handshake_server.go

/*
Copyright Suzhou Tongji Fintech Research Institute 2017 All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

	https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package gmtls

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/rsa"
	"crypto/subtle"
	"encoding/asn1"
	"errors"
	"fmt"
	"io"

	"github.com/tjfoc/gmsm/sm2"
)

// serverHandshakeState contains details of a server handshake in progress.
// It's discarded once the handshake has completed.
type serverHandshakeState struct {
	c                     *Conn
	clientHello           *clientHelloMsg
	hello                 *serverHelloMsg
	suite                 *cipherSuite
	ellipticOk            bool
	ecdsaOk               bool
	rsaDecryptOk          bool
	rsaSignOk             bool
	sessionState          *sessionState
	finishedHash          finishedHash
	masterSecret          []byte
	certsFromClient       [][]byte
	cert                  *Certificate
	cachedClientHelloInfo *ClientHelloInfo
}

// serverHandshake performs a TLS handshake as a server.
// c.out.Mutex <= L; c.handshakeMutex <= L.
func (c *Conn) serverHandshake() error {
	// If this is the first server handshake, we generate a random key to
	// encrypt the tickets with.
	c.config.serverInitOnce.Do(c.config.serverInit)

	hs := serverHandshakeState{
		c: c,
	}
	isResume, err := hs.readClientHello()
	if err != nil {
		return err
	}

	// For an overview of TLS handshaking, see https://tools.ietf.org/html/rfc5246#section-7.3
	c.buffering = true
	if isResume {
		// The client has included a session ticket and so we do an abbreviated handshake.
		if err := hs.doResumeHandshake(); err != nil {
			return err
		}
		if err := hs.establishKeys(); err != nil {
			return err
		}
		// ticketSupported is set in a resumption handshake if the
		// ticket from the client was encrypted with an old session
		// ticket key and thus a refreshed ticket should be sent.
		if hs.hello.ticketSupported {
			if err := hs.sendSessionTicket(); err != nil {
				return err
			}
		}
		if err := hs.sendFinished(c.serverFinished[:]); err != nil {
			return err
		}
		if _, err := c.flush(); err != nil {
			return err
		}
		c.clientFinishedIsFirst = false
		if err := hs.readFinished(nil); err != nil {
			return err
		}
		c.didResume = true
	} else {
		// The client didn't include a session ticket, or it wasn't
		// valid so we do a full handshake.
		if err := hs.doFullHandshake(); err != nil {
			return err
		}
		if err := hs.establishKeys(); err != nil {
			return err
		}
		if err := hs.readFinished(c.clientFinished[:]); err != nil {
			return err
		}
		c.clientFinishedIsFirst = true
		c.buffering = true
		if err := hs.sendSessionTicket(); err != nil {
			return err
		}
		if err := hs.sendFinished(nil); err != nil {
			return err
		}
		if _, err := c.flush(); err != nil {
			return err
		}
	}
	c.handshakeComplete = true

	return nil
}

// readClientHello reads a ClientHello message from the client and decides
// whether we will perform session resumption.
func (hs *serverHandshakeState) readClientHello() (isResume bool, err error) {
	c := hs.c

	msg, err := c.readHandshake()
	if err != nil {
		return false, err
	}
	var ok bool
	hs.clientHello, ok = msg.(*clientHelloMsg)
	if !ok {
		c.sendAlert(alertUnexpectedMessage)
		return false, unexpectedMessageError(hs.clientHello, msg)
	}

	if c.config.GetConfigForClient != nil {
		if newConfig, err := c.config.GetConfigForClient(hs.clientHelloInfo()); err != nil {
			c.sendAlert(alertInternalError)
			return false, err
		} else if newConfig != nil {
			newConfig.mutex.Lock()
			newConfig.originalConfig = c.config
			newConfig.mutex.Unlock()

			newConfig.serverInitOnce.Do(newConfig.serverInit)
			c.config = newConfig
		}
	}

	c.vers, ok = c.config.mutualVersion(hs.clientHello.vers)
	if !ok {
		c.sendAlert(alertProtocolVersion)
		return false, fmt.Errorf("tls: client offered an unsupported, maximum protocol version of %x", hs.clientHello.vers)
	}
	c.haveVers = true

	hs.hello = new(serverHelloMsg)

	supportedCurve := false
	preferredCurves := c.config.curvePreferences()
Curves:
	for _, curve := range hs.clientHello.supportedCurves {
		for _, supported := range preferredCurves {
			if supported == curve {
				supportedCurve = true
				break Curves
			}
		}
	}

	supportedPointFormat := false
	for _, pointFormat := range hs.clientHello.supportedPoints {
		if pointFormat == pointFormatUncompressed {
			supportedPointFormat = true
			break
		}
	}
	hs.ellipticOk = supportedCurve && supportedPointFormat

	foundCompression := false
	// We only support null compression, so check that the client offered it.
	for _, compression := range hs.clientHello.compressionMethods {
		if compression == compressionNone {
			foundCompression = true
			break
		}
	}

	if !foundCompression {
		c.sendAlert(alertHandshakeFailure)
		return false, errors.New("tls: client does not support uncompressed connections")
	}

	hs.hello.vers = c.vers
	hs.hello.random = make([]byte, 32)
	_, err = io.ReadFull(c.config.rand(), hs.hello.random)
	if err != nil {
		c.sendAlert(alertInternalError)
		return false, err
	}

	if len(hs.clientHello.secureRenegotiation) != 0 {
		c.sendAlert(alertHandshakeFailure)
		return false, errors.New("tls: initial handshake had non-empty renegotiation extension")
	}

	hs.hello.secureRenegotiationSupported = hs.clientHello.secureRenegotiationSupported
	hs.hello.compressionMethod = compressionNone
	if len(hs.clientHello.serverName) > 0 {
		c.serverName = hs.clientHello.serverName
	}

	if len(hs.clientHello.alpnProtocols) > 0 {
		if selectedProto, fallback := mutualProtocol(hs.clientHello.alpnProtocols, c.config.NextProtos); !fallback {
			hs.hello.alpnProtocol = selectedProto
			c.clientProtocol = selectedProto
		}
	} else {
		// Although sending an empty NPN extension is reasonable, Firefox has
		// had a bug around this. Best to send nothing at all if
		// c.config.NextProtos is empty. See
		// https://golang.org/issue/5445.
		if hs.clientHello.nextProtoNeg && len(c.config.NextProtos) > 0 {
			hs.hello.nextProtoNeg = true
			hs.hello.nextProtos = c.config.NextProtos
		}
	}

	hs.cert, err = c.config.getCertificate(hs.clientHelloInfo())
	if err != nil {
		c.sendAlert(alertInternalError)
		return false, err
	}
	if hs.clientHello.scts {
		hs.hello.scts = hs.cert.SignedCertificateTimestamps
	}

	if priv, ok := hs.cert.PrivateKey.(crypto.Signer); ok {
		switch priv.Public().(type) {
		case *ecdsa.PublicKey:
			hs.ecdsaOk = true
		case *rsa.PublicKey:
			hs.rsaSignOk = true
		case *sm2.PublicKey:
			hs.ecdsaOk = true
		default:
			c.sendAlert(alertInternalError)
			return false, fmt.Errorf("tls: unsupported signing key type (%T)", priv.Public())
		}
	}
	if priv, ok := hs.cert.PrivateKey.(crypto.Decrypter); ok {
		switch priv.Public().(type) {
		case *rsa.PublicKey:
			hs.rsaDecryptOk = true
		default:
			c.sendAlert(alertInternalError)
			return false, fmt.Errorf("tls: unsupported decryption key type (%T)", priv.Public())
		}
	}

	if hs.checkForResumption() {
		return true, nil
	}

	var preferenceList, supportedList []uint16
	if c.config.PreferServerCipherSuites {
		preferenceList = c.config.cipherSuites()
		supportedList = hs.clientHello.cipherSuites
	} else {
		preferenceList = hs.clientHello.cipherSuites
		supportedList = c.config.cipherSuites()
	}

	for _, id := range preferenceList {
		if hs.setCipherSuite(id, supportedList, c.vers) {
			break
		}
	}

	if hs.suite == nil {
		c.sendAlert(alertHandshakeFailure)
		return false, errors.New("tls: no cipher suite supported by both client and server")
	}

	// See https://tools.ietf.org/html/rfc7507.
	for _, id := range hs.clientHello.cipherSuites {
		if id == TLS_FALLBACK_SCSV {
			// The client is doing a fallback connection.
			if hs.clientHello.vers < c.config.maxVersion() {
				c.sendAlert(alertInappropriateFallback)
				return false, errors.New("tls: client using inappropriate protocol fallback")
			}
			break
		}
	}

	return false, nil
}

// checkForResumption reports whether we should perform resumption on this connection.
func (hs *serverHandshakeState) checkForResumption() bool {
	c := hs.c

	if c.config.SessionTicketsDisabled {
		return false
	}

	var ok bool
	var sessionTicket = append([]uint8{}, hs.clientHello.sessionTicket...)
	if hs.sessionState, ok = c.decryptTicket(sessionTicket); !ok {
		return false
	}

	// Never resume a session for a different TLS version.
	if c.vers != hs.sessionState.vers {
		return false
	}

	cipherSuiteOk := false
	// Check that the client is still offering the ciphersuite in the session.
	for _, id := range hs.clientHello.cipherSuites {
		if id == hs.sessionState.cipherSuite {
			cipherSuiteOk = true
			break
		}
	}
	if !cipherSuiteOk {
		return false
	}

	// Check that we also support the ciphersuite from the session.
	if !hs.setCipherSuite(hs.sessionState.cipherSuite, c.config.cipherSuites(), hs.sessionState.vers) {
		return false
	}

	sessionHasClientCerts := len(hs.sessionState.certificates) != 0
	needClientCerts := c.config.ClientAuth == RequireAnyClientCert || c.config.ClientAuth == RequireAndVerifyClientCert
	if needClientCerts && !sessionHasClientCerts {
		return false
	}
	if sessionHasClientCerts && c.config.ClientAuth == NoClientCert {
		return false
	}

	return true
}

func (hs *serverHandshakeState) doResumeHandshake() error {
	c := hs.c

	hs.hello.cipherSuite = hs.suite.id
	// We echo the client's session ID in the ServerHello to let it know
	// that we're doing a resumption.
	hs.hello.sessionId = hs.clientHello.sessionId
	hs.hello.ticketSupported = hs.sessionState.usedOldKey
	hs.finishedHash = newFinishedHash(c.vers, hs.suite)
	hs.finishedHash.discardHandshakeBuffer()
	hs.finishedHash.Write(hs.clientHello.marshal())
	hs.finishedHash.Write(hs.hello.marshal())
	if _, err := c.writeRecord(recordTypeHandshake, hs.hello.marshal()); err != nil {
		return err
	}

	if len(hs.sessionState.certificates) > 0 {
		if _, err := hs.processCertsFromClient(hs.sessionState.certificates); err != nil {
			return err
		}
	}

	hs.masterSecret = hs.sessionState.masterSecret

	return nil
}

func (hs *serverHandshakeState) doFullHandshake() error {
	c := hs.c

	if hs.clientHello.ocspStapling && len(hs.cert.OCSPStaple) > 0 {
		hs.hello.ocspStapling = true
	}

	hs.hello.ticketSupported = hs.clientHello.ticketSupported && !c.config.SessionTicketsDisabled
	hs.hello.cipherSuite = hs.suite.id

	hs.finishedHash = newFinishedHash(hs.c.vers, hs.suite)
	if c.config.ClientAuth == NoClientCert {
		// No need to keep a full record of the handshake if client
		// certificates won't be used.
		hs.finishedHash.discardHandshakeBuffer()
	}
	hs.finishedHash.Write(hs.clientHello.marshal())
	hs.finishedHash.Write(hs.hello.marshal())
	if _, err := c.writeRecord(recordTypeHandshake, hs.hello.marshal()); err != nil {
		return err
	}

	certMsg := new(certificateMsg)
	certMsg.certificates = hs.cert.Certificate
	hs.finishedHash.Write(certMsg.marshal())
	if _, err := c.writeRecord(recordTypeHandshake, certMsg.marshal()); err != nil {
		return err
	}

	if hs.hello.ocspStapling {
		certStatus := new(certificateStatusMsg)
		certStatus.statusType = statusTypeOCSP
		certStatus.response = hs.cert.OCSPStaple
		hs.finishedHash.Write(certStatus.marshal())
		if _, err := c.writeRecord(recordTypeHandshake, certStatus.marshal()); err != nil {
			return err
		}
	}

	keyAgreement := hs.suite.ka(c.vers)
	skx, err := keyAgreement.generateServerKeyExchange(c.config, hs.cert, hs.clientHello, hs.hello)
	if err != nil {
		c.sendAlert(alertHandshakeFailure)
		return err
	}
	if skx != nil {
		hs.finishedHash.Write(skx.marshal())
		if _, err := c.writeRecord(recordTypeHandshake, skx.marshal()); err != nil {
			return err
		}
	}

	if c.config.ClientAuth >= RequestClientCert {
		// Request a client certificate
		certReq := new(certificateRequestMsg)
		certReq.certificateTypes = []byte{
			byte(certTypeRSASign),
			byte(certTypeECDSASign),
		}
		if c.vers >= VersionTLS12 {
			certReq.hasSignatureAndHash = true
			certReq.signatureAndHashes = supportedSignatureAlgorithms
		}

		// An empty list of certificateAuthorities signals to
		// the client that it may send any certificate in response
		// to our request. When we know the CAs we trust, then
		// we can send them down, so that the client can choose
		// an appropriate certificate to give to us.
		if c.config.ClientCAs != nil {
			certReq.certificateAuthorities = c.config.ClientCAs.Subjects()
		}
		hs.finishedHash.Write(certReq.marshal())
		if _, err := c.writeRecord(recordTypeHandshake, certReq.marshal()); err != nil {
			return err
		}
	}

	helloDone := new(serverHelloDoneMsg)
	hs.finishedHash.Write(helloDone.marshal())
	if _, err := c.writeRecord(recordTypeHandshake, helloDone.marshal()); err != nil {
		return err
	}

	if _, err := c.flush(); err != nil {
		return err
	}

	var pub crypto.PublicKey // public key for client auth, if any

	msg, err := c.readHandshake()
	if err != nil {
		return err
	}

	var ok bool
	// If we requested a client certificate, then the client must send a
	// certificate message, even if it's empty.
	if c.config.ClientAuth >= RequestClientCert {
		if certMsg, ok = msg.(*certificateMsg); !ok {
			c.sendAlert(alertUnexpectedMessage)
			return unexpectedMessageError(certMsg, msg)
		}
		hs.finishedHash.Write(certMsg.marshal())

		if len(certMsg.certificates) == 0 {
			// The client didn't actually send a certificate
			switch c.config.ClientAuth {
			case RequireAnyClientCert, RequireAndVerifyClientCert:
				c.sendAlert(alertBadCertificate)
				return errors.New("tls: client didn't provide a certificate")
			}
		}

		pub, err = hs.processCertsFromClient(certMsg.certificates)
		if err != nil {
			return err
		}

		msg, err = c.readHandshake()
		if err != nil {
			return err
		}
	}

	// Get client key exchange
	ckx, ok := msg.(*clientKeyExchangeMsg)
	if !ok {
		c.sendAlert(alertUnexpectedMessage)
		return unexpectedMessageError(ckx, msg)
	}
	hs.finishedHash.Write(ckx.marshal())

	preMasterSecret, err := keyAgreement.processClientKeyExchange(c.config, hs.cert, ckx, c.vers)
	if err != nil {
		c.sendAlert(alertHandshakeFailure)
		return err
	}
	hs.masterSecret = masterFromPreMasterSecret(c.vers, hs.suite, preMasterSecret, hs.clientHello.random, hs.hello.random)
	if err := c.config.writeKeyLog(hs.clientHello.random, hs.masterSecret); err != nil {
		c.sendAlert(alertInternalError)
		return err
	}

	// If we received a client cert in response to our certificate request message,
	// the client will send us a certificateVerifyMsg immediately after the
	// clientKeyExchangeMsg. This message is a digest of all preceding
	// handshake-layer messages that is signed using the private key corresponding
	// to the client's certificate. This allows us to verify that the client is in
	// possession of the private key of the certificate.
	if len(c.peerCertificates) > 0 {
		msg, err = c.readHandshake()
		if err != nil {
			return err
		}
		certVerify, ok := msg.(*certificateVerifyMsg)
		if !ok {
			c.sendAlert(alertUnexpectedMessage)
			return unexpectedMessageError(certVerify, msg)
		}

		// Determine the signature type.
		var signatureAndHash signatureAndHash
		if certVerify.hasSignatureAndHash {
			signatureAndHash = certVerify.signatureAndHash
			if !isSupportedSignatureAndHash(signatureAndHash, supportedSignatureAlgorithms) {
				return errors.New("tls: unsupported hash function for client certificate")
			}
		} else {
			// Before TLS 1.2 the signature algorithm was implicit
			// from the key type, and only one hash per signature
			// algorithm was possible. Leave the hash as zero.
			switch pub.(type) {
			case *ecdsa.PublicKey:
				signatureAndHash.signature = signatureECDSA
			case *rsa.PublicKey:
				signatureAndHash.signature = signatureRSA
			}
		}

		switch key := pub.(type) {
		case *ecdsa.PublicKey:
			if signatureAndHash.signature != signatureECDSA {
				err = errors.New("tls: bad signature type for client's ECDSA certificate")
				break
			}
			ecdsaSig := new(ecdsaSignature)
			if _, err = asn1.Unmarshal(certVerify.signature, ecdsaSig); err != nil {
				break
			}
			if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
				err = errors.New("tls: ECDSA signature contained zero or negative values")
				break
			}
			var digest []byte
			if digest, _, err = hs.finishedHash.hashForClientCertificate(signatureAndHash, hs.masterSecret); err != nil {
				break
			}
			switch key.Curve {
			case sm2.P256Sm2():
				if !sm2.Sm2Verify(&sm2.PublicKey{
					X:     key.X,
					Y:     key.Y,
					Curve: key.Curve,
				}, digest, nil, ecdsaSig.R, ecdsaSig.S) {
					err = errors.New("tls: SM2 verification failure")
				}
			default:
				if !ecdsa.Verify(key, digest, ecdsaSig.R, ecdsaSig.S) {
					err = errors.New("tls: ECDSA verification failure")
				}
			}
		case *rsa.PublicKey:
			if signatureAndHash.signature != signatureRSA {
				err = errors.New("tls: bad signature type for client's RSA certificate")
				break
			}
			var digest []byte
			var hashFunc crypto.Hash
			if digest, hashFunc, err = hs.finishedHash.hashForClientCertificate(signatureAndHash, hs.masterSecret); err != nil {
				break
			}
			err = rsa.VerifyPKCS1v15(key, hashFunc, digest, certVerify.signature)
		}
		if err != nil {
			c.sendAlert(alertBadCertificate)
			return errors.New("tls: could not validate signature of connection nonces: " + err.Error())
		}

		hs.finishedHash.Write(certVerify.marshal())
	}

	hs.finishedHash.discardHandshakeBuffer()

	return nil
}

func (hs *serverHandshakeState) establishKeys() error {
	c := hs.c

	clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV :=
		keysFromMasterSecret(c.vers, hs.suite, hs.masterSecret, hs.clientHello.random, hs.hello.random, hs.suite.macLen, hs.suite.keyLen, hs.suite.ivLen)

	var clientCipher, serverCipher interface{}
	var clientHash, serverHash macFunction

	if hs.suite.aead == nil {
		clientCipher = hs.suite.cipher(clientKey, clientIV, true /* for reading */)
		clientHash = hs.suite.mac(c.vers, clientMAC)
		serverCipher = hs.suite.cipher(serverKey, serverIV, false /* not for reading */)
		serverHash = hs.suite.mac(c.vers, serverMAC)
	} else {
		clientCipher = hs.suite.aead(clientKey, clientIV)
		serverCipher = hs.suite.aead(serverKey, serverIV)
	}

	c.in.prepareCipherSpec(c.vers, clientCipher, clientHash)
	c.out.prepareCipherSpec(c.vers, serverCipher, serverHash)

	return nil
}

func (hs *serverHandshakeState) readFinished(out []byte) error {
	c := hs.c

	c.readRecord(recordTypeChangeCipherSpec)
	if c.in.err != nil {
		return c.in.err
	}

	if hs.hello.nextProtoNeg {
		msg, err := c.readHandshake()
		if err != nil {
			return err
		}
		nextProto, ok := msg.(*nextProtoMsg)
		if !ok {
			c.sendAlert(alertUnexpectedMessage)
			return unexpectedMessageError(nextProto, msg)
		}
		hs.finishedHash.Write(nextProto.marshal())
		c.clientProtocol = nextProto.proto
	}

	msg, err := c.readHandshake()
	if err != nil {
		return err
	}
	clientFinished, ok := msg.(*finishedMsg)
	if !ok {
		c.sendAlert(alertUnexpectedMessage)
		return unexpectedMessageError(clientFinished, msg)
	}

	verify := hs.finishedHash.clientSum(hs.masterSecret)
	if len(verify) != len(clientFinished.verifyData) ||
		subtle.ConstantTimeCompare(verify, clientFinished.verifyData) != 1 {
		c.sendAlert(alertHandshakeFailure)
		return errors.New("tls: client's Finished message is incorrect")
	}

	hs.finishedHash.Write(clientFinished.marshal())
	copy(out, verify)
	return nil
}

func (hs *serverHandshakeState) sendSessionTicket() error {
	if !hs.hello.ticketSupported {
		return nil
	}

	c := hs.c
	m := new(newSessionTicketMsg)

	var err error
	state := sessionState{
		vers:         c.vers,
		cipherSuite:  hs.suite.id,
		masterSecret: hs.masterSecret,
		certificates: hs.certsFromClient,
	}
	m.ticket, err = c.encryptTicket(&state)
	if err != nil {
		return err
	}

	hs.finishedHash.Write(m.marshal())
	if _, err := c.writeRecord(recordTypeHandshake, m.marshal()); err != nil {
		return err
	}

	return nil
}

func (hs *serverHandshakeState) 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.serverSum(hs.masterSecret)
	hs.finishedHash.Write(finished.marshal())
	if _, err := c.writeRecord(recordTypeHandshake, finished.marshal()); err != nil {
		return err
	}

	c.cipherSuite = hs.suite.id
	copy(out, finished.verifyData)

	return nil
}

// processCertsFromClient takes a chain of client certificates either from a
// Certificates message or from a sessionState and verifies them. It returns
// the public key of the leaf certificate.
func (hs *serverHandshakeState) processCertsFromClient(certificates [][]byte) (crypto.PublicKey, error) {
	c := hs.c

	hs.certsFromClient = certificates
	certs := make([]*sm2.Certificate, len(certificates))
	var err error
	for i, asn1Data := range certificates {
		if certs[i], err = sm2.ParseCertificate(asn1Data); err != nil {
			c.sendAlert(alertBadCertificate)
			return nil, errors.New("tls: failed to parse client certificate: " + err.Error())
		}
	}

	if c.config.ClientAuth >= VerifyClientCertIfGiven && len(certs) > 0 {
		opts := sm2.VerifyOptions{
			Roots:         c.config.ClientCAs,
			CurrentTime:   c.config.time(),
			Intermediates: sm2.NewCertPool(),
			KeyUsages:     []sm2.ExtKeyUsage{sm2.ExtKeyUsageClientAuth},
		}

		for _, cert := range certs[1:] {
			opts.Intermediates.AddCert(cert)
		}

		chains, err := certs[0].Verify(opts)
		if err != nil {
			c.sendAlert(alertBadCertificate)
			return nil, errors.New("tls: failed to verify client's certificate: " + err.Error())
		}

		c.verifiedChains = chains
	}

	if c.config.VerifyPeerCertificate != nil {
		if err := c.config.VerifyPeerCertificate(certificates, c.verifiedChains); err != nil {
			c.sendAlert(alertBadCertificate)
			return nil, err
		}
	}

	if len(certs) == 0 {
		return nil, nil
	}

	var pub crypto.PublicKey
	switch key := certs[0].PublicKey.(type) {
	case *ecdsa.PublicKey, *rsa.PublicKey:
		pub = key
	default:
		c.sendAlert(alertUnsupportedCertificate)
		return nil, fmt.Errorf("tls: client's certificate contains an unsupported public key of type %T", certs[0].PublicKey)
	}
	c.peerCertificates = certs
	return pub, nil
}

// setCipherSuite sets a cipherSuite with the given id as the serverHandshakeState
// suite if that cipher suite is acceptable to use.
// It returns a bool indicating if the suite was set.
func (hs *serverHandshakeState) setCipherSuite(id uint16, supportedCipherSuites []uint16, version uint16) bool {
	for _, supported := range supportedCipherSuites {
		if id == supported {
			var candidate *cipherSuite

			for _, s := range cipherSuites {
				if s.id == id {
					candidate = s
					break
				}
			}
			if candidate == nil {
				continue
			}
			// Don't select a ciphersuite which we can't
			// support for this client.
			if candidate.flags&suiteECDHE != 0 {
				if !hs.ellipticOk {
					continue
				}
				if candidate.flags&suiteECDSA != 0 {
					if !hs.ecdsaOk {
						continue
					}
				} else if !hs.rsaSignOk {
					continue
				}
			} else if !hs.rsaDecryptOk {
				continue
			}
			if version < VersionTLS12 && candidate.flags&suiteTLS12 != 0 {
				continue
			}
			hs.suite = candidate
			return true
		}
	}
	return false
}

// suppVersArray is the backing array of ClientHelloInfo.SupportedVersions
var suppVersArray = [...]uint16{VersionTLS12, VersionTLS11, VersionTLS10, VersionSSL30}

func (hs *serverHandshakeState) clientHelloInfo() *ClientHelloInfo {
	if hs.cachedClientHelloInfo != nil {
		return hs.cachedClientHelloInfo
	}

	var supportedVersions []uint16
	if hs.clientHello.vers > VersionTLS12 {
		supportedVersions = suppVersArray[:]
	} else if hs.clientHello.vers >= VersionSSL30 {
		supportedVersions = suppVersArray[VersionTLS12-hs.clientHello.vers:]
	}

	signatureSchemes := make([]SignatureScheme, 0, len(hs.clientHello.signatureAndHashes))
	for _, sah := range hs.clientHello.signatureAndHashes {
		signatureSchemes = append(signatureSchemes, SignatureScheme(sah.hash)<<8+SignatureScheme(sah.signature))
	}

	hs.cachedClientHelloInfo = &ClientHelloInfo{
		CipherSuites:      hs.clientHello.cipherSuites,
		ServerName:        hs.clientHello.serverName,
		SupportedCurves:   hs.clientHello.supportedCurves,
		SupportedPoints:   hs.clientHello.supportedPoints,
		SignatureSchemes:  signatureSchemes,
		SupportedProtos:   hs.clientHello.alpnProtocols,
		SupportedVersions: supportedVersions,
		Conn:              hs.c.conn,
	}

	return hs.cachedClientHelloInfo
}