Source file src/pkg/crypto/tls/handshake_client.go

     1	// Copyright 2009 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package tls
     6	
     7	import (
     8		"bytes"
     9		"crypto"
    10		"crypto/ecdsa"
    11		"crypto/ed25519"
    12		"crypto/rsa"
    13		"crypto/subtle"
    14		"crypto/x509"
    15		"errors"
    16		"fmt"
    17		"io"
    18		"net"
    19		"strconv"
    20		"strings"
    21		"sync/atomic"
    22		"time"
    23	)
    24	
    25	type clientHandshakeState struct {
    26		c            *Conn
    27		serverHello  *serverHelloMsg
    28		hello        *clientHelloMsg
    29		suite        *cipherSuite
    30		finishedHash finishedHash
    31		masterSecret []byte
    32		session      *ClientSessionState
    33	}
    34	
    35	func (c *Conn) makeClientHello() (*clientHelloMsg, ecdheParameters, error) {
    36		config := c.config
    37		if len(config.ServerName) == 0 && !config.InsecureSkipVerify {
    38			return nil, nil, errors.New("tls: either ServerName or InsecureSkipVerify must be specified in the tls.Config")
    39		}
    40	
    41		nextProtosLength := 0
    42		for _, proto := range config.NextProtos {
    43			if l := len(proto); l == 0 || l > 255 {
    44				return nil, nil, errors.New("tls: invalid NextProtos value")
    45			} else {
    46				nextProtosLength += 1 + l
    47			}
    48		}
    49		if nextProtosLength > 0xffff {
    50			return nil, nil, errors.New("tls: NextProtos values too large")
    51		}
    52	
    53		supportedVersions := config.supportedVersions(true)
    54		if len(supportedVersions) == 0 {
    55			return nil, nil, errors.New("tls: no supported versions satisfy MinVersion and MaxVersion")
    56		}
    57	
    58		clientHelloVersion := supportedVersions[0]
    59		// The version at the beginning of the ClientHello was capped at TLS 1.2
    60		// for compatibility reasons. The supported_versions extension is used
    61		// to negotiate versions now. See RFC 8446, Section 4.2.1.
    62		if clientHelloVersion > VersionTLS12 {
    63			clientHelloVersion = VersionTLS12
    64		}
    65	
    66		hello := &clientHelloMsg{
    67			vers:                         clientHelloVersion,
    68			compressionMethods:           []uint8{compressionNone},
    69			random:                       make([]byte, 32),
    70			sessionId:                    make([]byte, 32),
    71			ocspStapling:                 true,
    72			scts:                         true,
    73			serverName:                   hostnameInSNI(config.ServerName),
    74			supportedCurves:              config.curvePreferences(),
    75			supportedPoints:              []uint8{pointFormatUncompressed},
    76			nextProtoNeg:                 len(config.NextProtos) > 0,
    77			secureRenegotiationSupported: true,
    78			alpnProtocols:                config.NextProtos,
    79			supportedVersions:            supportedVersions,
    80		}
    81	
    82		if c.handshakes > 0 {
    83			hello.secureRenegotiation = c.clientFinished[:]
    84		}
    85	
    86		possibleCipherSuites := config.cipherSuites()
    87		hello.cipherSuites = make([]uint16, 0, len(possibleCipherSuites))
    88	
    89		for _, suiteId := range possibleCipherSuites {
    90			for _, suite := range cipherSuites {
    91				if suite.id != suiteId {
    92					continue
    93				}
    94				// Don't advertise TLS 1.2-only cipher suites unless
    95				// we're attempting TLS 1.2.
    96				if hello.vers < VersionTLS12 && suite.flags&suiteTLS12 != 0 {
    97					break
    98				}
    99				hello.cipherSuites = append(hello.cipherSuites, suiteId)
   100				break
   101			}
   102		}
   103	
   104		_, err := io.ReadFull(config.rand(), hello.random)
   105		if err != nil {
   106			return nil, nil, errors.New("tls: short read from Rand: " + err.Error())
   107		}
   108	
   109		// A random session ID is used to detect when the server accepted a ticket
   110		// and is resuming a session (see RFC 5077). In TLS 1.3, it's always set as
   111		// a compatibility measure (see RFC 8446, Section 4.1.2).
   112		if _, err := io.ReadFull(config.rand(), hello.sessionId); err != nil {
   113			return nil, nil, errors.New("tls: short read from Rand: " + err.Error())
   114		}
   115	
   116		if hello.vers >= VersionTLS12 {
   117			hello.supportedSignatureAlgorithms = supportedSignatureAlgorithms
   118		}
   119	
   120		var params ecdheParameters
   121		if hello.supportedVersions[0] == VersionTLS13 {
   122			hello.cipherSuites = append(hello.cipherSuites, defaultCipherSuitesTLS13()...)
   123	
   124			curveID := config.curvePreferences()[0]
   125			if _, ok := curveForCurveID(curveID); curveID != X25519 && !ok {
   126				return nil, nil, errors.New("tls: CurvePreferences includes unsupported curve")
   127			}
   128			params, err = generateECDHEParameters(config.rand(), curveID)
   129			if err != nil {
   130				return nil, nil, err
   131			}
   132			hello.keyShares = []keyShare{{group: curveID, data: params.PublicKey()}}
   133		}
   134	
   135		return hello, params, nil
   136	}
   137	
   138	func (c *Conn) clientHandshake() (err error) {
   139		if c.config == nil {
   140			c.config = defaultConfig()
   141		}
   142	
   143		// This may be a renegotiation handshake, in which case some fields
   144		// need to be reset.
   145		c.didResume = false
   146	
   147		hello, ecdheParams, err := c.makeClientHello()
   148		if err != nil {
   149			return err
   150		}
   151	
   152		cacheKey, session, earlySecret, binderKey := c.loadSession(hello)
   153		if cacheKey != "" && session != nil {
   154			defer func() {
   155				// If we got a handshake failure when resuming a session, throw away
   156				// the session ticket. See RFC 5077, Section 3.2.
   157				//
   158				// RFC 8446 makes no mention of dropping tickets on failure, but it
   159				// does require servers to abort on invalid binders, so we need to
   160				// delete tickets to recover from a corrupted PSK.
   161				if err != nil {
   162					c.config.ClientSessionCache.Put(cacheKey, nil)
   163				}
   164			}()
   165		}
   166	
   167		if _, err := c.writeRecord(recordTypeHandshake, hello.marshal()); err != nil {
   168			return err
   169		}
   170	
   171		msg, err := c.readHandshake()
   172		if err != nil {
   173			return err
   174		}
   175	
   176		serverHello, ok := msg.(*serverHelloMsg)
   177		if !ok {
   178			c.sendAlert(alertUnexpectedMessage)
   179			return unexpectedMessageError(serverHello, msg)
   180		}
   181	
   182		if err := c.pickTLSVersion(serverHello); err != nil {
   183			return err
   184		}
   185	
   186		if c.vers == VersionTLS13 {
   187			hs := &clientHandshakeStateTLS13{
   188				c:           c,
   189				serverHello: serverHello,
   190				hello:       hello,
   191				ecdheParams: ecdheParams,
   192				session:     session,
   193				earlySecret: earlySecret,
   194				binderKey:   binderKey,
   195			}
   196	
   197			// In TLS 1.3, session tickets are delivered after the handshake.
   198			return hs.handshake()
   199		}
   200	
   201		hs := &clientHandshakeState{
   202			c:           c,
   203			serverHello: serverHello,
   204			hello:       hello,
   205			session:     session,
   206		}
   207	
   208		if err := hs.handshake(); err != nil {
   209			return err
   210		}
   211	
   212		// If we had a successful handshake and hs.session is different from
   213		// the one already cached - cache a new one.
   214		if cacheKey != "" && hs.session != nil && session != hs.session {
   215			c.config.ClientSessionCache.Put(cacheKey, hs.session)
   216		}
   217	
   218		return nil
   219	}
   220	
   221	func (c *Conn) loadSession(hello *clientHelloMsg) (cacheKey string,
   222		session *ClientSessionState, earlySecret, binderKey []byte) {
   223		if c.config.SessionTicketsDisabled || c.config.ClientSessionCache == nil {
   224			return "", nil, nil, nil
   225		}
   226	
   227		hello.ticketSupported = true
   228	
   229		if hello.supportedVersions[0] == VersionTLS13 {
   230			// Require DHE on resumption as it guarantees forward secrecy against
   231			// compromise of the session ticket key. See RFC 8446, Section 4.2.9.
   232			hello.pskModes = []uint8{pskModeDHE}
   233		}
   234	
   235		// Session resumption is not allowed if renegotiating because
   236		// renegotiation is primarily used to allow a client to send a client
   237		// certificate, which would be skipped if session resumption occurred.
   238		if c.handshakes != 0 {
   239			return "", nil, nil, nil
   240		}
   241	
   242		// Try to resume a previously negotiated TLS session, if available.
   243		cacheKey = clientSessionCacheKey(c.conn.RemoteAddr(), c.config)
   244		session, ok := c.config.ClientSessionCache.Get(cacheKey)
   245		if !ok || session == nil {
   246			return cacheKey, nil, nil, nil
   247		}
   248	
   249		// Check that version used for the previous session is still valid.
   250		versOk := false
   251		for _, v := range hello.supportedVersions {
   252			if v == session.vers {
   253				versOk = true
   254				break
   255			}
   256		}
   257		if !versOk {
   258			return cacheKey, nil, nil, nil
   259		}
   260	
   261		// Check that the cached server certificate is not expired, and that it's
   262		// valid for the ServerName. This should be ensured by the cache key, but
   263		// protect the application from a faulty ClientSessionCache implementation.
   264		if !c.config.InsecureSkipVerify {
   265			if len(session.verifiedChains) == 0 {
   266				// The original connection had InsecureSkipVerify, while this doesn't.
   267				return cacheKey, nil, nil, nil
   268			}
   269			serverCert := session.serverCertificates[0]
   270			if c.config.time().After(serverCert.NotAfter) {
   271				// Expired certificate, delete the entry.
   272				c.config.ClientSessionCache.Put(cacheKey, nil)
   273				return cacheKey, nil, nil, nil
   274			}
   275			if err := serverCert.VerifyHostname(c.config.ServerName); err != nil {
   276				return cacheKey, nil, nil, nil
   277			}
   278		}
   279	
   280		if session.vers != VersionTLS13 {
   281			// In TLS 1.2 the cipher suite must match the resumed session. Ensure we
   282			// are still offering it.
   283			if mutualCipherSuite(hello.cipherSuites, session.cipherSuite) == nil {
   284				return cacheKey, nil, nil, nil
   285			}
   286	
   287			hello.sessionTicket = session.sessionTicket
   288			return
   289		}
   290	
   291		// Check that the session ticket is not expired.
   292		if c.config.time().After(session.useBy) {
   293			c.config.ClientSessionCache.Put(cacheKey, nil)
   294			return cacheKey, nil, nil, nil
   295		}
   296	
   297		// In TLS 1.3 the KDF hash must match the resumed session. Ensure we
   298		// offer at least one cipher suite with that hash.
   299		cipherSuite := cipherSuiteTLS13ByID(session.cipherSuite)
   300		if cipherSuite == nil {
   301			return cacheKey, nil, nil, nil
   302		}
   303		cipherSuiteOk := false
   304		for _, offeredID := range hello.cipherSuites {
   305			offeredSuite := cipherSuiteTLS13ByID(offeredID)
   306			if offeredSuite != nil && offeredSuite.hash == cipherSuite.hash {
   307				cipherSuiteOk = true
   308				break
   309			}
   310		}
   311		if !cipherSuiteOk {
   312			return cacheKey, nil, nil, nil
   313		}
   314	
   315		// Set the pre_shared_key extension. See RFC 8446, Section 4.2.11.1.
   316		ticketAge := uint32(c.config.time().Sub(session.receivedAt) / time.Millisecond)
   317		identity := pskIdentity{
   318			label:               session.sessionTicket,
   319			obfuscatedTicketAge: ticketAge + session.ageAdd,
   320		}
   321		hello.pskIdentities = []pskIdentity{identity}
   322		hello.pskBinders = [][]byte{make([]byte, cipherSuite.hash.Size())}
   323	
   324		// Compute the PSK binders. See RFC 8446, Section 4.2.11.2.
   325		psk := cipherSuite.expandLabel(session.masterSecret, "resumption",
   326			session.nonce, cipherSuite.hash.Size())
   327		earlySecret = cipherSuite.extract(psk, nil)
   328		binderKey = cipherSuite.deriveSecret(earlySecret, resumptionBinderLabel, nil)
   329		transcript := cipherSuite.hash.New()
   330		transcript.Write(hello.marshalWithoutBinders())
   331		pskBinders := [][]byte{cipherSuite.finishedHash(binderKey, transcript)}
   332		hello.updateBinders(pskBinders)
   333	
   334		return
   335	}
   336	
   337	func (c *Conn) pickTLSVersion(serverHello *serverHelloMsg) error {
   338		peerVersion := serverHello.vers
   339		if serverHello.supportedVersion != 0 {
   340			peerVersion = serverHello.supportedVersion
   341		}
   342	
   343		vers, ok := c.config.mutualVersion(true, []uint16{peerVersion})
   344		if !ok {
   345			c.sendAlert(alertProtocolVersion)
   346			return fmt.Errorf("tls: server selected unsupported protocol version %x", peerVersion)
   347		}
   348	
   349		c.vers = vers
   350		c.haveVers = true
   351		c.in.version = vers
   352		c.out.version = vers
   353	
   354		return nil
   355	}
   356	
   357	// Does the handshake, either a full one or resumes old session. Requires hs.c,
   358	// hs.hello, hs.serverHello, and, optionally, hs.session to be set.
   359	func (hs *clientHandshakeState) handshake() error {
   360		c := hs.c
   361	
   362		isResume, err := hs.processServerHello()
   363		if err != nil {
   364			return err
   365		}
   366	
   367		hs.finishedHash = newFinishedHash(c.vers, hs.suite)
   368	
   369		// No signatures of the handshake are needed in a resumption.
   370		// Otherwise, in a full handshake, if we don't have any certificates
   371		// configured then we will never send a CertificateVerify message and
   372		// thus no signatures are needed in that case either.
   373		if isResume || (len(c.config.Certificates) == 0 && c.config.GetClientCertificate == nil) {
   374			hs.finishedHash.discardHandshakeBuffer()
   375		}
   376	
   377		hs.finishedHash.Write(hs.hello.marshal())
   378		hs.finishedHash.Write(hs.serverHello.marshal())
   379	
   380		c.buffering = true
   381		if isResume {
   382			if err := hs.establishKeys(); err != nil {
   383				return err
   384			}
   385			if err := hs.readSessionTicket(); err != nil {
   386				return err
   387			}
   388			if err := hs.readFinished(c.serverFinished[:]); err != nil {
   389				return err
   390			}
   391			c.clientFinishedIsFirst = false
   392			if err := hs.sendFinished(c.clientFinished[:]); err != nil {
   393				return err
   394			}
   395			if _, err := c.flush(); err != nil {
   396				return err
   397			}
   398		} else {
   399			if err := hs.doFullHandshake(); err != nil {
   400				return err
   401			}
   402			if err := hs.establishKeys(); err != nil {
   403				return err
   404			}
   405			if err := hs.sendFinished(c.clientFinished[:]); err != nil {
   406				return err
   407			}
   408			if _, err := c.flush(); err != nil {
   409				return err
   410			}
   411			c.clientFinishedIsFirst = true
   412			if err := hs.readSessionTicket(); err != nil {
   413				return err
   414			}
   415			if err := hs.readFinished(c.serverFinished[:]); err != nil {
   416				return err
   417			}
   418		}
   419	
   420		c.ekm = ekmFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.hello.random, hs.serverHello.random)
   421		c.didResume = isResume
   422		atomic.StoreUint32(&c.handshakeStatus, 1)
   423	
   424		return nil
   425	}
   426	
   427	func (hs *clientHandshakeState) pickCipherSuite() error {
   428		if hs.suite = mutualCipherSuite(hs.hello.cipherSuites, hs.serverHello.cipherSuite); hs.suite == nil {
   429			hs.c.sendAlert(alertHandshakeFailure)
   430			return errors.New("tls: server chose an unconfigured cipher suite")
   431		}
   432	
   433		hs.c.cipherSuite = hs.suite.id
   434		return nil
   435	}
   436	
   437	func (hs *clientHandshakeState) doFullHandshake() error {
   438		c := hs.c
   439	
   440		msg, err := c.readHandshake()
   441		if err != nil {
   442			return err
   443		}
   444		certMsg, ok := msg.(*certificateMsg)
   445		if !ok || len(certMsg.certificates) == 0 {
   446			c.sendAlert(alertUnexpectedMessage)
   447			return unexpectedMessageError(certMsg, msg)
   448		}
   449		hs.finishedHash.Write(certMsg.marshal())
   450	
   451		if c.handshakes == 0 {
   452			// If this is the first handshake on a connection, process and
   453			// (optionally) verify the server's certificates.
   454			if err := c.verifyServerCertificate(certMsg.certificates); err != nil {
   455				return err
   456			}
   457		} else {
   458			// This is a renegotiation handshake. We require that the
   459			// server's identity (i.e. leaf certificate) is unchanged and
   460			// thus any previous trust decision is still valid.
   461			//
   462			// See https://mitls.org/pages/attacks/3SHAKE for the
   463			// motivation behind this requirement.
   464			if !bytes.Equal(c.peerCertificates[0].Raw, certMsg.certificates[0]) {
   465				c.sendAlert(alertBadCertificate)
   466				return errors.New("tls: server's identity changed during renegotiation")
   467			}
   468		}
   469	
   470		msg, err = c.readHandshake()
   471		if err != nil {
   472			return err
   473		}
   474	
   475		cs, ok := msg.(*certificateStatusMsg)
   476		if ok {
   477			// RFC4366 on Certificate Status Request:
   478			// The server MAY return a "certificate_status" message.
   479	
   480			if !hs.serverHello.ocspStapling {
   481				// If a server returns a "CertificateStatus" message, then the
   482				// server MUST have included an extension of type "status_request"
   483				// with empty "extension_data" in the extended server hello.
   484	
   485				c.sendAlert(alertUnexpectedMessage)
   486				return errors.New("tls: received unexpected CertificateStatus message")
   487			}
   488			hs.finishedHash.Write(cs.marshal())
   489	
   490			c.ocspResponse = cs.response
   491	
   492			msg, err = c.readHandshake()
   493			if err != nil {
   494				return err
   495			}
   496		}
   497	
   498		keyAgreement := hs.suite.ka(c.vers)
   499	
   500		skx, ok := msg.(*serverKeyExchangeMsg)
   501		if ok {
   502			hs.finishedHash.Write(skx.marshal())
   503			err = keyAgreement.processServerKeyExchange(c.config, hs.hello, hs.serverHello, c.peerCertificates[0], skx)
   504			if err != nil {
   505				c.sendAlert(alertUnexpectedMessage)
   506				return err
   507			}
   508	
   509			msg, err = c.readHandshake()
   510			if err != nil {
   511				return err
   512			}
   513		}
   514	
   515		var chainToSend *Certificate
   516		var certRequested bool
   517		certReq, ok := msg.(*certificateRequestMsg)
   518		if ok {
   519			certRequested = true
   520			hs.finishedHash.Write(certReq.marshal())
   521	
   522			cri := certificateRequestInfoFromMsg(certReq)
   523			if chainToSend, err = c.getClientCertificate(cri); err != nil {
   524				c.sendAlert(alertInternalError)
   525				return err
   526			}
   527	
   528			msg, err = c.readHandshake()
   529			if err != nil {
   530				return err
   531			}
   532		}
   533	
   534		shd, ok := msg.(*serverHelloDoneMsg)
   535		if !ok {
   536			c.sendAlert(alertUnexpectedMessage)
   537			return unexpectedMessageError(shd, msg)
   538		}
   539		hs.finishedHash.Write(shd.marshal())
   540	
   541		// If the server requested a certificate then we have to send a
   542		// Certificate message, even if it's empty because we don't have a
   543		// certificate to send.
   544		if certRequested {
   545			certMsg = new(certificateMsg)
   546			certMsg.certificates = chainToSend.Certificate
   547			hs.finishedHash.Write(certMsg.marshal())
   548			if _, err := c.writeRecord(recordTypeHandshake, certMsg.marshal()); err != nil {
   549				return err
   550			}
   551		}
   552	
   553		preMasterSecret, ckx, err := keyAgreement.generateClientKeyExchange(c.config, hs.hello, c.peerCertificates[0])
   554		if err != nil {
   555			c.sendAlert(alertInternalError)
   556			return err
   557		}
   558		if ckx != nil {
   559			hs.finishedHash.Write(ckx.marshal())
   560			if _, err := c.writeRecord(recordTypeHandshake, ckx.marshal()); err != nil {
   561				return err
   562			}
   563		}
   564	
   565		if chainToSend != nil && len(chainToSend.Certificate) > 0 {
   566			certVerify := &certificateVerifyMsg{
   567				hasSignatureAlgorithm: c.vers >= VersionTLS12,
   568			}
   569	
   570			key, ok := chainToSend.PrivateKey.(crypto.Signer)
   571			if !ok {
   572				c.sendAlert(alertInternalError)
   573				return fmt.Errorf("tls: client certificate private key of type %T does not implement crypto.Signer", chainToSend.PrivateKey)
   574			}
   575	
   576			signatureAlgorithm, sigType, hashFunc, err := pickSignatureAlgorithm(key.Public(), certReq.supportedSignatureAlgorithms, supportedSignatureAlgorithmsTLS12, c.vers)
   577			if err != nil {
   578				c.sendAlert(alertInternalError)
   579				return err
   580			}
   581			// SignatureAndHashAlgorithm was introduced in TLS 1.2.
   582			if certVerify.hasSignatureAlgorithm {
   583				certVerify.signatureAlgorithm = signatureAlgorithm
   584			}
   585			signed, err := hs.finishedHash.hashForClientCertificate(sigType, hashFunc, hs.masterSecret)
   586			if err != nil {
   587				c.sendAlert(alertInternalError)
   588				return err
   589			}
   590			signOpts := crypto.SignerOpts(hashFunc)
   591			if sigType == signatureRSAPSS {
   592				signOpts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: hashFunc}
   593			}
   594			certVerify.signature, err = key.Sign(c.config.rand(), signed, signOpts)
   595			if err != nil {
   596				c.sendAlert(alertInternalError)
   597				return err
   598			}
   599	
   600			hs.finishedHash.Write(certVerify.marshal())
   601			if _, err := c.writeRecord(recordTypeHandshake, certVerify.marshal()); err != nil {
   602				return err
   603			}
   604		}
   605	
   606		hs.masterSecret = masterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret, hs.hello.random, hs.serverHello.random)
   607		if err := c.config.writeKeyLog(keyLogLabelTLS12, hs.hello.random, hs.masterSecret); err != nil {
   608			c.sendAlert(alertInternalError)
   609			return errors.New("tls: failed to write to key log: " + err.Error())
   610		}
   611	
   612		hs.finishedHash.discardHandshakeBuffer()
   613	
   614		return nil
   615	}
   616	
   617	func (hs *clientHandshakeState) establishKeys() error {
   618		c := hs.c
   619	
   620		clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV :=
   621			keysFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.hello.random, hs.serverHello.random, hs.suite.macLen, hs.suite.keyLen, hs.suite.ivLen)
   622		var clientCipher, serverCipher interface{}
   623		var clientHash, serverHash macFunction
   624		if hs.suite.cipher != nil {
   625			clientCipher = hs.suite.cipher(clientKey, clientIV, false /* not for reading */)
   626			clientHash = hs.suite.mac(c.vers, clientMAC)
   627			serverCipher = hs.suite.cipher(serverKey, serverIV, true /* for reading */)
   628			serverHash = hs.suite.mac(c.vers, serverMAC)
   629		} else {
   630			clientCipher = hs.suite.aead(clientKey, clientIV)
   631			serverCipher = hs.suite.aead(serverKey, serverIV)
   632		}
   633	
   634		c.in.prepareCipherSpec(c.vers, serverCipher, serverHash)
   635		c.out.prepareCipherSpec(c.vers, clientCipher, clientHash)
   636		return nil
   637	}
   638	
   639	func (hs *clientHandshakeState) serverResumedSession() bool {
   640		// If the server responded with the same sessionId then it means the
   641		// sessionTicket is being used to resume a TLS session.
   642		return hs.session != nil && hs.hello.sessionId != nil &&
   643			bytes.Equal(hs.serverHello.sessionId, hs.hello.sessionId)
   644	}
   645	
   646	func (hs *clientHandshakeState) processServerHello() (bool, error) {
   647		c := hs.c
   648	
   649		if err := hs.pickCipherSuite(); err != nil {
   650			return false, err
   651		}
   652	
   653		if hs.serverHello.compressionMethod != compressionNone {
   654			c.sendAlert(alertUnexpectedMessage)
   655			return false, errors.New("tls: server selected unsupported compression format")
   656		}
   657	
   658		if c.handshakes == 0 && hs.serverHello.secureRenegotiationSupported {
   659			c.secureRenegotiation = true
   660			if len(hs.serverHello.secureRenegotiation) != 0 {
   661				c.sendAlert(alertHandshakeFailure)
   662				return false, errors.New("tls: initial handshake had non-empty renegotiation extension")
   663			}
   664		}
   665	
   666		if c.handshakes > 0 && c.secureRenegotiation {
   667			var expectedSecureRenegotiation [24]byte
   668			copy(expectedSecureRenegotiation[:], c.clientFinished[:])
   669			copy(expectedSecureRenegotiation[12:], c.serverFinished[:])
   670			if !bytes.Equal(hs.serverHello.secureRenegotiation, expectedSecureRenegotiation[:]) {
   671				c.sendAlert(alertHandshakeFailure)
   672				return false, errors.New("tls: incorrect renegotiation extension contents")
   673			}
   674		}
   675	
   676		clientDidNPN := hs.hello.nextProtoNeg
   677		clientDidALPN := len(hs.hello.alpnProtocols) > 0
   678		serverHasNPN := hs.serverHello.nextProtoNeg
   679		serverHasALPN := len(hs.serverHello.alpnProtocol) > 0
   680	
   681		if !clientDidNPN && serverHasNPN {
   682			c.sendAlert(alertHandshakeFailure)
   683			return false, errors.New("tls: server advertised unrequested NPN extension")
   684		}
   685	
   686		if !clientDidALPN && serverHasALPN {
   687			c.sendAlert(alertHandshakeFailure)
   688			return false, errors.New("tls: server advertised unrequested ALPN extension")
   689		}
   690	
   691		if serverHasNPN && serverHasALPN {
   692			c.sendAlert(alertHandshakeFailure)
   693			return false, errors.New("tls: server advertised both NPN and ALPN extensions")
   694		}
   695	
   696		if serverHasALPN {
   697			c.clientProtocol = hs.serverHello.alpnProtocol
   698			c.clientProtocolFallback = false
   699		}
   700		c.scts = hs.serverHello.scts
   701	
   702		if !hs.serverResumedSession() {
   703			return false, nil
   704		}
   705	
   706		if hs.session.vers != c.vers {
   707			c.sendAlert(alertHandshakeFailure)
   708			return false, errors.New("tls: server resumed a session with a different version")
   709		}
   710	
   711		if hs.session.cipherSuite != hs.suite.id {
   712			c.sendAlert(alertHandshakeFailure)
   713			return false, errors.New("tls: server resumed a session with a different cipher suite")
   714		}
   715	
   716		// Restore masterSecret and peerCerts from previous state
   717		hs.masterSecret = hs.session.masterSecret
   718		c.peerCertificates = hs.session.serverCertificates
   719		c.verifiedChains = hs.session.verifiedChains
   720		return true, nil
   721	}
   722	
   723	func (hs *clientHandshakeState) readFinished(out []byte) error {
   724		c := hs.c
   725	
   726		if err := c.readChangeCipherSpec(); err != nil {
   727			return err
   728		}
   729	
   730		msg, err := c.readHandshake()
   731		if err != nil {
   732			return err
   733		}
   734		serverFinished, ok := msg.(*finishedMsg)
   735		if !ok {
   736			c.sendAlert(alertUnexpectedMessage)
   737			return unexpectedMessageError(serverFinished, msg)
   738		}
   739	
   740		verify := hs.finishedHash.serverSum(hs.masterSecret)
   741		if len(verify) != len(serverFinished.verifyData) ||
   742			subtle.ConstantTimeCompare(verify, serverFinished.verifyData) != 1 {
   743			c.sendAlert(alertHandshakeFailure)
   744			return errors.New("tls: server's Finished message was incorrect")
   745		}
   746		hs.finishedHash.Write(serverFinished.marshal())
   747		copy(out, verify)
   748		return nil
   749	}
   750	
   751	func (hs *clientHandshakeState) readSessionTicket() error {
   752		if !hs.serverHello.ticketSupported {
   753			return nil
   754		}
   755	
   756		c := hs.c
   757		msg, err := c.readHandshake()
   758		if err != nil {
   759			return err
   760		}
   761		sessionTicketMsg, ok := msg.(*newSessionTicketMsg)
   762		if !ok {
   763			c.sendAlert(alertUnexpectedMessage)
   764			return unexpectedMessageError(sessionTicketMsg, msg)
   765		}
   766		hs.finishedHash.Write(sessionTicketMsg.marshal())
   767	
   768		hs.session = &ClientSessionState{
   769			sessionTicket:      sessionTicketMsg.ticket,
   770			vers:               c.vers,
   771			cipherSuite:        hs.suite.id,
   772			masterSecret:       hs.masterSecret,
   773			serverCertificates: c.peerCertificates,
   774			verifiedChains:     c.verifiedChains,
   775			receivedAt:         c.config.time(),
   776		}
   777	
   778		return nil
   779	}
   780	
   781	func (hs *clientHandshakeState) sendFinished(out []byte) error {
   782		c := hs.c
   783	
   784		if _, err := c.writeRecord(recordTypeChangeCipherSpec, []byte{1}); err != nil {
   785			return err
   786		}
   787		if hs.serverHello.nextProtoNeg {
   788			nextProto := new(nextProtoMsg)
   789			proto, fallback := mutualProtocol(c.config.NextProtos, hs.serverHello.nextProtos)
   790			nextProto.proto = proto
   791			c.clientProtocol = proto
   792			c.clientProtocolFallback = fallback
   793	
   794			hs.finishedHash.Write(nextProto.marshal())
   795			if _, err := c.writeRecord(recordTypeHandshake, nextProto.marshal()); err != nil {
   796				return err
   797			}
   798		}
   799	
   800		finished := new(finishedMsg)
   801		finished.verifyData = hs.finishedHash.clientSum(hs.masterSecret)
   802		hs.finishedHash.Write(finished.marshal())
   803		if _, err := c.writeRecord(recordTypeHandshake, finished.marshal()); err != nil {
   804			return err
   805		}
   806		copy(out, finished.verifyData)
   807		return nil
   808	}
   809	
   810	// verifyServerCertificate parses and verifies the provided chain, setting
   811	// c.verifiedChains and c.peerCertificates or sending the appropriate alert.
   812	func (c *Conn) verifyServerCertificate(certificates [][]byte) error {
   813		certs := make([]*x509.Certificate, len(certificates))
   814		for i, asn1Data := range certificates {
   815			cert, err := x509.ParseCertificate(asn1Data)
   816			if err != nil {
   817				c.sendAlert(alertBadCertificate)
   818				return errors.New("tls: failed to parse certificate from server: " + err.Error())
   819			}
   820			certs[i] = cert
   821		}
   822	
   823		if !c.config.InsecureSkipVerify {
   824			opts := x509.VerifyOptions{
   825				Roots:         c.config.RootCAs,
   826				CurrentTime:   c.config.time(),
   827				DNSName:       c.config.ServerName,
   828				Intermediates: x509.NewCertPool(),
   829			}
   830			for _, cert := range certs[1:] {
   831				opts.Intermediates.AddCert(cert)
   832			}
   833			var err error
   834			c.verifiedChains, err = certs[0].Verify(opts)
   835			if err != nil {
   836				c.sendAlert(alertBadCertificate)
   837				return err
   838			}
   839		}
   840	
   841		if c.config.VerifyPeerCertificate != nil {
   842			if err := c.config.VerifyPeerCertificate(certificates, c.verifiedChains); err != nil {
   843				c.sendAlert(alertBadCertificate)
   844				return err
   845			}
   846		}
   847	
   848		switch certs[0].PublicKey.(type) {
   849		case *rsa.PublicKey, *ecdsa.PublicKey, ed25519.PublicKey:
   850			break
   851		default:
   852			c.sendAlert(alertUnsupportedCertificate)
   853			return fmt.Errorf("tls: server's certificate contains an unsupported type of public key: %T", certs[0].PublicKey)
   854		}
   855	
   856		c.peerCertificates = certs
   857	
   858		return nil
   859	}
   860	
   861	// tls11SignatureSchemes contains the signature schemes that we synthesise for
   862	// a TLS <= 1.1 connection, based on the supported certificate types.
   863	var (
   864		tls11SignatureSchemes      = []SignatureScheme{ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1}
   865		tls11SignatureSchemesECDSA = tls11SignatureSchemes[:3]
   866		tls11SignatureSchemesRSA   = tls11SignatureSchemes[3:]
   867	)
   868	
   869	// certificateRequestInfoFromMsg generates a CertificateRequestInfo from a TLS
   870	// <= 1.2 CertificateRequest, making an effort to fill in missing information.
   871	func certificateRequestInfoFromMsg(certReq *certificateRequestMsg) *CertificateRequestInfo {
   872		var rsaAvail, ecAvail bool
   873		for _, certType := range certReq.certificateTypes {
   874			switch certType {
   875			case certTypeRSASign:
   876				rsaAvail = true
   877			case certTypeECDSASign:
   878				ecAvail = true
   879			}
   880		}
   881	
   882		cri := &CertificateRequestInfo{
   883			AcceptableCAs: certReq.certificateAuthorities,
   884		}
   885	
   886		if !certReq.hasSignatureAlgorithm {
   887			// Prior to TLS 1.2, the signature schemes were not
   888			// included in the certificate request message. In this
   889			// case we use a plausible list based on the acceptable
   890			// certificate types.
   891			switch {
   892			case rsaAvail && ecAvail:
   893				cri.SignatureSchemes = tls11SignatureSchemes
   894			case rsaAvail:
   895				cri.SignatureSchemes = tls11SignatureSchemesRSA
   896			case ecAvail:
   897				cri.SignatureSchemes = tls11SignatureSchemesECDSA
   898			}
   899			return cri
   900		}
   901	
   902		// Filter the signature schemes based on the certificate types.
   903		// See RFC 5246, Section 7.4.4 (where it calls this "somewhat complicated").
   904		cri.SignatureSchemes = make([]SignatureScheme, 0, len(certReq.supportedSignatureAlgorithms))
   905		for _, sigScheme := range certReq.supportedSignatureAlgorithms {
   906			switch signatureFromSignatureScheme(sigScheme) {
   907			case signatureECDSA, signatureEd25519:
   908				if ecAvail {
   909					cri.SignatureSchemes = append(cri.SignatureSchemes, sigScheme)
   910				}
   911			case signatureRSAPSS, signaturePKCS1v15:
   912				if rsaAvail {
   913					cri.SignatureSchemes = append(cri.SignatureSchemes, sigScheme)
   914				}
   915			}
   916		}
   917	
   918		return cri
   919	}
   920	
   921	func (c *Conn) getClientCertificate(cri *CertificateRequestInfo) (*Certificate, error) {
   922		if c.config.GetClientCertificate != nil {
   923			return c.config.GetClientCertificate(cri)
   924		}
   925	
   926		// We need to search our list of client certs for one
   927		// where SignatureAlgorithm is acceptable to the server and the
   928		// Issuer is in AcceptableCAs.
   929		for i, chain := range c.config.Certificates {
   930			sigOK := false
   931			for _, alg := range signatureSchemesForCertificate(c.vers, &chain) {
   932				if isSupportedSignatureAlgorithm(alg, cri.SignatureSchemes) {
   933					sigOK = true
   934					break
   935				}
   936			}
   937			if !sigOK {
   938				continue
   939			}
   940	
   941			if len(cri.AcceptableCAs) == 0 {
   942				return &chain, nil
   943			}
   944	
   945			for j, cert := range chain.Certificate {
   946				x509Cert := chain.Leaf
   947				// Parse the certificate if this isn't the leaf node, or if
   948				// chain.Leaf was nil.
   949				if j != 0 || x509Cert == nil {
   950					var err error
   951					if x509Cert, err = x509.ParseCertificate(cert); err != nil {
   952						c.sendAlert(alertInternalError)
   953						return nil, errors.New("tls: failed to parse configured certificate chain #" + strconv.Itoa(i) + ": " + err.Error())
   954					}
   955				}
   956	
   957				for _, ca := range cri.AcceptableCAs {
   958					if bytes.Equal(x509Cert.RawIssuer, ca) {
   959						return &chain, nil
   960					}
   961				}
   962			}
   963		}
   964	
   965		// No acceptable certificate found. Don't send a certificate.
   966		return new(Certificate), nil
   967	}
   968	
   969	// clientSessionCacheKey returns a key used to cache sessionTickets that could
   970	// be used to resume previously negotiated TLS sessions with a server.
   971	func clientSessionCacheKey(serverAddr net.Addr, config *Config) string {
   972		if len(config.ServerName) > 0 {
   973			return config.ServerName
   974		}
   975		return serverAddr.String()
   976	}
   977	
   978	// mutualProtocol finds the mutual Next Protocol Negotiation or ALPN protocol
   979	// given list of possible protocols and a list of the preference order. The
   980	// first list must not be empty. It returns the resulting protocol and flag
   981	// indicating if the fallback case was reached.
   982	func mutualProtocol(protos, preferenceProtos []string) (string, bool) {
   983		for _, s := range preferenceProtos {
   984			for _, c := range protos {
   985				if s == c {
   986					return s, false
   987				}
   988			}
   989		}
   990	
   991		return protos[0], true
   992	}
   993	
   994	// hostnameInSNI converts name into an approriate hostname for SNI.
   995	// Literal IP addresses and absolute FQDNs are not permitted as SNI values.
   996	// See RFC 6066, Section 3.
   997	func hostnameInSNI(name string) string {
   998		host := name
   999		if len(host) > 0 && host[0] == '[' && host[len(host)-1] == ']' {
  1000			host = host[1 : len(host)-1]
  1001		}
  1002		if i := strings.LastIndex(host, "%"); i > 0 {
  1003			host = host[:i]
  1004		}
  1005		if net.ParseIP(host) != nil {
  1006			return ""
  1007		}
  1008		for len(name) > 0 && name[len(name)-1] == '.' {
  1009			name = name[:len(name)-1]
  1010		}
  1011		return name
  1012	}
  1013	

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