {
+                       return nil, err
+               }
+       }
+       pk := PublicKey{prv.C, prv.Mode, keyX, keyY}
+       return pk.Raw(), nil
+}