Source file src/crypto/tls/handshake_client.go

Documentation: crypto/tls

     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/rsa"
    12  	"crypto/subtle"
    13  	"crypto/x509"
    14  	"errors"
    15  	"fmt"
    16  	"io"
    17  	"net"
    18  	"strconv"
    19  	"strings"
    20  	"sync/atomic"
    21  	"time"
    22  )
    23  
    24  type clientHandshakeState struct {
    25  	c            *Conn
    26  	serverHello  *serverHelloMsg
    27  	hello        *clientHelloMsg
    28  	suite        *cipherSuite
    29  	finishedHash finishedHash
    30  	masterSecret []byte
    31  	session      *ClientSessionState
    32  }
    33  
    34  func (c *Conn) makeClientHello() (*clientHelloMsg, ecdheParameters, error) {
    35  	config := c.config
    36  	if len(config.ServerName) == 0 && !config.InsecureSkipVerify {
    37  		return nil, nil, errors.New("tls: either ServerName or InsecureSkipVerify must be specified in the tls.Config")
    38  	}
    39  
    40  	nextProtosLength := 0
    41  	for _, proto := range config.NextProtos {
    42  		if l := len(proto); l == 0 || l > 255 {
    43  			return nil, nil, errors.New("tls: invalid NextProtos value")
    44  		} else {
    45  			nextProtosLength += 1 + l
    46  		}
    47  	}
    48  	if nextProtosLength > 0xffff {
    49  		return nil, nil, errors.New("tls: NextProtos values too large")
    50  	}
    51  
    52  	supportedVersions := config.supportedVersions(true)
    53  	if len(supportedVersions) == 0 {
    54  		return nil, nil, errors.New("tls: no supported versions satisfy MinVersion and MaxVersion")
    55  	}
    56  
    57  	clientHelloVersion := supportedVersions[0]
    58  	// The version at the beginning of the ClientHello was capped at TLS 1.2
    59  	// for compatibility reasons. The supported_versions extension is used
    60  	// to negotiate versions now. See RFC 8446, Section 4.2.1.
    61  	if clientHelloVersion > VersionTLS12 {
    62  		clientHelloVersion = VersionTLS12
    63  	}
    64  
    65  	hello := &clientHelloMsg{
    66  		vers:                         clientHelloVersion,
    67  		compressionMethods:           []uint8{compressionNone},
    68  		random:                       make([]byte, 32),
    69  		sessionId:                    make([]byte, 32),
    70  		ocspStapling:                 true,
    71  		scts:                         true,
    72  		serverName:                   hostnameInSNI(config.ServerName),
    73  		supportedCurves:              config.curvePreferences(),
    74  		supportedPoints:              []uint8{pointFormatUncompressed},
    75  		nextProtoNeg:                 len(config.NextProtos) > 0,
    76  		secureRenegotiationSupported: true,
    77  		alpnProtocols:                config.NextProtos,
    78  		supportedVersions:            supportedVersions,
    79  	}
    80  
    81  	if c.handshakes > 0 {
    82  		hello.secureRenegotiation = c.clientFinished[:]
    83  	}
    84  
    85  	possibleCipherSuites := config.cipherSuites()
    86  	hello.cipherSuites = make([]uint16, 0, len(possibleCipherSuites))
    87  
    88  NextCipherSuite:
    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  				continue
    98  			}
    99  			hello.cipherSuites = append(hello.cipherSuites, suiteId)
   100  			continue NextCipherSuite
   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  		digest, 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(), digest, 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  
   831  		for i, cert := range certs {
   832  			if i == 0 {
   833  				continue
   834  			}
   835  			opts.Intermediates.AddCert(cert)
   836  		}
   837  		var err error
   838  		c.verifiedChains, err = certs[0].Verify(opts)
   839  		if err != nil {
   840  			c.sendAlert(alertBadCertificate)
   841  			return err
   842  		}
   843  	}
   844  
   845  	if c.config.VerifyPeerCertificate != nil {
   846  		if err := c.config.VerifyPeerCertificate(certificates, c.verifiedChains); err != nil {
   847  			c.sendAlert(alertBadCertificate)
   848  			return err
   849  		}
   850  	}
   851  
   852  	switch certs[0].PublicKey.(type) {
   853  	case *rsa.PublicKey, *ecdsa.PublicKey:
   854  		break
   855  	default:
   856  		c.sendAlert(alertUnsupportedCertificate)
   857  		return fmt.Errorf("tls: server's certificate contains an unsupported type of public key: %T", certs[0].PublicKey)
   858  	}
   859  
   860  	c.peerCertificates = certs
   861  
   862  	return nil
   863  }
   864  
   865  // tls11SignatureSchemes contains the signature schemes that we synthesise for
   866  // a TLS <= 1.1 connection, based on the supported certificate types.
   867  var (
   868  	tls11SignatureSchemes      = []SignatureScheme{ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1}
   869  	tls11SignatureSchemesECDSA = tls11SignatureSchemes[:3]
   870  	tls11SignatureSchemesRSA   = tls11SignatureSchemes[3:]
   871  )
   872  
   873  // certificateRequestInfoFromMsg generates a CertificateRequestInfo from a TLS
   874  // <= 1.2 CertificateRequest, making an effort to fill in missing information.
   875  func certificateRequestInfoFromMsg(certReq *certificateRequestMsg) *CertificateRequestInfo {
   876  	var rsaAvail, ecdsaAvail bool
   877  	for _, certType := range certReq.certificateTypes {
   878  		switch certType {
   879  		case certTypeRSASign:
   880  			rsaAvail = true
   881  		case certTypeECDSASign:
   882  			ecdsaAvail = true
   883  		}
   884  	}
   885  
   886  	cri := &CertificateRequestInfo{
   887  		AcceptableCAs: certReq.certificateAuthorities,
   888  	}
   889  
   890  	if !certReq.hasSignatureAlgorithm {
   891  		// Prior to TLS 1.2, the signature schemes were not
   892  		// included in the certificate request message. In this
   893  		// case we use a plausible list based on the acceptable
   894  		// certificate types.
   895  		switch {
   896  		case rsaAvail && ecdsaAvail:
   897  			cri.SignatureSchemes = tls11SignatureSchemes
   898  		case rsaAvail:
   899  			cri.SignatureSchemes = tls11SignatureSchemesRSA
   900  		case ecdsaAvail:
   901  			cri.SignatureSchemes = tls11SignatureSchemesECDSA
   902  		}
   903  		return cri
   904  	}
   905  
   906  	// In TLS 1.2, the signature schemes apply to both the certificate chain and
   907  	// the leaf key, while the certificate types only apply to the leaf key.
   908  	// See RFC 5246, Section 7.4.4 (where it calls this "somewhat complicated").
   909  	// Filter the signature schemes based on the certificate type.
   910  	cri.SignatureSchemes = make([]SignatureScheme, 0, len(certReq.supportedSignatureAlgorithms))
   911  	for _, sigScheme := range certReq.supportedSignatureAlgorithms {
   912  		switch signatureFromSignatureScheme(sigScheme) {
   913  		case signatureECDSA:
   914  			if ecdsaAvail {
   915  				cri.SignatureSchemes = append(cri.SignatureSchemes, sigScheme)
   916  			}
   917  		case signatureRSAPSS, signaturePKCS1v15:
   918  			if rsaAvail {
   919  				cri.SignatureSchemes = append(cri.SignatureSchemes, sigScheme)
   920  			}
   921  		}
   922  	}
   923  
   924  	return cri
   925  }
   926  
   927  func (c *Conn) getClientCertificate(cri *CertificateRequestInfo) (*Certificate, error) {
   928  	if c.config.GetClientCertificate != nil {
   929  		return c.config.GetClientCertificate(cri)
   930  	}
   931  
   932  	// We need to search our list of client certs for one
   933  	// where SignatureAlgorithm is acceptable to the server and the
   934  	// Issuer is in AcceptableCAs.
   935  	for i, chain := range c.config.Certificates {
   936  		sigOK := false
   937  		for _, alg := range signatureSchemesForCertificate(c.vers, &chain) {
   938  			if isSupportedSignatureAlgorithm(alg, cri.SignatureSchemes) {
   939  				sigOK = true
   940  				break
   941  			}
   942  		}
   943  		if !sigOK {
   944  			continue
   945  		}
   946  
   947  		if len(cri.AcceptableCAs) == 0 {
   948  			return &chain, nil
   949  		}
   950  
   951  		for j, cert := range chain.Certificate {
   952  			x509Cert := chain.Leaf
   953  			// Parse the certificate if this isn't the leaf node, or if
   954  			// chain.Leaf was nil.
   955  			if j != 0 || x509Cert == nil {
   956  				var err error
   957  				if x509Cert, err = x509.ParseCertificate(cert); err != nil {
   958  					c.sendAlert(alertInternalError)
   959  					return nil, errors.New("tls: failed to parse configured certificate chain #" + strconv.Itoa(i) + ": " + err.Error())
   960  				}
   961  			}
   962  
   963  			for _, ca := range cri.AcceptableCAs {
   964  				if bytes.Equal(x509Cert.RawIssuer, ca) {
   965  					return &chain, nil
   966  				}
   967  			}
   968  		}
   969  	}
   970  
   971  	// No acceptable certificate found. Don't send a certificate.
   972  	return new(Certificate), nil
   973  }
   974  
   975  // clientSessionCacheKey returns a key used to cache sessionTickets that could
   976  // be used to resume previously negotiated TLS sessions with a server.
   977  func clientSessionCacheKey(serverAddr net.Addr, config *Config) string {
   978  	if len(config.ServerName) > 0 {
   979  		return config.ServerName
   980  	}
   981  	return serverAddr.String()
   982  }
   983  
   984  // mutualProtocol finds the mutual Next Protocol Negotiation or ALPN protocol
   985  // given list of possible protocols and a list of the preference order. The
   986  // first list must not be empty. It returns the resulting protocol and flag
   987  // indicating if the fallback case was reached.
   988  func mutualProtocol(protos, preferenceProtos []string) (string, bool) {
   989  	for _, s := range preferenceProtos {
   990  		for _, c := range protos {
   991  			if s == c {
   992  				return s, false
   993  			}
   994  		}
   995  	}
   996  
   997  	return protos[0], true
   998  }
   999  
  1000  // hostnameInSNI converts name into an approriate hostname for SNI.
  1001  // Literal IP addresses and absolute FQDNs are not permitted as SNI values.
  1002  // See RFC 6066, Section 3.
  1003  func hostnameInSNI(name string) string {
  1004  	host := name
  1005  	if len(host) > 0 && host[0] == '[' && host[len(host)-1] == ']' {
  1006  		host = host[1 : len(host)-1]
  1007  	}
  1008  	if i := strings.LastIndex(host, "%"); i > 0 {
  1009  		host = host[:i]
  1010  	}
  1011  	if net.ParseIP(host) != nil {
  1012  		return ""
  1013  	}
  1014  	for len(name) > 0 && name[len(name)-1] == '.' {
  1015  		name = name[:len(name)-1]
  1016  	}
  1017  	return name
  1018  }
  1019  

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