Added replay protection

7 files changed, 227 insertions, 42 deletions

diff --git a/src/keypair.go b/src/keypair.go
index b24dbe4..b5f46df 100644
--- a/src/keypair.go
+++ b/src/keypair.go
@@ -7,13 +7,14 @@ import (
 )
 
 type KeyPair struct {
-	receive     cipher.AEAD
-	send        cipher.AEAD
-	sendNonce   uint64
-	isInitiator bool
-	created     time.Time
-	localIndex  uint32
-	remoteIndex uint32
+	receive      cipher.AEAD
+	replayFilter ReplayFilter
+	send         cipher.AEAD
+	sendNonce    uint64
+	isInitiator  bool
+	created      time.Time
+	localIndex   uint32
+	remoteIndex  uint32
 }
 
 type KeyPairs struct {
diff --git a/src/misc.go b/src/misc.go
index 75561b2..fc75c0d 100644
--- a/src/misc.go
+++ b/src/misc.go
@@ -19,6 +19,13 @@ func min(a uint, b uint) uint {
 	return a
 }
 
+func minUint64(a uint64, b uint64) uint64 {
+	if a > b {
+		return b
+	}
+	return a
+}
+
 func signalSend(c chan struct{}) {
 	select {
 	case c <- struct{}{}:
diff --git a/src/noise_protocol.go b/src/noise_protocol.go
index a90fe4c..bfa3797 100644
--- a/src/noise_protocol.go
+++ b/src/noise_protocol.go
@@ -415,6 +415,9 @@ func (device *Device) ConsumeMessageResponse(msg *MessageResponse) *Peer {
 	return lookup.peer
 }
 
+/* Derives a new key-pair from the current handshake state
+ *
+ */
 func (peer *Peer) NewKeyPair() *KeyPair {
 	handshake := &peer.handshake
 	handshake.mutex.Lock()
@@ -445,10 +448,11 @@ func (peer *Peer) NewKeyPair() *KeyPair {
 	// create AEAD instances
 
 	keyPair := new(KeyPair)
+	keyPair.created = time.Now()
 	keyPair.send, _ = chacha20poly1305.New(sendKey[:])
 	keyPair.receive, _ = chacha20poly1305.New(recvKey[:])
 	keyPair.sendNonce = 0
-	keyPair.created = time.Now()
+	keyPair.replayFilter.Init()
 	keyPair.isInitiator = isInitiator
 	keyPair.localIndex = peer.handshake.localIndex
 	keyPair.remoteIndex = peer.handshake.remoteIndex
@@ -462,8 +466,6 @@ func (peer *Peer) NewKeyPair() *KeyPair {
 	})
 	handshake.localIndex = 0
 
-	// TODO: start timer for keypair (clearing)
-
 	// rotate key pairs
 
 	kp := &peer.keyPairs
diff --git a/src/receive.go b/src/receive.go
index e780c66..6530c47 100644
--- a/src/receive.go
+++ b/src/receive.go
@@ -432,6 +432,10 @@ func (peer *Peer) RoutineSequentialReceiver() {
 
 			// check for replay
 
+			if !elem.keyPair.replayFilter.ValidateCounter(elem.counter) {
+				return
+			}
+
 			// time (passive) keep-alive
 
 			peer.TimerStartKeepalive()
diff --git a/src/replay.go b/src/replay.go
new file mode 100644
index 0000000..49c7e08
--- /dev/null
+++ b/src/replay.go
@@ -0,0 +1,71 @@
+package main
+
+/* 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
+}
diff --git a/src/replay_test.go b/src/replay_test.go
new file mode 100644
index 0000000..e75c5c1
--- /dev/null
+++ b/src/replay_test.go
@@ -0,0 +1,114 @@
+package main
+
+import (
+	"testing"
+)
+
+/* Ported from the linux kernel implementation
+ *
+ *
+ */
+
+/* Copyright (C) 2015-2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. */
+
+func TestReplay(t *testing.T) {
+	var filter ReplayFilter
+
+	T_LIM := CounterWindowSize + 1
+
+	testNumber := 0
+	T := func(n uint64, v bool) {
+		testNumber++
+		if filter.ValidateCounter(n) != v {
+			t.Fatal("Test", testNumber, "failed", n, v)
+		}
+	}
+
+	filter.Init()
+
+	/*  1 */ T(0, true)
+	/*  2 */ T(1, true)
+	/*  3 */ T(1, false)
+	/*  4 */ T(9, true)
+	/*  5 */ T(8, true)
+	/*  6 */ T(7, true)
+	/*  7 */ T(7, false)
+	/*  8 */ T(T_LIM, true)
+	/*  9 */ T(T_LIM-1, true)
+	/* 10 */ T(T_LIM-1, false)
+	/* 11 */ T(T_LIM-2, true)
+	/* 12 */ T(2, true)
+	/* 13 */ T(2, false)
+	/* 14 */ T(T_LIM+16, true)
+	/* 15 */ T(3, false)
+	/* 16 */ T(T_LIM+16, false)
+	/* 17 */ T(T_LIM*4, true)
+	/* 18 */ T(T_LIM*4-(T_LIM-1), true)
+	/* 19 */ T(10, false)
+	/* 20 */ T(T_LIM*4-T_LIM, false)
+	/* 21 */ T(T_LIM*4-(T_LIM+1), false)
+	/* 22 */ T(T_LIM*4-(T_LIM-2), true)
+	/* 23 */ T(T_LIM*4+1-T_LIM, false)
+	/* 24 */ T(0, false)
+	/* 25 */ T(RejectAfterMessages, false)
+	/* 26 */ T(RejectAfterMessages-1, true)
+	/* 27 */ T(RejectAfterMessages, false)
+	/* 28 */ T(RejectAfterMessages-1, false)
+	/* 29 */ T(RejectAfterMessages-2, true)
+	/* 30 */ T(RejectAfterMessages+1, false)
+	/* 31 */ T(RejectAfterMessages+2, false)
+	/* 32 */ T(RejectAfterMessages-2, false)
+	/* 33 */ T(RejectAfterMessages-3, true)
+	/* 34 */ T(0, false)
+
+	t.Log("Bulk test 1")
+	filter.Init()
+	testNumber = 0
+	for i := uint64(1); i <= CounterWindowSize; i++ {
+		T(i, true)
+	}
+	T(0, true)
+	T(0, false)
+
+	t.Log("Bulk test 2")
+	filter.Init()
+	testNumber = 0
+	for i := uint64(2); i <= CounterWindowSize+1; i++ {
+		T(i, true)
+	}
+	T(1, true)
+	T(0, false)
+
+	t.Log("Bulk test 3")
+	filter.Init()
+	testNumber = 0
+	for i := CounterWindowSize + 1; i > 0; i-- {
+		T(i, true)
+	}
+
+	t.Log("Bulk test 4")
+	filter.Init()
+	testNumber = 0
+	for i := CounterWindowSize + 2; i > 1; i-- {
+		T(i, true)
+	}
+	T(0, false)
+
+	t.Log("Bulk test 5")
+	filter.Init()
+	testNumber = 0
+	for i := CounterWindowSize; i > 0; i-- {
+		T(i, true)
+	}
+	T(CounterWindowSize+1, true)
+	T(0, false)
+
+	t.Log("Bulk test 6")
+	filter.Init()
+	testNumber = 0
+	for i := CounterWindowSize; i > 0; i-- {
+		T(i, true)
+	}
+	T(0, true)
+	T(CounterWindowSize+1, true)
+}
diff --git a/src/timers.go b/src/timers.go
index 26926c2..70e0766 100644
--- a/src/timers.go
+++ b/src/timers.go
@@ -12,22 +12,15 @@ import (
  *
  */
 func (peer *Peer) KeepKeyFreshSending() {
-	send := func() bool {
-		peer.keyPairs.mutex.RLock()
-		defer peer.keyPairs.mutex.RUnlock()
-
-		kp := peer.keyPairs.current
-		if kp == nil {
-			return false
-		}
-
-		if !kp.isInitiator {
-			return false
-		}
-
-		nonce := atomic.LoadUint64(&kp.sendNonce)
-		return nonce > RekeyAfterMessages || time.Now().Sub(kp.created) > RekeyAfterTime
-	}()
+	kp := peer.keyPairs.Current()
+	if kp == nil {
+		return
+	}
+	if !kp.isInitiator {
+		return
+	}
+	nonce := atomic.LoadUint64(&kp.sendNonce)
+	send := nonce > RekeyAfterMessages || time.Now().Sub(kp.created) > RekeyAfterTime
 	if send {
 		signalSend(peer.signal.handshakeBegin)
 	}
@@ -37,22 +30,15 @@ func (peer *Peer) KeepKeyFreshSending() {
  *
  */
 func (peer *Peer) KeepKeyFreshReceiving() {
-	send := func() bool {
-		peer.keyPairs.mutex.RLock()
-		defer peer.keyPairs.mutex.RUnlock()
-
-		kp := peer.keyPairs.current
-		if kp == nil {
-			return false
-		}
-
-		if !kp.isInitiator {
-			return false
-		}
-
-		nonce := atomic.LoadUint64(&kp.sendNonce)
-		return nonce > RekeyAfterMessages || time.Now().Sub(kp.created) > RekeyAfterTimeReceiving
-	}()
+	kp := peer.keyPairs.Current()
+	if kp == nil {
+		return
+	}
+	if !kp.isInitiator {
+		return
+	}
+	nonce := atomic.LoadUint64(&kp.sendNonce)
+	send := nonce > RekeyAfterMessages || time.Now().Sub(kp.created) > RekeyAfterTimeReceiving
 	if send {
 		signalSend(peer.signal.handshakeBegin)
 	}