// Copyright 2009 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. package tls import ( "bytes" "context" "crypto" "crypto/ecdsa" "crypto/ed25519" "crypto/rsa" "crypto/subtle" "crypto/x509" "errors" "fmt" "hash" "io" "net" "strings" "sync/atomic" "time" ) type clientHandshakeState struct { c *Conn ctx context.Context serverHello *serverHelloMsg hello *clientHelloMsg suite *cipherSuite finishedHash finishedHash masterSecret []byte session *ClientSessionState } func (c *Conn) makeClientHello() (*clientHelloMsg, ecdheParameters, error) { config := c.config if len(config.ServerName) == 0 && !config.InsecureSkipVerify { return nil, nil, errors.New("tls: either ServerName or InsecureSkipVerify must be specified in the tls.Config") } nextProtosLength := 0 for _, proto := range config.NextProtos { if l := len(proto); l == 0 || l > 255 { return nil, nil, errors.New("tls: invalid NextProtos value") } else { nextProtosLength += 1 + l } } if nextProtosLength > 0xffff { return nil, nil, errors.New("tls: NextProtos values too large") } supportedVersions := config.supportedVersions(roleClient) if len(supportedVersions) == 0 { return nil, nil, errors.New("tls: no supported versions satisfy MinVersion and MaxVersion") } clientHelloVersion := config.maxSupportedVersion(roleClient) // The version at the beginning of the ClientHello was capped at TLS 1.2 // for compatibility reasons. The supported_versions extension is used // to negotiate versions now. See RFC 8446, Section 4.2.1. if clientHelloVersion > VersionTLS12 { clientHelloVersion = VersionTLS12 } hello := &clientHelloMsg{ vers: clientHelloVersion, compressionMethods: []uint8{compressionNone}, random: make([]byte, 32), sessionId: make([]byte, 32), ocspStapling: true, scts: true, serverName: hostnameInSNI(config.ServerName), supportedCurves: config.curvePreferences(), supportedPoints: []uint8{pointFormatUncompressed}, secureRenegotiationSupported: true, alpnProtocols: config.NextProtos, supportedVersions: supportedVersions, } if c.handshakes > 0 { hello.secureRenegotiation = c.clientFinished[:] } preferenceOrder := cipherSuitesPreferenceOrder if !hasAESGCMHardwareSupport { preferenceOrder = cipherSuitesPreferenceOrderNoAES } configCipherSuites := config.cipherSuites() hello.cipherSuites = make([]uint16, 0, len(configCipherSuites)) for _, suiteId := range preferenceOrder { suite := mutualCipherSuite(configCipherSuites, suiteId) if suite == nil { continue } // Don't advertise TLS 1.2-only cipher suites unless // we're attempting TLS 1.2. if hello.vers < VersionTLS12 && suite.flags&suiteTLS12 != 0 { continue } hello.cipherSuites = append(hello.cipherSuites, suiteId) } _, err := io.ReadFull(config.rand(), hello.random) if err != nil { return nil, nil, errors.New("tls: short read from Rand: " + err.Error()) } // A random session ID is used to detect when the server accepted a ticket // and is resuming a session (see RFC 5077). In TLS 1.3, it's always set as // a compatibility measure (see RFC 8446, Section 4.1.2). if _, err := io.ReadFull(config.rand(), hello.sessionId); err != nil { return nil, nil, errors.New("tls: short read from Rand: " + err.Error()) } if hello.vers >= VersionTLS12 { hello.supportedSignatureAlgorithms = supportedSignatureAlgorithms } var params ecdheParameters if hello.supportedVersions[0] == VersionTLS13 { if hasAESGCMHardwareSupport { hello.cipherSuites = append(hello.cipherSuites, defaultCipherSuitesTLS13...) } else { hello.cipherSuites = append(hello.cipherSuites, defaultCipherSuitesTLS13NoAES...) } curveID := config.curvePreferences()[0] if _, ok := curveForCurveID(curveID); curveID != X25519 && !ok { return nil, nil, errors.New("tls: CurvePreferences includes unsupported curve") } params, err = generateECDHEParameters(config.rand(), curveID) if err != nil { return nil, nil, err } hello.keyShares = []keyShare{{group: curveID, data: params.PublicKey()}} } return hello, params, nil } func (c *Conn) clientHandshake(ctx context.Context) (err error) { if c.config == nil { c.config = defaultConfig() } // This may be a renegotiation handshake, in which case some fields // need to be reset. c.didResume = false hello, ecdheParams, err := c.makeClientHello() if err != nil { return err } c.serverName = hello.serverName cacheKey, session, earlySecret, binderKey := c.loadSession(hello) if cacheKey != "" && session != nil { defer func() { // If we got a handshake failure when resuming a session, throw away // the session ticket. See RFC 5077, Section 3.2. // // RFC 8446 makes no mention of dropping tickets on failure, but it // does require servers to abort on invalid binders, so we need to // delete tickets to recover from a corrupted PSK. if err != nil { c.config.ClientSessionCache.Put(cacheKey, nil) } }() } if _, err := c.writeRecord(recordTypeHandshake, hello.marshal()); err != nil { return err } msg, err := c.readHandshake() if err != nil { return err } serverHello, ok := msg.(*serverHelloMsg) if !ok { c.sendAlert(alertUnexpectedMessage) return unexpectedMessageError(serverHello, msg) } if err := c.pickTLSVersion(serverHello); err != nil { return err } // If we are negotiating a protocol version that's lower than what we // support, check for the server downgrade canaries. // See RFC 8446, Section 4.1.3. maxVers := c.config.maxSupportedVersion(roleClient) tls12Downgrade := string(serverHello.random[24:]) == downgradeCanaryTLS12 tls11Downgrade := string(serverHello.random[24:]) == downgradeCanaryTLS11 if maxVers == VersionTLS13 && c.vers <= VersionTLS12 && (tls12Downgrade || tls11Downgrade) || maxVers == VersionTLS12 && c.vers <= VersionTLS11 && tls11Downgrade { c.sendAlert(alertIllegalParameter) return errors.New("tls: downgrade attempt detected, possibly due to a MitM attack or a broken middlebox") } if c.vers == VersionTLS13 { hs := &clientHandshakeStateTLS13{ c: c, ctx: ctx, serverHello: serverHello, hello: hello, ecdheParams: ecdheParams, session: session, earlySecret: earlySecret, binderKey: binderKey, } // In TLS 1.3, session tickets are delivered after the handshake. return hs.handshake() } hs := &clientHandshakeState{ c: c, ctx: ctx, serverHello: serverHello, hello: hello, session: session, } if err := hs.handshake(); err != nil { return err } // If we had a successful handshake and hs.session is different from // the one already cached - cache a new one. if cacheKey != "" && hs.session != nil && session != hs.session { c.config.ClientSessionCache.Put(cacheKey, hs.session) } return nil } func (c *Conn) loadSession(hello *clientHelloMsg) (cacheKey string, session *ClientSessionState, earlySecret, binderKey []byte) { if c.config.SessionTicketsDisabled || c.config.ClientSessionCache == nil { return "", nil, nil, nil } hello.ticketSupported = true if hello.supportedVersions[0] == VersionTLS13 { // Require DHE on resumption as it guarantees forward secrecy against // compromise of the session ticket key. See RFC 8446, Section 4.2.9. hello.pskModes = []uint8{pskModeDHE} } // Session resumption is not allowed if renegotiating because // renegotiation is primarily used to allow a client to send a client // certificate, which would be skipped if session resumption occurred. if c.handshakes != 0 { return "", nil, nil, nil } // Try to resume a previously negotiated TLS session, if available. cacheKey = clientSessionCacheKey(c.conn.RemoteAddr(), c.config) session, ok := c.config.ClientSessionCache.Get(cacheKey) if !ok || session == nil { return cacheKey, nil, nil, nil } // Check that version used for the previous session is still valid. versOk := false for _, v := range hello.supportedVersions { if v == session.vers { versOk = true break } } if !versOk { return cacheKey, nil, nil, nil } // Check that the cached server certificate is not expired, and that it's // valid for the ServerName. This should be ensured by the cache key, but // protect the application from a faulty ClientSessionCache implementation. if !c.config.InsecureSkipVerify { if len(session.verifiedChains) == 0 { // The original connection had InsecureSkipVerify, while this doesn't. return cacheKey, nil, nil, nil } serverCert := session.serverCertificates[0] if c.config.time().After(serverCert.NotAfter) { // Expired certificate, delete the entry. c.config.ClientSessionCache.Put(cacheKey, nil) return cacheKey, nil, nil, nil } if err := serverCert.VerifyHostname(c.config.ServerName); err != nil { return cacheKey, nil, nil, nil } } if session.vers != VersionTLS13 { // In TLS 1.2 the cipher suite must match the resumed session. Ensure we // are still offering it. if mutualCipherSuite(hello.cipherSuites, session.cipherSuite) == nil { return cacheKey, nil, nil, nil } hello.sessionTicket = session.sessionTicket return } // Check that the session ticket is not expired. if c.config.time().After(session.useBy) { c.config.ClientSessionCache.Put(cacheKey, nil) return cacheKey, nil, nil, nil } // In TLS 1.3 the KDF hash must match the resumed session. Ensure we // offer at least one cipher suite with that hash. cipherSuite := cipherSuiteTLS13ByID(session.cipherSuite) if cipherSuite == nil { return cacheKey, nil, nil, nil } cipherSuiteOk := false for _, offeredID := range hello.cipherSuites { offeredSuite := cipherSuiteTLS13ByID(offeredID) if offeredSuite != nil && offeredSuite.hash == cipherSuite.hash { cipherSuiteOk = true break } } if !cipherSuiteOk { return cacheKey, nil, nil, nil } // Set the pre_shared_key extension. See RFC 8446, Section 4.2.11.1. ticketAge := uint32(c.config.time().Sub(session.receivedAt) / time.Millisecond) identity := pskIdentity{ label: session.sessionTicket, obfuscatedTicketAge: ticketAge + session.ageAdd, } hello.pskIdentities = []pskIdentity{identity} hello.pskBinders = [][]byte{make([]byte, cipherSuite.hash.Size())} // Compute the PSK binders. See RFC 8446, Section 4.2.11.2. psk := cipherSuite.expandLabel(session.masterSecret, "resumption", session.nonce, cipherSuite.hash.Size()) earlySecret = cipherSuite.extract(psk, nil) binderKey = cipherSuite.deriveSecret(earlySecret, resumptionBinderLabel, nil) transcript := cipherSuite.hash.New() transcript.Write(hello.marshalWithoutBinders()) pskBinders := [][]byte{cipherSuite.finishedHash(binderKey, transcript)} hello.updateBinders(pskBinders) return } func (c *Conn) pickTLSVersion(serverHello *serverHelloMsg) error { peerVersion := serverHello.vers if serverHello.supportedVersion != 0 { peerVersion = serverHello.supportedVersion } vers, ok := c.config.mutualVersion(roleClient, []uint16{peerVersion}) if !ok { c.sendAlert(alertProtocolVersion) return fmt.Errorf("tls: server selected unsupported protocol version %x", peerVersion) } c.vers = vers c.haveVers = true c.in.version = vers c.out.version = vers return nil } // Does the handshake, either a full one or resumes old session. Requires hs.c, // hs.hello, hs.serverHello, and, optionally, hs.session to be set. func (hs *clientHandshakeState) handshake() error { c := hs.c isResume, err := hs.processServerHello() if err != nil { return err } hs.finishedHash = newFinishedHash(c.vers, hs.suite) // No signatures of the handshake are needed in a resumption. // Otherwise, in a full handshake, if we don't have any certificates // configured then we will never send a CertificateVerify message and // thus no signatures are needed in that case either. if isResume || (len(c.config.Certificates) == 0 && c.config.GetClientCertificate == nil) { hs.finishedHash.discardHandshakeBuffer() } hs.finishedHash.Write(hs.hello.marshal()) hs.finishedHash.Write(hs.serverHello.marshal()) c.buffering = true c.didResume = isResume if isResume { if err := hs.establishKeys(); err != nil { return err } if err := hs.readSessionTicket(); err != nil { return err } if err := hs.readFinished(c.serverFinished[:]); err != nil { return err } c.clientFinishedIsFirst = false // Make sure the connection is still being verified whether or not this // is a resumption. Resumptions currently don't reverify certificates so // they don't call verifyServerCertificate. See Issue 31641. if c.config.VerifyConnection != nil { if err := c.config.VerifyConnection(c.connectionStateLocked()); err != nil { c.sendAlert(alertBadCertificate) return err } } if err := hs.sendFinished(c.clientFinished[:]); err != nil { return err } if _, err := c.flush(); err != nil { return err } } else { if err := hs.doFullHandshake(); err != nil { return err } if err := hs.establishKeys(); err != nil { return err } if err := hs.sendFinished(c.clientFinished[:]); err != nil { return err } if _, err := c.flush(); err != nil { return err } c.clientFinishedIsFirst = true if err := hs.readSessionTicket(); err != nil { return err } if err := hs.readFinished(c.serverFinished[:]); err != nil { return err } } c.ekm = ekmFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.hello.random, hs.serverHello.random) atomic.StoreUint32(&c.handshakeStatus, 1) return nil } func (hs *clientHandshakeState) pickCipherSuite() error { if hs.suite = mutualCipherSuite(hs.hello.cipherSuites, hs.serverHello.cipherSuite); hs.suite == nil { hs.c.sendAlert(alertHandshakeFailure) return errors.New("tls: server chose an unconfigured cipher suite") } hs.c.cipherSuite = hs.suite.id return nil } func (hs *clientHandshakeState) doFullHandshake() error { c := hs.c msg, err := c.readHandshake() if err != nil { return err } certMsg, ok := msg.(*certificateMsg) if !ok || len(certMsg.certificates) == 0 { c.sendAlert(alertUnexpectedMessage) return unexpectedMessageError(certMsg, msg) } hs.finishedHash.Write(certMsg.marshal()) msg, err = c.readHandshake() if err != nil { return err } cs, ok := msg.(*certificateStatusMsg) if ok { // RFC4366 on Certificate Status Request: // The server MAY return a "certificate_status" message. if !hs.serverHello.ocspStapling { // If a server returns a "CertificateStatus" message, then the // server MUST have included an extension of type "status_request" // with empty "extension_data" in the extended server hello. c.sendAlert(alertUnexpectedMessage) return errors.New("tls: received unexpected CertificateStatus message") } hs.finishedHash.Write(cs.marshal()) c.ocspResponse = cs.response msg, err = c.readHandshake() if err != nil { return err } } if c.handshakes == 0 { // If this is the first handshake on a connection, process and // (optionally) verify the server's certificates. if err := c.verifyServerCertificate(certMsg.certificates); err != nil { return err } } else { // This is a renegotiation handshake. We require that the // server's identity (i.e. leaf certificate) is unchanged and // thus any previous trust decision is still valid. // // See https://mitls.org/pages/attacks/3SHAKE for the // motivation behind this requirement. if !bytes.Equal(c.peerCertificates[0].Raw, certMsg.certificates[0]) { c.sendAlert(alertBadCertificate) return errors.New("tls: server's identity changed during renegotiation") } } keyAgreement := hs.suite.ka(c.vers) skx, ok := msg.(*serverKeyExchangeMsg) if ok { hs.finishedHash.Write(skx.marshal()) err = keyAgreement.processServerKeyExchange(c.config, hs.hello, hs.serverHello, c.peerCertificates[0], skx) if err != nil { c.sendAlert(alertUnexpectedMessage) return err } msg, err = c.readHandshake() if err != nil { return err } } var chainToSend *Certificate var certRequested bool certReq, ok := msg.(*certificateRequestMsg) if ok { certRequested = true hs.finishedHash.Write(certReq.marshal()) cri := certificateRequestInfoFromMsg(hs.ctx, c.vers, certReq) if chainToSend, err = c.getClientCertificate(cri); err != nil { c.sendAlert(alertInternalError) return err } msg, err = c.readHandshake() if err != nil { return err } } shd, ok := msg.(*serverHelloDoneMsg) if !ok { c.sendAlert(alertUnexpectedMessage) return unexpectedMessageError(shd, msg) } hs.finishedHash.Write(shd.marshal()) // If the server requested a certificate then we have to send a // Certificate message, even if it's empty because we don't have a // certificate to send. if certRequested { certMsg = new(certificateMsg) certMsg.certificates = chainToSend.Certificate hs.finishedHash.Write(certMsg.marshal()) if _, err := c.writeRecord(recordTypeHandshake, certMsg.marshal()); err != nil { return err } } preMasterSecret, ckx, err := keyAgreement.generateClientKeyExchange(c.config, hs.hello, c.peerCertificates[0]) if err != nil { c.sendAlert(alertInternalError) return err } if ckx != nil { hs.finishedHash.Write(ckx.marshal()) if _, err := c.writeRecord(recordTypeHandshake, ckx.marshal()); err != nil { return err } } if chainToSend != nil && len(chainToSend.Certificate) > 0 { certVerify := &certificateVerifyMsg{} key, ok := chainToSend.PrivateKey.(crypto.Signer) if !ok { c.sendAlert(alertInternalError) return fmt.Errorf("tls: client certificate private key of type %T does not implement crypto.Signer", chainToSend.PrivateKey) } var sigType uint8 var sigHash crypto.Hash if c.vers >= VersionTLS12 { signatureAlgorithm, err := selectSignatureScheme(c.vers, chainToSend, certReq.supportedSignatureAlgorithms) if err != nil { c.sendAlert(alertIllegalParameter) return err } sigType, sigHash, err = typeAndHashFromSignatureScheme(signatureAlgorithm) if err != nil { return c.sendAlert(alertInternalError) } certVerify.hasSignatureAlgorithm = true certVerify.signatureAlgorithm = signatureAlgorithm } else { sigType, sigHash, err = legacyTypeAndHashFromPublicKey(key.Public()) if err != nil { c.sendAlert(alertIllegalParameter) return err } } signed := hs.finishedHash.hashForClientCertificate(sigType, sigHash, hs.masterSecret) signOpts := crypto.SignerOpts(sigHash) if sigType == signatureRSAPSS { signOpts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: sigHash} } certVerify.signature, err = key.Sign(c.config.rand(), signed, signOpts) if err != nil { c.sendAlert(alertInternalError) return err } hs.finishedHash.Write(certVerify.marshal()) if _, err := c.writeRecord(recordTypeHandshake, certVerify.marshal()); err != nil { return err } } hs.masterSecret = masterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret, hs.hello.random, hs.serverHello.random) if err := c.config.writeKeyLog(keyLogLabelTLS12, hs.hello.random, hs.masterSecret); err != nil { c.sendAlert(alertInternalError) return errors.New("tls: failed to write to key log: " + err.Error()) } hs.finishedHash.discardHandshakeBuffer() return nil } func (hs *clientHandshakeState) establishKeys() error { c := hs.c clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV := keysFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.hello.random, hs.serverHello.random, hs.suite.macLen, hs.suite.keyLen, hs.suite.ivLen) var clientCipher, serverCipher any var clientHash, serverHash hash.Hash if hs.suite.cipher != nil { clientCipher = hs.suite.cipher(clientKey, clientIV, false /* not for reading */) clientHash = hs.suite.mac(clientMAC) serverCipher = hs.suite.cipher(serverKey, serverIV, true /* for reading */) serverHash = hs.suite.mac(serverMAC) } else { clientCipher = hs.suite.aead(clientKey, clientIV) serverCipher = hs.suite.aead(serverKey, serverIV) } c.in.prepareCipherSpec(c.vers, serverCipher, serverHash) c.out.prepareCipherSpec(c.vers, clientCipher, clientHash) return nil } func (hs *clientHandshakeState) serverResumedSession() bool { // If the server responded with the same sessionId then it means the // sessionTicket is being used to resume a TLS session. return hs.session != nil && hs.hello.sessionId != nil && bytes.Equal(hs.serverHello.sessionId, hs.hello.sessionId) } func (hs *clientHandshakeState) processServerHello() (bool, error) { c := hs.c if err := hs.pickCipherSuite(); err != nil { return false, err } if hs.serverHello.compressionMethod != compressionNone { c.sendAlert(alertUnexpectedMessage) return false, errors.New("tls: server selected unsupported compression format") } if c.handshakes == 0 && hs.serverHello.secureRenegotiationSupported { c.secureRenegotiation = true if len(hs.serverHello.secureRenegotiation) != 0 { c.sendAlert(alertHandshakeFailure) return false, errors.New("tls: initial handshake had non-empty renegotiation extension") } } if c.handshakes > 0 && c.secureRenegotiation { var expectedSecureRenegotiation [24]byte copy(expectedSecureRenegotiation[:], c.clientFinished[:]) copy(expectedSecureRenegotiation[12:], c.serverFinished[:]) if !bytes.Equal(hs.serverHello.secureRenegotiation, expectedSecureRenegotiation[:]) { c.sendAlert(alertHandshakeFailure) return false, errors.New("tls: incorrect renegotiation extension contents") } } if err := checkALPN(hs.hello.alpnProtocols, hs.serverHello.alpnProtocol); err != nil { c.sendAlert(alertUnsupportedExtension) return false, err } c.clientProtocol = hs.serverHello.alpnProtocol c.scts = hs.serverHello.scts if !hs.serverResumedSession() { return false, nil } if hs.session.vers != c.vers { c.sendAlert(alertHandshakeFailure) return false, errors.New("tls: server resumed a session with a different version") } if hs.session.cipherSuite != hs.suite.id { c.sendAlert(alertHandshakeFailure) return false, errors.New("tls: server resumed a session with a different cipher suite") } // Restore masterSecret, peerCerts, and ocspResponse from previous state hs.masterSecret = hs.session.masterSecret c.peerCertificates = hs.session.serverCertificates c.verifiedChains = hs.session.verifiedChains c.ocspResponse = hs.session.ocspResponse // Let the ServerHello SCTs override the session SCTs from the original // connection, if any are provided if len(c.scts) == 0 && len(hs.session.scts) != 0 { c.scts = hs.session.scts } return true, nil } // checkALPN ensure that the server's choice of ALPN protocol is compatible with // the protocols that we advertised in the Client Hello. func checkALPN(clientProtos []string, serverProto string) error { if serverProto == "" { return nil } if len(clientProtos) == 0 { return errors.New("tls: server advertised unrequested ALPN extension") } for _, proto := range clientProtos { if proto == serverProto { return nil } } return errors.New("tls: server selected unadvertised ALPN protocol") } func (hs *clientHandshakeState) readFinished(out []byte) error { c := hs.c if err := c.readChangeCipherSpec(); err != nil { return err } msg, err := c.readHandshake() if err != nil { return err } serverFinished, ok := msg.(*finishedMsg) if !ok { c.sendAlert(alertUnexpectedMessage) return unexpectedMessageError(serverFinished, msg) } verify := hs.finishedHash.serverSum(hs.masterSecret) if len(verify) != len(serverFinished.verifyData) || subtle.ConstantTimeCompare(verify, serverFinished.verifyData) != 1 { c.sendAlert(alertHandshakeFailure) return errors.New("tls: server's Finished message was incorrect") } hs.finishedHash.Write(serverFinished.marshal()) copy(out, verify) return nil } func (hs *clientHandshakeState) readSessionTicket() error { if !hs.serverHello.ticketSupported { return nil } c := hs.c msg, err := c.readHandshake() if err != nil { return err } sessionTicketMsg, ok := msg.(*newSessionTicketMsg) if !ok { c.sendAlert(alertUnexpectedMessage) return unexpectedMessageError(sessionTicketMsg, msg) } hs.finishedHash.Write(sessionTicketMsg.marshal()) hs.session = &ClientSessionState{ sessionTicket: sessionTicketMsg.ticket, vers: c.vers, cipherSuite: hs.suite.id, masterSecret: hs.masterSecret, serverCertificates: c.peerCertificates, verifiedChains: c.verifiedChains, receivedAt: c.config.time(), ocspResponse: c.ocspResponse, scts: c.scts, } return nil } func (hs *clientHandshakeState) sendFinished(out []byte) error { c := hs.c if _, err := c.writeRecord(recordTypeChangeCipherSpec, []byte{1}); err != nil { return err } finished := new(finishedMsg) finished.verifyData = hs.finishedHash.clientSum(hs.masterSecret) hs.finishedHash.Write(finished.marshal()) if _, err := c.writeRecord(recordTypeHandshake, finished.marshal()); err != nil { return err } copy(out, finished.verifyData) return nil } // verifyServerCertificate parses and verifies the provided chain, setting // c.verifiedChains and c.peerCertificates or sending the appropriate alert. func (c *Conn) verifyServerCertificate(certificates [][]byte) error { certs := make([]*x509.Certificate, len(certificates)) for i, asn1Data := range certificates { cert, err := x509.ParseCertificate(asn1Data) if err != nil { c.sendAlert(alertBadCertificate) return errors.New("tls: failed to parse certificate from server: " + err.Error()) } certs[i] = cert } if !c.config.InsecureSkipVerify { opts := x509.VerifyOptions{ Roots: c.config.RootCAs, CurrentTime: c.config.time(), DNSName: c.config.ServerName, Intermediates: x509.NewCertPool(), } for _, cert := range certs[1:] { opts.Intermediates.AddCert(cert) } var err error c.verifiedChains, err = certs[0].Verify(opts) if err != nil { c.sendAlert(alertBadCertificate) return err } } switch certs[0].PublicKey.(type) { case *rsa.PublicKey, *ecdsa.PublicKey, ed25519.PublicKey: break default: c.sendAlert(alertUnsupportedCertificate) return fmt.Errorf("tls: server's certificate contains an unsupported type of public key: %T", certs[0].PublicKey) } c.peerCertificates = certs if c.config.VerifyPeerCertificate != nil { if err := c.config.VerifyPeerCertificate(certificates, c.verifiedChains); err != nil { c.sendAlert(alertBadCertificate) return err } } if c.config.VerifyConnection != nil { if err := c.config.VerifyConnection(c.connectionStateLocked()); err != nil { c.sendAlert(alertBadCertificate) return err } } return nil } // certificateRequestInfoFromMsg generates a CertificateRequestInfo from a TLS // <= 1.2 CertificateRequest, making an effort to fill in missing information. func certificateRequestInfoFromMsg(ctx context.Context, vers uint16, certReq *certificateRequestMsg) *CertificateRequestInfo { cri := &CertificateRequestInfo{ AcceptableCAs: certReq.certificateAuthorities, Version: vers, ctx: ctx, } var rsaAvail, ecAvail bool for _, certType := range certReq.certificateTypes { switch certType { case certTypeRSASign: rsaAvail = true case certTypeECDSASign: ecAvail = true } } if !certReq.hasSignatureAlgorithm { // Prior to TLS 1.2, signature schemes did not exist. In this case we // make up a list based on the acceptable certificate types, to help // GetClientCertificate and SupportsCertificate select the right certificate. // The hash part of the SignatureScheme is a lie here, because // TLS 1.0 and 1.1 always use MD5+SHA1 for RSA and SHA1 for ECDSA. switch { case rsaAvail && ecAvail: cri.SignatureSchemes = []SignatureScheme{ ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1, } case rsaAvail: cri.SignatureSchemes = []SignatureScheme{ PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1, } case ecAvail: cri.SignatureSchemes = []SignatureScheme{ ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512, } } return cri } // Filter the signature schemes based on the certificate types. // See RFC 5246, Section 7.4.4 (where it calls this "somewhat complicated"). cri.SignatureSchemes = make([]SignatureScheme, 0, len(certReq.supportedSignatureAlgorithms)) for _, sigScheme := range certReq.supportedSignatureAlgorithms { sigType, _, err := typeAndHashFromSignatureScheme(sigScheme) if err != nil { continue } switch sigType { case signatureECDSA, signatureEd25519: if ecAvail { cri.SignatureSchemes = append(cri.SignatureSchemes, sigScheme) } case signatureRSAPSS, signaturePKCS1v15: if rsaAvail { cri.SignatureSchemes = append(cri.SignatureSchemes, sigScheme) } } } return cri } func (c *Conn) getClientCertificate(cri *CertificateRequestInfo) (*Certificate, error) { if c.config.GetClientCertificate != nil { return c.config.GetClientCertificate(cri) } for _, chain := range c.config.Certificates { if err := cri.SupportsCertificate(&chain); err != nil { continue } return &chain, nil } // No acceptable certificate found. Don't send a certificate. return new(Certificate), nil } // clientSessionCacheKey returns a key used to cache sessionTickets that could // be used to resume previously negotiated TLS sessions with a server. func clientSessionCacheKey(serverAddr net.Addr, config *Config) string { if len(config.ServerName) > 0 { return config.ServerName } return serverAddr.String() } // hostnameInSNI converts name into an appropriate hostname for SNI. // Literal IP addresses and absolute FQDNs are not permitted as SNI values. // See RFC 6066, Section 3. func hostnameInSNI(name string) string { host := name if len(host) > 0 && host[0] == '[' && host[len(host)-1] == ']' { host = host[1 : len(host)-1] } if i := strings.LastIndex(host, "%"); i > 0 { host = host[:i] } if net.ParseIP(host) != nil { return "" } for len(name) > 0 && name[len(name)-1] == '.' { name = name[:len(name)-1] } return name }