Source file src/crypto/tls/handshake_client.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package tls
     6  
     7  import (
     8  	"bytes"
     9  	"context"
    10  	"crypto"
    11  	"crypto/ecdsa"
    12  	"crypto/ed25519"
    13  	"crypto/internal/hpke"
    14  	"crypto/internal/mlkem768"
    15  	"crypto/rsa"
    16  	"crypto/subtle"
    17  	"crypto/x509"
    18  	"errors"
    19  	"fmt"
    20  	"hash"
    21  	"internal/byteorder"
    22  	"internal/godebug"
    23  	"io"
    24  	"net"
    25  	"strconv"
    26  	"strings"
    27  	"time"
    28  )
    29  
    30  type clientHandshakeState struct {
    31  	c            *Conn
    32  	ctx          context.Context
    33  	serverHello  *serverHelloMsg
    34  	hello        *clientHelloMsg
    35  	suite        *cipherSuite
    36  	finishedHash finishedHash
    37  	masterSecret []byte
    38  	session      *SessionState // the session being resumed
    39  	ticket       []byte        // a fresh ticket received during this handshake
    40  }
    41  
    42  var testingOnlyForceClientHelloSignatureAlgorithms []SignatureScheme
    43  
    44  func (c *Conn) makeClientHello() (*clientHelloMsg, *keySharePrivateKeys, *echContext, error) {
    45  	config := c.config
    46  	if len(config.ServerName) == 0 && !config.InsecureSkipVerify {
    47  		return nil, nil, nil, errors.New("tls: either ServerName or InsecureSkipVerify must be specified in the tls.Config")
    48  	}
    49  
    50  	nextProtosLength := 0
    51  	for _, proto := range config.NextProtos {
    52  		if l := len(proto); l == 0 || l > 255 {
    53  			return nil, nil, nil, errors.New("tls: invalid NextProtos value")
    54  		} else {
    55  			nextProtosLength += 1 + l
    56  		}
    57  	}
    58  	if nextProtosLength > 0xffff {
    59  		return nil, nil, nil, errors.New("tls: NextProtos values too large")
    60  	}
    61  
    62  	supportedVersions := config.supportedVersions(roleClient)
    63  	if len(supportedVersions) == 0 {
    64  		return nil, nil, nil, errors.New("tls: no supported versions satisfy MinVersion and MaxVersion")
    65  	}
    66  	maxVersion := config.maxSupportedVersion(roleClient)
    67  
    68  	hello := &clientHelloMsg{
    69  		vers:                         maxVersion,
    70  		compressionMethods:           []uint8{compressionNone},
    71  		random:                       make([]byte, 32),
    72  		extendedMasterSecret:         true,
    73  		ocspStapling:                 true,
    74  		scts:                         true,
    75  		serverName:                   hostnameInSNI(config.ServerName),
    76  		supportedCurves:              config.curvePreferences(maxVersion),
    77  		supportedPoints:              []uint8{pointFormatUncompressed},
    78  		secureRenegotiationSupported: true,
    79  		alpnProtocols:                config.NextProtos,
    80  		supportedVersions:            supportedVersions,
    81  	}
    82  
    83  	// The version at the beginning of the ClientHello was capped at TLS 1.2
    84  	// for compatibility reasons. The supported_versions extension is used
    85  	// to negotiate versions now. See RFC 8446, Section 4.2.1.
    86  	if hello.vers > VersionTLS12 {
    87  		hello.vers = VersionTLS12
    88  	}
    89  
    90  	if c.handshakes > 0 {
    91  		hello.secureRenegotiation = c.clientFinished[:]
    92  	}
    93  
    94  	preferenceOrder := cipherSuitesPreferenceOrder
    95  	if !hasAESGCMHardwareSupport {
    96  		preferenceOrder = cipherSuitesPreferenceOrderNoAES
    97  	}
    98  	configCipherSuites := config.cipherSuites()
    99  	hello.cipherSuites = make([]uint16, 0, len(configCipherSuites))
   100  
   101  	for _, suiteId := range preferenceOrder {
   102  		suite := mutualCipherSuite(configCipherSuites, suiteId)
   103  		if suite == nil {
   104  			continue
   105  		}
   106  		// Don't advertise TLS 1.2-only cipher suites unless
   107  		// we're attempting TLS 1.2.
   108  		if maxVersion < VersionTLS12 && suite.flags&suiteTLS12 != 0 {
   109  			continue
   110  		}
   111  		hello.cipherSuites = append(hello.cipherSuites, suiteId)
   112  	}
   113  
   114  	_, err := io.ReadFull(config.rand(), hello.random)
   115  	if err != nil {
   116  		return nil, nil, nil, errors.New("tls: short read from Rand: " + err.Error())
   117  	}
   118  
   119  	// A random session ID is used to detect when the server accepted a ticket
   120  	// and is resuming a session (see RFC 5077). In TLS 1.3, it's always set as
   121  	// a compatibility measure (see RFC 8446, Section 4.1.2).
   122  	//
   123  	// The session ID is not set for QUIC connections (see RFC 9001, Section 8.4).
   124  	if c.quic == nil {
   125  		hello.sessionId = make([]byte, 32)
   126  		if _, err := io.ReadFull(config.rand(), hello.sessionId); err != nil {
   127  			return nil, nil, nil, errors.New("tls: short read from Rand: " + err.Error())
   128  		}
   129  	}
   130  
   131  	if maxVersion >= VersionTLS12 {
   132  		hello.supportedSignatureAlgorithms = supportedSignatureAlgorithms()
   133  	}
   134  	if testingOnlyForceClientHelloSignatureAlgorithms != nil {
   135  		hello.supportedSignatureAlgorithms = testingOnlyForceClientHelloSignatureAlgorithms
   136  	}
   137  
   138  	var keyShareKeys *keySharePrivateKeys
   139  	if hello.supportedVersions[0] == VersionTLS13 {
   140  		// Reset the list of ciphers when the client only supports TLS 1.3.
   141  		if len(hello.supportedVersions) == 1 {
   142  			hello.cipherSuites = nil
   143  		}
   144  		if hasAESGCMHardwareSupport {
   145  			hello.cipherSuites = append(hello.cipherSuites, defaultCipherSuitesTLS13...)
   146  		} else {
   147  			hello.cipherSuites = append(hello.cipherSuites, defaultCipherSuitesTLS13NoAES...)
   148  		}
   149  
   150  		curveID := config.curvePreferences(maxVersion)[0]
   151  		keyShareKeys = &keySharePrivateKeys{curveID: curveID}
   152  		if curveID == x25519Kyber768Draft00 {
   153  			keyShareKeys.ecdhe, err = generateECDHEKey(config.rand(), X25519)
   154  			if err != nil {
   155  				return nil, nil, nil, err
   156  			}
   157  			seed := make([]byte, mlkem768.SeedSize)
   158  			if _, err := io.ReadFull(config.rand(), seed); err != nil {
   159  				return nil, nil, nil, err
   160  			}
   161  			keyShareKeys.kyber, err = mlkem768.NewKeyFromSeed(seed)
   162  			if err != nil {
   163  				return nil, nil, nil, err
   164  			}
   165  			// For draft-tls-westerbaan-xyber768d00-03, we send both a hybrid
   166  			// and a standard X25519 key share, since most servers will only
   167  			// support the latter. We reuse the same X25519 ephemeral key for
   168  			// both, as allowed by draft-ietf-tls-hybrid-design-09, Section 3.2.
   169  			hello.keyShares = []keyShare{
   170  				{group: x25519Kyber768Draft00, data: append(keyShareKeys.ecdhe.PublicKey().Bytes(),
   171  					keyShareKeys.kyber.EncapsulationKey()...)},
   172  				{group: X25519, data: keyShareKeys.ecdhe.PublicKey().Bytes()},
   173  			}
   174  		} else {
   175  			if _, ok := curveForCurveID(curveID); !ok {
   176  				return nil, nil, nil, errors.New("tls: CurvePreferences includes unsupported curve")
   177  			}
   178  			keyShareKeys.ecdhe, err = generateECDHEKey(config.rand(), curveID)
   179  			if err != nil {
   180  				return nil, nil, nil, err
   181  			}
   182  			hello.keyShares = []keyShare{{group: curveID, data: keyShareKeys.ecdhe.PublicKey().Bytes()}}
   183  		}
   184  	}
   185  
   186  	if c.quic != nil {
   187  		p, err := c.quicGetTransportParameters()
   188  		if err != nil {
   189  			return nil, nil, nil, err
   190  		}
   191  		if p == nil {
   192  			p = []byte{}
   193  		}
   194  		hello.quicTransportParameters = p
   195  	}
   196  
   197  	var ech *echContext
   198  	if c.config.EncryptedClientHelloConfigList != nil {
   199  		if c.config.MinVersion != 0 && c.config.MinVersion < VersionTLS13 {
   200  			return nil, nil, nil, errors.New("tls: MinVersion must be >= VersionTLS13 if EncryptedClientHelloConfigList is populated")
   201  		}
   202  		if c.config.MaxVersion != 0 && c.config.MaxVersion <= VersionTLS12 {
   203  			return nil, nil, nil, errors.New("tls: MaxVersion must be >= VersionTLS13 if EncryptedClientHelloConfigList is populated")
   204  		}
   205  		echConfigs, err := parseECHConfigList(c.config.EncryptedClientHelloConfigList)
   206  		if err != nil {
   207  			return nil, nil, nil, err
   208  		}
   209  		echConfig := pickECHConfig(echConfigs)
   210  		if echConfig == nil {
   211  			return nil, nil, nil, errors.New("tls: EncryptedClientHelloConfigList contains no valid configs")
   212  		}
   213  		ech = &echContext{config: echConfig}
   214  		hello.encryptedClientHello = []byte{1} // indicate inner hello
   215  		// We need to explicitly set these 1.2 fields to nil, as we do not
   216  		// marshal them when encoding the inner hello, otherwise transcripts
   217  		// will later mismatch.
   218  		hello.supportedPoints = nil
   219  		hello.ticketSupported = false
   220  		hello.secureRenegotiationSupported = false
   221  		hello.extendedMasterSecret = false
   222  
   223  		echPK, err := hpke.ParseHPKEPublicKey(ech.config.KemID, ech.config.PublicKey)
   224  		if err != nil {
   225  			return nil, nil, nil, err
   226  		}
   227  		suite, err := pickECHCipherSuite(ech.config.SymmetricCipherSuite)
   228  		if err != nil {
   229  			return nil, nil, nil, err
   230  		}
   231  		ech.kdfID, ech.aeadID = suite.KDFID, suite.AEADID
   232  		info := append([]byte("tls ech\x00"), ech.config.raw...)
   233  		ech.encapsulatedKey, ech.hpkeContext, err = hpke.SetupSender(ech.config.KemID, suite.KDFID, suite.AEADID, echPK, info)
   234  		if err != nil {
   235  			return nil, nil, nil, err
   236  		}
   237  	}
   238  
   239  	return hello, keyShareKeys, ech, nil
   240  }
   241  
   242  type echContext struct {
   243  	config          *echConfig
   244  	hpkeContext     *hpke.Sender
   245  	encapsulatedKey []byte
   246  	innerHello      *clientHelloMsg
   247  	innerTranscript hash.Hash
   248  	kdfID           uint16
   249  	aeadID          uint16
   250  	echRejected     bool
   251  }
   252  
   253  func (c *Conn) clientHandshake(ctx context.Context) (err error) {
   254  	if c.config == nil {
   255  		c.config = defaultConfig()
   256  	}
   257  
   258  	// This may be a renegotiation handshake, in which case some fields
   259  	// need to be reset.
   260  	c.didResume = false
   261  
   262  	hello, keyShareKeys, ech, err := c.makeClientHello()
   263  	if err != nil {
   264  		return err
   265  	}
   266  
   267  	session, earlySecret, binderKey, err := c.loadSession(hello)
   268  	if err != nil {
   269  		return err
   270  	}
   271  	if session != nil {
   272  		defer func() {
   273  			// If we got a handshake failure when resuming a session, throw away
   274  			// the session ticket. See RFC 5077, Section 3.2.
   275  			//
   276  			// RFC 8446 makes no mention of dropping tickets on failure, but it
   277  			// does require servers to abort on invalid binders, so we need to
   278  			// delete tickets to recover from a corrupted PSK.
   279  			if err != nil {
   280  				if cacheKey := c.clientSessionCacheKey(); cacheKey != "" {
   281  					c.config.ClientSessionCache.Put(cacheKey, nil)
   282  				}
   283  			}
   284  		}()
   285  	}
   286  
   287  	if ech != nil {
   288  		// Split hello into inner and outer
   289  		ech.innerHello = hello.clone()
   290  
   291  		// Overwrite the server name in the outer hello with the public facing
   292  		// name.
   293  		hello.serverName = string(ech.config.PublicName)
   294  		// Generate a new random for the outer hello.
   295  		hello.random = make([]byte, 32)
   296  		_, err = io.ReadFull(c.config.rand(), hello.random)
   297  		if err != nil {
   298  			return errors.New("tls: short read from Rand: " + err.Error())
   299  		}
   300  
   301  		// NOTE: we don't do PSK GREASE, in line with boringssl, it's meant to
   302  		// work around _possibly_ broken middleboxes, but there is little-to-no
   303  		// evidence that this is actually a problem.
   304  
   305  		if err := computeAndUpdateOuterECHExtension(hello, ech.innerHello, ech, true); err != nil {
   306  			return err
   307  		}
   308  	}
   309  
   310  	c.serverName = hello.serverName
   311  
   312  	if _, err := c.writeHandshakeRecord(hello, nil); err != nil {
   313  		return err
   314  	}
   315  
   316  	if hello.earlyData {
   317  		suite := cipherSuiteTLS13ByID(session.cipherSuite)
   318  		transcript := suite.hash.New()
   319  		if err := transcriptMsg(hello, transcript); err != nil {
   320  			return err
   321  		}
   322  		earlyTrafficSecret := suite.deriveSecret(earlySecret, clientEarlyTrafficLabel, transcript)
   323  		c.quicSetWriteSecret(QUICEncryptionLevelEarly, suite.id, earlyTrafficSecret)
   324  	}
   325  
   326  	// serverHelloMsg is not included in the transcript
   327  	msg, err := c.readHandshake(nil)
   328  	if err != nil {
   329  		return err
   330  	}
   331  
   332  	serverHello, ok := msg.(*serverHelloMsg)
   333  	if !ok {
   334  		c.sendAlert(alertUnexpectedMessage)
   335  		return unexpectedMessageError(serverHello, msg)
   336  	}
   337  
   338  	if err := c.pickTLSVersion(serverHello); err != nil {
   339  		return err
   340  	}
   341  
   342  	// If we are negotiating a protocol version that's lower than what we
   343  	// support, check for the server downgrade canaries.
   344  	// See RFC 8446, Section 4.1.3.
   345  	maxVers := c.config.maxSupportedVersion(roleClient)
   346  	tls12Downgrade := string(serverHello.random[24:]) == downgradeCanaryTLS12
   347  	tls11Downgrade := string(serverHello.random[24:]) == downgradeCanaryTLS11
   348  	if maxVers == VersionTLS13 && c.vers <= VersionTLS12 && (tls12Downgrade || tls11Downgrade) ||
   349  		maxVers == VersionTLS12 && c.vers <= VersionTLS11 && tls11Downgrade {
   350  		c.sendAlert(alertIllegalParameter)
   351  		return errors.New("tls: downgrade attempt detected, possibly due to a MitM attack or a broken middlebox")
   352  	}
   353  
   354  	if c.vers == VersionTLS13 {
   355  		hs := &clientHandshakeStateTLS13{
   356  			c:            c,
   357  			ctx:          ctx,
   358  			serverHello:  serverHello,
   359  			hello:        hello,
   360  			keyShareKeys: keyShareKeys,
   361  			session:      session,
   362  			earlySecret:  earlySecret,
   363  			binderKey:    binderKey,
   364  			echContext:   ech,
   365  		}
   366  		return hs.handshake()
   367  	}
   368  
   369  	hs := &clientHandshakeState{
   370  		c:           c,
   371  		ctx:         ctx,
   372  		serverHello: serverHello,
   373  		hello:       hello,
   374  		session:     session,
   375  	}
   376  	return hs.handshake()
   377  }
   378  
   379  func (c *Conn) loadSession(hello *clientHelloMsg) (
   380  	session *SessionState, earlySecret, binderKey []byte, err error) {
   381  	if c.config.SessionTicketsDisabled || c.config.ClientSessionCache == nil {
   382  		return nil, nil, nil, nil
   383  	}
   384  
   385  	echInner := bytes.Equal(hello.encryptedClientHello, []byte{1})
   386  
   387  	// ticketSupported is a TLS 1.2 extension (as TLS 1.3 replaced tickets with PSK
   388  	// identities) and ECH requires and forces TLS 1.3.
   389  	hello.ticketSupported = true && !echInner
   390  
   391  	if hello.supportedVersions[0] == VersionTLS13 {
   392  		// Require DHE on resumption as it guarantees forward secrecy against
   393  		// compromise of the session ticket key. See RFC 8446, Section 4.2.9.
   394  		hello.pskModes = []uint8{pskModeDHE}
   395  	}
   396  
   397  	// Session resumption is not allowed if renegotiating because
   398  	// renegotiation is primarily used to allow a client to send a client
   399  	// certificate, which would be skipped if session resumption occurred.
   400  	if c.handshakes != 0 {
   401  		return nil, nil, nil, nil
   402  	}
   403  
   404  	// Try to resume a previously negotiated TLS session, if available.
   405  	cacheKey := c.clientSessionCacheKey()
   406  	if cacheKey == "" {
   407  		return nil, nil, nil, nil
   408  	}
   409  	cs, ok := c.config.ClientSessionCache.Get(cacheKey)
   410  	if !ok || cs == nil {
   411  		return nil, nil, nil, nil
   412  	}
   413  	session = cs.session
   414  
   415  	// Check that version used for the previous session is still valid.
   416  	versOk := false
   417  	for _, v := range hello.supportedVersions {
   418  		if v == session.version {
   419  			versOk = true
   420  			break
   421  		}
   422  	}
   423  	if !versOk {
   424  		return nil, nil, nil, nil
   425  	}
   426  
   427  	// Check that the cached server certificate is not expired, and that it's
   428  	// valid for the ServerName. This should be ensured by the cache key, but
   429  	// protect the application from a faulty ClientSessionCache implementation.
   430  	if c.config.time().After(session.peerCertificates[0].NotAfter) {
   431  		// Expired certificate, delete the entry.
   432  		c.config.ClientSessionCache.Put(cacheKey, nil)
   433  		return nil, nil, nil, nil
   434  	}
   435  	if !c.config.InsecureSkipVerify {
   436  		if len(session.verifiedChains) == 0 {
   437  			// The original connection had InsecureSkipVerify, while this doesn't.
   438  			return nil, nil, nil, nil
   439  		}
   440  		if err := session.peerCertificates[0].VerifyHostname(c.config.ServerName); err != nil {
   441  			return nil, nil, nil, nil
   442  		}
   443  	}
   444  
   445  	if session.version != VersionTLS13 {
   446  		// In TLS 1.2 the cipher suite must match the resumed session. Ensure we
   447  		// are still offering it.
   448  		if mutualCipherSuite(hello.cipherSuites, session.cipherSuite) == nil {
   449  			return nil, nil, nil, nil
   450  		}
   451  
   452  		hello.sessionTicket = session.ticket
   453  		return
   454  	}
   455  
   456  	// Check that the session ticket is not expired.
   457  	if c.config.time().After(time.Unix(int64(session.useBy), 0)) {
   458  		c.config.ClientSessionCache.Put(cacheKey, nil)
   459  		return nil, nil, nil, nil
   460  	}
   461  
   462  	// In TLS 1.3 the KDF hash must match the resumed session. Ensure we
   463  	// offer at least one cipher suite with that hash.
   464  	cipherSuite := cipherSuiteTLS13ByID(session.cipherSuite)
   465  	if cipherSuite == nil {
   466  		return nil, nil, nil, nil
   467  	}
   468  	cipherSuiteOk := false
   469  	for _, offeredID := range hello.cipherSuites {
   470  		offeredSuite := cipherSuiteTLS13ByID(offeredID)
   471  		if offeredSuite != nil && offeredSuite.hash == cipherSuite.hash {
   472  			cipherSuiteOk = true
   473  			break
   474  		}
   475  	}
   476  	if !cipherSuiteOk {
   477  		return nil, nil, nil, nil
   478  	}
   479  
   480  	if c.quic != nil {
   481  		if c.quic.enableSessionEvents {
   482  			c.quicResumeSession(session)
   483  		}
   484  
   485  		// For 0-RTT, the cipher suite has to match exactly, and we need to be
   486  		// offering the same ALPN.
   487  		if session.EarlyData && mutualCipherSuiteTLS13(hello.cipherSuites, session.cipherSuite) != nil {
   488  			for _, alpn := range hello.alpnProtocols {
   489  				if alpn == session.alpnProtocol {
   490  					hello.earlyData = true
   491  					break
   492  				}
   493  			}
   494  		}
   495  	}
   496  
   497  	// Set the pre_shared_key extension. See RFC 8446, Section 4.2.11.1.
   498  	ticketAge := c.config.time().Sub(time.Unix(int64(session.createdAt), 0))
   499  	identity := pskIdentity{
   500  		label:               session.ticket,
   501  		obfuscatedTicketAge: uint32(ticketAge/time.Millisecond) + session.ageAdd,
   502  	}
   503  	hello.pskIdentities = []pskIdentity{identity}
   504  	hello.pskBinders = [][]byte{make([]byte, cipherSuite.hash.Size())}
   505  
   506  	// Compute the PSK binders. See RFC 8446, Section 4.2.11.2.
   507  	earlySecret = cipherSuite.extract(session.secret, nil)
   508  	binderKey = cipherSuite.deriveSecret(earlySecret, resumptionBinderLabel, nil)
   509  	transcript := cipherSuite.hash.New()
   510  	if err := computeAndUpdatePSK(hello, binderKey, transcript, cipherSuite.finishedHash); err != nil {
   511  		return nil, nil, nil, err
   512  	}
   513  
   514  	return
   515  }
   516  
   517  func (c *Conn) pickTLSVersion(serverHello *serverHelloMsg) error {
   518  	peerVersion := serverHello.vers
   519  	if serverHello.supportedVersion != 0 {
   520  		peerVersion = serverHello.supportedVersion
   521  	}
   522  
   523  	vers, ok := c.config.mutualVersion(roleClient, []uint16{peerVersion})
   524  	if !ok {
   525  		c.sendAlert(alertProtocolVersion)
   526  		return fmt.Errorf("tls: server selected unsupported protocol version %x", peerVersion)
   527  	}
   528  
   529  	c.vers = vers
   530  	c.haveVers = true
   531  	c.in.version = vers
   532  	c.out.version = vers
   533  
   534  	return nil
   535  }
   536  
   537  // Does the handshake, either a full one or resumes old session. Requires hs.c,
   538  // hs.hello, hs.serverHello, and, optionally, hs.session to be set.
   539  func (hs *clientHandshakeState) handshake() error {
   540  	c := hs.c
   541  
   542  	isResume, err := hs.processServerHello()
   543  	if err != nil {
   544  		return err
   545  	}
   546  
   547  	hs.finishedHash = newFinishedHash(c.vers, hs.suite)
   548  
   549  	// No signatures of the handshake are needed in a resumption.
   550  	// Otherwise, in a full handshake, if we don't have any certificates
   551  	// configured then we will never send a CertificateVerify message and
   552  	// thus no signatures are needed in that case either.
   553  	if isResume || (len(c.config.Certificates) == 0 && c.config.GetClientCertificate == nil) {
   554  		hs.finishedHash.discardHandshakeBuffer()
   555  	}
   556  
   557  	if err := transcriptMsg(hs.hello, &hs.finishedHash); err != nil {
   558  		return err
   559  	}
   560  	if err := transcriptMsg(hs.serverHello, &hs.finishedHash); err != nil {
   561  		return err
   562  	}
   563  
   564  	c.buffering = true
   565  	c.didResume = isResume
   566  	if isResume {
   567  		if err := hs.establishKeys(); err != nil {
   568  			return err
   569  		}
   570  		if err := hs.readSessionTicket(); err != nil {
   571  			return err
   572  		}
   573  		if err := hs.readFinished(c.serverFinished[:]); err != nil {
   574  			return err
   575  		}
   576  		c.clientFinishedIsFirst = false
   577  		// Make sure the connection is still being verified whether or not this
   578  		// is a resumption. Resumptions currently don't reverify certificates so
   579  		// they don't call verifyServerCertificate. See Issue 31641.
   580  		if c.config.VerifyConnection != nil {
   581  			if err := c.config.VerifyConnection(c.connectionStateLocked()); err != nil {
   582  				c.sendAlert(alertBadCertificate)
   583  				return err
   584  			}
   585  		}
   586  		if err := hs.sendFinished(c.clientFinished[:]); err != nil {
   587  			return err
   588  		}
   589  		if _, err := c.flush(); err != nil {
   590  			return err
   591  		}
   592  	} else {
   593  		if err := hs.doFullHandshake(); err != nil {
   594  			return err
   595  		}
   596  		if err := hs.establishKeys(); err != nil {
   597  			return err
   598  		}
   599  		if err := hs.sendFinished(c.clientFinished[:]); err != nil {
   600  			return err
   601  		}
   602  		if _, err := c.flush(); err != nil {
   603  			return err
   604  		}
   605  		c.clientFinishedIsFirst = true
   606  		if err := hs.readSessionTicket(); err != nil {
   607  			return err
   608  		}
   609  		if err := hs.readFinished(c.serverFinished[:]); err != nil {
   610  			return err
   611  		}
   612  	}
   613  	if err := hs.saveSessionTicket(); err != nil {
   614  		return err
   615  	}
   616  
   617  	c.ekm = ekmFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.hello.random, hs.serverHello.random)
   618  	c.isHandshakeComplete.Store(true)
   619  
   620  	return nil
   621  }
   622  
   623  func (hs *clientHandshakeState) pickCipherSuite() error {
   624  	if hs.suite = mutualCipherSuite(hs.hello.cipherSuites, hs.serverHello.cipherSuite); hs.suite == nil {
   625  		hs.c.sendAlert(alertHandshakeFailure)
   626  		return errors.New("tls: server chose an unconfigured cipher suite")
   627  	}
   628  
   629  	if hs.c.config.CipherSuites == nil && !needFIPS() && rsaKexCiphers[hs.suite.id] {
   630  		tlsrsakex.Value() // ensure godebug is initialized
   631  		tlsrsakex.IncNonDefault()
   632  	}
   633  	if hs.c.config.CipherSuites == nil && !needFIPS() && tdesCiphers[hs.suite.id] {
   634  		tls3des.Value() // ensure godebug is initialized
   635  		tls3des.IncNonDefault()
   636  	}
   637  
   638  	hs.c.cipherSuite = hs.suite.id
   639  	return nil
   640  }
   641  
   642  func (hs *clientHandshakeState) doFullHandshake() error {
   643  	c := hs.c
   644  
   645  	msg, err := c.readHandshake(&hs.finishedHash)
   646  	if err != nil {
   647  		return err
   648  	}
   649  	certMsg, ok := msg.(*certificateMsg)
   650  	if !ok || len(certMsg.certificates) == 0 {
   651  		c.sendAlert(alertUnexpectedMessage)
   652  		return unexpectedMessageError(certMsg, msg)
   653  	}
   654  
   655  	msg, err = c.readHandshake(&hs.finishedHash)
   656  	if err != nil {
   657  		return err
   658  	}
   659  
   660  	cs, ok := msg.(*certificateStatusMsg)
   661  	if ok {
   662  		// RFC4366 on Certificate Status Request:
   663  		// The server MAY return a "certificate_status" message.
   664  
   665  		if !hs.serverHello.ocspStapling {
   666  			// If a server returns a "CertificateStatus" message, then the
   667  			// server MUST have included an extension of type "status_request"
   668  			// with empty "extension_data" in the extended server hello.
   669  
   670  			c.sendAlert(alertUnexpectedMessage)
   671  			return errors.New("tls: received unexpected CertificateStatus message")
   672  		}
   673  
   674  		c.ocspResponse = cs.response
   675  
   676  		msg, err = c.readHandshake(&hs.finishedHash)
   677  		if err != nil {
   678  			return err
   679  		}
   680  	}
   681  
   682  	if c.handshakes == 0 {
   683  		// If this is the first handshake on a connection, process and
   684  		// (optionally) verify the server's certificates.
   685  		if err := c.verifyServerCertificate(certMsg.certificates); err != nil {
   686  			return err
   687  		}
   688  	} else {
   689  		// This is a renegotiation handshake. We require that the
   690  		// server's identity (i.e. leaf certificate) is unchanged and
   691  		// thus any previous trust decision is still valid.
   692  		//
   693  		// See https://mitls.org/pages/attacks/3SHAKE for the
   694  		// motivation behind this requirement.
   695  		if !bytes.Equal(c.peerCertificates[0].Raw, certMsg.certificates[0]) {
   696  			c.sendAlert(alertBadCertificate)
   697  			return errors.New("tls: server's identity changed during renegotiation")
   698  		}
   699  	}
   700  
   701  	keyAgreement := hs.suite.ka(c.vers)
   702  
   703  	skx, ok := msg.(*serverKeyExchangeMsg)
   704  	if ok {
   705  		err = keyAgreement.processServerKeyExchange(c.config, hs.hello, hs.serverHello, c.peerCertificates[0], skx)
   706  		if err != nil {
   707  			c.sendAlert(alertUnexpectedMessage)
   708  			return err
   709  		}
   710  		if len(skx.key) >= 3 && skx.key[0] == 3 /* named curve */ {
   711  			c.curveID = CurveID(byteorder.BeUint16(skx.key[1:]))
   712  		}
   713  
   714  		msg, err = c.readHandshake(&hs.finishedHash)
   715  		if err != nil {
   716  			return err
   717  		}
   718  	}
   719  
   720  	var chainToSend *Certificate
   721  	var certRequested bool
   722  	certReq, ok := msg.(*certificateRequestMsg)
   723  	if ok {
   724  		certRequested = true
   725  
   726  		cri := certificateRequestInfoFromMsg(hs.ctx, c.vers, certReq)
   727  		if chainToSend, err = c.getClientCertificate(cri); err != nil {
   728  			c.sendAlert(alertInternalError)
   729  			return err
   730  		}
   731  
   732  		msg, err = c.readHandshake(&hs.finishedHash)
   733  		if err != nil {
   734  			return err
   735  		}
   736  	}
   737  
   738  	shd, ok := msg.(*serverHelloDoneMsg)
   739  	if !ok {
   740  		c.sendAlert(alertUnexpectedMessage)
   741  		return unexpectedMessageError(shd, msg)
   742  	}
   743  
   744  	// If the server requested a certificate then we have to send a
   745  	// Certificate message, even if it's empty because we don't have a
   746  	// certificate to send.
   747  	if certRequested {
   748  		certMsg = new(certificateMsg)
   749  		certMsg.certificates = chainToSend.Certificate
   750  		if _, err := hs.c.writeHandshakeRecord(certMsg, &hs.finishedHash); err != nil {
   751  			return err
   752  		}
   753  	}
   754  
   755  	preMasterSecret, ckx, err := keyAgreement.generateClientKeyExchange(c.config, hs.hello, c.peerCertificates[0])
   756  	if err != nil {
   757  		c.sendAlert(alertInternalError)
   758  		return err
   759  	}
   760  	if ckx != nil {
   761  		if _, err := hs.c.writeHandshakeRecord(ckx, &hs.finishedHash); err != nil {
   762  			return err
   763  		}
   764  	}
   765  
   766  	if hs.serverHello.extendedMasterSecret {
   767  		c.extMasterSecret = true
   768  		hs.masterSecret = extMasterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret,
   769  			hs.finishedHash.Sum())
   770  	} else {
   771  		hs.masterSecret = masterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret,
   772  			hs.hello.random, hs.serverHello.random)
   773  	}
   774  	if err := c.config.writeKeyLog(keyLogLabelTLS12, hs.hello.random, hs.masterSecret); err != nil {
   775  		c.sendAlert(alertInternalError)
   776  		return errors.New("tls: failed to write to key log: " + err.Error())
   777  	}
   778  
   779  	if chainToSend != nil && len(chainToSend.Certificate) > 0 {
   780  		certVerify := &certificateVerifyMsg{}
   781  
   782  		key, ok := chainToSend.PrivateKey.(crypto.Signer)
   783  		if !ok {
   784  			c.sendAlert(alertInternalError)
   785  			return fmt.Errorf("tls: client certificate private key of type %T does not implement crypto.Signer", chainToSend.PrivateKey)
   786  		}
   787  
   788  		var sigType uint8
   789  		var sigHash crypto.Hash
   790  		if c.vers >= VersionTLS12 {
   791  			signatureAlgorithm, err := selectSignatureScheme(c.vers, chainToSend, certReq.supportedSignatureAlgorithms)
   792  			if err != nil {
   793  				c.sendAlert(alertIllegalParameter)
   794  				return err
   795  			}
   796  			sigType, sigHash, err = typeAndHashFromSignatureScheme(signatureAlgorithm)
   797  			if err != nil {
   798  				return c.sendAlert(alertInternalError)
   799  			}
   800  			certVerify.hasSignatureAlgorithm = true
   801  			certVerify.signatureAlgorithm = signatureAlgorithm
   802  		} else {
   803  			sigType, sigHash, err = legacyTypeAndHashFromPublicKey(key.Public())
   804  			if err != nil {
   805  				c.sendAlert(alertIllegalParameter)
   806  				return err
   807  			}
   808  		}
   809  
   810  		signed := hs.finishedHash.hashForClientCertificate(sigType, sigHash)
   811  		signOpts := crypto.SignerOpts(sigHash)
   812  		if sigType == signatureRSAPSS {
   813  			signOpts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: sigHash}
   814  		}
   815  		certVerify.signature, err = key.Sign(c.config.rand(), signed, signOpts)
   816  		if err != nil {
   817  			c.sendAlert(alertInternalError)
   818  			return err
   819  		}
   820  
   821  		if _, err := hs.c.writeHandshakeRecord(certVerify, &hs.finishedHash); err != nil {
   822  			return err
   823  		}
   824  	}
   825  
   826  	hs.finishedHash.discardHandshakeBuffer()
   827  
   828  	return nil
   829  }
   830  
   831  func (hs *clientHandshakeState) establishKeys() error {
   832  	c := hs.c
   833  
   834  	clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV :=
   835  		keysFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.hello.random, hs.serverHello.random, hs.suite.macLen, hs.suite.keyLen, hs.suite.ivLen)
   836  	var clientCipher, serverCipher any
   837  	var clientHash, serverHash hash.Hash
   838  	if hs.suite.cipher != nil {
   839  		clientCipher = hs.suite.cipher(clientKey, clientIV, false /* not for reading */)
   840  		clientHash = hs.suite.mac(clientMAC)
   841  		serverCipher = hs.suite.cipher(serverKey, serverIV, true /* for reading */)
   842  		serverHash = hs.suite.mac(serverMAC)
   843  	} else {
   844  		clientCipher = hs.suite.aead(clientKey, clientIV)
   845  		serverCipher = hs.suite.aead(serverKey, serverIV)
   846  	}
   847  
   848  	c.in.prepareCipherSpec(c.vers, serverCipher, serverHash)
   849  	c.out.prepareCipherSpec(c.vers, clientCipher, clientHash)
   850  	return nil
   851  }
   852  
   853  func (hs *clientHandshakeState) serverResumedSession() bool {
   854  	// If the server responded with the same sessionId then it means the
   855  	// sessionTicket is being used to resume a TLS session.
   856  	return hs.session != nil && hs.hello.sessionId != nil &&
   857  		bytes.Equal(hs.serverHello.sessionId, hs.hello.sessionId)
   858  }
   859  
   860  func (hs *clientHandshakeState) processServerHello() (bool, error) {
   861  	c := hs.c
   862  
   863  	if err := hs.pickCipherSuite(); err != nil {
   864  		return false, err
   865  	}
   866  
   867  	if hs.serverHello.compressionMethod != compressionNone {
   868  		c.sendAlert(alertUnexpectedMessage)
   869  		return false, errors.New("tls: server selected unsupported compression format")
   870  	}
   871  
   872  	if c.handshakes == 0 && hs.serverHello.secureRenegotiationSupported {
   873  		c.secureRenegotiation = true
   874  		if len(hs.serverHello.secureRenegotiation) != 0 {
   875  			c.sendAlert(alertHandshakeFailure)
   876  			return false, errors.New("tls: initial handshake had non-empty renegotiation extension")
   877  		}
   878  	}
   879  
   880  	if c.handshakes > 0 && c.secureRenegotiation {
   881  		var expectedSecureRenegotiation [24]byte
   882  		copy(expectedSecureRenegotiation[:], c.clientFinished[:])
   883  		copy(expectedSecureRenegotiation[12:], c.serverFinished[:])
   884  		if !bytes.Equal(hs.serverHello.secureRenegotiation, expectedSecureRenegotiation[:]) {
   885  			c.sendAlert(alertHandshakeFailure)
   886  			return false, errors.New("tls: incorrect renegotiation extension contents")
   887  		}
   888  	}
   889  
   890  	if err := checkALPN(hs.hello.alpnProtocols, hs.serverHello.alpnProtocol, false); err != nil {
   891  		c.sendAlert(alertUnsupportedExtension)
   892  		return false, err
   893  	}
   894  	c.clientProtocol = hs.serverHello.alpnProtocol
   895  
   896  	c.scts = hs.serverHello.scts
   897  
   898  	if !hs.serverResumedSession() {
   899  		return false, nil
   900  	}
   901  
   902  	if hs.session.version != c.vers {
   903  		c.sendAlert(alertHandshakeFailure)
   904  		return false, errors.New("tls: server resumed a session with a different version")
   905  	}
   906  
   907  	if hs.session.cipherSuite != hs.suite.id {
   908  		c.sendAlert(alertHandshakeFailure)
   909  		return false, errors.New("tls: server resumed a session with a different cipher suite")
   910  	}
   911  
   912  	// RFC 7627, Section 5.3
   913  	if hs.session.extMasterSecret != hs.serverHello.extendedMasterSecret {
   914  		c.sendAlert(alertHandshakeFailure)
   915  		return false, errors.New("tls: server resumed a session with a different EMS extension")
   916  	}
   917  
   918  	// Restore master secret and certificates from previous state
   919  	hs.masterSecret = hs.session.secret
   920  	c.extMasterSecret = hs.session.extMasterSecret
   921  	c.peerCertificates = hs.session.peerCertificates
   922  	c.activeCertHandles = hs.c.activeCertHandles
   923  	c.verifiedChains = hs.session.verifiedChains
   924  	c.ocspResponse = hs.session.ocspResponse
   925  	// Let the ServerHello SCTs override the session SCTs from the original
   926  	// connection, if any are provided
   927  	if len(c.scts) == 0 && len(hs.session.scts) != 0 {
   928  		c.scts = hs.session.scts
   929  	}
   930  
   931  	return true, nil
   932  }
   933  
   934  // checkALPN ensure that the server's choice of ALPN protocol is compatible with
   935  // the protocols that we advertised in the Client Hello.
   936  func checkALPN(clientProtos []string, serverProto string, quic bool) error {
   937  	if serverProto == "" {
   938  		if quic && len(clientProtos) > 0 {
   939  			// RFC 9001, Section 8.1
   940  			return errors.New("tls: server did not select an ALPN protocol")
   941  		}
   942  		return nil
   943  	}
   944  	if len(clientProtos) == 0 {
   945  		return errors.New("tls: server advertised unrequested ALPN extension")
   946  	}
   947  	for _, proto := range clientProtos {
   948  		if proto == serverProto {
   949  			return nil
   950  		}
   951  	}
   952  	return errors.New("tls: server selected unadvertised ALPN protocol")
   953  }
   954  
   955  func (hs *clientHandshakeState) readFinished(out []byte) error {
   956  	c := hs.c
   957  
   958  	if err := c.readChangeCipherSpec(); err != nil {
   959  		return err
   960  	}
   961  
   962  	// finishedMsg is included in the transcript, but not until after we
   963  	// check the client version, since the state before this message was
   964  	// sent is used during verification.
   965  	msg, err := c.readHandshake(nil)
   966  	if err != nil {
   967  		return err
   968  	}
   969  	serverFinished, ok := msg.(*finishedMsg)
   970  	if !ok {
   971  		c.sendAlert(alertUnexpectedMessage)
   972  		return unexpectedMessageError(serverFinished, msg)
   973  	}
   974  
   975  	verify := hs.finishedHash.serverSum(hs.masterSecret)
   976  	if len(verify) != len(serverFinished.verifyData) ||
   977  		subtle.ConstantTimeCompare(verify, serverFinished.verifyData) != 1 {
   978  		c.sendAlert(alertHandshakeFailure)
   979  		return errors.New("tls: server's Finished message was incorrect")
   980  	}
   981  
   982  	if err := transcriptMsg(serverFinished, &hs.finishedHash); err != nil {
   983  		return err
   984  	}
   985  
   986  	copy(out, verify)
   987  	return nil
   988  }
   989  
   990  func (hs *clientHandshakeState) readSessionTicket() error {
   991  	if !hs.serverHello.ticketSupported {
   992  		return nil
   993  	}
   994  	c := hs.c
   995  
   996  	if !hs.hello.ticketSupported {
   997  		c.sendAlert(alertIllegalParameter)
   998  		return errors.New("tls: server sent unrequested session ticket")
   999  	}
  1000  
  1001  	msg, err := c.readHandshake(&hs.finishedHash)
  1002  	if err != nil {
  1003  		return err
  1004  	}
  1005  	sessionTicketMsg, ok := msg.(*newSessionTicketMsg)
  1006  	if !ok {
  1007  		c.sendAlert(alertUnexpectedMessage)
  1008  		return unexpectedMessageError(sessionTicketMsg, msg)
  1009  	}
  1010  
  1011  	hs.ticket = sessionTicketMsg.ticket
  1012  	return nil
  1013  }
  1014  
  1015  func (hs *clientHandshakeState) saveSessionTicket() error {
  1016  	if hs.ticket == nil {
  1017  		return nil
  1018  	}
  1019  	c := hs.c
  1020  
  1021  	cacheKey := c.clientSessionCacheKey()
  1022  	if cacheKey == "" {
  1023  		return nil
  1024  	}
  1025  
  1026  	session := c.sessionState()
  1027  	session.secret = hs.masterSecret
  1028  	session.ticket = hs.ticket
  1029  
  1030  	cs := &ClientSessionState{session: session}
  1031  	c.config.ClientSessionCache.Put(cacheKey, cs)
  1032  	return nil
  1033  }
  1034  
  1035  func (hs *clientHandshakeState) sendFinished(out []byte) error {
  1036  	c := hs.c
  1037  
  1038  	if err := c.writeChangeCipherRecord(); err != nil {
  1039  		return err
  1040  	}
  1041  
  1042  	finished := new(finishedMsg)
  1043  	finished.verifyData = hs.finishedHash.clientSum(hs.masterSecret)
  1044  	if _, err := hs.c.writeHandshakeRecord(finished, &hs.finishedHash); err != nil {
  1045  		return err
  1046  	}
  1047  	copy(out, finished.verifyData)
  1048  	return nil
  1049  }
  1050  
  1051  // defaultMaxRSAKeySize is the maximum RSA key size in bits that we are willing
  1052  // to verify the signatures of during a TLS handshake.
  1053  const defaultMaxRSAKeySize = 8192
  1054  
  1055  var tlsmaxrsasize = godebug.New("tlsmaxrsasize")
  1056  
  1057  func checkKeySize(n int) (max int, ok bool) {
  1058  	if v := tlsmaxrsasize.Value(); v != "" {
  1059  		if max, err := strconv.Atoi(v); err == nil {
  1060  			if (n <= max) != (n <= defaultMaxRSAKeySize) {
  1061  				tlsmaxrsasize.IncNonDefault()
  1062  			}
  1063  			return max, n <= max
  1064  		}
  1065  	}
  1066  	return defaultMaxRSAKeySize, n <= defaultMaxRSAKeySize
  1067  }
  1068  
  1069  // verifyServerCertificate parses and verifies the provided chain, setting
  1070  // c.verifiedChains and c.peerCertificates or sending the appropriate alert.
  1071  func (c *Conn) verifyServerCertificate(certificates [][]byte) error {
  1072  	activeHandles := make([]*activeCert, len(certificates))
  1073  	certs := make([]*x509.Certificate, len(certificates))
  1074  	for i, asn1Data := range certificates {
  1075  		cert, err := globalCertCache.newCert(asn1Data)
  1076  		if err != nil {
  1077  			c.sendAlert(alertBadCertificate)
  1078  			return errors.New("tls: failed to parse certificate from server: " + err.Error())
  1079  		}
  1080  		if cert.cert.PublicKeyAlgorithm == x509.RSA {
  1081  			n := cert.cert.PublicKey.(*rsa.PublicKey).N.BitLen()
  1082  			if max, ok := checkKeySize(n); !ok {
  1083  				c.sendAlert(alertBadCertificate)
  1084  				return fmt.Errorf("tls: server sent certificate containing RSA key larger than %d bits", max)
  1085  			}
  1086  		}
  1087  		activeHandles[i] = cert
  1088  		certs[i] = cert.cert
  1089  	}
  1090  
  1091  	echRejected := c.config.EncryptedClientHelloConfigList != nil && !c.echAccepted
  1092  	if echRejected {
  1093  		if c.config.EncryptedClientHelloRejectionVerify != nil {
  1094  			if err := c.config.EncryptedClientHelloRejectionVerify(c.connectionStateLocked()); err != nil {
  1095  				c.sendAlert(alertBadCertificate)
  1096  				return err
  1097  			}
  1098  		} else {
  1099  			opts := x509.VerifyOptions{
  1100  				Roots:         c.config.RootCAs,
  1101  				CurrentTime:   c.config.time(),
  1102  				DNSName:       c.serverName,
  1103  				Intermediates: x509.NewCertPool(),
  1104  			}
  1105  
  1106  			for _, cert := range certs[1:] {
  1107  				opts.Intermediates.AddCert(cert)
  1108  			}
  1109  			var err error
  1110  			c.verifiedChains, err = certs[0].Verify(opts)
  1111  			if err != nil {
  1112  				c.sendAlert(alertBadCertificate)
  1113  				return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
  1114  			}
  1115  		}
  1116  	} else if !c.config.InsecureSkipVerify {
  1117  		opts := x509.VerifyOptions{
  1118  			Roots:         c.config.RootCAs,
  1119  			CurrentTime:   c.config.time(),
  1120  			DNSName:       c.config.ServerName,
  1121  			Intermediates: x509.NewCertPool(),
  1122  		}
  1123  
  1124  		for _, cert := range certs[1:] {
  1125  			opts.Intermediates.AddCert(cert)
  1126  		}
  1127  		var err error
  1128  		c.verifiedChains, err = certs[0].Verify(opts)
  1129  		if err != nil {
  1130  			c.sendAlert(alertBadCertificate)
  1131  			return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
  1132  		}
  1133  	}
  1134  
  1135  	switch certs[0].PublicKey.(type) {
  1136  	case *rsa.PublicKey, *ecdsa.PublicKey, ed25519.PublicKey:
  1137  		break
  1138  	default:
  1139  		c.sendAlert(alertUnsupportedCertificate)
  1140  		return fmt.Errorf("tls: server's certificate contains an unsupported type of public key: %T", certs[0].PublicKey)
  1141  	}
  1142  
  1143  	c.activeCertHandles = activeHandles
  1144  	c.peerCertificates = certs
  1145  
  1146  	if c.config.VerifyPeerCertificate != nil && !echRejected {
  1147  		if err := c.config.VerifyPeerCertificate(certificates, c.verifiedChains); err != nil {
  1148  			c.sendAlert(alertBadCertificate)
  1149  			return err
  1150  		}
  1151  	}
  1152  
  1153  	if c.config.VerifyConnection != nil && !echRejected {
  1154  		if err := c.config.VerifyConnection(c.connectionStateLocked()); err != nil {
  1155  			c.sendAlert(alertBadCertificate)
  1156  			return err
  1157  		}
  1158  	}
  1159  
  1160  	return nil
  1161  }
  1162  
  1163  // certificateRequestInfoFromMsg generates a CertificateRequestInfo from a TLS
  1164  // <= 1.2 CertificateRequest, making an effort to fill in missing information.
  1165  func certificateRequestInfoFromMsg(ctx context.Context, vers uint16, certReq *certificateRequestMsg) *CertificateRequestInfo {
  1166  	cri := &CertificateRequestInfo{
  1167  		AcceptableCAs: certReq.certificateAuthorities,
  1168  		Version:       vers,
  1169  		ctx:           ctx,
  1170  	}
  1171  
  1172  	var rsaAvail, ecAvail bool
  1173  	for _, certType := range certReq.certificateTypes {
  1174  		switch certType {
  1175  		case certTypeRSASign:
  1176  			rsaAvail = true
  1177  		case certTypeECDSASign:
  1178  			ecAvail = true
  1179  		}
  1180  	}
  1181  
  1182  	if !certReq.hasSignatureAlgorithm {
  1183  		// Prior to TLS 1.2, signature schemes did not exist. In this case we
  1184  		// make up a list based on the acceptable certificate types, to help
  1185  		// GetClientCertificate and SupportsCertificate select the right certificate.
  1186  		// The hash part of the SignatureScheme is a lie here, because
  1187  		// TLS 1.0 and 1.1 always use MD5+SHA1 for RSA and SHA1 for ECDSA.
  1188  		switch {
  1189  		case rsaAvail && ecAvail:
  1190  			cri.SignatureSchemes = []SignatureScheme{
  1191  				ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512,
  1192  				PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1,
  1193  			}
  1194  		case rsaAvail:
  1195  			cri.SignatureSchemes = []SignatureScheme{
  1196  				PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1,
  1197  			}
  1198  		case ecAvail:
  1199  			cri.SignatureSchemes = []SignatureScheme{
  1200  				ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512,
  1201  			}
  1202  		}
  1203  		return cri
  1204  	}
  1205  
  1206  	// Filter the signature schemes based on the certificate types.
  1207  	// See RFC 5246, Section 7.4.4 (where it calls this "somewhat complicated").
  1208  	cri.SignatureSchemes = make([]SignatureScheme, 0, len(certReq.supportedSignatureAlgorithms))
  1209  	for _, sigScheme := range certReq.supportedSignatureAlgorithms {
  1210  		sigType, _, err := typeAndHashFromSignatureScheme(sigScheme)
  1211  		if err != nil {
  1212  			continue
  1213  		}
  1214  		switch sigType {
  1215  		case signatureECDSA, signatureEd25519:
  1216  			if ecAvail {
  1217  				cri.SignatureSchemes = append(cri.SignatureSchemes, sigScheme)
  1218  			}
  1219  		case signatureRSAPSS, signaturePKCS1v15:
  1220  			if rsaAvail {
  1221  				cri.SignatureSchemes = append(cri.SignatureSchemes, sigScheme)
  1222  			}
  1223  		}
  1224  	}
  1225  
  1226  	return cri
  1227  }
  1228  
  1229  func (c *Conn) getClientCertificate(cri *CertificateRequestInfo) (*Certificate, error) {
  1230  	if c.config.GetClientCertificate != nil {
  1231  		return c.config.GetClientCertificate(cri)
  1232  	}
  1233  
  1234  	for _, chain := range c.config.Certificates {
  1235  		if err := cri.SupportsCertificate(&chain); err != nil {
  1236  			continue
  1237  		}
  1238  		return &chain, nil
  1239  	}
  1240  
  1241  	// No acceptable certificate found. Don't send a certificate.
  1242  	return new(Certificate), nil
  1243  }
  1244  
  1245  // clientSessionCacheKey returns a key used to cache sessionTickets that could
  1246  // be used to resume previously negotiated TLS sessions with a server.
  1247  func (c *Conn) clientSessionCacheKey() string {
  1248  	if len(c.config.ServerName) > 0 {
  1249  		return c.config.ServerName
  1250  	}
  1251  	if c.conn != nil {
  1252  		return c.conn.RemoteAddr().String()
  1253  	}
  1254  	return ""
  1255  }
  1256  
  1257  // hostnameInSNI converts name into an appropriate hostname for SNI.
  1258  // Literal IP addresses and absolute FQDNs are not permitted as SNI values.
  1259  // See RFC 6066, Section 3.
  1260  func hostnameInSNI(name string) string {
  1261  	host := name
  1262  	if len(host) > 0 && host[0] == '[' && host[len(host)-1] == ']' {
  1263  		host = host[1 : len(host)-1]
  1264  	}
  1265  	if i := strings.LastIndex(host, "%"); i > 0 {
  1266  		host = host[:i]
  1267  	}
  1268  	if net.ParseIP(host) != nil {
  1269  		return ""
  1270  	}
  1271  	for len(name) > 0 && name[len(name)-1] == '.' {
  1272  		name = name[:len(name)-1]
  1273  	}
  1274  	return name
  1275  }
  1276  
  1277  func computeAndUpdatePSK(m *clientHelloMsg, binderKey []byte, transcript hash.Hash, finishedHash func([]byte, hash.Hash) []byte) error {
  1278  	helloBytes, err := m.marshalWithoutBinders()
  1279  	if err != nil {
  1280  		return err
  1281  	}
  1282  	transcript.Write(helloBytes)
  1283  	pskBinders := [][]byte{finishedHash(binderKey, transcript)}
  1284  	return m.updateBinders(pskBinders)
  1285  }
  1286  

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