crypto/tls: disable RC4 by default.

RC4 is frowned upon[1] at this point and major providers are disabling it
by default[2].

Those who still need RC4 support in crypto/tls can enable it by
specifying the CipherSuites slice in crypto/tls.Config explicitly.

Fixes #10094.

[1] https://tools.ietf.org/html/rfc7465
[2] https://blog.cloudflare.com/killing-rc4-the-long-goodbye/

Change-Id: Ia03a456f7e7a4362b706392b0e3c4cc93ce06f9f
Reviewed-on: https://go-review.googlesource.com/7647
Reviewed-by: Andrew Gerrand <adg@golang.org>

diff --git a/src/crypto/tls/cipher_suites.go b/src/crypto/tls/cipher_suites.go
index 4b4695ad8e354caaa84190d3c6c9577e04cbb69e..b315436c1fb499f85957b0e6ed51fb44657189b8 100644 (file)
--- a/src/crypto/tls/cipher_suites.go
+++ b/src/crypto/tls/cipher_suites.go
@@ -49,6 +49,9 @@ const (
        // suiteTLS12 indicates that the cipher suite should only be advertised
        // and accepted when using TLS 1.2.
        suiteTLS12
+       // suiteDefaultOff indicates that this cipher suite is not included by
+       // default.
+       suiteDefaultOff
 )
 
 // A cipherSuite is a specific combination of key agreement, cipher and MAC
@@ -75,13 +78,13 @@ var cipherSuites = []*cipherSuite{
        {TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, 16, 0, 4, ecdheECDSAKA, suiteECDHE | suiteECDSA | suiteTLS12, nil, nil, aeadAESGCM, crypto.SHA256},
        {TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, 32, 0, 4, ecdheRSAKA, suiteECDHE | suiteTLS12, nil, nil, aeadAESGCM, crypto.SHA384},
        {TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384, 32, 0, 4, ecdheECDSAKA, suiteECDHE | suiteECDSA | suiteTLS12, nil, nil, aeadAESGCM, crypto.SHA384},
-       {TLS_ECDHE_RSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheRSAKA, suiteECDHE, cipherRC4, macSHA1, nil, crypto.SHA256},
-       {TLS_ECDHE_ECDSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheECDSAKA, suiteECDHE | suiteECDSA, cipherRC4, macSHA1, nil, crypto.SHA256},
+       {TLS_ECDHE_RSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheRSAKA, suiteECDHE | suiteDefaultOff, cipherRC4, macSHA1, nil, crypto.SHA256},
+       {TLS_ECDHE_ECDSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheECDSAKA, suiteECDHE | suiteECDSA | suiteDefaultOff, cipherRC4, macSHA1, nil, crypto.SHA256},
        {TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, ecdheRSAKA, suiteECDHE, cipherAES, macSHA1, nil, crypto.SHA256},
        {TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA, 16, 20, 16, ecdheECDSAKA, suiteECDHE | suiteECDSA, cipherAES, macSHA1, nil, crypto.SHA256},
        {TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA, 32, 20, 16, ecdheRSAKA, suiteECDHE, cipherAES, macSHA1, nil, crypto.SHA256},
        {TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA, 32, 20, 16, ecdheECDSAKA, suiteECDHE | suiteECDSA, cipherAES, macSHA1, nil, crypto.SHA256},
-       {TLS_RSA_WITH_RC4_128_SHA, 16, 20, 0, rsaKA, 0, cipherRC4, macSHA1, nil, crypto.SHA256},
+       {TLS_RSA_WITH_RC4_128_SHA, 16, 20, 0, rsaKA, suiteDefaultOff, cipherRC4, macSHA1, nil, crypto.SHA256},
        {TLS_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, rsaKA, 0, cipherAES, macSHA1, nil, crypto.SHA256},
        {TLS_RSA_WITH_AES_256_CBC_SHA, 32, 20, 16, rsaKA, 0, cipherAES, macSHA1, nil, crypto.SHA256},
        {TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, ecdheRSAKA, suiteECDHE, cipher3DES, macSHA1, nil, crypto.SHA256},

diff --git a/src/crypto/tls/common.go b/src/crypto/tls/common.go
index 89ae140fea59d77046fa5d0c928d6c03ff721019..43b3f6b1d8bb7be9996e601c6566c66ad6a9ba73 100644 (file)
--- a/src/crypto/tls/common.go
+++ b/src/crypto/tls/common.go
@@ -611,9 +611,12 @@ func defaultCipherSuites() []uint16 {
 }
 
 func initDefaultCipherSuites() {
-       varDefaultCipherSuites = make([]uint16, len(cipherSuites))
-       for i, suite := range cipherSuites {
-               varDefaultCipherSuites[i] = suite.id
+       varDefaultCipherSuites = make([]uint16, 0, len(cipherSuites))
+       for _, suite := range cipherSuites {
+               if suite.flags&suiteDefaultOff != 0 {
+                       continue
+               }
+               varDefaultCipherSuites = append(varDefaultCipherSuites, suite.id)
        }
 }
 

diff --git a/src/crypto/tls/handshake_server_test.go b/src/crypto/tls/handshake_server_test.go
index f0ef26000affe96d0a815f8a9f5bc209b1e362e7..af5cadb959fb815e56e97f050731bd92c4f9fd74 100644 (file)
--- a/src/crypto/tls/handshake_server_test.go
+++ b/src/crypto/tls/handshake_server_test.go
@@ -37,6 +37,15 @@ func (zeroSource) Read(b []byte) (n int, err error) {
 
 var testConfig *Config
 
+func allCipherSuites() []uint16 {
+       ids := make([]uint16, len(cipherSuites))
+       for i, suite := range cipherSuites {
+               ids[i] = suite.id
+       }
+
+       return ids
+}
+
 func init() {
        testConfig = &Config{
                Time:               func() time.Time { return time.Unix(0, 0) },
@@ -45,6 +54,7 @@ func init() {
                InsecureSkipVerify: true,
                MinVersion:         VersionSSL30,
                MaxVersion:         VersionTLS12,
+               CipherSuites:       allCipherSuites(),
        }
        testConfig.Certificates[0].Certificate = [][]byte{testRSACertificate}
        testConfig.Certificates[0].PrivateKey = testRSAPrivateKey
@@ -53,7 +63,7 @@ func init() {
        testConfig.BuildNameToCertificate()
 }
 
-func testClientHelloFailure(t *testing.T, m handshakeMessage, expectedSubStr string) {
+func testClientHelloFailure(t *testing.T, serverConfig *Config, m handshakeMessage, expectedSubStr string) {
        // Create in-memory network connection,
        // send message to server.  Should return
        // expected error.
@@ -66,7 +76,7 @@ func testClientHelloFailure(t *testing.T, m handshakeMessage, expectedSubStr str
                cli.writeRecord(recordTypeHandshake, m.marshal())
                c.Close()
        }()
-       err := Server(s, testConfig).Handshake()
+       err := Server(s, serverConfig).Handshake()
        s.Close()
        if err == nil || !strings.Contains(err.Error(), expectedSubStr) {
                t.Errorf("Got error: %s; expected to match substring '%s'", err, expectedSubStr)
@@ -74,14 +84,14 @@ func testClientHelloFailure(t *testing.T, m handshakeMessage, expectedSubStr str
 }
 
 func TestSimpleError(t *testing.T) {
-       testClientHelloFailure(t, &serverHelloDoneMsg{}, "unexpected handshake message")
+       testClientHelloFailure(t, testConfig, &serverHelloDoneMsg{}, "unexpected handshake message")
 }
 
 var badProtocolVersions = []uint16{0x0000, 0x0005, 0x0100, 0x0105, 0x0200, 0x0205}
 
 func TestRejectBadProtocolVersion(t *testing.T) {
        for _, v := range badProtocolVersions {
-               testClientHelloFailure(t, &clientHelloMsg{vers: v}, "unsupported, maximum protocol version")
+               testClientHelloFailure(t, testConfig, &clientHelloMsg{vers: v}, "unsupported, maximum protocol version")
        }
 }
 
@@ -91,7 +101,7 @@ func TestNoSuiteOverlap(t *testing.T) {
                cipherSuites:       []uint16{0xff00},
                compressionMethods: []uint8{0},
        }
-       testClientHelloFailure(t, clientHello, "no cipher suite supported by both client and server")
+       testClientHelloFailure(t, testConfig, clientHello, "no cipher suite supported by both client and server")
 }
 
 func TestNoCompressionOverlap(t *testing.T) {
@@ -100,7 +110,20 @@ func TestNoCompressionOverlap(t *testing.T) {
                cipherSuites:       []uint16{TLS_RSA_WITH_RC4_128_SHA},
                compressionMethods: []uint8{0xff},
        }
-       testClientHelloFailure(t, clientHello, "client does not support uncompressed connections")
+       testClientHelloFailure(t, testConfig, clientHello, "client does not support uncompressed connections")
+}
+
+func TestNoRC4ByDefault(t *testing.T) {
+       clientHello := &clientHelloMsg{
+               vers:               0x0301,
+               cipherSuites:       []uint16{TLS_RSA_WITH_RC4_128_SHA},
+               compressionMethods: []uint8{0},
+       }
+       serverConfig := *testConfig
+       // Reset the enabled cipher suites to nil in order to test the
+       // defaults.
+       serverConfig.CipherSuites = nil
+       testClientHelloFailure(t, &serverConfig, clientHello, "no cipher suite supported by both client and server")
 }
 
 func TestRenegotiationExtension(t *testing.T) {