85 lines
1.8 KiB
Go
85 lines
1.8 KiB
Go
/* SPDX-License-Identifier: GPL-2.0
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*
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* Copyright (C) 2017-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
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* Copyright (C) 2017-2018 Mathias N. Hall-Andersen <mathias@hall-andersen.dk>.
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*/
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package replay
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/* Implementation of RFC6479
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* https://tools.ietf.org/html/rfc6479
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*
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* The implementation is not safe for concurrent use!
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*/
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const (
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// See: https://golang.org/src/math/big/arith.go
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_Wordm = ^uintptr(0)
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_WordLogSize = _Wordm>>8&1 + _Wordm>>16&1 + _Wordm>>32&1
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_WordSize = 1 << _WordLogSize
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)
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const (
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CounterRedundantBitsLog = _WordLogSize + 3
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CounterRedundantBits = _WordSize * 8
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CounterBitsTotal = 2048
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CounterWindowSize = uint64(CounterBitsTotal - CounterRedundantBits)
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)
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const (
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BacktrackWords = CounterBitsTotal / _WordSize
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)
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func minUint64(a uint64, b uint64) uint64 {
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if a > b {
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return b
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}
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return a
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}
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type ReplayFilter struct {
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counter uint64
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backtrack [BacktrackWords]uintptr
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}
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func (filter *ReplayFilter) Init() {
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filter.counter = 0
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filter.backtrack[0] = 0
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}
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func (filter *ReplayFilter) ValidateCounter(counter uint64, limit uint64) bool {
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if counter >= limit {
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return false
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}
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indexWord := counter >> CounterRedundantBitsLog
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if counter > filter.counter {
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// move window forward
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current := filter.counter >> CounterRedundantBitsLog
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diff := minUint64(indexWord-current, BacktrackWords)
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for i := uint64(1); i <= diff; i++ {
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filter.backtrack[(current+i)%BacktrackWords] = 0
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}
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filter.counter = counter
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} else if filter.counter-counter > CounterWindowSize {
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// behind current window
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return false
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}
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indexWord %= BacktrackWords
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indexBit := counter & uint64(CounterRedundantBits-1)
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// check and set bit
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oldValue := filter.backtrack[indexWord]
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newValue := oldValue | (1 << indexBit)
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filter.backtrack[indexWord] = newValue
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return oldValue != newValue
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}
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