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// 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 (
"crypto"
"crypto/ecdsa"
"crypto/rsa"
"crypto/subtle"
"crypto/x509"
"encoding/asn1"
"errors"
"fmt"
"io"
)
// 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
sessionState *sessionState
finishedHash finishedHash
masterSecret []byte
certsFromClient [][]byte
cert *Certificate
}
// serverHandshake performs a TLS handshake as a server.
func (c *Conn) serverHandshake() error {
config := c.config
// If this is the first server handshake, we generate a random key to
// encrypt the tickets with.
config.serverInitOnce.Do(config.serverInit)
hs := serverHandshakeState{
c: c,
}
isResume, err := hs.readClientHello()
if err != nil {
return err
}
hs.finishedHash = newFinishedHash(hs.c.vers, hs.suite.tls12Hash)
hs.finishedHash.Write(hs.clientHello.marshal())
// For an overview of TLS handshaking, see https://tools.ietf.org/html/rfc5246#section-7.3
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
}
if err := hs.sendFinished(c.firstFinished[:]); err != nil {
return err
}
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.firstFinished[:]); err != nil {
return err
}
if err := hs.sendSessionTicket(); err != nil {
return err
}
if err := hs.sendFinished(nil); 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) {
config := hs.c.config
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)
}
c.vers, ok = 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 := 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(config.rand(), hs.hello.random)
if err != nil {
c.sendAlert(alertInternalError)
return false, err
}
hs.hello.secureRenegotiation = hs.clientHello.secureRenegotiation
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
// config.NextProtos is empty. See
// https://golang.org/issue/5445.
if hs.clientHello.nextProtoNeg && len(config.NextProtos) > 0 {
hs.hello.nextProtoNeg = true
hs.hello.nextProtos = config.NextProtos
}
}
if len(config.Certificates) == 0 {
c.sendAlert(alertInternalError)
return false, errors.New("tls: no certificates configured")
}
hs.cert = &config.Certificates[0]
if len(hs.clientHello.serverName) > 0 {
chi := &ClientHelloInfo{
CipherSuites: hs.clientHello.cipherSuites,
ServerName: hs.clientHello.serverName,
SupportedCurves: hs.clientHello.supportedCurves,
SupportedPoints: hs.clientHello.supportedPoints,
}
if hs.cert, err = config.getCertificate(chi); err != nil {
c.sendAlert(alertInternalError)
return false, err
}
}
_, hs.ecdsaOk = hs.cert.PrivateKey.(*ecdsa.PrivateKey)
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.suite = c.tryCipherSuite(id, supportedList, c.vers, hs.ellipticOk, hs.ecdsaOk); hs.suite != nil {
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/draft-ietf-tls-downgrade-scsv-00.
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 inppropriate protocol fallback")
}
break
}
}
return false, nil
}
// checkForResumption returns true if 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
}
if hs.sessionState.vers > hs.clientHello.vers {
return false
}
if vers, ok := c.config.mutualVersion(hs.sessionState.vers); !ok || 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.
hs.suite = c.tryCipherSuite(hs.sessionState.cipherSuite, c.config.cipherSuites(), hs.sessionState.vers, hs.ellipticOk, hs.ecdsaOk)
if hs.suite == nil {
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.finishedHash.Write(hs.hello.marshal())
c.writeRecord(recordTypeHandshake, hs.hello.marshal())
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 {
config := hs.c.config
c := hs.c
if hs.clientHello.ocspStapling && len(hs.cert.OCSPStaple) > 0 {
hs.hello.ocspStapling = true
}
hs.hello.ticketSupported = hs.clientHello.ticketSupported && !config.SessionTicketsDisabled
hs.hello.cipherSuite = hs.suite.id
hs.finishedHash.Write(hs.hello.marshal())
c.writeRecord(recordTypeHandshake, hs.hello.marshal())
certMsg := new(certificateMsg)
certMsg.certificates = hs.cert.Certificate
hs.finishedHash.Write(certMsg.marshal())
c.writeRecord(recordTypeHandshake, certMsg.marshal())
if hs.hello.ocspStapling {
certStatus := new(certificateStatusMsg)
certStatus.statusType = statusTypeOCSP
certStatus.response = hs.cert.OCSPStaple
hs.finishedHash.Write(certStatus.marshal())
c.writeRecord(recordTypeHandshake, certStatus.marshal())
}
keyAgreement := hs.suite.ka(c.vers)
skx, err := keyAgreement.generateServerKeyExchange(config, hs.cert, hs.clientHello, hs.hello)
if err != nil {
c.sendAlert(alertHandshakeFailure)
return err
}
if skx != nil {
hs.finishedHash.Write(skx.marshal())
c.writeRecord(recordTypeHandshake, skx.marshal())
}
if 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 = supportedClientCertSignatureAlgorithms
}
// 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 config.ClientCAs != nil {
certReq.certificateAuthorities = config.ClientCAs.Subjects()
}
hs.finishedHash.Write(certReq.marshal())
c.writeRecord(recordTypeHandshake, certReq.marshal())
}
helloDone := new(serverHelloDoneMsg)
hs.finishedHash.Write(helloDone.marshal())
c.writeRecord(recordTypeHandshake, helloDone.marshal())
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 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 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())
// 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)
}
switch key := pub.(type) {
case *ecdsa.PublicKey:
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("ECDSA signature contained zero or negative values")
break
}
digest, _, _ := hs.finishedHash.hashForClientCertificate(signatureECDSA)
if !ecdsa.Verify(key, digest, ecdsaSig.R, ecdsaSig.S) {
err = errors.New("ECDSA verification failure")
break
}
case *rsa.PublicKey:
digest, hashFunc, _ := hs.finishedHash.hashForClientCertificate(signatureRSA)
err = rsa.VerifyPKCS1v15(key, hashFunc, digest, certVerify.signature)
}
if err != nil {
c.sendAlert(alertBadCertificate)
return errors.New("could not validate signature of connection nonces: " + err.Error())
}
hs.finishedHash.Write(certVerify.marshal())
}
preMasterSecret, err := keyAgreement.processClientKeyExchange(config, hs.cert, ckx, c.vers)
if err != nil {
c.sendAlert(alertHandshakeFailure)
return err
}
hs.masterSecret = masterFromPreMasterSecret(c.vers, hs.suite.tls12Hash, preMasterSecret, hs.clientHello.random, hs.hello.random)
return nil
}
func (hs *serverHandshakeState) establishKeys() error {
c := hs.c
clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV :=
keysFromMasterSecret(c.vers, hs.suite.tls12Hash, 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 err := c.in.error(); err != nil {
return 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())
c.writeRecord(recordTypeHandshake, m.marshal())
return nil
}
func (hs *serverHandshakeState) sendFinished(out []byte) error {
c := hs.c
c.writeRecord(recordTypeChangeCipherSpec, []byte{1})
finished := new(finishedMsg)
finished.verifyData = hs.finishedHash.serverSum(hs.masterSecret)
hs.finishedHash.Write(finished.marshal())
c.writeRecord(recordTypeHandshake, finished.marshal())
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([]*x509.Certificate, len(certificates))
var err error
for i, asn1Data := range certificates {
if certs[i], err = x509.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 := x509.VerifyOptions{
Roots: c.config.ClientCAs,
CurrentTime: c.config.time(),
Intermediates: x509.NewCertPool(),
KeyUsages: []x509.ExtKeyUsage{x509.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())
}
ok := false
for _, ku := range certs[0].ExtKeyUsage {
if ku == x509.ExtKeyUsageClientAuth {
ok = true
break
}
}
if !ok {
c.sendAlert(alertHandshakeFailure)
return nil, errors.New("tls: client's certificate's extended key usage doesn't permit it to be used for client authentication")
}
c.verifiedChains = chains
}
if len(certs) > 0 {
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
}
return nil, nil
}
// tryCipherSuite returns a cipherSuite with the given id if that cipher suite
// is acceptable to use.
func (c *Conn) tryCipherSuite(id uint16, supportedCipherSuites []uint16, version uint16, ellipticOk, ecdsaOk bool) *cipherSuite {
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) && !ellipticOk {
continue
}
if (candidate.flags&suiteECDSA != 0) != ecdsaOk {
continue
}
if version < VersionTLS12 && candidate.flags&suiteTLS12 != 0 {
continue
}
return candidate
}
}
return nil
}