forked from hardcoresushi/DroidFS
49 lines
1.2 KiB
Go
49 lines
1.2 KiB
Go
// Copyright 2012 Aaron Jacobs. All Rights Reserved.
|
|
// Author: aaronjjacobs@gmail.com (Aaron Jacobs)
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
package siv
|
|
|
|
import (
|
|
"bytes"
|
|
"crypto/aes"
|
|
|
|
"../common"
|
|
)
|
|
|
|
var dblRb []byte
|
|
|
|
func init() {
|
|
dblRb = append(bytes.Repeat([]byte{0x00}, 15), 0x87)
|
|
}
|
|
|
|
// Given a 128-bit binary string, shift the string left by one bit and XOR the
|
|
// result with 0x00...87 if the bit shifted off was one. This is the dbl
|
|
// function of RFC 5297.
|
|
func dbl(b []byte) []byte {
|
|
if len(b) != aes.BlockSize {
|
|
panic("dbl requires a 16-byte buffer.")
|
|
}
|
|
|
|
shiftedOne := common.Msb(b) == 1
|
|
b = common.ShiftLeft(b)
|
|
if shiftedOne {
|
|
tmp := make([]byte, aes.BlockSize)
|
|
common.Xor(tmp, b, dblRb)
|
|
b = tmp
|
|
}
|
|
|
|
return b
|
|
}
|