+// 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 gost34112012256
+
+import (
+ "crypto/hmac"
+ "hash"
+)
+
+type KDF struct {
+ h hash.Hash
+}
+
+func NewKDF(key []byte) *KDF {
+ return &KDF{hmac.New(New, key)}
+}
+
+func (kdf *KDF) Derive(dst, label, seed []byte) (r []byte) {
+ kdf.h.Write([]byte{0x01})
+ kdf.h.Write(label)
+ kdf.h.Write([]byte{0x00})
+ kdf.h.Write(seed)
+ kdf.h.Write([]byte{0x01})
+ kdf.h.Write([]byte{0x00})
+ r = kdf.h.Sum(dst)
+ kdf.h.Reset()
+ return r
+}