mirror of https://gitlab.com/yawning/obfs4
Add replay detection to handshakes.
This is done by maintaining a map keyed off the SipHash-2-4 digest of the MAC_C component of the handshake. Collisions, while possible are unlikely in the extreme and are thus treated as replays. In concept this is fairly similar to the ScrambleSuit `replay.py` code, with a few modifications: * There is a upper bound on how large the replay filter can grow. Currently this is set to 102400 entries, though it is unlikely that this limit will be hit. * A doubly linked list is also maintained parallel to the map, so the filter compaction process does not need to iterate over the entire filter.merge-requests/3/head
Yawning Angel
10 years ago
parent
7dd875fe4c
commit
fd4e3c7c74
@ -0,0 +1,138 @@
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/*
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* Copyright (c) 2014, Yawning Angel <yawning at torproject dot org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* * Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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package obfs4
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import (
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"container/list"
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"crypto/rand"
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"encoding/binary"
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"sync"
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"github.com/dchest/siphash"
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)
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// maxFilterSize is the maximum capacity of the replay filter. The busiest
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// bridge I know about processes something along the order of 3000 connections
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// per day. The maximum timespan any entry can live in the filter is 2 hours,
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// so this value should be sufficient.
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const maxFilterSize = 100 * 1024
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// replayFilter is a simple filter designed only to answer if it has seen a
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// given byte sequence before. It is based around comparing the SipHash-2-4
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// digest of data to match against. Collisions are treated as positive matches
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// however, the probability of such occurences is negligible.
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type replayFilter struct {
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lock sync.Mutex
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key [2]uint64
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filter map[uint64]*filterEntry
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fifo *list.List
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}
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type filterEntry struct {
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firstSeen int64
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hash uint64
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element *list.Element
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}
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// newReplayFilter creates a new replayFilter instance.
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func newReplayFilter() (filter *replayFilter, err error) {
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// Initialize the SipHash-2-4 instance with a random key.
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var key [16]byte
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_, err = rand.Read(key[:])
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if err != nil {
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return
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}
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filter = new(replayFilter)
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filter.key[0] = binary.BigEndian.Uint64(key[0:8])
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filter.key[1] = binary.BigEndian.Uint64(key[8:16])
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filter.filter = make(map[uint64]*filterEntry)
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filter.fifo = list.New()
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return
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}
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// testAndSet queries the filter for buf, adds it if it was not present and
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// returns if it has added the entry or not.
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func (f *replayFilter) testAndSet(now int64, buf []byte) bool {
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hash := siphash.Hash(f.key[0], f.key[1], buf)
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f.lock.Lock()
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defer f.lock.Unlock()
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f.compactFilter(now)
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entry := f.filter[hash]
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if entry != nil {
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return true
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}
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entry = new(filterEntry)
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entry.hash = hash
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entry.firstSeen = now
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entry.element = f.fifo.PushBack(entry)
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f.filter[hash] = entry
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return false
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}
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// compactFilter purges entries that are too old to be relevant. If the filter
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// is filled to maxFilterCapacity, it will force purge a single entry.
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func (f *replayFilter) compactFilter(now int64) {
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e := f.fifo.Front()
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for e != nil {
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entry, _ := e.Value.(*filterEntry)
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// If the filter is at max capacity, force purge at least one entry.
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if f.fifo.Len() < maxFilterSize {
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deltaT := now - entry.firstSeen
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if deltaT < 0 {
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// Aeeeeeee, the system time jumped backwards, potentially by
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// a lot. This will eventually self-correct, but "eventually"
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// could be a long time. As much as this sucks, jettison the
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// entire filter.
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f.filter = make(map[uint64]*filterEntry)
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f.fifo = list.New()
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return
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}
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if deltaT < 3600*2 {
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// Why yes, this is 2 hours. The MAC code includes a hour
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// resolution timestamp, but to deal with clock skew, it
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// accepts time +- 1 hour.
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break
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}
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}
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eNext := e.Next()
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f.filter[entry.hash] = nil
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f.fifo.Remove(entry.element)
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entry.element = nil
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e = eNext
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}
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}
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/* vim :set ts=4 sw=4 sts=4 noet : */
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@ -0,0 +1,92 @@
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/*
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* Copyright (c) 2014, Yawning Angel <yawning at torproject dot org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* * Redistributions of source code must retain the above copyright notice,
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* this list of conditions and the following disclaimer.
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*
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* * Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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package obfs4
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import (
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"testing"
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)
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func TestReplayFilter(t *testing.T) {
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f, err := newReplayFilter()
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if err != nil {
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t.Fatal("newReplayFilter failed:", err)
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}
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buf := []byte("This is a test of the Emergency Broadcast System.")
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var now int64 = 3600
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// testAndSet into empty filter, returns false (not present).
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set := f.testAndSet(now, buf)
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if set {
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t.Fatal("testAndSet empty filter returned true")
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}
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// testAndSet into filter containing entry, should return true(present).
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set = f.testAndSet(now, buf)
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if !set {
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t.Fatal("testAndSet populated filter (replayed) returned false")
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}
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buf2 := []byte("This concludes this test of the Emergency Broadcast System.")
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now += 3600 * 2
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// testAndSet with time advanced.
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set = f.testAndSet(now, buf2)
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if set {
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t.Fatal("testAndSet populated filter, 2nd entry returned true")
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}
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set = f.testAndSet(now, buf2)
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if !set {
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t.Fatal("testAndSet populated filter, 2nd entry (replayed) returned false")
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}
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// Ensure that the first entry has been removed by compact.
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set = f.testAndSet(now, buf)
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if set {
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t.Fatal("testAndSet populated filter, compact check returned true")
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}
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// Ensure that the filter gets reaped if the clock jumps backwards.
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now = 0
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set = f.testAndSet(now, buf)
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if set {
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t.Fatal("testAndSet populated filter, backward time jump returned true")
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}
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if len(f.filter) != 1 {
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t.Fatal("filter map has a unexpected number of entries:", len(f.filter))
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}
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if f.fifo.Len() != 1 {
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t.Fatal("filter fifo has a unexpected number of entries:", f.fifo.Len())
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}
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// Ensure that the entry is properly added after reaping.
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set = f.testAndSet(now, buf)
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if !set {
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t.Fatal("testAndSet populated filter, post-backward clock jump (replayed) returned false")
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}
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}
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