X-Git-Url: http://www.git.cypherpunks.ru/?a=blobdiff_plain;f=gost34112012256%2Fesptree.go;fp=gost34112012256%2Fesptree.go;h=dceaeb705bef921faf3f40cf9a72dd688881117d;hb=c07494bbd559b9d00f391e28cfd070e18afe9900;hp=0000000000000000000000000000000000000000;hpb=107600dede989f0cc479b5a72c5f97e174307154;p=gogost.git

diff --git a/gost34112012256/esptree.go b/gost34112012256/esptree.go
new file mode 100644
index 0000000..dceaeb7
--- /dev/null
+++ b/gost34112012256/esptree.go
@@ -0,0 +1,60 @@
+// 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/subtle"
+)
+
+type ESPTree struct {
+	keyRoot []byte
+	isPrev  [5]byte
+	key     []byte
+}
+
+func NewESPTree(keyRoot []byte) *ESPTree {
+	key := make([]byte, len(keyRoot))
+	copy(key, keyRoot)
+	t := &ESPTree{
+		keyRoot: key,
+		key:     make([]byte, Size),
+	}
+	t.isPrev[0] += 1 // invalidate cache
+	t.DeriveCached([]byte{0x00, 0x00, 0x00, 0x00, 0x00})
+	return t
+}
+
+func (t *ESPTree) DeriveCached(is []byte) ([]byte, bool) {
+	if len(is) != 1+2+2 {
+		panic("invalid i1+i2+i3 input")
+	}
+	if subtle.ConstantTimeCompare(t.isPrev[:], is) == 1 {
+		return t.key, true
+	}
+	kdf1 := NewKDF(t.keyRoot)
+	kdf2 := NewKDF(kdf1.Derive(t.key[:0], []byte("level1"), append([]byte{0}, is[0])))
+	kdf3 := NewKDF(kdf2.Derive(t.key[:0], []byte("level2"), is[1:3]))
+	kdf3.Derive(t.key[:0], []byte("level3"), is[3:5])
+	copy(t.isPrev[:], is)
+	return t.key, false
+}
+
+func (t *ESPTree) Derive(is []byte) []byte {
+	keyDerived := make([]byte, Size)
+	key, _ := t.DeriveCached(is)
+	copy(keyDerived, key)
+	return keyDerived
+}