Source file src/crypto/tls/handshake_server.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  	"context"
     9  	"crypto"
    10  	"crypto/ecdsa"
    11  	"crypto/ed25519"
    12  	"crypto/rsa"
    13  	"crypto/subtle"
    14  	"crypto/tls/internal/fips140tls"
    15  	"crypto/x509"
    16  	"errors"
    17  	"fmt"
    18  	"hash"
    19  	"internal/byteorder"
    20  	"io"
    21  	"time"
    22  )
    23  
    24  // serverHandshakeState contains details of a server handshake in progress.
    25  // It's discarded once the handshake has completed.
    26  type serverHandshakeState struct {
    27  	c            *Conn
    28  	ctx          context.Context
    29  	clientHello  *clientHelloMsg
    30  	hello        *serverHelloMsg
    31  	suite        *cipherSuite
    32  	ecdheOk      bool
    33  	ecSignOk     bool
    34  	rsaDecryptOk bool
    35  	rsaSignOk    bool
    36  	sessionState *SessionState
    37  	finishedHash finishedHash
    38  	masterSecret []byte
    39  	cert         *Certificate
    40  }
    41  
    42  // serverHandshake performs a TLS handshake as a server.
    43  func (c *Conn) serverHandshake(ctx context.Context) error {
    44  	clientHello, ech, err := c.readClientHello(ctx)
    45  	if err != nil {
    46  		return err
    47  	}
    48  
    49  	if c.vers == VersionTLS13 {
    50  		hs := serverHandshakeStateTLS13{
    51  			c:           c,
    52  			ctx:         ctx,
    53  			clientHello: clientHello,
    54  			echContext:  ech,
    55  		}
    56  		return hs.handshake()
    57  	}
    58  
    59  	hs := serverHandshakeState{
    60  		c:           c,
    61  		ctx:         ctx,
    62  		clientHello: clientHello,
    63  	}
    64  	return hs.handshake()
    65  }
    66  
    67  func (hs *serverHandshakeState) handshake() error {
    68  	c := hs.c
    69  
    70  	if err := hs.processClientHello(); err != nil {
    71  		return err
    72  	}
    73  
    74  	// For an overview of TLS handshaking, see RFC 5246, Section 7.3.
    75  	c.buffering = true
    76  	if err := hs.checkForResumption(); err != nil {
    77  		return err
    78  	}
    79  	if hs.sessionState != nil {
    80  		// The client has included a session ticket and so we do an abbreviated handshake.
    81  		if err := hs.doResumeHandshake(); err != nil {
    82  			return err
    83  		}
    84  		if err := hs.establishKeys(); err != nil {
    85  			return err
    86  		}
    87  		if err := hs.sendSessionTicket(); err != nil {
    88  			return err
    89  		}
    90  		if err := hs.sendFinished(c.serverFinished[:]); err != nil {
    91  			return err
    92  		}
    93  		if _, err := c.flush(); err != nil {
    94  			return err
    95  		}
    96  		c.clientFinishedIsFirst = false
    97  		if err := hs.readFinished(nil); err != nil {
    98  			return err
    99  		}
   100  	} else {
   101  		// The client didn't include a session ticket, or it wasn't
   102  		// valid so we do a full handshake.
   103  		if err := hs.pickCipherSuite(); err != nil {
   104  			return err
   105  		}
   106  		if err := hs.doFullHandshake(); err != nil {
   107  			return err
   108  		}
   109  		if err := hs.establishKeys(); err != nil {
   110  			return err
   111  		}
   112  		if err := hs.readFinished(c.clientFinished[:]); err != nil {
   113  			return err
   114  		}
   115  		c.clientFinishedIsFirst = true
   116  		c.buffering = true
   117  		if err := hs.sendSessionTicket(); err != nil {
   118  			return err
   119  		}
   120  		if err := hs.sendFinished(nil); err != nil {
   121  			return err
   122  		}
   123  		if _, err := c.flush(); err != nil {
   124  			return err
   125  		}
   126  	}
   127  
   128  	c.ekm = ekmFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.clientHello.random, hs.hello.random)
   129  	c.isHandshakeComplete.Store(true)
   130  
   131  	return nil
   132  }
   133  
   134  // readClientHello reads a ClientHello message and selects the protocol version.
   135  func (c *Conn) readClientHello(ctx context.Context) (*clientHelloMsg, *echServerContext, error) {
   136  	// clientHelloMsg is included in the transcript, but we haven't initialized
   137  	// it yet. The respective handshake functions will record it themselves.
   138  	msg, err := c.readHandshake(nil)
   139  	if err != nil {
   140  		return nil, nil, err
   141  	}
   142  	clientHello, ok := msg.(*clientHelloMsg)
   143  	if !ok {
   144  		c.sendAlert(alertUnexpectedMessage)
   145  		return nil, nil, unexpectedMessageError(clientHello, msg)
   146  	}
   147  
   148  	// ECH processing has to be done before we do any other negotiation based on
   149  	// the contents of the client hello, since we may swap it out completely.
   150  	var ech *echServerContext
   151  	if len(clientHello.encryptedClientHello) != 0 {
   152  		clientHello, ech, err = c.processECHClientHello(clientHello)
   153  		if err != nil {
   154  			return nil, nil, err
   155  		}
   156  	}
   157  
   158  	var configForClient *Config
   159  	originalConfig := c.config
   160  	if c.config.GetConfigForClient != nil {
   161  		chi := clientHelloInfo(ctx, c, clientHello)
   162  		if configForClient, err = c.config.GetConfigForClient(chi); err != nil {
   163  			c.sendAlert(alertInternalError)
   164  			return nil, nil, err
   165  		} else if configForClient != nil {
   166  			c.config = configForClient
   167  		}
   168  	}
   169  	c.ticketKeys = originalConfig.ticketKeys(configForClient)
   170  
   171  	clientVersions := clientHello.supportedVersions
   172  	if len(clientHello.supportedVersions) == 0 {
   173  		clientVersions = supportedVersionsFromMax(clientHello.vers)
   174  	}
   175  	c.vers, ok = c.config.mutualVersion(roleServer, clientVersions)
   176  	if !ok {
   177  		c.sendAlert(alertProtocolVersion)
   178  		return nil, nil, fmt.Errorf("tls: client offered only unsupported versions: %x", clientVersions)
   179  	}
   180  	c.haveVers = true
   181  	c.in.version = c.vers
   182  	c.out.version = c.vers
   183  
   184  	// This check reflects some odd specification implied behavior. Client-facing servers
   185  	// are supposed to reject hellos with outer ECH and inner ECH that offers 1.2, but
   186  	// backend servers are allowed to accept hellos with inner ECH that offer 1.2, since
   187  	// they cannot expect client-facing servers to behave properly. Since we act as both
   188  	// a client-facing and backend server, we only enforce 1.3 being negotiated if we
   189  	// saw a hello with outer ECH first. The spec probably should've made this an error,
   190  	// but it didn't, and this matches the boringssl behavior.
   191  	if c.vers != VersionTLS13 && (ech != nil && !ech.inner) {
   192  		c.sendAlert(alertIllegalParameter)
   193  		return nil, nil, errors.New("tls: Encrypted Client Hello cannot be used pre-TLS 1.3")
   194  	}
   195  
   196  	if c.config.MinVersion == 0 && c.vers < VersionTLS12 {
   197  		tls10server.Value() // ensure godebug is initialized
   198  		tls10server.IncNonDefault()
   199  	}
   200  
   201  	return clientHello, ech, nil
   202  }
   203  
   204  func (hs *serverHandshakeState) processClientHello() error {
   205  	c := hs.c
   206  
   207  	hs.hello = new(serverHelloMsg)
   208  	hs.hello.vers = c.vers
   209  
   210  	foundCompression := false
   211  	// We only support null compression, so check that the client offered it.
   212  	for _, compression := range hs.clientHello.compressionMethods {
   213  		if compression == compressionNone {
   214  			foundCompression = true
   215  			break
   216  		}
   217  	}
   218  
   219  	if !foundCompression {
   220  		c.sendAlert(alertHandshakeFailure)
   221  		return errors.New("tls: client does not support uncompressed connections")
   222  	}
   223  
   224  	hs.hello.random = make([]byte, 32)
   225  	serverRandom := hs.hello.random
   226  	// Downgrade protection canaries. See RFC 8446, Section 4.1.3.
   227  	maxVers := c.config.maxSupportedVersion(roleServer)
   228  	if maxVers >= VersionTLS12 && c.vers < maxVers || testingOnlyForceDowngradeCanary {
   229  		if c.vers == VersionTLS12 {
   230  			copy(serverRandom[24:], downgradeCanaryTLS12)
   231  		} else {
   232  			copy(serverRandom[24:], downgradeCanaryTLS11)
   233  		}
   234  		serverRandom = serverRandom[:24]
   235  	}
   236  	_, err := io.ReadFull(c.config.rand(), serverRandom)
   237  	if err != nil {
   238  		c.sendAlert(alertInternalError)
   239  		return err
   240  	}
   241  
   242  	if len(hs.clientHello.secureRenegotiation) != 0 {
   243  		c.sendAlert(alertHandshakeFailure)
   244  		return errors.New("tls: initial handshake had non-empty renegotiation extension")
   245  	}
   246  
   247  	hs.hello.extendedMasterSecret = hs.clientHello.extendedMasterSecret
   248  	hs.hello.secureRenegotiationSupported = hs.clientHello.secureRenegotiationSupported
   249  	hs.hello.compressionMethod = compressionNone
   250  	if len(hs.clientHello.serverName) > 0 {
   251  		c.serverName = hs.clientHello.serverName
   252  	}
   253  
   254  	selectedProto, err := negotiateALPN(c.config.NextProtos, hs.clientHello.alpnProtocols, false)
   255  	if err != nil {
   256  		c.sendAlert(alertNoApplicationProtocol)
   257  		return err
   258  	}
   259  	hs.hello.alpnProtocol = selectedProto
   260  	c.clientProtocol = selectedProto
   261  
   262  	hs.cert, err = c.config.getCertificate(clientHelloInfo(hs.ctx, c, hs.clientHello))
   263  	if err != nil {
   264  		if err == errNoCertificates {
   265  			c.sendAlert(alertUnrecognizedName)
   266  		} else {
   267  			c.sendAlert(alertInternalError)
   268  		}
   269  		return err
   270  	}
   271  	if hs.clientHello.scts {
   272  		hs.hello.scts = hs.cert.SignedCertificateTimestamps
   273  	}
   274  
   275  	hs.ecdheOk = supportsECDHE(c.config, c.vers, hs.clientHello.supportedCurves, hs.clientHello.supportedPoints)
   276  
   277  	if hs.ecdheOk && len(hs.clientHello.supportedPoints) > 0 {
   278  		// Although omitting the ec_point_formats extension is permitted, some
   279  		// old OpenSSL version will refuse to handshake if not present.
   280  		//
   281  		// Per RFC 4492, section 5.1.2, implementations MUST support the
   282  		// uncompressed point format. See golang.org/issue/31943.
   283  		hs.hello.supportedPoints = []uint8{pointFormatUncompressed}
   284  	}
   285  
   286  	if priv, ok := hs.cert.PrivateKey.(crypto.Signer); ok {
   287  		switch priv.Public().(type) {
   288  		case *ecdsa.PublicKey:
   289  			hs.ecSignOk = true
   290  		case ed25519.PublicKey:
   291  			hs.ecSignOk = true
   292  		case *rsa.PublicKey:
   293  			hs.rsaSignOk = true
   294  		default:
   295  			c.sendAlert(alertInternalError)
   296  			return fmt.Errorf("tls: unsupported signing key type (%T)", priv.Public())
   297  		}
   298  	}
   299  	if priv, ok := hs.cert.PrivateKey.(crypto.Decrypter); ok {
   300  		switch priv.Public().(type) {
   301  		case *rsa.PublicKey:
   302  			hs.rsaDecryptOk = true
   303  		default:
   304  			c.sendAlert(alertInternalError)
   305  			return fmt.Errorf("tls: unsupported decryption key type (%T)", priv.Public())
   306  		}
   307  	}
   308  
   309  	return nil
   310  }
   311  
   312  // negotiateALPN picks a shared ALPN protocol that both sides support in server
   313  // preference order. If ALPN is not configured or the peer doesn't support it,
   314  // it returns "" and no error.
   315  func negotiateALPN(serverProtos, clientProtos []string, quic bool) (string, error) {
   316  	if len(serverProtos) == 0 || len(clientProtos) == 0 {
   317  		if quic && len(serverProtos) != 0 {
   318  			// RFC 9001, Section 8.1
   319  			return "", fmt.Errorf("tls: client did not request an application protocol")
   320  		}
   321  		return "", nil
   322  	}
   323  	var http11fallback bool
   324  	for _, s := range serverProtos {
   325  		for _, c := range clientProtos {
   326  			if s == c {
   327  				return s, nil
   328  			}
   329  			if s == "h2" && c == "http/1.1" {
   330  				http11fallback = true
   331  			}
   332  		}
   333  	}
   334  	// As a special case, let http/1.1 clients connect to h2 servers as if they
   335  	// didn't support ALPN. We used not to enforce protocol overlap, so over
   336  	// time a number of HTTP servers were configured with only "h2", but
   337  	// expected to accept connections from "http/1.1" clients. See Issue 46310.
   338  	if http11fallback {
   339  		return "", nil
   340  	}
   341  	return "", fmt.Errorf("tls: client requested unsupported application protocols (%s)", clientProtos)
   342  }
   343  
   344  // supportsECDHE returns whether ECDHE key exchanges can be used with this
   345  // pre-TLS 1.3 client.
   346  func supportsECDHE(c *Config, version uint16, supportedCurves []CurveID, supportedPoints []uint8) bool {
   347  	supportsCurve := false
   348  	for _, curve := range supportedCurves {
   349  		if c.supportsCurve(version, curve) {
   350  			supportsCurve = true
   351  			break
   352  		}
   353  	}
   354  
   355  	supportsPointFormat := false
   356  	for _, pointFormat := range supportedPoints {
   357  		if pointFormat == pointFormatUncompressed {
   358  			supportsPointFormat = true
   359  			break
   360  		}
   361  	}
   362  	// Per RFC 8422, Section 5.1.2, if the Supported Point Formats extension is
   363  	// missing, uncompressed points are supported. If supportedPoints is empty,
   364  	// the extension must be missing, as an empty extension body is rejected by
   365  	// the parser. See https://go.dev/issue/49126.
   366  	if len(supportedPoints) == 0 {
   367  		supportsPointFormat = true
   368  	}
   369  
   370  	return supportsCurve && supportsPointFormat
   371  }
   372  
   373  func (hs *serverHandshakeState) pickCipherSuite() error {
   374  	c := hs.c
   375  
   376  	preferenceList := c.config.cipherSuites(isAESGCMPreferred(hs.clientHello.cipherSuites))
   377  
   378  	hs.suite = selectCipherSuite(preferenceList, hs.clientHello.cipherSuites, hs.cipherSuiteOk)
   379  	if hs.suite == nil {
   380  		c.sendAlert(alertHandshakeFailure)
   381  		return errors.New("tls: no cipher suite supported by both client and server")
   382  	}
   383  	c.cipherSuite = hs.suite.id
   384  
   385  	if c.config.CipherSuites == nil && !fips140tls.Required() && rsaKexCiphers[hs.suite.id] {
   386  		tlsrsakex.Value() // ensure godebug is initialized
   387  		tlsrsakex.IncNonDefault()
   388  	}
   389  	if c.config.CipherSuites == nil && !fips140tls.Required() && tdesCiphers[hs.suite.id] {
   390  		tls3des.Value() // ensure godebug is initialized
   391  		tls3des.IncNonDefault()
   392  	}
   393  
   394  	for _, id := range hs.clientHello.cipherSuites {
   395  		if id == TLS_FALLBACK_SCSV {
   396  			// The client is doing a fallback connection. See RFC 7507.
   397  			if hs.clientHello.vers < c.config.maxSupportedVersion(roleServer) {
   398  				c.sendAlert(alertInappropriateFallback)
   399  				return errors.New("tls: client using inappropriate protocol fallback")
   400  			}
   401  			break
   402  		}
   403  	}
   404  
   405  	return nil
   406  }
   407  
   408  func (hs *serverHandshakeState) cipherSuiteOk(c *cipherSuite) bool {
   409  	if c.flags&suiteECDHE != 0 {
   410  		if !hs.ecdheOk {
   411  			return false
   412  		}
   413  		if c.flags&suiteECSign != 0 {
   414  			if !hs.ecSignOk {
   415  				return false
   416  			}
   417  		} else if !hs.rsaSignOk {
   418  			return false
   419  		}
   420  	} else if !hs.rsaDecryptOk {
   421  		return false
   422  	}
   423  	if hs.c.vers < VersionTLS12 && c.flags&suiteTLS12 != 0 {
   424  		return false
   425  	}
   426  	return true
   427  }
   428  
   429  // checkForResumption reports whether we should perform resumption on this connection.
   430  func (hs *serverHandshakeState) checkForResumption() error {
   431  	c := hs.c
   432  
   433  	if c.config.SessionTicketsDisabled {
   434  		return nil
   435  	}
   436  
   437  	var sessionState *SessionState
   438  	if c.config.UnwrapSession != nil {
   439  		ss, err := c.config.UnwrapSession(hs.clientHello.sessionTicket, c.connectionStateLocked())
   440  		if err != nil {
   441  			return err
   442  		}
   443  		if ss == nil {
   444  			return nil
   445  		}
   446  		sessionState = ss
   447  	} else {
   448  		plaintext := c.config.decryptTicket(hs.clientHello.sessionTicket, c.ticketKeys)
   449  		if plaintext == nil {
   450  			return nil
   451  		}
   452  		ss, err := ParseSessionState(plaintext)
   453  		if err != nil {
   454  			return nil
   455  		}
   456  		sessionState = ss
   457  	}
   458  
   459  	// TLS 1.2 tickets don't natively have a lifetime, but we want to avoid
   460  	// re-wrapping the same master secret in different tickets over and over for
   461  	// too long, weakening forward secrecy.
   462  	createdAt := time.Unix(int64(sessionState.createdAt), 0)
   463  	if c.config.time().Sub(createdAt) > maxSessionTicketLifetime {
   464  		return nil
   465  	}
   466  
   467  	// Never resume a session for a different TLS version.
   468  	if c.vers != sessionState.version {
   469  		return nil
   470  	}
   471  
   472  	cipherSuiteOk := false
   473  	// Check that the client is still offering the ciphersuite in the session.
   474  	for _, id := range hs.clientHello.cipherSuites {
   475  		if id == sessionState.cipherSuite {
   476  			cipherSuiteOk = true
   477  			break
   478  		}
   479  	}
   480  	if !cipherSuiteOk {
   481  		return nil
   482  	}
   483  
   484  	// Check that we also support the ciphersuite from the session.
   485  	suite := selectCipherSuite([]uint16{sessionState.cipherSuite},
   486  		c.config.supportedCipherSuites(), hs.cipherSuiteOk)
   487  	if suite == nil {
   488  		return nil
   489  	}
   490  
   491  	sessionHasClientCerts := len(sessionState.peerCertificates) != 0
   492  	needClientCerts := requiresClientCert(c.config.ClientAuth)
   493  	if needClientCerts && !sessionHasClientCerts {
   494  		return nil
   495  	}
   496  	if sessionHasClientCerts && c.config.ClientAuth == NoClientCert {
   497  		return nil
   498  	}
   499  	if sessionHasClientCerts && c.config.time().After(sessionState.peerCertificates[0].NotAfter) {
   500  		return nil
   501  	}
   502  	if sessionHasClientCerts && c.config.ClientAuth >= VerifyClientCertIfGiven &&
   503  		len(sessionState.verifiedChains) == 0 {
   504  		return nil
   505  	}
   506  
   507  	// RFC 7627, Section 5.3
   508  	if !sessionState.extMasterSecret && hs.clientHello.extendedMasterSecret {
   509  		return nil
   510  	}
   511  	if sessionState.extMasterSecret && !hs.clientHello.extendedMasterSecret {
   512  		// Aborting is somewhat harsh, but it's a MUST and it would indicate a
   513  		// weird downgrade in client capabilities.
   514  		return errors.New("tls: session supported extended_master_secret but client does not")
   515  	}
   516  	if !sessionState.extMasterSecret && fips140tls.Required() {
   517  		// FIPS 140-3 requires the use of Extended Master Secret.
   518  		return nil
   519  	}
   520  
   521  	c.peerCertificates = sessionState.peerCertificates
   522  	c.ocspResponse = sessionState.ocspResponse
   523  	c.scts = sessionState.scts
   524  	c.verifiedChains = sessionState.verifiedChains
   525  	c.extMasterSecret = sessionState.extMasterSecret
   526  	hs.sessionState = sessionState
   527  	hs.suite = suite
   528  	c.curveID = sessionState.curveID
   529  	c.didResume = true
   530  	return nil
   531  }
   532  
   533  func (hs *serverHandshakeState) doResumeHandshake() error {
   534  	c := hs.c
   535  
   536  	hs.hello.cipherSuite = hs.suite.id
   537  	c.cipherSuite = hs.suite.id
   538  	// We echo the client's session ID in the ServerHello to let it know
   539  	// that we're doing a resumption.
   540  	hs.hello.sessionId = hs.clientHello.sessionId
   541  	// We always send a new session ticket, even if it wraps the same master
   542  	// secret and it's potentially encrypted with the same key, to help the
   543  	// client avoid cross-connection tracking from a network observer.
   544  	hs.hello.ticketSupported = true
   545  	hs.finishedHash = newFinishedHash(c.vers, hs.suite)
   546  	hs.finishedHash.discardHandshakeBuffer()
   547  	if err := transcriptMsg(hs.clientHello, &hs.finishedHash); err != nil {
   548  		return err
   549  	}
   550  	if _, err := hs.c.writeHandshakeRecord(hs.hello, &hs.finishedHash); err != nil {
   551  		return err
   552  	}
   553  
   554  	if c.config.VerifyConnection != nil {
   555  		if err := c.config.VerifyConnection(c.connectionStateLocked()); err != nil {
   556  			c.sendAlert(alertBadCertificate)
   557  			return err
   558  		}
   559  	}
   560  
   561  	hs.masterSecret = hs.sessionState.secret
   562  
   563  	return nil
   564  }
   565  
   566  func (hs *serverHandshakeState) doFullHandshake() error {
   567  	c := hs.c
   568  
   569  	if hs.clientHello.ocspStapling && len(hs.cert.OCSPStaple) > 0 {
   570  		hs.hello.ocspStapling = true
   571  	}
   572  
   573  	hs.hello.ticketSupported = hs.clientHello.ticketSupported && !c.config.SessionTicketsDisabled
   574  	hs.hello.cipherSuite = hs.suite.id
   575  
   576  	hs.finishedHash = newFinishedHash(hs.c.vers, hs.suite)
   577  	if c.config.ClientAuth == NoClientCert {
   578  		// No need to keep a full record of the handshake if client
   579  		// certificates won't be used.
   580  		hs.finishedHash.discardHandshakeBuffer()
   581  	}
   582  	if err := transcriptMsg(hs.clientHello, &hs.finishedHash); err != nil {
   583  		return err
   584  	}
   585  	if _, err := hs.c.writeHandshakeRecord(hs.hello, &hs.finishedHash); err != nil {
   586  		return err
   587  	}
   588  
   589  	certMsg := new(certificateMsg)
   590  	certMsg.certificates = hs.cert.Certificate
   591  	if _, err := hs.c.writeHandshakeRecord(certMsg, &hs.finishedHash); err != nil {
   592  		return err
   593  	}
   594  
   595  	if hs.hello.ocspStapling {
   596  		certStatus := new(certificateStatusMsg)
   597  		certStatus.response = hs.cert.OCSPStaple
   598  		if _, err := hs.c.writeHandshakeRecord(certStatus, &hs.finishedHash); err != nil {
   599  			return err
   600  		}
   601  	}
   602  
   603  	keyAgreement := hs.suite.ka(c.vers)
   604  	skx, err := keyAgreement.generateServerKeyExchange(c.config, hs.cert, hs.clientHello, hs.hello)
   605  	if err != nil {
   606  		c.sendAlert(alertHandshakeFailure)
   607  		return err
   608  	}
   609  	if skx != nil {
   610  		if len(skx.key) >= 3 && skx.key[0] == 3 /* named curve */ {
   611  			c.curveID = CurveID(byteorder.BEUint16(skx.key[1:]))
   612  		}
   613  		if _, err := hs.c.writeHandshakeRecord(skx, &hs.finishedHash); err != nil {
   614  			return err
   615  		}
   616  	}
   617  
   618  	var certReq *certificateRequestMsg
   619  	if c.config.ClientAuth >= RequestClientCert {
   620  		// Request a client certificate
   621  		certReq = new(certificateRequestMsg)
   622  		certReq.certificateTypes = []byte{
   623  			byte(certTypeRSASign),
   624  			byte(certTypeECDSASign),
   625  		}
   626  		if c.vers >= VersionTLS12 {
   627  			certReq.hasSignatureAlgorithm = true
   628  			certReq.supportedSignatureAlgorithms = supportedSignatureAlgorithms()
   629  		}
   630  
   631  		// An empty list of certificateAuthorities signals to
   632  		// the client that it may send any certificate in response
   633  		// to our request. When we know the CAs we trust, then
   634  		// we can send them down, so that the client can choose
   635  		// an appropriate certificate to give to us.
   636  		if c.config.ClientCAs != nil {
   637  			certReq.certificateAuthorities = c.config.ClientCAs.Subjects()
   638  		}
   639  		if _, err := hs.c.writeHandshakeRecord(certReq, &hs.finishedHash); err != nil {
   640  			return err
   641  		}
   642  	}
   643  
   644  	helloDone := new(serverHelloDoneMsg)
   645  	if _, err := hs.c.writeHandshakeRecord(helloDone, &hs.finishedHash); err != nil {
   646  		return err
   647  	}
   648  
   649  	if _, err := c.flush(); err != nil {
   650  		return err
   651  	}
   652  
   653  	var pub crypto.PublicKey // public key for client auth, if any
   654  
   655  	msg, err := c.readHandshake(&hs.finishedHash)
   656  	if err != nil {
   657  		return err
   658  	}
   659  
   660  	// If we requested a client certificate, then the client must send a
   661  	// certificate message, even if it's empty.
   662  	if c.config.ClientAuth >= RequestClientCert {
   663  		certMsg, ok := msg.(*certificateMsg)
   664  		if !ok {
   665  			c.sendAlert(alertUnexpectedMessage)
   666  			return unexpectedMessageError(certMsg, msg)
   667  		}
   668  
   669  		if err := c.processCertsFromClient(Certificate{
   670  			Certificate: certMsg.certificates,
   671  		}); err != nil {
   672  			return err
   673  		}
   674  		if len(certMsg.certificates) != 0 {
   675  			pub = c.peerCertificates[0].PublicKey
   676  		}
   677  
   678  		msg, err = c.readHandshake(&hs.finishedHash)
   679  		if err != nil {
   680  			return err
   681  		}
   682  	}
   683  	if c.config.VerifyConnection != nil {
   684  		if err := c.config.VerifyConnection(c.connectionStateLocked()); err != nil {
   685  			c.sendAlert(alertBadCertificate)
   686  			return err
   687  		}
   688  	}
   689  
   690  	// Get client key exchange
   691  	ckx, ok := msg.(*clientKeyExchangeMsg)
   692  	if !ok {
   693  		c.sendAlert(alertUnexpectedMessage)
   694  		return unexpectedMessageError(ckx, msg)
   695  	}
   696  
   697  	preMasterSecret, err := keyAgreement.processClientKeyExchange(c.config, hs.cert, ckx, c.vers)
   698  	if err != nil {
   699  		c.sendAlert(alertIllegalParameter)
   700  		return err
   701  	}
   702  	if hs.hello.extendedMasterSecret {
   703  		c.extMasterSecret = true
   704  		hs.masterSecret = extMasterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret,
   705  			hs.finishedHash.Sum())
   706  	} else {
   707  		if fips140tls.Required() {
   708  			c.sendAlert(alertHandshakeFailure)
   709  			return errors.New("tls: FIPS 140-3 requires the use of Extended Master Secret")
   710  		}
   711  		hs.masterSecret = masterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret,
   712  			hs.clientHello.random, hs.hello.random)
   713  	}
   714  	if err := c.config.writeKeyLog(keyLogLabelTLS12, hs.clientHello.random, hs.masterSecret); err != nil {
   715  		c.sendAlert(alertInternalError)
   716  		return err
   717  	}
   718  
   719  	// If we received a client cert in response to our certificate request message,
   720  	// the client will send us a certificateVerifyMsg immediately after the
   721  	// clientKeyExchangeMsg. This message is a digest of all preceding
   722  	// handshake-layer messages that is signed using the private key corresponding
   723  	// to the client's certificate. This allows us to verify that the client is in
   724  	// possession of the private key of the certificate.
   725  	if len(c.peerCertificates) > 0 {
   726  		// certificateVerifyMsg is included in the transcript, but not until
   727  		// after we verify the handshake signature, since the state before
   728  		// this message was sent is used.
   729  		msg, err = c.readHandshake(nil)
   730  		if err != nil {
   731  			return err
   732  		}
   733  		certVerify, ok := msg.(*certificateVerifyMsg)
   734  		if !ok {
   735  			c.sendAlert(alertUnexpectedMessage)
   736  			return unexpectedMessageError(certVerify, msg)
   737  		}
   738  
   739  		var sigType uint8
   740  		var sigHash crypto.Hash
   741  		if c.vers >= VersionTLS12 {
   742  			if !isSupportedSignatureAlgorithm(certVerify.signatureAlgorithm, certReq.supportedSignatureAlgorithms) {
   743  				c.sendAlert(alertIllegalParameter)
   744  				return errors.New("tls: client certificate used with invalid signature algorithm")
   745  			}
   746  			sigType, sigHash, err = typeAndHashFromSignatureScheme(certVerify.signatureAlgorithm)
   747  			if err != nil {
   748  				return c.sendAlert(alertInternalError)
   749  			}
   750  		} else {
   751  			sigType, sigHash, err = legacyTypeAndHashFromPublicKey(pub)
   752  			if err != nil {
   753  				c.sendAlert(alertIllegalParameter)
   754  				return err
   755  			}
   756  		}
   757  
   758  		signed := hs.finishedHash.hashForClientCertificate(sigType, sigHash)
   759  		if err := verifyHandshakeSignature(sigType, pub, sigHash, signed, certVerify.signature); err != nil {
   760  			c.sendAlert(alertDecryptError)
   761  			return errors.New("tls: invalid signature by the client certificate: " + err.Error())
   762  		}
   763  
   764  		if err := transcriptMsg(certVerify, &hs.finishedHash); err != nil {
   765  			return err
   766  		}
   767  	}
   768  
   769  	hs.finishedHash.discardHandshakeBuffer()
   770  
   771  	return nil
   772  }
   773  
   774  func (hs *serverHandshakeState) establishKeys() error {
   775  	c := hs.c
   776  
   777  	clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV :=
   778  		keysFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.clientHello.random, hs.hello.random, hs.suite.macLen, hs.suite.keyLen, hs.suite.ivLen)
   779  
   780  	var clientCipher, serverCipher any
   781  	var clientHash, serverHash hash.Hash
   782  
   783  	if hs.suite.aead == nil {
   784  		clientCipher = hs.suite.cipher(clientKey, clientIV, true /* for reading */)
   785  		clientHash = hs.suite.mac(clientMAC)
   786  		serverCipher = hs.suite.cipher(serverKey, serverIV, false /* not for reading */)
   787  		serverHash = hs.suite.mac(serverMAC)
   788  	} else {
   789  		clientCipher = hs.suite.aead(clientKey, clientIV)
   790  		serverCipher = hs.suite.aead(serverKey, serverIV)
   791  	}
   792  
   793  	c.in.prepareCipherSpec(c.vers, clientCipher, clientHash)
   794  	c.out.prepareCipherSpec(c.vers, serverCipher, serverHash)
   795  
   796  	return nil
   797  }
   798  
   799  func (hs *serverHandshakeState) readFinished(out []byte) error {
   800  	c := hs.c
   801  
   802  	if err := c.readChangeCipherSpec(); err != nil {
   803  		return err
   804  	}
   805  
   806  	// finishedMsg is included in the transcript, but not until after we
   807  	// check the client version, since the state before this message was
   808  	// sent is used during verification.
   809  	msg, err := c.readHandshake(nil)
   810  	if err != nil {
   811  		return err
   812  	}
   813  	clientFinished, ok := msg.(*finishedMsg)
   814  	if !ok {
   815  		c.sendAlert(alertUnexpectedMessage)
   816  		return unexpectedMessageError(clientFinished, msg)
   817  	}
   818  
   819  	verify := hs.finishedHash.clientSum(hs.masterSecret)
   820  	if len(verify) != len(clientFinished.verifyData) ||
   821  		subtle.ConstantTimeCompare(verify, clientFinished.verifyData) != 1 {
   822  		c.sendAlert(alertHandshakeFailure)
   823  		return errors.New("tls: client's Finished message is incorrect")
   824  	}
   825  
   826  	if err := transcriptMsg(clientFinished, &hs.finishedHash); err != nil {
   827  		return err
   828  	}
   829  
   830  	copy(out, verify)
   831  	return nil
   832  }
   833  
   834  func (hs *serverHandshakeState) sendSessionTicket() error {
   835  	if !hs.hello.ticketSupported {
   836  		return nil
   837  	}
   838  
   839  	c := hs.c
   840  	m := new(newSessionTicketMsg)
   841  
   842  	state := c.sessionState()
   843  	state.secret = hs.masterSecret
   844  	if hs.sessionState != nil {
   845  		// If this is re-wrapping an old key, then keep
   846  		// the original time it was created.
   847  		state.createdAt = hs.sessionState.createdAt
   848  	}
   849  	if c.config.WrapSession != nil {
   850  		var err error
   851  		m.ticket, err = c.config.WrapSession(c.connectionStateLocked(), state)
   852  		if err != nil {
   853  			return err
   854  		}
   855  	} else {
   856  		stateBytes, err := state.Bytes()
   857  		if err != nil {
   858  			return err
   859  		}
   860  		m.ticket, err = c.config.encryptTicket(stateBytes, c.ticketKeys)
   861  		if err != nil {
   862  			return err
   863  		}
   864  	}
   865  
   866  	if _, err := hs.c.writeHandshakeRecord(m, &hs.finishedHash); err != nil {
   867  		return err
   868  	}
   869  
   870  	return nil
   871  }
   872  
   873  func (hs *serverHandshakeState) sendFinished(out []byte) error {
   874  	c := hs.c
   875  
   876  	if err := c.writeChangeCipherRecord(); err != nil {
   877  		return err
   878  	}
   879  
   880  	finished := new(finishedMsg)
   881  	finished.verifyData = hs.finishedHash.serverSum(hs.masterSecret)
   882  	if _, err := hs.c.writeHandshakeRecord(finished, &hs.finishedHash); err != nil {
   883  		return err
   884  	}
   885  
   886  	copy(out, finished.verifyData)
   887  
   888  	return nil
   889  }
   890  
   891  // processCertsFromClient takes a chain of client certificates either from a
   892  // Certificates message and verifies them.
   893  func (c *Conn) processCertsFromClient(certificate Certificate) error {
   894  	certificates := certificate.Certificate
   895  	certs := make([]*x509.Certificate, len(certificates))
   896  	var err error
   897  	for i, asn1Data := range certificates {
   898  		if certs[i], err = x509.ParseCertificate(asn1Data); err != nil {
   899  			c.sendAlert(alertDecodeError)
   900  			return errors.New("tls: failed to parse client certificate: " + err.Error())
   901  		}
   902  		if certs[i].PublicKeyAlgorithm == x509.RSA {
   903  			n := certs[i].PublicKey.(*rsa.PublicKey).N.BitLen()
   904  			if max, ok := checkKeySize(n); !ok {
   905  				c.sendAlert(alertBadCertificate)
   906  				return fmt.Errorf("tls: client sent certificate containing RSA key larger than %d bits", max)
   907  			}
   908  		}
   909  	}
   910  
   911  	if len(certs) == 0 && requiresClientCert(c.config.ClientAuth) {
   912  		if c.vers == VersionTLS13 {
   913  			c.sendAlert(alertCertificateRequired)
   914  		} else {
   915  			c.sendAlert(alertBadCertificate)
   916  		}
   917  		return errors.New("tls: client didn't provide a certificate")
   918  	}
   919  
   920  	if c.config.ClientAuth >= VerifyClientCertIfGiven && len(certs) > 0 {
   921  		opts := x509.VerifyOptions{
   922  			Roots:         c.config.ClientCAs,
   923  			CurrentTime:   c.config.time(),
   924  			Intermediates: x509.NewCertPool(),
   925  			KeyUsages:     []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
   926  		}
   927  
   928  		for _, cert := range certs[1:] {
   929  			opts.Intermediates.AddCert(cert)
   930  		}
   931  
   932  		chains, err := certs[0].Verify(opts)
   933  		if err != nil {
   934  			var errCertificateInvalid x509.CertificateInvalidError
   935  			if errors.As(err, &x509.UnknownAuthorityError{}) {
   936  				c.sendAlert(alertUnknownCA)
   937  			} else if errors.As(err, &errCertificateInvalid) && errCertificateInvalid.Reason == x509.Expired {
   938  				c.sendAlert(alertCertificateExpired)
   939  			} else {
   940  				c.sendAlert(alertBadCertificate)
   941  			}
   942  			return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
   943  		}
   944  
   945  		c.verifiedChains, err = fipsAllowedChains(chains)
   946  		if err != nil {
   947  			c.sendAlert(alertBadCertificate)
   948  			return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
   949  		}
   950  	}
   951  
   952  	c.peerCertificates = certs
   953  	c.ocspResponse = certificate.OCSPStaple
   954  	c.scts = certificate.SignedCertificateTimestamps
   955  
   956  	if len(certs) > 0 {
   957  		switch certs[0].PublicKey.(type) {
   958  		case *ecdsa.PublicKey, *rsa.PublicKey, ed25519.PublicKey:
   959  		default:
   960  			c.sendAlert(alertUnsupportedCertificate)
   961  			return fmt.Errorf("tls: client certificate contains an unsupported public key of type %T", certs[0].PublicKey)
   962  		}
   963  	}
   964  
   965  	if c.config.VerifyPeerCertificate != nil {
   966  		if err := c.config.VerifyPeerCertificate(certificates, c.verifiedChains); err != nil {
   967  			c.sendAlert(alertBadCertificate)
   968  			return err
   969  		}
   970  	}
   971  
   972  	return nil
   973  }
   974  
   975  func clientHelloInfo(ctx context.Context, c *Conn, clientHello *clientHelloMsg) *ClientHelloInfo {
   976  	supportedVersions := clientHello.supportedVersions
   977  	if len(clientHello.supportedVersions) == 0 {
   978  		supportedVersions = supportedVersionsFromMax(clientHello.vers)
   979  	}
   980  
   981  	return &ClientHelloInfo{
   982  		CipherSuites:      clientHello.cipherSuites,
   983  		ServerName:        clientHello.serverName,
   984  		SupportedCurves:   clientHello.supportedCurves,
   985  		SupportedPoints:   clientHello.supportedPoints,
   986  		SignatureSchemes:  clientHello.supportedSignatureAlgorithms,
   987  		SupportedProtos:   clientHello.alpnProtocols,
   988  		SupportedVersions: supportedVersions,
   989  		Extensions:        clientHello.extensions,
   990  		Conn:              c.conn,
   991  		config:            c.config,
   992  		ctx:               ctx,
   993  	}
   994  }
   995  

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