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