fix: don't fail the handshake when the libp2p extension is critical

crypto.go

@@ -24,6 +24,7 @@ const certificatePrefix = "libp2p-tls-handshake:"
 const alpn string = "libp2p"
 
 var extensionID = getPrefixedExtensionID([]int{1, 1})
+var extensionCritical bool // so we can mark the extension critical in tests
 
 type signedKey struct {
 	PubKey    []byte
@@ -113,25 +114,32 @@ func PubKeyFromCertChain(chain []*x509.Certificate) (ic.PubKey, error) {
 	cert := chain[0]
 	pool := x509.NewCertPool()
 	pool.AddCert(cert)
-	if _, err := cert.Verify(x509.VerifyOptions{Roots: pool}); err != nil {
-		// If we return an x509 error here, it will be sent on the wire.
-		// Wrap the error to avoid that.
-		return nil, fmt.Errorf("certificate verification failed: %s", err)
-	}
-
 	var found bool
 	var keyExt pkix.Extension
 	// find the libp2p key extension, skipping all unknown extensions
 	for _, ext := range cert.Extensions {
 		if extensionIDEqual(ext.Id, extensionID) {
 			keyExt = ext
 			found = true
+			for i, oident := range cert.UnhandledCriticalExtensions {
+				if oident.Equal(ext.Id) {
+					// delete the extension from UnhandledCriticalExtensions
+					cert.UnhandledCriticalExtensions = append(cert.UnhandledCriticalExtensions[:i], cert.UnhandledCriticalExtensions[i+1:]...)
+					break
+				}
+			}
 			break
 		}
 	}
 	if !found {
 		return nil, errors.New("expected certificate to contain the key extension")
 	}
+	if _, err := cert.Verify(x509.VerifyOptions{Roots: pool}); err != nil {
+		// If we return an x509 error here, it will be sent on the wire.
+		// Wrap the error to avoid that.
+		return nil, fmt.Errorf("certificate verification failed: %s", err)
+	}
+
 	var sk signedKey
 	if _, err := asn1.Unmarshal(keyExt.Value, &sk); err != nil {
 		return nil, fmt.Errorf("unmarshalling signed certificate failed: %s", err)
@@ -190,7 +198,7 @@ func keyToCertificate(sk ic.PrivKey) (*tls.Certificate, error) {
 		NotAfter:     time.Now().Add(certValidityPeriod),
 		// after calling CreateCertificate, these will end up in Certificate.Extensions
 		ExtraExtensions: []pkix.Extension{
-			{Id: extensionID, Value: value},
+			{Id: extensionID, Critical: extensionCritical, Value: value},
 		},
 	}
 	certDER, err := x509.CreateCertificate(rand.Reader, tmpl, tmpl, certKey.Public(), certKey)

transport_test.go

@@ -87,42 +87,50 @@ var _ = Describe("Transport", func() {
 		clientID, clientKey = createPeer()
 	})
 
-	It("handshakes", func() {
-		clientTransport, err := New(clientKey)
-		Expect(err).ToNot(HaveOccurred())
-		serverTransport, err := New(serverKey)
-		Expect(err).ToNot(HaveOccurred())
+	Context("successful handshakes", func() {
+		for _, critical := range []bool{true, false} {
+			crit := critical
 
-		clientInsecureConn, serverInsecureConn := connect()
+			It(fmt.Sprintf("handshakes, extension critical: %t", crit), func() {
+				extensionCritical = crit
+				defer func() { extensionCritical = false }()
+				clientTransport, err := New(clientKey)
+				Expect(err).ToNot(HaveOccurred())
+				serverTransport, err := New(serverKey)
+				Expect(err).ToNot(HaveOccurred())
 
-		serverConnChan := make(chan sec.SecureConn)
-		go func() {
-			defer GinkgoRecover()
-			serverConn, err := serverTransport.SecureInbound(context.Background(), serverInsecureConn)
-			Expect(err).ToNot(HaveOccurred())
-			serverConnChan <- serverConn
-		}()
-		clientConn, err := clientTransport.SecureOutbound(context.Background(), clientInsecureConn, serverID)
-		Expect(err).ToNot(HaveOccurred())
-		var serverConn sec.SecureConn
-		Eventually(serverConnChan).Should(Receive(&serverConn))
-		defer clientConn.Close()
-		defer serverConn.Close()
-		Expect(clientConn.LocalPeer()).To(Equal(clientID))
-		Expect(serverConn.LocalPeer()).To(Equal(serverID))
-		Expect(clientConn.LocalPrivateKey()).To(Equal(clientKey))
-		Expect(serverConn.LocalPrivateKey()).To(Equal(serverKey))
-		Expect(clientConn.RemotePeer()).To(Equal(serverID))
-		Expect(serverConn.RemotePeer()).To(Equal(clientID))
-		Expect(clientConn.RemotePublicKey()).To(Equal(serverKey.GetPublic()))
-		Expect(serverConn.RemotePublicKey()).To(Equal(clientKey.GetPublic()))
-		// exchange some data
-		_, err = serverConn.Write([]byte("foobar"))
-		Expect(err).ToNot(HaveOccurred())
-		b := make([]byte, 6)
-		_, err = clientConn.Read(b)
-		Expect(err).ToNot(HaveOccurred())
-		Expect(string(b)).To(Equal("foobar"))
+				clientInsecureConn, serverInsecureConn := connect()
+
+				serverConnChan := make(chan sec.SecureConn)
+				go func() {
+					defer GinkgoRecover()
+					serverConn, err := serverTransport.SecureInbound(context.Background(), serverInsecureConn)
+					Expect(err).ToNot(HaveOccurred())
+					serverConnChan <- serverConn
+				}()
+				clientConn, err := clientTransport.SecureOutbound(context.Background(), clientInsecureConn, serverID)
+				Expect(err).ToNot(HaveOccurred())
+				var serverConn sec.SecureConn
+				Eventually(serverConnChan).Should(Receive(&serverConn))
+				defer clientConn.Close()
+				defer serverConn.Close()
+				Expect(clientConn.LocalPeer()).To(Equal(clientID))
+				Expect(serverConn.LocalPeer()).To(Equal(serverID))
+				Expect(clientConn.LocalPrivateKey()).To(Equal(clientKey))
+				Expect(serverConn.LocalPrivateKey()).To(Equal(serverKey))
+				Expect(clientConn.RemotePeer()).To(Equal(serverID))
+				Expect(serverConn.RemotePeer()).To(Equal(clientID))
+				Expect(clientConn.RemotePublicKey()).To(Equal(serverKey.GetPublic()))
+				Expect(serverConn.RemotePublicKey()).To(Equal(clientKey.GetPublic()))
+				// exchange some data
+				_, err = serverConn.Write([]byte("foobar"))
+				Expect(err).ToNot(HaveOccurred())
+				b := make([]byte, 6)
+				_, err = clientConn.Read(b)
+				Expect(err).ToNot(HaveOccurred())
+				Expect(string(b)).To(Equal("foobar"))
+			})
+		}
 	})
 
 	It("fails when the context of the outgoing connection is canceled", func() {
@@ -243,6 +251,9 @@ var _ = Describe("Transport", func() {
 				SerialNumber: big.NewInt(1),
 				NotBefore:    time.Now().Add(-time.Hour),
 				NotAfter:     time.Now().Add(-time.Minute),
+				ExtraExtensions: []pkix.Extension{
+					{Id: extensionID, Value: []byte("foobar")},
+				},
 			})
 			identity.config.Certificates = []tls.Certificate{cert}
 		}