Support plaintext crypto method for protocol header encryption

client.go

@@ -586,9 +586,9 @@ func (cl *Client) noLongerHalfOpen(t *Torrent, addr string) {
 
 // Performs initiator handshakes and returns a connection. Returns nil
 // *connection if no connection for valid reasons.
-func (cl *Client) handshakesConnection(ctx context.Context, nc net.Conn, t *Torrent, encrypted, utp bool) (c *connection, err error) {
+func (cl *Client) handshakesConnection(ctx context.Context, nc net.Conn, t *Torrent, encryptHeader, utp bool) (c *connection, err error) {
 	c = cl.newConnection(nc)
-	c.encrypted = encrypted
+	c.headerEncrypted = encryptHeader
 	c.uTP = utp
 	ctx, cancel := context.WithTimeout(ctx, handshakesTimeout)
 	defer cancel()
@@ -616,8 +616,8 @@ func (cl *Client) establishOutgoingConn(t *Torrent, addr string) (c *connection,
 	if nc == nil {
 		return
 	}
-	encryptFirst := !cl.config.DisableEncryption && !cl.config.PreferNoEncryption
+	obfuscatedHeaderFirst := !cl.config.DisableEncryption && !cl.config.PreferNoEncryption
-	c, err = cl.handshakesConnection(ctx, nc, t, encryptFirst, utp)
+	c, err = cl.handshakesConnection(ctx, nc, t, obfuscatedHeaderFirst, utp)
 	if err != nil {
 		nc.Close()
 		return
@@ -625,8 +625,12 @@ func (cl *Client) establishOutgoingConn(t *Torrent, addr string) (c *connection,
 		return
 	}
 	nc.Close()
-	if cl.config.DisableEncryption || cl.config.ForceEncryption {
+	if cl.config.ForceEncryption {
-		// There's no alternate encryption case to try.
+		// We should have just tried with an obfuscated header. A plaintext
+		// header can't result in an encrypted connection, so we're done.
+		if !obfuscatedHeaderFirst {
+			panic(cl.config.EncryptionPolicy)
+		}
 		return
 	}
 	// Try again with encryption if we didn't earlier, or without if we did,
@@ -640,7 +644,7 @@ func (cl *Client) establishOutgoingConn(t *Torrent, addr string) (c *connection,
 		err = fmt.Errorf("error dialing for unencrypted connection: %s", err)
 		return
 	}
-	c, err = cl.handshakesConnection(ctx, nc, t, !encryptFirst, utp)
+	c, err = cl.handshakesConnection(ctx, nc, t, !obfuscatedHeaderFirst, utp)
 	if err != nil || c == nil {
 		nc.Close()
 	}
@@ -829,13 +833,23 @@ func (r deadlineReader) Read(b []byte) (n int, err error) {
 	return
 }
 
-func maybeReceiveEncryptedHandshake(rw io.ReadWriter, skeys mse.SecretKeyIter) (ret io.ReadWriter, encrypted bool, err error) {
+func handleEncryption(
+	rw io.ReadWriter,
+	skeys mse.SecretKeyIter,
+	policy EncryptionPolicy,
+) (
+	ret io.ReadWriter,
+	headerEncrypted bool,
+	cryptoMethod uint32,
+	err error,
+) {
+	if !policy.ForceEncryption {
 		var protocol [len(pp.Protocol)]byte
 		_, err = io.ReadFull(rw, protocol[:])
 		if err != nil {
 			return
 		}
-	ret = struct {
+		rw = struct {
 			io.Reader
 			io.Writer
 		}{
@@ -843,20 +857,50 @@ func maybeReceiveEncryptedHandshake(rw io.ReadWriter, skeys mse.SecretKeyIter) (
 			rw,
 		}
 		if string(protocol[:]) == pp.Protocol {
+			ret = rw
 			return
 		}
-	encrypted = true
+	}
-	ret, err = mse.ReceiveHandshakeLazy(ret, skeys)
+	headerEncrypted = true
+	ret, err = mse.ReceiveHandshake(rw, skeys, func(provides uint32) uint32 {
+		cryptoMethod = func() uint32 {
+			switch {
+			case policy.ForceEncryption:
+				return mse.CryptoMethodRC4
+			case policy.DisableEncryption:
+				return mse.CryptoMethodPlaintext
+			case policy.PreferNoEncryption && provides&mse.CryptoMethodPlaintext != 0:
+				return mse.CryptoMethodPlaintext
+			default:
+				return mse.DefaultCryptoSelector(provides)
+			}
+		}()
+		return cryptoMethod
+	})
 	return
 }
 
 func (cl *Client) initiateHandshakes(c *connection, t *Torrent) (ok bool, err error) {
-	if c.encrypted {
+	if c.headerEncrypted {
 		var rw io.ReadWriter
-		rw, err = mse.InitiateHandshake(struct {
+		rw, err = mse.InitiateHandshake(
+			struct {
 				io.Reader
 				io.Writer
-		}{c.r, c.w}, t.infoHash[:], nil)
+			}{c.r, c.w},
+			t.infoHash[:],
+			nil,
+			func() uint32 {
+				switch {
+				case cl.config.ForceEncryption:
+					return mse.CryptoMethodRC4
+				case cl.config.DisableEncryption:
+					return mse.CryptoMethodPlaintext
+				default:
+					return mse.AllSupportedCrypto
+				}
+			}(),
+		)
 		c.setRW(rw)
 		if err != nil {
 			return
@@ -882,9 +926,8 @@ func (cl *Client) forSkeys(f func([]byte) bool) {
 
 // Do encryption and bittorrent handshakes as receiver.
 func (cl *Client) receiveHandshakes(c *connection) (t *Torrent, err error) {
-	if !cl.config.DisableEncryption {
 	var rw io.ReadWriter
-		rw, c.encrypted, err = maybeReceiveEncryptedHandshake(c.rw(), cl.forSkeys)
+	rw, c.headerEncrypted, c.cryptoMethod, err = handleEncryption(c.rw(), cl.forSkeys, cl.config.EncryptionPolicy)
 	c.setRW(rw)
 	if err != nil {
 		if err == mse.ErrNoSecretKeyMatch {
@@ -892,8 +935,7 @@ func (cl *Client) receiveHandshakes(c *connection) (t *Torrent, err error) {
 		}
 		return
 	}
-	}
+	if cl.config.ForceEncryption && !c.headerEncrypted {
-	if cl.config.ForceEncryption && !c.encrypted {
 		err = errors.New("connection not encrypted")
 		return
 	}

cmd/torrent/main.go

@@ -23,21 +23,6 @@ import (
 	"github.com/anacrolix/torrent/storage"
 )
 
-func resolvedPeerAddrs(ss []string) (ret []torrent.Peer, err error) {
-	for _, s := range ss {
-		var addr *net.TCPAddr
-		addr, err = net.ResolveTCPAddr("tcp", s)
-		if err != nil {
-			return
-		}
-		ret = append(ret, torrent.Peer{
-			IP:   addr.IP,
-			Port: addr.Port,
-		})
-	}
-	return
-}
-
 func torrentBar(t *torrent.Torrent) {
 	bar := uiprogress.AddBar(1)
 	bar.AppendCompleted()

config.go

@@ -51,12 +51,16 @@ type Config struct {
 	// used.
 	DefaultStorage storage.ClientImpl
 
-	DisableEncryption  bool `long:"disable-encryption"`
+	EncryptionPolicy
-	ForceEncryption    bool // Don't allow unobfuscated connections.
-	PreferNoEncryption bool
 
 	IPBlocklist iplist.Ranger
 	DisableIPv6 bool `long:"disable-ipv6"`
 	// Perform logging and any other behaviour that will help debug.
 	Debug bool `help:"enable debug logging"`
 }
+
+type EncryptionPolicy struct {
+	DisableEncryption  bool
+	ForceEncryption    bool // Don't allow unobfuscated connections.
+	PreferNoEncryption bool
+}

connection.go

@@ -14,6 +14,8 @@ import (
 	"sync"
 	"time"
 
+	"github.com/anacrolix/torrent/mse"
+
 	"github.com/anacrolix/missinggo"
 	"github.com/anacrolix/missinggo/bitmap"
 	"github.com/anacrolix/missinggo/iter"
@@ -43,7 +45,8 @@ type connection struct {
 	w io.Writer
 	r io.Reader
 	// True if the connection is operating over MSE obfuscation.
-	encrypted bool
+	headerEncrypted bool
+	cryptoMethod    uint32
 	Discovery       peerSource
 	uTP             bool
 	closed          missinggo.Event
@@ -148,8 +151,10 @@ func (cn *connection) connectionFlags() (ret string) {
 	c := func(b byte) {
 		ret += string([]byte{b})
 	}
-	if cn.encrypted {
+	if cn.cryptoMethod == mse.CryptoMethodRC4 {
 		c('E')
+	} else if cn.headerEncrypted {
+		c('e')
 	}
 	ret += string(cn.Discovery)
 	if cn.uTP {

mse/mse.go

@@ -24,9 +24,9 @@ import (
 const (
 	maxPadLen = 512
 
-	cryptoMethodPlaintext = 1
+	CryptoMethodPlaintext = 1
-	cryptoMethodRC4       = 2
+	CryptoMethodRC4       = 2
-	AllSupportedCrypto    = cryptoMethodPlaintext | cryptoMethodRC4
+	AllSupportedCrypto    = CryptoMethodPlaintext | CryptoMethodRC4
 )
 
 var (
@@ -409,9 +409,9 @@ func (h *handshake) initerSteps() (ret io.ReadWriter, err error) {
 		return
 	}
 	switch method & h.cryptoProvides {
-	case cryptoMethodRC4:
+	case CryptoMethodRC4:
 		ret = readWriter{r, &cipherWriter{e, h.conn, nil}}
-	case cryptoMethodPlaintext:
+	case CryptoMethodPlaintext:
 		ret = h.conn
 	default:
 		err = fmt.Errorf("receiver chose unsupported method: %x", method)
@@ -482,12 +482,12 @@ func (h *handshake) receiverSteps() (ret io.ReadWriter, err error) {
 		return
 	}
 	switch chosen {
-	case cryptoMethodRC4:
+	case CryptoMethodRC4:
 		ret = readWriter{
 			io.MultiReader(bytes.NewReader(h.ia), r),
 			&cipherWriter{w.c, h.conn, nil},
 		}
-	case cryptoMethodPlaintext:
+	case CryptoMethodPlaintext:
 		ret = readWriter{
 			io.MultiReader(bytes.NewReader(h.ia), h.conn),
 			h.conn,
@@ -538,11 +538,11 @@ func InitiateHandshake(rw io.ReadWriter, skey []byte, initialPayload []byte, cry
 	return h.Do()
 }
 
-func ReceiveHandshake(rw io.ReadWriter, skeys [][]byte, selectCrypto func(uint32) uint32) (ret io.ReadWriter, err error) {
+func ReceiveHandshake(rw io.ReadWriter, skeys SecretKeyIter, selectCrypto func(uint32) uint32) (ret io.ReadWriter, err error) {
 	h := handshake{
 		conn:         rw,
 		initer:       false,
-		skeys:        sliceIter(skeys),
+		skeys:        skeys,
 		chooseMethod: selectCrypto,
 	}
 	return h.Do()
@@ -562,22 +562,11 @@ func sliceIter(skeys [][]byte) SecretKeyIter {
 // returns false or exhausted.
 type SecretKeyIter func(callback func(skey []byte) (more bool))
 
-// Doesn't unpack the secret keys until it needs to, and through the passed
-// function.
-func ReceiveHandshakeLazy(rw io.ReadWriter, skeys SecretKeyIter) (ret io.ReadWriter, err error) {
-	h := handshake{
-		conn:   rw,
-		initer: false,
-		skeys:  skeys,
-	}
-	return h.Do()
-}
-
 func DefaultCryptoSelector(provided uint32) uint32 {
-	if provided&cryptoMethodRC4 != 0 {
+	if provided&CryptoMethodRC4 != 0 {
-		return cryptoMethodRC4
+		return CryptoMethodRC4
 	}
-	return cryptoMethodPlaintext
+	return CryptoMethodPlaintext
 }
 
 type CryptoSelector func(uint32) uint32

mse/mse_test.go

@@ -71,7 +71,7 @@ func handshakeTest(t testing.TB, ia []byte, aData, bData string, cryptoProvides
 	}()
 	go func() {
 		defer wg.Done()
-		b, err := ReceiveHandshake(b, [][]byte{[]byte("nope"), []byte("yep"), []byte("maybe")}, cryptoSelect)
+		b, err := ReceiveHandshake(b, sliceIter([][]byte{[]byte("nope"), []byte("yep"), []byte("maybe")}), cryptoSelect)
 		if err != nil {
 			t.Fatal(err)
 			return
@@ -103,7 +103,7 @@ func TestHandshakeDefault(t *testing.T) {
 }
 
 func TestHandshakeSelectPlaintext(t *testing.T) {
-	allHandshakeTests(t, AllSupportedCrypto, func(uint32) uint32 { return cryptoMethodPlaintext })
+	allHandshakeTests(t, AllSupportedCrypto, func(uint32) uint32 { return CryptoMethodPlaintext })
 }
 
 func BenchmarkHandshakeDefault(b *testing.B) {
@@ -180,7 +180,7 @@ func benchmarkStream(t *testing.B, crypto uint32) {
 		}()
 		func() {
 			defer bc.Close()
-			rw, err := ReceiveHandshake(bc, [][]byte{[]byte("cats")}, func(uint32) uint32 { return crypto })
+			rw, err := ReceiveHandshake(bc, sliceIter([][]byte{[]byte("cats")}), func(uint32) uint32 { return crypto })
 			require.NoError(t, err)
 			require.NoError(t, readAndWrite(rw, br, b))
 		}()
@@ -201,11 +201,11 @@ func benchmarkStream(t *testing.B, crypto uint32) {
 }
 
 func BenchmarkStreamRC4(t *testing.B) {
-	benchmarkStream(t, cryptoMethodRC4)
+	benchmarkStream(t, CryptoMethodRC4)
 }
 
 func BenchmarkStreamPlaintext(t *testing.B) {
-	benchmarkStream(t, cryptoMethodPlaintext)
+	benchmarkStream(t, CryptoMethodPlaintext)
 }
 
 func BenchmarkPipeRC4(t *testing.B) {