go.cypherpunks.ru namespace usage

[gogost.git] / gost3413 / padding.go

diff --git a/gost3413/padding.go b/gost3413/padding.go
new file mode 100644 (file)
index 0000000..f094141
--- /dev/null
+++ b/gost3413/padding.go
@@ -0,0 +1,48 @@
+// 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/>.
+
+// GOST R 34.13-2015 padding methods.
+package gost3413
+
+func PadSize(dataSize, blockSize int) int {
+       if dataSize < blockSize {
+               return blockSize - dataSize
+       }
+       if dataSize%blockSize == 0 {
+               return 0
+       }
+       return blockSize - dataSize%blockSize
+}
+
+func Pad1(data []byte, blockSize int) []byte {
+       padSize := PadSize(len(data), blockSize)
+       if padSize == 0 {
+               return data
+       }
+       return append(data, make([]byte, padSize)...)
+}
+
+func Pad2(data []byte, blockSize int) []byte {
+       pad := make([]byte, 1+PadSize(len(data)+1, blockSize))
+       pad[0] = byte(0x80)
+       return append(data, pad...)
+}
+
+func Pad3(data []byte, blockSize int) []byte {
+       if PadSize(len(data), blockSize) == 0 {
+               return data
+       }
+       return Pad2(data, blockSize)
+}