Source file src/crypto/tls/handshake_server.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  	"context"
     9  	"crypto"
    10  	"crypto/ecdsa"
    11  	"crypto/ed25519"
    12  	"crypto/rsa"
    13  	"crypto/subtle"
    14  	"crypto/x509"
    15  	"errors"
    16  	"fmt"
    17  	"hash"
    18  	"io"
    19  	"sync/atomic"
    20  	"time"
    21  )
    22  
    23  // serverHandshakeState contains details of a server handshake in progress.
    24  // It's discarded once the handshake has completed.
    25  type serverHandshakeState struct {
    26  	c            *Conn
    27  	ctx          context.Context
    28  	clientHello  *clientHelloMsg
    29  	hello        *serverHelloMsg
    30  	suite        *cipherSuite
    31  	ecdheOk      bool
    32  	ecSignOk     bool
    33  	rsaDecryptOk bool
    34  	rsaSignOk    bool
    35  	sessionState *sessionState
    36  	finishedHash finishedHash
    37  	masterSecret []byte
    38  	cert         *Certificate
    39  }
    40  
    41  // serverHandshake performs a TLS handshake as a server.
    42  func (c *Conn) serverHandshake(ctx context.Context) error {
    43  	clientHello, err := c.readClientHello(ctx)
    44  	if err != nil {
    45  		return err
    46  	}
    47  
    48  	if c.vers == VersionTLS13 {
    49  		hs := serverHandshakeStateTLS13{
    50  			c:           c,
    51  			ctx:         ctx,
    52  			clientHello: clientHello,
    53  		}
    54  		return hs.handshake()
    55  	}
    56  
    57  	hs := serverHandshakeState{
    58  		c:           c,
    59  		ctx:         ctx,
    60  		clientHello: clientHello,
    61  	}
    62  	return hs.handshake()
    63  }
    64  
    65  func (hs *serverHandshakeState) handshake() error {
    66  	c := hs.c
    67  
    68  	if err := hs.processClientHello(); err != nil {
    69  		return err
    70  	}
    71  
    72  	// For an overview of TLS handshaking, see RFC 5246, Section 7.3.
    73  	c.buffering = true
    74  	if hs.checkForResumption() {
    75  		// The client has included a session ticket and so we do an abbreviated handshake.
    76  		c.didResume = true
    77  		if err := hs.doResumeHandshake(); err != nil {
    78  			return err
    79  		}
    80  		if err := hs.establishKeys(); err != nil {
    81  			return err
    82  		}
    83  		if err := hs.sendSessionTicket(); err != nil {
    84  			return err
    85  		}
    86  		if err := hs.sendFinished(c.serverFinished[:]); err != nil {
    87  			return err
    88  		}
    89  		if _, err := c.flush(); err != nil {
    90  			return err
    91  		}
    92  		c.clientFinishedIsFirst = false
    93  		if err := hs.readFinished(nil); err != nil {
    94  			return err
    95  		}
    96  	} else {
    97  		// The client didn't include a session ticket, or it wasn't
    98  		// valid so we do a full handshake.
    99  		if err := hs.pickCipherSuite(); err != nil {
   100  			return err
   101  		}
   102  		if err := hs.doFullHandshake(); err != nil {
   103  			return err
   104  		}
   105  		if err := hs.establishKeys(); err != nil {
   106  			return err
   107  		}
   108  		if err := hs.readFinished(c.clientFinished[:]); err != nil {
   109  			return err
   110  		}
   111  		c.clientFinishedIsFirst = true
   112  		c.buffering = true
   113  		if err := hs.sendSessionTicket(); err != nil {
   114  			return err
   115  		}
   116  		if err := hs.sendFinished(nil); err != nil {
   117  			return err
   118  		}
   119  		if _, err := c.flush(); err != nil {
   120  			return err
   121  		}
   122  	}
   123  
   124  	c.ekm = ekmFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.clientHello.random, hs.hello.random)
   125  	atomic.StoreUint32(&c.handshakeStatus, 1)
   126  
   127  	return nil
   128  }
   129  
   130  // readClientHello reads a ClientHello message and selects the protocol version.
   131  func (c *Conn) readClientHello(ctx context.Context) (*clientHelloMsg, error) {
   132  	msg, err := c.readHandshake()
   133  	if err != nil {
   134  		return nil, err
   135  	}
   136  	clientHello, ok := msg.(*clientHelloMsg)
   137  	if !ok {
   138  		c.sendAlert(alertUnexpectedMessage)
   139  		return nil, unexpectedMessageError(clientHello, msg)
   140  	}
   141  
   142  	var configForClient *Config
   143  	originalConfig := c.config
   144  	if c.config.GetConfigForClient != nil {
   145  		chi := clientHelloInfo(ctx, c, clientHello)
   146  		if configForClient, err = c.config.GetConfigForClient(chi); err != nil {
   147  			c.sendAlert(alertInternalError)
   148  			return nil, err
   149  		} else if configForClient != nil {
   150  			c.config = configForClient
   151  		}
   152  	}
   153  	c.ticketKeys = originalConfig.ticketKeys(configForClient)
   154  
   155  	clientVersions := clientHello.supportedVersions
   156  	if len(clientHello.supportedVersions) == 0 {
   157  		clientVersions = supportedVersionsFromMax(clientHello.vers)
   158  	}
   159  	c.vers, ok = c.config.mutualVersion(roleServer, clientVersions)
   160  	if !ok {
   161  		c.sendAlert(alertProtocolVersion)
   162  		return nil, fmt.Errorf("tls: client offered only unsupported versions: %x", clientVersions)
   163  	}
   164  	c.haveVers = true
   165  	c.in.version = c.vers
   166  	c.out.version = c.vers
   167  
   168  	return clientHello, nil
   169  }
   170  
   171  func (hs *serverHandshakeState) processClientHello() error {
   172  	c := hs.c
   173  
   174  	hs.hello = new(serverHelloMsg)
   175  	hs.hello.vers = c.vers
   176  
   177  	foundCompression := false
   178  	// We only support null compression, so check that the client offered it.
   179  	for _, compression := range hs.clientHello.compressionMethods {
   180  		if compression == compressionNone {
   181  			foundCompression = true
   182  			break
   183  		}
   184  	}
   185  
   186  	if !foundCompression {
   187  		c.sendAlert(alertHandshakeFailure)
   188  		return errors.New("tls: client does not support uncompressed connections")
   189  	}
   190  
   191  	hs.hello.random = make([]byte, 32)
   192  	serverRandom := hs.hello.random
   193  	// Downgrade protection canaries. See RFC 8446, Section 4.1.3.
   194  	maxVers := c.config.maxSupportedVersion(roleServer)
   195  	if maxVers >= VersionTLS12 && c.vers < maxVers || testingOnlyForceDowngradeCanary {
   196  		if c.vers == VersionTLS12 {
   197  			copy(serverRandom[24:], downgradeCanaryTLS12)
   198  		} else {
   199  			copy(serverRandom[24:], downgradeCanaryTLS11)
   200  		}
   201  		serverRandom = serverRandom[:24]
   202  	}
   203  	_, err := io.ReadFull(c.config.rand(), serverRandom)
   204  	if err != nil {
   205  		c.sendAlert(alertInternalError)
   206  		return err
   207  	}
   208  
   209  	if len(hs.clientHello.secureRenegotiation) != 0 {
   210  		c.sendAlert(alertHandshakeFailure)
   211  		return errors.New("tls: initial handshake had non-empty renegotiation extension")
   212  	}
   213  
   214  	hs.hello.secureRenegotiationSupported = hs.clientHello.secureRenegotiationSupported
   215  	hs.hello.compressionMethod = compressionNone
   216  	if len(hs.clientHello.serverName) > 0 {
   217  		c.serverName = hs.clientHello.serverName
   218  	}
   219  
   220  	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols)
   221  	if err != nil {
   222  		c.sendAlert(alertNoApplicationProtocol)
   223  		return err
   224  	}
   225  	hs.hello.alpnProtocol = selectedProto
   226  	c.clientProtocol = selectedProto
   227  
   228  	hs.cert, err = c.config.getCertificate(clientHelloInfo(hs.ctx, c, hs.clientHello))
   229  	if err != nil {
   230  		if err == errNoCertificates {
   231  			c.sendAlert(alertUnrecognizedName)
   232  		} else {
   233  			c.sendAlert(alertInternalError)
   234  		}
   235  		return err
   236  	}
   237  	if hs.clientHello.scts {
   238  		hs.hello.scts = hs.cert.SignedCertificateTimestamps
   239  	}
   240  
   241  	hs.ecdheOk = supportsECDHE(c.config, hs.clientHello.supportedCurves, hs.clientHello.supportedPoints)
   242  
   243  	if hs.ecdheOk && len(hs.clientHello.supportedPoints) > 0 {
   244  		// Although omitting the ec_point_formats extension is permitted, some
   245  		// old OpenSSL version will refuse to handshake if not present.
   246  		//
   247  		// Per RFC 4492, section 5.1.2, implementations MUST support the
   248  		// uncompressed point format. See golang.org/issue/31943.
   249  		hs.hello.supportedPoints = []uint8{pointFormatUncompressed}
   250  	}
   251  
   252  	if priv, ok := hs.cert.PrivateKey.(crypto.Signer); ok {
   253  		switch priv.Public().(type) {
   254  		case *ecdsa.PublicKey:
   255  			hs.ecSignOk = true
   256  		case ed25519.PublicKey:
   257  			hs.ecSignOk = true
   258  		case *rsa.PublicKey:
   259  			hs.rsaSignOk = true
   260  		default:
   261  			c.sendAlert(alertInternalError)
   262  			return fmt.Errorf("tls: unsupported signing key type (%T)", priv.Public())
   263  		}
   264  	}
   265  	if priv, ok := hs.cert.PrivateKey.(crypto.Decrypter); ok {
   266  		switch priv.Public().(type) {
   267  		case *rsa.PublicKey:
   268  			hs.rsaDecryptOk = true
   269  		default:
   270  			c.sendAlert(alertInternalError)
   271  			return fmt.Errorf("tls: unsupported decryption key type (%T)", priv.Public())
   272  		}
   273  	}
   274  
   275  	return nil
   276  }
   277  
   278  // negotiateALPN picks a shared ALPN protocol that both sides support in server
   279  // preference order. If ALPN is not configured or the peer doesn't support it,
   280  // it returns "" and no error.
   281  func negotiateALPN(serverProtos, clientProtos []string) (string, error) {
   282  	if len(serverProtos) == 0 || len(clientProtos) == 0 {
   283  		return "", nil
   284  	}
   285  	var http11fallback bool
   286  	for _, s := range serverProtos {
   287  		for _, c := range clientProtos {
   288  			if s == c {
   289  				return s, nil
   290  			}
   291  			if s == "h2" && c == "http/1.1" {
   292  				http11fallback = true
   293  			}
   294  		}
   295  	}
   296  	// As a special case, let http/1.1 clients connect to h2 servers as if they
   297  	// didn't support ALPN. We used not to enforce protocol overlap, so over
   298  	// time a number of HTTP servers were configured with only "h2", but
   299  	// expected to accept connections from "http/1.1" clients. See Issue 46310.
   300  	if http11fallback {
   301  		return "", nil
   302  	}
   303  	return "", fmt.Errorf("tls: client requested unsupported application protocols (%s)", clientProtos)
   304  }
   305  
   306  // supportsECDHE returns whether ECDHE key exchanges can be used with this
   307  // pre-TLS 1.3 client.
   308  func supportsECDHE(c *Config, supportedCurves []CurveID, supportedPoints []uint8) bool {
   309  	supportsCurve := false
   310  	for _, curve := range supportedCurves {
   311  		if c.supportsCurve(curve) {
   312  			supportsCurve = true
   313  			break
   314  		}
   315  	}
   316  
   317  	supportsPointFormat := false
   318  	for _, pointFormat := range supportedPoints {
   319  		if pointFormat == pointFormatUncompressed {
   320  			supportsPointFormat = true
   321  			break
   322  		}
   323  	}
   324  	// Per RFC 8422, Section 5.1.2, if the Supported Point Formats extension is
   325  	// missing, uncompressed points are supported. If supportedPoints is empty,
   326  	// the extension must be missing, as an empty extension body is rejected by
   327  	// the parser. See https://go.dev/issue/49126.
   328  	if len(supportedPoints) == 0 {
   329  		supportsPointFormat = true
   330  	}
   331  
   332  	return supportsCurve && supportsPointFormat
   333  }
   334  
   335  func (hs *serverHandshakeState) pickCipherSuite() error {
   336  	c := hs.c
   337  
   338  	preferenceOrder := cipherSuitesPreferenceOrder
   339  	if !hasAESGCMHardwareSupport || !aesgcmPreferred(hs.clientHello.cipherSuites) {
   340  		preferenceOrder = cipherSuitesPreferenceOrderNoAES
   341  	}
   342  
   343  	configCipherSuites := c.config.cipherSuites()
   344  	preferenceList := make([]uint16, 0, len(configCipherSuites))
   345  	for _, suiteID := range preferenceOrder {
   346  		for _, id := range configCipherSuites {
   347  			if id == suiteID {
   348  				preferenceList = append(preferenceList, id)
   349  				break
   350  			}
   351  		}
   352  	}
   353  
   354  	hs.suite = selectCipherSuite(preferenceList, hs.clientHello.cipherSuites, hs.cipherSuiteOk)
   355  	if hs.suite == nil {
   356  		c.sendAlert(alertHandshakeFailure)
   357  		return errors.New("tls: no cipher suite supported by both client and server")
   358  	}
   359  	c.cipherSuite = hs.suite.id
   360  
   361  	for _, id := range hs.clientHello.cipherSuites {
   362  		if id == TLS_FALLBACK_SCSV {
   363  			// The client is doing a fallback connection. See RFC 7507.
   364  			if hs.clientHello.vers < c.config.maxSupportedVersion(roleServer) {
   365  				c.sendAlert(alertInappropriateFallback)
   366  				return errors.New("tls: client using inappropriate protocol fallback")
   367  			}
   368  			break
   369  		}
   370  	}
   371  
   372  	return nil
   373  }
   374  
   375  func (hs *serverHandshakeState) cipherSuiteOk(c *cipherSuite) bool {
   376  	if c.flags&suiteECDHE != 0 {
   377  		if !hs.ecdheOk {
   378  			return false
   379  		}
   380  		if c.flags&suiteECSign != 0 {
   381  			if !hs.ecSignOk {
   382  				return false
   383  			}
   384  		} else if !hs.rsaSignOk {
   385  			return false
   386  		}
   387  	} else if !hs.rsaDecryptOk {
   388  		return false
   389  	}
   390  	if hs.c.vers < VersionTLS12 && c.flags&suiteTLS12 != 0 {
   391  		return false
   392  	}
   393  	return true
   394  }
   395  
   396  // checkForResumption reports whether we should perform resumption on this connection.
   397  func (hs *serverHandshakeState) checkForResumption() bool {
   398  	c := hs.c
   399  
   400  	if c.config.SessionTicketsDisabled {
   401  		return false
   402  	}
   403  
   404  	plaintext, usedOldKey := c.decryptTicket(hs.clientHello.sessionTicket)
   405  	if plaintext == nil {
   406  		return false
   407  	}
   408  	hs.sessionState = &sessionState{usedOldKey: usedOldKey}
   409  	ok := hs.sessionState.unmarshal(plaintext)
   410  	if !ok {
   411  		return false
   412  	}
   413  
   414  	createdAt := time.Unix(int64(hs.sessionState.createdAt), 0)
   415  	if c.config.time().Sub(createdAt) > maxSessionTicketLifetime {
   416  		return false
   417  	}
   418  
   419  	// Never resume a session for a different TLS version.
   420  	if c.vers != hs.sessionState.vers {
   421  		return false
   422  	}
   423  
   424  	cipherSuiteOk := false
   425  	// Check that the client is still offering the ciphersuite in the session.
   426  	for _, id := range hs.clientHello.cipherSuites {
   427  		if id == hs.sessionState.cipherSuite {
   428  			cipherSuiteOk = true
   429  			break
   430  		}
   431  	}
   432  	if !cipherSuiteOk {
   433  		return false
   434  	}
   435  
   436  	// Check that we also support the ciphersuite from the session.
   437  	hs.suite = selectCipherSuite([]uint16{hs.sessionState.cipherSuite},
   438  		c.config.cipherSuites(), hs.cipherSuiteOk)
   439  	if hs.suite == nil {
   440  		return false
   441  	}
   442  
   443  	sessionHasClientCerts := len(hs.sessionState.certificates) != 0
   444  	needClientCerts := requiresClientCert(c.config.ClientAuth)
   445  	if needClientCerts && !sessionHasClientCerts {
   446  		return false
   447  	}
   448  	if sessionHasClientCerts && c.config.ClientAuth == NoClientCert {
   449  		return false
   450  	}
   451  
   452  	return true
   453  }
   454  
   455  func (hs *serverHandshakeState) doResumeHandshake() error {
   456  	c := hs.c
   457  
   458  	hs.hello.cipherSuite = hs.suite.id
   459  	c.cipherSuite = hs.suite.id
   460  	// We echo the client's session ID in the ServerHello to let it know
   461  	// that we're doing a resumption.
   462  	hs.hello.sessionId = hs.clientHello.sessionId
   463  	hs.hello.ticketSupported = hs.sessionState.usedOldKey
   464  	hs.finishedHash = newFinishedHash(c.vers, hs.suite)
   465  	hs.finishedHash.discardHandshakeBuffer()
   466  	hs.finishedHash.Write(hs.clientHello.marshal())
   467  	hs.finishedHash.Write(hs.hello.marshal())
   468  	if _, err := c.writeRecord(recordTypeHandshake, hs.hello.marshal()); err != nil {
   469  		return err
   470  	}
   471  
   472  	if err := c.processCertsFromClient(Certificate{
   473  		Certificate: hs.sessionState.certificates,
   474  	}); err != nil {
   475  		return err
   476  	}
   477  
   478  	if c.config.VerifyConnection != nil {
   479  		if err := c.config.VerifyConnection(c.connectionStateLocked()); err != nil {
   480  			c.sendAlert(alertBadCertificate)
   481  			return err
   482  		}
   483  	}
   484  
   485  	hs.masterSecret = hs.sessionState.masterSecret
   486  
   487  	return nil
   488  }
   489  
   490  func (hs *serverHandshakeState) doFullHandshake() error {
   491  	c := hs.c
   492  
   493  	if hs.clientHello.ocspStapling && len(hs.cert.OCSPStaple) > 0 {
   494  		hs.hello.ocspStapling = true
   495  	}
   496  
   497  	hs.hello.ticketSupported = hs.clientHello.ticketSupported && !c.config.SessionTicketsDisabled
   498  	hs.hello.cipherSuite = hs.suite.id
   499  
   500  	hs.finishedHash = newFinishedHash(hs.c.vers, hs.suite)
   501  	if c.config.ClientAuth == NoClientCert {
   502  		// No need to keep a full record of the handshake if client
   503  		// certificates won't be used.
   504  		hs.finishedHash.discardHandshakeBuffer()
   505  	}
   506  	hs.finishedHash.Write(hs.clientHello.marshal())
   507  	hs.finishedHash.Write(hs.hello.marshal())
   508  	if _, err := c.writeRecord(recordTypeHandshake, hs.hello.marshal()); err != nil {
   509  		return err
   510  	}
   511  
   512  	certMsg := new(certificateMsg)
   513  	certMsg.certificates = hs.cert.Certificate
   514  	hs.finishedHash.Write(certMsg.marshal())
   515  	if _, err := c.writeRecord(recordTypeHandshake, certMsg.marshal()); err != nil {
   516  		return err
   517  	}
   518  
   519  	if hs.hello.ocspStapling {
   520  		certStatus := new(certificateStatusMsg)
   521  		certStatus.response = hs.cert.OCSPStaple
   522  		hs.finishedHash.Write(certStatus.marshal())
   523  		if _, err := c.writeRecord(recordTypeHandshake, certStatus.marshal()); err != nil {
   524  			return err
   525  		}
   526  	}
   527  
   528  	keyAgreement := hs.suite.ka(c.vers)
   529  	skx, err := keyAgreement.generateServerKeyExchange(c.config, hs.cert, hs.clientHello, hs.hello)
   530  	if err != nil {
   531  		c.sendAlert(alertHandshakeFailure)
   532  		return err
   533  	}
   534  	if skx != nil {
   535  		hs.finishedHash.Write(skx.marshal())
   536  		if _, err := c.writeRecord(recordTypeHandshake, skx.marshal()); err != nil {
   537  			return err
   538  		}
   539  	}
   540  
   541  	var certReq *certificateRequestMsg
   542  	if c.config.ClientAuth >= RequestClientCert {
   543  		// Request a client certificate
   544  		certReq = new(certificateRequestMsg)
   545  		certReq.certificateTypes = []byte{
   546  			byte(certTypeRSASign),
   547  			byte(certTypeECDSASign),
   548  		}
   549  		if c.vers >= VersionTLS12 {
   550  			certReq.hasSignatureAlgorithm = true
   551  			certReq.supportedSignatureAlgorithms = supportedSignatureAlgorithms()
   552  		}
   553  
   554  		// An empty list of certificateAuthorities signals to
   555  		// the client that it may send any certificate in response
   556  		// to our request. When we know the CAs we trust, then
   557  		// we can send them down, so that the client can choose
   558  		// an appropriate certificate to give to us.
   559  		if c.config.ClientCAs != nil {
   560  			certReq.certificateAuthorities = c.config.ClientCAs.Subjects()
   561  		}
   562  		hs.finishedHash.Write(certReq.marshal())
   563  		if _, err := c.writeRecord(recordTypeHandshake, certReq.marshal()); err != nil {
   564  			return err
   565  		}
   566  	}
   567  
   568  	helloDone := new(serverHelloDoneMsg)
   569  	hs.finishedHash.Write(helloDone.marshal())
   570  	if _, err := c.writeRecord(recordTypeHandshake, helloDone.marshal()); err != nil {
   571  		return err
   572  	}
   573  
   574  	if _, err := c.flush(); err != nil {
   575  		return err
   576  	}
   577  
   578  	var pub crypto.PublicKey // public key for client auth, if any
   579  
   580  	msg, err := c.readHandshake()
   581  	if err != nil {
   582  		return err
   583  	}
   584  
   585  	// If we requested a client certificate, then the client must send a
   586  	// certificate message, even if it's empty.
   587  	if c.config.ClientAuth >= RequestClientCert {
   588  		certMsg, ok := msg.(*certificateMsg)
   589  		if !ok {
   590  			c.sendAlert(alertUnexpectedMessage)
   591  			return unexpectedMessageError(certMsg, msg)
   592  		}
   593  		hs.finishedHash.Write(certMsg.marshal())
   594  
   595  		if err := c.processCertsFromClient(Certificate{
   596  			Certificate: certMsg.certificates,
   597  		}); err != nil {
   598  			return err
   599  		}
   600  		if len(certMsg.certificates) != 0 {
   601  			pub = c.peerCertificates[0].PublicKey
   602  		}
   603  
   604  		msg, err = c.readHandshake()
   605  		if err != nil {
   606  			return err
   607  		}
   608  	}
   609  	if c.config.VerifyConnection != nil {
   610  		if err := c.config.VerifyConnection(c.connectionStateLocked()); err != nil {
   611  			c.sendAlert(alertBadCertificate)
   612  			return err
   613  		}
   614  	}
   615  
   616  	// Get client key exchange
   617  	ckx, ok := msg.(*clientKeyExchangeMsg)
   618  	if !ok {
   619  		c.sendAlert(alertUnexpectedMessage)
   620  		return unexpectedMessageError(ckx, msg)
   621  	}
   622  	hs.finishedHash.Write(ckx.marshal())
   623  
   624  	preMasterSecret, err := keyAgreement.processClientKeyExchange(c.config, hs.cert, ckx, c.vers)
   625  	if err != nil {
   626  		c.sendAlert(alertHandshakeFailure)
   627  		return err
   628  	}
   629  	hs.masterSecret = masterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret, hs.clientHello.random, hs.hello.random)
   630  	if err := c.config.writeKeyLog(keyLogLabelTLS12, hs.clientHello.random, hs.masterSecret); err != nil {
   631  		c.sendAlert(alertInternalError)
   632  		return err
   633  	}
   634  
   635  	// If we received a client cert in response to our certificate request message,
   636  	// the client will send us a certificateVerifyMsg immediately after the
   637  	// clientKeyExchangeMsg. This message is a digest of all preceding
   638  	// handshake-layer messages that is signed using the private key corresponding
   639  	// to the client's certificate. This allows us to verify that the client is in
   640  	// possession of the private key of the certificate.
   641  	if len(c.peerCertificates) > 0 {
   642  		msg, err = c.readHandshake()
   643  		if err != nil {
   644  			return err
   645  		}
   646  		certVerify, ok := msg.(*certificateVerifyMsg)
   647  		if !ok {
   648  			c.sendAlert(alertUnexpectedMessage)
   649  			return unexpectedMessageError(certVerify, msg)
   650  		}
   651  
   652  		var sigType uint8
   653  		var sigHash crypto.Hash
   654  		if c.vers >= VersionTLS12 {
   655  			if !isSupportedSignatureAlgorithm(certVerify.signatureAlgorithm, certReq.supportedSignatureAlgorithms) {
   656  				c.sendAlert(alertIllegalParameter)
   657  				return errors.New("tls: client certificate used with invalid signature algorithm")
   658  			}
   659  			sigType, sigHash, err = typeAndHashFromSignatureScheme(certVerify.signatureAlgorithm)
   660  			if err != nil {
   661  				return c.sendAlert(alertInternalError)
   662  			}
   663  		} else {
   664  			sigType, sigHash, err = legacyTypeAndHashFromPublicKey(pub)
   665  			if err != nil {
   666  				c.sendAlert(alertIllegalParameter)
   667  				return err
   668  			}
   669  		}
   670  
   671  		signed := hs.finishedHash.hashForClientCertificate(sigType, sigHash, hs.masterSecret)
   672  		if err := verifyHandshakeSignature(sigType, pub, sigHash, signed, certVerify.signature); err != nil {
   673  			c.sendAlert(alertDecryptError)
   674  			return errors.New("tls: invalid signature by the client certificate: " + err.Error())
   675  		}
   676  
   677  		hs.finishedHash.Write(certVerify.marshal())
   678  	}
   679  
   680  	hs.finishedHash.discardHandshakeBuffer()
   681  
   682  	return nil
   683  }
   684  
   685  func (hs *serverHandshakeState) establishKeys() error {
   686  	c := hs.c
   687  
   688  	clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV :=
   689  		keysFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.clientHello.random, hs.hello.random, hs.suite.macLen, hs.suite.keyLen, hs.suite.ivLen)
   690  
   691  	var clientCipher, serverCipher any
   692  	var clientHash, serverHash hash.Hash
   693  
   694  	if hs.suite.aead == nil {
   695  		clientCipher = hs.suite.cipher(clientKey, clientIV, true /* for reading */)
   696  		clientHash = hs.suite.mac(clientMAC)
   697  		serverCipher = hs.suite.cipher(serverKey, serverIV, false /* not for reading */)
   698  		serverHash = hs.suite.mac(serverMAC)
   699  	} else {
   700  		clientCipher = hs.suite.aead(clientKey, clientIV)
   701  		serverCipher = hs.suite.aead(serverKey, serverIV)
   702  	}
   703  
   704  	c.in.prepareCipherSpec(c.vers, clientCipher, clientHash)
   705  	c.out.prepareCipherSpec(c.vers, serverCipher, serverHash)
   706  
   707  	return nil
   708  }
   709  
   710  func (hs *serverHandshakeState) readFinished(out []byte) error {
   711  	c := hs.c
   712  
   713  	if err := c.readChangeCipherSpec(); err != nil {
   714  		return err
   715  	}
   716  
   717  	msg, err := c.readHandshake()
   718  	if err != nil {
   719  		return err
   720  	}
   721  	clientFinished, ok := msg.(*finishedMsg)
   722  	if !ok {
   723  		c.sendAlert(alertUnexpectedMessage)
   724  		return unexpectedMessageError(clientFinished, msg)
   725  	}
   726  
   727  	verify := hs.finishedHash.clientSum(hs.masterSecret)
   728  	if len(verify) != len(clientFinished.verifyData) ||
   729  		subtle.ConstantTimeCompare(verify, clientFinished.verifyData) != 1 {
   730  		c.sendAlert(alertHandshakeFailure)
   731  		return errors.New("tls: client's Finished message is incorrect")
   732  	}
   733  
   734  	hs.finishedHash.Write(clientFinished.marshal())
   735  	copy(out, verify)
   736  	return nil
   737  }
   738  
   739  func (hs *serverHandshakeState) sendSessionTicket() error {
   740  	// ticketSupported is set in a resumption handshake if the
   741  	// ticket from the client was encrypted with an old session
   742  	// ticket key and thus a refreshed ticket should be sent.
   743  	if !hs.hello.ticketSupported {
   744  		return nil
   745  	}
   746  
   747  	c := hs.c
   748  	m := new(newSessionTicketMsg)
   749  
   750  	createdAt := uint64(c.config.time().Unix())
   751  	if hs.sessionState != nil {
   752  		// If this is re-wrapping an old key, then keep
   753  		// the original time it was created.
   754  		createdAt = hs.sessionState.createdAt
   755  	}
   756  
   757  	var certsFromClient [][]byte
   758  	for _, cert := range c.peerCertificates {
   759  		certsFromClient = append(certsFromClient, cert.Raw)
   760  	}
   761  	state := sessionState{
   762  		vers:         c.vers,
   763  		cipherSuite:  hs.suite.id,
   764  		createdAt:    createdAt,
   765  		masterSecret: hs.masterSecret,
   766  		certificates: certsFromClient,
   767  	}
   768  	var err error
   769  	m.ticket, err = c.encryptTicket(state.marshal())
   770  	if err != nil {
   771  		return err
   772  	}
   773  
   774  	hs.finishedHash.Write(m.marshal())
   775  	if _, err := c.writeRecord(recordTypeHandshake, m.marshal()); err != nil {
   776  		return err
   777  	}
   778  
   779  	return nil
   780  }
   781  
   782  func (hs *serverHandshakeState) sendFinished(out []byte) error {
   783  	c := hs.c
   784  
   785  	if _, err := c.writeRecord(recordTypeChangeCipherSpec, []byte{1}); err != nil {
   786  		return err
   787  	}
   788  
   789  	finished := new(finishedMsg)
   790  	finished.verifyData = hs.finishedHash.serverSum(hs.masterSecret)
   791  	hs.finishedHash.Write(finished.marshal())
   792  	if _, err := c.writeRecord(recordTypeHandshake, finished.marshal()); err != nil {
   793  		return err
   794  	}
   795  
   796  	copy(out, finished.verifyData)
   797  
   798  	return nil
   799  }
   800  
   801  // processCertsFromClient takes a chain of client certificates either from a
   802  // Certificates message or from a sessionState and verifies them. It returns
   803  // the public key of the leaf certificate.
   804  func (c *Conn) processCertsFromClient(certificate Certificate) error {
   805  	certificates := certificate.Certificate
   806  	certs := make([]*x509.Certificate, len(certificates))
   807  	var err error
   808  	for i, asn1Data := range certificates {
   809  		if certs[i], err = x509.ParseCertificate(asn1Data); err != nil {
   810  			c.sendAlert(alertBadCertificate)
   811  			return errors.New("tls: failed to parse client certificate: " + err.Error())
   812  		}
   813  	}
   814  
   815  	if len(certs) == 0 && requiresClientCert(c.config.ClientAuth) {
   816  		c.sendAlert(alertBadCertificate)
   817  		return errors.New("tls: client didn't provide a certificate")
   818  	}
   819  
   820  	if c.config.ClientAuth >= VerifyClientCertIfGiven && len(certs) > 0 {
   821  		opts := x509.VerifyOptions{
   822  			Roots:         c.config.ClientCAs,
   823  			CurrentTime:   c.config.time(),
   824  			Intermediates: x509.NewCertPool(),
   825  			KeyUsages:     []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
   826  		}
   827  
   828  		for _, cert := range certs[1:] {
   829  			opts.Intermediates.AddCert(cert)
   830  		}
   831  
   832  		chains, err := certs[0].Verify(opts)
   833  		if err != nil {
   834  			c.sendAlert(alertBadCertificate)
   835  			return errors.New("tls: failed to verify client certificate: " + err.Error())
   836  		}
   837  
   838  		c.verifiedChains = chains
   839  	}
   840  
   841  	c.peerCertificates = certs
   842  	c.ocspResponse = certificate.OCSPStaple
   843  	c.scts = certificate.SignedCertificateTimestamps
   844  
   845  	if len(certs) > 0 {
   846  		switch certs[0].PublicKey.(type) {
   847  		case *ecdsa.PublicKey, *rsa.PublicKey, ed25519.PublicKey:
   848  		default:
   849  			c.sendAlert(alertUnsupportedCertificate)
   850  			return fmt.Errorf("tls: client certificate contains an unsupported public key of type %T", certs[0].PublicKey)
   851  		}
   852  	}
   853  
   854  	if c.config.VerifyPeerCertificate != nil {
   855  		if err := c.config.VerifyPeerCertificate(certificates, c.verifiedChains); err != nil {
   856  			c.sendAlert(alertBadCertificate)
   857  			return err
   858  		}
   859  	}
   860  
   861  	return nil
   862  }
   863  
   864  func clientHelloInfo(ctx context.Context, c *Conn, clientHello *clientHelloMsg) *ClientHelloInfo {
   865  	supportedVersions := clientHello.supportedVersions
   866  	if len(clientHello.supportedVersions) == 0 {
   867  		supportedVersions = supportedVersionsFromMax(clientHello.vers)
   868  	}
   869  
   870  	return &ClientHelloInfo{
   871  		CipherSuites:      clientHello.cipherSuites,
   872  		ServerName:        clientHello.serverName,
   873  		SupportedCurves:   clientHello.supportedCurves,
   874  		SupportedPoints:   clientHello.supportedPoints,
   875  		SignatureSchemes:  clientHello.supportedSignatureAlgorithms,
   876  		SupportedProtos:   clientHello.alpnProtocols,
   877  		SupportedVersions: supportedVersions,
   878  		Conn:              c.conn,
   879  		config:            c.config,
   880  		ctx:               ctx,
   881  	}
   882  }
   883  

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