Add support for tls PreferServerCipherSuites

command/agent/config-test-fixtures/basic.hcl

@@ -156,6 +156,9 @@ tls {
     key_file = "pipe"
     rpc_upgrade_mode = true
     verify_https_client = true
+    tls_prefer_server_cipher_suites = true
+    tls_cipher_suites = "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256"
+    tls_min_version = "tls12"
 }
 sentinel {
     import "foo" {

command/agent/config_parse.go

@@ -763,6 +763,7 @@ func parseTLSConfig(result **config.TLSConfig, list *ast.ObjectList) error {
 		"verify_https_client",
 		"tls_cipher_suites",
 		"tls_min_version",
+		"tls_prefer_server_cipher_suites",
 	}
 
 	if err := helper.CheckHCLKeys(listVal, valid); err != nil {

command/agent/config_parse_test.go

@@ -167,14 +167,17 @@ func TestConfig_Parse(t *testing.T) {
 					Token:                "12345",
 				},
 				TLSConfig: &config.TLSConfig{
-					EnableHTTP:           true,
-					EnableRPC:            true,
-					VerifyServerHostname: true,
-					CAFile:               "foo",
-					CertFile:             "bar",
-					KeyFile:              "pipe",
-					RPCUpgradeMode:       true,
-					VerifyHTTPSClient:    true,
+					EnableHTTP:                  true,
+					EnableRPC:                   true,
+					VerifyServerHostname:        true,
+					CAFile:                      "foo",
+					CertFile:                    "bar",
+					KeyFile:                     "pipe",
+					RPCUpgradeMode:              true,
+					VerifyHTTPSClient:           true,
+					TLSPreferServerCipherSuites: true,
+					TLSCipherSuites:             "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
+					TLSMinVersion:               "tls12",
 				},
 				HTTPAPIResponseHeaders: map[string]string{
 					"Access-Control-Allow-Origin": "*",

helper/tlsutil/config.go

@@ -107,6 +107,12 @@ type Config struct {
 
 	// MinVersion contains the minimum SSL/TLS version that is accepted.
 	MinVersion 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
+	// the order of elements in CipherSuites, is used.
+	PreferServerCipherSuites bool
 }
 
 func NewTLSConfiguration(newConf *config.TLSConfig, verifyIncoming, verifyOutgoing bool) (*Config, error) {
@@ -121,15 +127,16 @@ func NewTLSConfiguration(newConf *config.TLSConfig, verifyIncoming, verifyOutgoi
 	}
 
 	return &Config{
-		VerifyIncoming:       verifyIncoming,
-		VerifyOutgoing:       verifyOutgoing,
-		VerifyServerHostname: newConf.VerifyServerHostname,
-		CAFile:               newConf.CAFile,
-		CertFile:             newConf.CertFile,
-		KeyFile:              newConf.KeyFile,
-		KeyLoader:            newConf.GetKeyLoader(),
-		CipherSuites:         ciphers,
-		MinVersion:           minVersion,
+		VerifyIncoming:           verifyIncoming,
+		VerifyOutgoing:           verifyOutgoing,
+		VerifyServerHostname:     newConf.VerifyServerHostname,
+		CAFile:                   newConf.CAFile,
+		CertFile:                 newConf.CertFile,
+		KeyFile:                  newConf.KeyFile,
+		KeyLoader:                newConf.GetKeyLoader(),
+		CipherSuites:             ciphers,
+		MinVersion:               minVersion,
+		PreferServerCipherSuites: newConf.TLSPreferServerCipherSuites,
 	}, nil
 }
 
@@ -184,10 +191,11 @@ func (c *Config) OutgoingTLSConfig() (*tls.Config, error) {
 	}
 	// Create the tlsConfig
 	tlsConfig := &tls.Config{
-		RootCAs:            x509.NewCertPool(),
-		InsecureSkipVerify: true,
-		CipherSuites:       c.CipherSuites,
-		MinVersion:         c.MinVersion,
+		RootCAs:                  x509.NewCertPool(),
+		InsecureSkipVerify:       true,
+		CipherSuites:             c.CipherSuites,
+		MinVersion:               c.MinVersion,
+		PreferServerCipherSuites: c.PreferServerCipherSuites,
 	}
 	if c.VerifyServerHostname {
 		tlsConfig.InsecureSkipVerify = false
@@ -304,10 +312,11 @@ func WrapTLSClient(conn net.Conn, tlsConfig *tls.Config) (net.Conn, error) {
 func (c *Config) IncomingTLSConfig() (*tls.Config, error) {
 	// Create the tlsConfig
 	tlsConfig := &tls.Config{
-		ClientCAs:    x509.NewCertPool(),
-		ClientAuth:   tls.NoClientCert,
-		CipherSuites: c.CipherSuites,
-		MinVersion:   c.MinVersion,
+		ClientCAs:                x509.NewCertPool(),
+		ClientAuth:               tls.NoClientCert,
+		CipherSuites:             c.CipherSuites,
+		MinVersion:               c.MinVersion,
+		PreferServerCipherSuites: c.PreferServerCipherSuites,
 	}
 
 	// Parse the CA cert if any

helper/tlsutil/config_test.go

@@ -167,6 +167,60 @@ func TestConfig_OutgoingTLS_WithKeyPair(t *testing.T) {
 	assert.NotNil(cert)
 }
 
+func TestConfig_OutgoingTLS_PreferServerCipherSuites(t *testing.T) {
+	require := require.New(t)
+
+	{
+		conf := &Config{
+			VerifyOutgoing: true,
+			CAFile:         cacert,
+		}
+		tlsConfig, err := conf.OutgoingTLSConfig()
+		require.Nil(err)
+		require.Equal(tlsConfig.PreferServerCipherSuites, false)
+	}
+	{
+		conf := &Config{
+			VerifyOutgoing: true,
+			CAFile:         cacert,
+			PreferServerCipherSuites: true,
+		}
+		tlsConfig, err := conf.OutgoingTLSConfig()
+		require.Nil(err)
+		require.Equal(tlsConfig.PreferServerCipherSuites, true)
+	}
+}
+
+func TestConfig_OutgoingTLS_TLSCipherSuites(t *testing.T) {
+	require := require.New(t)
+
+	{
+		defaultCiphers := []uint16{
+			tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+		}
+		conf := &Config{
+			VerifyOutgoing: true,
+			CAFile:         cacert,
+			CipherSuites:   defaultCiphers,
+		}
+		tlsConfig, err := conf.OutgoingTLSConfig()
+		require.Nil(err)
+		require.Equal(tlsConfig.CipherSuites, defaultCiphers)
+	}
+	{
+		conf := &Config{
+			VerifyOutgoing: true,
+			CAFile:         cacert,
+			CipherSuites:   []uint16{tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305},
+		}
+		tlsConfig, err := conf.OutgoingTLSConfig()
+		require.Nil(err)
+		require.Equal(tlsConfig.CipherSuites, []uint16{tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305})
+	}
+}
+
 func startTLSServer(config *Config) (net.Conn, chan error) {
 	errc := make(chan error, 1)
 
@@ -416,6 +470,51 @@ func TestConfig_IncomingTLS_NoVerify(t *testing.T) {
 	}
 }
 
+func TestConfig_IncomingTLS_PreferServerCipherSuites(t *testing.T) {
+	require := require.New(t)
+
+	{
+		conf := &Config{}
+		tlsConfig, err := conf.IncomingTLSConfig()
+		require.Nil(err)
+		require.Equal(tlsConfig.PreferServerCipherSuites, false)
+	}
+	{
+		conf := &Config{
+			PreferServerCipherSuites: true,
+		}
+		tlsConfig, err := conf.IncomingTLSConfig()
+		require.Nil(err)
+		require.Equal(tlsConfig.PreferServerCipherSuites, true)
+	}
+}
+
+func TestConfig_IncomingTLS_TLSCipherSuites(t *testing.T) {
+	require := require.New(t)
+
+	{
+		defaultCiphers := []uint16{
+			tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+		}
+		conf := &Config{
+			CipherSuites: defaultCiphers,
+		}
+		tlsConfig, err := conf.IncomingTLSConfig()
+		require.Nil(err)
+		require.Equal(tlsConfig.CipherSuites, defaultCiphers)
+	}
+	{
+		conf := &Config{
+			CipherSuites: []uint16{tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305},
+		}
+		tlsConfig, err := conf.IncomingTLSConfig()
+		require.Nil(err)
+		require.Equal(tlsConfig.CipherSuites, []uint16{tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305})
+	}
+}
+
 func TestConfig_ParseCiphers_Valid(t *testing.T) {
 	require := require.New(t)
 

nomad/structs/config/tls.go

@@ -63,6 +63,12 @@ type TLSConfig struct {
 	// TLSMinVersion is used to set the minimum TLS version used for TLS
 	// connections. Should be either "tls10", "tls11", or "tls12".
 	TLSMinVersion string `mapstructure:"tls_min_version"`
+
+	// TLSPreferServerCipherSuites 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
+	// the order of elements in CipherSuites, is used.
+	TLSPreferServerCipherSuites bool `mapstructure:"tls_prefer_server_cipher_suites"`
 }
 
 type KeyLoader struct {
@@ -158,6 +164,8 @@ func (t *TLSConfig) Copy() *TLSConfig {
 	new.TLSCipherSuites = t.TLSCipherSuites
 	new.TLSMinVersion = t.TLSMinVersion
 
+	new.TLSPreferServerCipherSuites = t.TLSPreferServerCipherSuites
+
 	new.SetChecksum()
 
 	return new
@@ -211,6 +219,9 @@ func (t *TLSConfig) Merge(b *TLSConfig) *TLSConfig {
 	if b.TLSMinVersion != "" {
 		result.TLSMinVersion = b.TLSMinVersion
 	}
+	if b.TLSPreferServerCipherSuites {
+		result.TLSPreferServerCipherSuites = true
+	}
 	return result
 }
 

nomad/structs/config/tls_test.go

@@ -15,14 +15,15 @@ func TestTLSConfig_Merge(t *testing.T) {
 	}
 
 	b := &TLSConfig{
-		EnableHTTP:           true,
-		EnableRPC:            true,
-		VerifyServerHostname: true,
-		CAFile:               "test-ca-file-2",
-		CertFile:             "test-cert-file-2",
-		RPCUpgradeMode:       true,
-		TLSCipherSuites:      "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
-		TLSMinVersion:        "tls12",
+		EnableHTTP:                  true,
+		EnableRPC:                   true,
+		VerifyServerHostname:        true,
+		CAFile:                      "test-ca-file-2",
+		CertFile:                    "test-cert-file-2",
+		RPCUpgradeMode:              true,
+		TLSCipherSuites:             "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
+		TLSMinVersion:               "tls12",
+		TLSPreferServerCipherSuites: true,
 	}
 
 	new := a.Merge(b)
@@ -173,10 +174,12 @@ func TestTLS_Copy(t *testing.T) {
 		fookey  = "../../../helper/tlsutil/testdata/nomad-foo-key.pem"
 	)
 	a := &TLSConfig{
-		CAFile:          cafile,
-		CertFile:        foocert,
-		KeyFile:         fookey,
-		TLSCipherSuites: "TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305",
+		CAFile:                      cafile,
+		CertFile:                    foocert,
+		KeyFile:                     fookey,
+		TLSCipherSuites:             "TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305",
+		TLSMinVersion:               "tls12",
+		TLSPreferServerCipherSuites: true,
 	}
 	a.SetChecksum()
 

website/source/docs/agent/configuration/tls.html.md

@@ -67,6 +67,9 @@ the [Agent's Gossip and RPC Encryption](/docs/agent/encryption.html).
 - `tls_min_version` - Specifies the minimum supported version of TLS. Accepted
   values are "tls10", "tls11", "tls12". Defaults to TLS 1.2.
 
+- tls_prefer_server_cipher_suites - This option will cause Nomad to prefer the
+  server's ciphersuite over the client ciphersuites.
+
 - `verify_https_client` `(bool: false)` - Specifies agents should require
   client certificates for all incoming HTTPS requests. The client certificates
   must be signed by the same CA as Nomad.