63 lines
1.7 KiB
Go
63 lines
1.7 KiB
Go
/* SPDX-License-Identifier: MIT
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*
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* Copyright (C) 2017-2021 WireGuard LLC. All Rights Reserved.
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*/
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// Package replay implements an efficient anti-replay algorithm as specified in RFC 6479.
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package replay
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type block uint64
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const (
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blockBitLog = 6 // 1<<6 == 64 bits
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blockBits = 1 << blockBitLog // must be power of 2
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ringBlocks = 1 << 7 // must be power of 2
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windowSize = (ringBlocks - 1) * blockBits
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blockMask = ringBlocks - 1
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bitMask = blockBits - 1
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)
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// A Filter rejects replayed messages by checking if message counter value is
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// within a sliding window of previously received messages.
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// The zero value for Filter is an empty filter ready to use.
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// Filters are unsafe for concurrent use.
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type Filter struct {
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last uint64
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ring [ringBlocks]block
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}
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// Reset resets the filter to empty state.
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func (f *Filter) Reset() {
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f.last = 0
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f.ring[0] = 0
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}
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// ValidateCounter checks if the counter should be accepted.
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// Overlimit counters (>= limit) are always rejected.
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func (f *Filter) 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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indexBlock := counter >> blockBitLog
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if counter > f.last { // move window forward
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current := f.last >> blockBitLog
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diff := indexBlock - current
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if diff > ringBlocks {
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diff = ringBlocks // cap diff to clear the whole ring
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}
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for i := current + 1; i <= current+diff; i++ {
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f.ring[i&blockMask] = 0
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}
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f.last = counter
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} else if f.last-counter > windowSize { // behind current window
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return false
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}
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// check and set bit
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indexBlock &= blockMask
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indexBit := counter & bitMask
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old := f.ring[indexBlock]
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new := old | 1<<indexBit
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f.ring[indexBlock] = new
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return old != new
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}
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