Merge branch 'covertdtls' into 'main'

Add covert-dtls to proxy and client

See merge request tpo/anti-censorship/pluggable-transports/snowflake!448

client/lib/rendezvous.go

@@ -177,23 +177,26 @@ type WebRTCDialer struct {
 	webrtcConfig *webrtc.Configuration
 	max          int
 
-	eventLogger event.SnowflakeEventReceiver
-	proxy       *url.URL
+	eventLogger   event.SnowflakeEventReceiver
+	proxy         *url.URL
+	dtlsRandomize bool
+	dtlsMimic     bool
 }
 
 // Deprecated: Use NewWebRTCDialerWithEventsAndProxy instead
 func NewWebRTCDialer(broker *BrokerChannel, iceServers []webrtc.ICEServer, max int) *WebRTCDialer {
-	return NewWebRTCDialerWithEventsAndProxy(broker, iceServers, max, nil, nil)
+	return NewWebRTCDialerWithEventsAndProxy(broker, iceServers, max, nil, nil, false, false)
 }
 
 // Deprecated: Use NewWebRTCDialerWithEventsAndProxy instead
 func NewWebRTCDialerWithEvents(broker *BrokerChannel, iceServers []webrtc.ICEServer, max int, eventLogger event.SnowflakeEventReceiver) *WebRTCDialer {
-	return NewWebRTCDialerWithEventsAndProxy(broker, iceServers, max, eventLogger, nil)
+	return NewWebRTCDialerWithEventsAndProxy(broker, iceServers, max, eventLogger, nil, false, false)
 }
 
 // NewWebRTCDialerWithEventsAndProxy constructs a new WebRTCDialer.
 func NewWebRTCDialerWithEventsAndProxy(broker *BrokerChannel, iceServers []webrtc.ICEServer, max int,
 	eventLogger event.SnowflakeEventReceiver, proxy *url.URL,
+	dtlsRandomize bool, dtlsMimic bool,
 ) *WebRTCDialer {
 	config := webrtc.Configuration{
 		ICEServers: iceServers,
@@ -204,8 +207,10 @@ func NewWebRTCDialerWithEventsAndProxy(broker *BrokerChannel, iceServers []webrt
 		webrtcConfig:  &config,
 		max:           max,
 
-		eventLogger: eventLogger,
-		proxy:       proxy,
+		eventLogger:   eventLogger,
+		proxy:         proxy,
+		dtlsRandomize: dtlsRandomize,
+		dtlsMimic:     dtlsMimic,
 	}
 }
 
@@ -213,7 +218,7 @@ func NewWebRTCDialerWithEventsAndProxy(broker *BrokerChannel, iceServers []webrt
 func (w WebRTCDialer) Catch() (*WebRTCPeer, error) {
 	// TODO: [#25591] Fetch ICE server information from Broker.
 	// TODO: [#25596] Consider TURN servers here too.
-	return NewWebRTCPeerWithEventsAndProxy(w.webrtcConfig, w.BrokerChannel, w.eventLogger, w.proxy)
+	return NewWebRTCPeerWithEventsAndProxy(w.webrtcConfig, w.BrokerChannel, w.eventLogger, w.proxy, w.dtlsRandomize, w.dtlsMimic)
 }
 
 // GetMax returns the maximum number of snowflakes to collect.

client/lib/snowflake.go

@@ -118,6 +118,8 @@ type ClientConfig struct {
 	BridgeFingerprint string
 	// CommunicationProxy is the proxy address for network communication
 	CommunicationProxy *url.URL
+	DTLSRandomize      bool
+	DTLSMimic          bool
 }
 
 // NewSnowflakeClient creates a new Snowflake transport client that can spawn multiple
@@ -161,7 +163,7 @@ func NewSnowflakeClient(config ClientConfig) (*Transport, error) {
 		max = config.Max
 	}
 	eventsLogger := event.NewSnowflakeEventDispatcher()
-	transport := &Transport{dialer: NewWebRTCDialerWithEventsAndProxy(broker, iceServers, max, eventsLogger, config.CommunicationProxy), eventDispatcher: eventsLogger}
+	transport := &Transport{dialer: NewWebRTCDialerWithEventsAndProxy(broker, iceServers, max, eventsLogger, config.CommunicationProxy, config.DTLSRandomize, config.DTLSMimic), eventDispatcher: eventsLogger}
 
 	return transport, nil
 }

client/lib/webrtc.go

@@ -11,10 +11,13 @@ import (
 	"sync"
 	"time"
 
+	"github.com/pion/dtls/v3"
 	"github.com/pion/ice/v4"
 	"github.com/pion/transport/v3"
 	"github.com/pion/transport/v3/stdnet"
 	"github.com/pion/webrtc/v4"
+	"github.com/theodorsm/covert-dtls/pkg/mimicry"
+	"github.com/theodorsm/covert-dtls/pkg/randomize"
 
 	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/event"
 	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/proxy"
@@ -49,7 +52,7 @@ type WebRTCPeer struct {
 func NewWebRTCPeer(
 	config *webrtc.Configuration, broker *BrokerChannel,
 ) (*WebRTCPeer, error) {
-	return NewWebRTCPeerWithEventsAndProxy(config, broker, nil, nil)
+	return NewWebRTCPeerWithEventsAndProxy(config, broker, nil, nil, false, false)
 }
 
 // Deprecated: Use NewWebRTCPeerWithEventsAndProxy Instead.
@@ -57,7 +60,7 @@ func NewWebRTCPeerWithEvents(
 	config *webrtc.Configuration, broker *BrokerChannel,
 	eventsLogger event.SnowflakeEventReceiver,
 ) (*WebRTCPeer, error) {
-	return NewWebRTCPeerWithEventsAndProxy(config, broker, eventsLogger, nil)
+	return NewWebRTCPeerWithEventsAndProxy(config, broker, eventsLogger, nil, false, false)
 }
 
 // NewWebRTCPeerWithEventsAndProxy constructs a WebRTC PeerConnection to a snowflake proxy.
@@ -68,6 +71,7 @@ func NewWebRTCPeerWithEvents(
 func NewWebRTCPeerWithEventsAndProxy(
 	config *webrtc.Configuration, broker *BrokerChannel,
 	eventsLogger event.SnowflakeEventReceiver, proxy *url.URL,
+	dtlsRandomize bool, dtlsMimic bool,
 ) (*WebRTCPeer, error) {
 	if eventsLogger == nil {
 		eventsLogger = event.NewSnowflakeEventDispatcher()
@@ -92,7 +96,7 @@ func NewWebRTCPeerWithEventsAndProxy(
 	connection.eventsLogger = eventsLogger
 	connection.proxy = proxy
 
-	err := connection.connect(config, broker)
+	err := connection.connect(config, broker, dtlsRandomize, dtlsMimic)
 	if err != nil {
 		connection.Close()
 		return nil, err
@@ -166,10 +170,9 @@ func (c *WebRTCPeer) checkForStaleness(timeout time.Duration) {
 
 // connect does the bulk of the work: gather ICE candidates, send the SDP offer to broker,
 // receive an answer from broker, and wait for data channel to open
-func (c *WebRTCPeer) connect(config *webrtc.Configuration, broker *BrokerChannel) error {
+func (c *WebRTCPeer) connect(config *webrtc.Configuration, broker *BrokerChannel, dtlsRandomize bool, dtlsMimic bool) error {
 	log.Println(c.id, " connecting...")
-
-	err := c.preparePeerConnection(config, broker.keepLocalAddresses)
+	err := c.preparePeerConnection(config, broker.keepLocalAddresses, dtlsRandomize, dtlsMimic)
 	localDescription := c.pc.LocalDescription()
 	c.eventsLogger.OnNewSnowflakeEvent(event.EventOnOfferCreated{
 		WebRTCLocalDescription: localDescription,
@@ -213,6 +216,8 @@ func (c *WebRTCPeer) connect(config *webrtc.Configuration, broker *BrokerChannel
 func (c *WebRTCPeer) preparePeerConnection(
 	config *webrtc.Configuration,
 	keepLocalAddresses bool,
+	dtlsRandomize bool,
+	dtlsMimic bool,
 ) error {
 	var err error
 	s := webrtc.SettingEngine{}
@@ -245,6 +250,24 @@ func (c *WebRTCPeer) preparePeerConnection(
 	}
 
 	s.SetNet(vnet)
+
+	if dtlsRandomize {
+		rand := randomize.RandomizedMessageClientHello{RandomALPN: true}
+		s.SetDTLSClientHelloMessageHook(rand.Hook)
+	} else if dtlsMimic {
+		mimic := &mimicry.MimickedClientHello{}
+		profiles := []dtls.SRTPProtectionProfile{
+			dtls.SRTP_AES128_CM_HMAC_SHA1_80,
+			dtls.SRTP_AES128_CM_HMAC_SHA1_32,
+			dtls.SRTP_AEAD_AES_128_GCM,
+			dtls.SRTP_AEAD_AES_256_GCM,
+			dtls.SRTP_AES256_CM_SHA1_32,
+			dtls.SRTP_AES256_CM_SHA1_80,
+		}
+		s.SetSRTPProtectionProfiles(profiles...)
+		s.SetDTLSClientHelloMessageHook(mimic.Hook)
+	}
+
 	api := webrtc.NewAPI(webrtc.WithSettingEngine(s))
 	c.pc, err = api.NewPeerConnection(*config)
 	if err != nil {

client/snowflake.go

@@ -174,6 +174,8 @@ func main() {
 	max := flag.Int("max", DefaultSnowflakeCapacity,
 		"capacity for number of multiplexed WebRTC peers")
 	versionFlag := flag.Bool("version", false, "display version info to stderr and quit")
+	dtlsRandomize := flag.Bool("dtls-randomize", false, "randomize DTLS client hello")
+	dtlsMimic := flag.Bool("dtls-mimic", false, "mimic DTLS client hello of Chrome and Firefox")
 
 	// Deprecated
 	oldLogToStateDir := flag.Bool("logToStateDir", false, "use -log-to-state-dir instead")
@@ -186,6 +188,10 @@ func main() {
 		os.Exit(0)
 	}
 
+	if *dtlsMimic && *dtlsRandomize {
+		log.Fatal("Cannot both Randomize and Mimic DTLS client hello")
+	}
+
 	log.SetFlags(log.LstdFlags | log.LUTC)
 
 	// Don't write to stderr; versions of tor earlier than about 0.3.5.6 do
@@ -240,6 +246,8 @@ func main() {
 		ICEAddresses:       iceAddresses,
 		KeepLocalAddresses: *keepLocalAddresses || *oldKeepLocalAddresses,
 		Max:                *max,
+		DTLSRandomize:      *dtlsRandomize,
+		DTLSMimic:          *dtlsMimic,
 	}
 
 	// Begin goptlib client process.