package main /* Copyright (C) 2015-2017 Jason A. Donenfeld . All Rights Reserved. */ /* Implementation of RFC6479 * https://tools.ietf.org/html/rfc6479 * * The implementation is not safe for concurrent use! */ const ( // See: https://golang.org/src/math/big/arith.go _Wordm = ^uintptr(0) _WordLogSize = _Wordm>>8&1 + _Wordm>>16&1 + _Wordm>>32&1 _WordSize = 1 << _WordLogSize ) const ( CounterRedundantBitsLog = _WordLogSize + 3 CounterRedundantBits = _WordSize * 8 CounterBitsTotal = 2048 CounterWindowSize = uint64(CounterBitsTotal - CounterRedundantBits) ) const ( BacktrackWords = CounterBitsTotal / _WordSize ) type ReplayFilter struct { counter uint64 backtrack [BacktrackWords]uintptr } func (filter *ReplayFilter) Init() { filter.counter = 0 filter.backtrack[0] = 0 } func (filter *ReplayFilter) ValidateCounter(counter uint64) bool { if counter >= RejectAfterMessages { return false } indexWord := counter >> CounterRedundantBitsLog if counter > filter.counter { // move window forward current := filter.counter >> CounterRedundantBitsLog diff := minUint64(indexWord-current, BacktrackWords) for i := uint64(1); i <= diff; i++ { filter.backtrack[(current+i)%BacktrackWords] = 0 } filter.counter = counter } else if filter.counter-counter > CounterWindowSize { // behind current window return false } indexWord %= BacktrackWords indexBit := counter & uint64(CounterRedundantBits-1) // check and set bit oldValue := filter.backtrack[indexWord] newValue := oldValue | (1 << indexBit) filter.backtrack[indexWord] = newValue return oldValue != newValue }