forked from hardcoresushi/DroidFS
99 lines
2.5 KiB
Go
99 lines
2.5 KiB
Go
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// 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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"fmt"
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"../cmac"
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"../common"
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)
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var s2vZero []byte
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func init() {
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s2vZero = bytes.Repeat([]byte{0x00}, aes.BlockSize)
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}
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// The output size of the s2v function.
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const s2vSize = cmac.Size
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// Run the S2V "string to vector" function of RFC 5297 using the input key and
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// string vector, which must be non-empty. (RFC 5297 defines S2V to handle the
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// empty vector case, but it is never used that way by higher-level functions.)
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//
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// If provided, the supplied scatch space will be used to avoid an allocation.
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// It should be (but is not required to be) as large as the last element of
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// strings.
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//
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// The result is guaranteed to be of length s2vSize.
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func s2v(key []byte, strings [][]byte, scratch []byte) []byte {
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numStrings := len(strings)
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if numStrings == 0 {
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panic("strings vector must be non-empty.")
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}
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// Create a CMAC hash.
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h, err := cmac.New(key)
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if err != nil {
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panic(fmt.Sprintf("cmac.New: %v", err))
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}
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// Initialize.
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if _, err := h.Write(s2vZero); err != nil {
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panic(fmt.Sprintf("h.Write: %v", err))
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}
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d := h.Sum([]byte{})
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h.Reset()
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// Handle all strings but the last.
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for i := 0; i < numStrings-1; i++ {
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if _, err := h.Write(strings[i]); err != nil {
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panic(fmt.Sprintf("h.Write: %v", err))
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}
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common.Xor(d, dbl(d), h.Sum([]byte{}))
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h.Reset()
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}
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// Handle the last string.
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lastString := strings[numStrings-1]
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var t []byte
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if len(lastString) >= aes.BlockSize {
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// Make an output buffer the length of lastString.
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if cap(scratch) >= len(lastString) {
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t = scratch[:len(lastString)]
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} else {
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t = make([]byte, len(lastString))
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}
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// XOR d on the end of lastString.
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xorend(t, lastString, d)
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} else {
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t = make([]byte, aes.BlockSize)
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common.Xor(t, dbl(d), common.PadBlock(lastString))
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}
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if _, err := h.Write(t); err != nil {
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panic(fmt.Sprintf("h.Write: %v", err))
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}
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return h.Sum([]byte{})
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}
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