crypto/tls: remove TLS13CipherSuites.

To allow clients to advertise both TLS 1.2 and TLS 1.3 cipher suites,
remove the distinction between both suites. TLS 1.3 suites are now
always included in the default cipher list (and the client will send it
if MaxVersion allows for it).

Since TLS 1.3 is expected to become the default MaxVersion and
applications might have set only TLS 1.2 cipher suites in their
configuration, TLS 1.3 cipher suites are added when none are present.

Alternatively, I considered disallowing overriding the TLS 1.3 suites,
but that requires more complexity and has not much benefits. Provide a
mechanism and do not dictate policy, application developers might want
to fix a cipher suite for testing other implementations for example.

Fixes https://github.com/cloudflare/tls-tris/pull/22

cipher_suites.go

@@ -389,7 +389,7 @@ func mutualCipherSuite(have []uint16, want uint16) *cipherSuite {
 //
 // Taken from http://www.iana.org/assignments/tls-parameters/tls-parameters.xml
 const (
-	// TLS 1.0 - 1.2 cipher suites. To be used in Config.CipherSuites.
+	// TLS 1.0 - 1.2 cipher suites.
 	TLS_RSA_WITH_RC4_128_SHA                uint16 = 0x0005
 	TLS_RSA_WITH_3DES_EDE_CBC_SHA           uint16 = 0x000a
 	TLS_RSA_WITH_AES_128_CBC_SHA            uint16 = 0x002f
@@ -413,7 +413,7 @@ const (
 	TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305    uint16 = 0xcca8
 	TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305  uint16 = 0xcca9
 
-	// TLS 1.3+ cipher suites. To be used in Config.TLS13CipherSuites.
+	// TLS 1.3+ cipher suites.
 	TLS_AES_128_GCM_SHA256       uint16 = 0x1301
 	TLS_AES_256_GCM_SHA384       uint16 = 0x1302
 	TLS_CHACHA20_POLY1305_SHA256 uint16 = 0x1303

common.go

@@ -510,10 +510,6 @@ type Config struct {
 	// supported by the implementation.
 	CipherSuites []uint16
 
-	// TLS13CipherSuites is a list of supported cipher suites to be used in
-	// TLS 1.3. If nil, uses a list of suites supported by the implementation.
-	TLS13CipherSuites []uint16
-
 	// PreferServerCipherSuites controls whether the server selects the
 	// client's most preferred ciphersuite, or the server's most preferred
 	// ciphersuite. If true then the server's preference, as expressed in
@@ -659,7 +655,6 @@ func (c *Config) Clone() *Config {
 		ClientCAs:                   c.ClientCAs,
 		InsecureSkipVerify:          c.InsecureSkipVerify,
 		CipherSuites:                c.CipherSuites,
-		TLS13CipherSuites:           c.TLS13CipherSuites,
 		PreferServerCipherSuites:    c.PreferServerCipherSuites,
 		SessionTicketsDisabled:      c.SessionTicketsDisabled,
 		SessionTicketKey:            c.SessionTicketKey,
@@ -756,17 +751,30 @@ func (c *Config) time() time.Time {
 	return t()
 }
 
-func (c *Config) cipherSuites(version uint16) []uint16 {
-	if version >= VersionTLS13 {
-		s := c.TLS13CipherSuites
-		if s == nil {
-			s = defaultTLS13CipherSuites()
+func hasOverlappingCipherSuites(cs1, cs2 []uint16) bool {
+	for _, c1 := range cs1 {
+		for _, c2 := range cs2 {
+			if c1 == c2 {
+				return true
+			}
 		}
-		return s
 	}
+	return false
+}
+
+func (c *Config) cipherSuites() []uint16 {
 	s := c.CipherSuites
 	if s == nil {
 		s = defaultCipherSuites()
+	} else if c.maxVersion() >= VersionTLS13 {
+		// Ensure that TLS 1.3 suites are always present, but respect
+		// the application cipher suite preferences.
+		s13 := defaultTLS13CipherSuites()
+		if !hasOverlappingCipherSuites(s, s13) {
+			allSuites := make([]uint16, len(s13)+len(s))
+			allSuites = append(allSuites, s13...)
+			s = append(allSuites, s...)
+		}
 	}
 	return s
 }
@@ -1089,9 +1097,7 @@ func initDefaultCipherSuites() {
 	}
 
 	varDefaultTLS13CipherSuites = make([]uint16, 0, len(cipherSuites))
-	for _, topCipher := range topTLS13CipherSuites {
-		varDefaultTLS13CipherSuites = append(varDefaultTLS13CipherSuites, topCipher)
-	}
+	varDefaultTLS13CipherSuites = append(varDefaultTLS13CipherSuites, topTLS13CipherSuites...)
 	varDefaultCipherSuites = make([]uint16, 0, len(cipherSuites))
 	varDefaultCipherSuites = append(varDefaultCipherSuites, topCipherSuites...)
 
@@ -1116,6 +1122,7 @@ NextCipherSuite:
 			varDefaultCipherSuites = append(varDefaultCipherSuites, suite.id)
 		}
 	}
+	varDefaultCipherSuites = append(varDefaultTLS13CipherSuites, varDefaultCipherSuites...)
 }
 
 func unexpectedMessageError(wanted, got interface{}) error {

handshake_client.go

@@ -74,7 +74,7 @@ func (c *Conn) clientHandshake() error {
 		hello.secureRenegotiation = c.clientFinished[:]
 	}
 
-	possibleCipherSuites := c.config.cipherSuites(c.vers)
+	possibleCipherSuites := c.config.cipherSuites()
 	hello.cipherSuites = make([]uint16, 0, len(possibleCipherSuites))
 
 NextCipherSuite:

handshake_server.go

@@ -321,11 +321,11 @@ Curves:
 
 	var preferenceList, supportedList []uint16
 	if c.config.PreferServerCipherSuites {
-		preferenceList = c.config.cipherSuites(c.vers)
+		preferenceList = c.config.cipherSuites()
 		supportedList = hs.clientHello.cipherSuites
 	} else {
 		preferenceList = hs.clientHello.cipherSuites
-		supportedList = c.config.cipherSuites(c.vers)
+		supportedList = c.config.cipherSuites()
 	}
 
 	for _, id := range preferenceList {
@@ -387,7 +387,7 @@ func (hs *serverHandshakeState) checkForResumption() bool {
 	}
 
 	// Check that we also support the ciphersuite from the session.
-	if !hs.setCipherSuite(hs.sessionState.cipherSuite, c.config.cipherSuites(c.vers), hs.sessionState.vers) {
+	if !hs.setCipherSuite(hs.sessionState.cipherSuite, c.config.cipherSuites(), hs.sessionState.vers) {
 		return false
 	}
 

handshake_server_test.go

@@ -49,18 +49,6 @@ func allCipherSuites() []uint16 {
 	return ids
 }
 
-func allTLS13CipherSuites() []uint16 {
-	var ids []uint16
-	for _, suite := range cipherSuites {
-		if suite.flags&suiteTLS13 == 0 {
-			continue
-		}
-		ids = append(ids, suite.id)
-	}
-
-	return ids
-}
-
 func init() {
 	testConfig = &Config{
 		Time:               func() time.Time { return time.Unix(0, 0) },
@@ -70,7 +58,6 @@ func init() {
 		MinVersion:         VersionSSL30,
 		MaxVersion:         VersionTLS12,
 		CipherSuites:       allCipherSuites(),
-		TLS13CipherSuites:  allTLS13CipherSuites(),
 	}
 	testConfig.Certificates[0].Certificate = [][]byte{testRSACertificate}
 	testConfig.Certificates[0].PrivateKey = testRSAPrivateKey

tls_test.go

@@ -648,7 +648,6 @@ func TestCloneNonFuncFields(t *testing.T) {
 		case "SessionTicketKey":
 			f.Set(reflect.ValueOf([32]byte{}))
 		case "CipherSuites":
-		case "TLS13CipherSuites":
 			f.Set(reflect.ValueOf([]uint16{1, 2}))
 		case "CurvePreferences":
 			f.Set(reflect.ValueOf([]CurveID{CurveP256}))