th5/handshake_client.go

// 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/hmac"
	"crypto/rc4"
	"crypto/rsa"
	"crypto/subtle"
	"crypto/x509"
	"io"
	"os"
)

func (c *Conn) clientHandshake() os.Error {
	finishedHash := newFinishedHash()

	if c.config == nil {
		c.config = defaultConfig()
	}

	hello := &clientHelloMsg{
		vers:               maxVersion,
		cipherSuites:       []uint16{TLS_RSA_WITH_RC4_128_SHA},
		compressionMethods: []uint8{compressionNone},
		random:             make([]byte, 32),
		ocspStapling:       true,
		serverName:         c.config.ServerName,
	}

	t := uint32(c.config.Time())
	hello.random[0] = byte(t >> 24)
	hello.random[1] = byte(t >> 16)
	hello.random[2] = byte(t >> 8)
	hello.random[3] = byte(t)
	_, err := io.ReadFull(c.config.Rand, hello.random[4:])
	if err != nil {
		c.sendAlert(alertInternalError)
		return os.ErrorString("short read from Rand")
	}

	finishedHash.Write(hello.marshal())
	c.writeRecord(recordTypeHandshake, hello.marshal())

	msg, err := c.readHandshake()
	if err != nil {
		return err
	}
	serverHello, ok := msg.(*serverHelloMsg)
	if !ok {
		return c.sendAlert(alertUnexpectedMessage)
	}
	finishedHash.Write(serverHello.marshal())

	vers, ok := mutualVersion(serverHello.vers)
	if !ok {
		c.sendAlert(alertProtocolVersion)
	}
	c.vers = vers
	c.haveVers = true

	if serverHello.cipherSuite != TLS_RSA_WITH_RC4_128_SHA ||
		serverHello.compressionMethod != compressionNone {
		return c.sendAlert(alertUnexpectedMessage)
	}

	msg, err = c.readHandshake()
	if err != nil {
		return err
	}
	certMsg, ok := msg.(*certificateMsg)
	if !ok || len(certMsg.certificates) == 0 {
		return c.sendAlert(alertUnexpectedMessage)
	}
	finishedHash.Write(certMsg.marshal())

	certs := make([]*x509.Certificate, len(certMsg.certificates))
	for i, asn1Data := range certMsg.certificates {
		cert, err := x509.ParseCertificate(asn1Data)
		if err != nil {
			c.sendAlert(alertBadCertificate)
			return os.ErrorString("failed to parse certificate from server: " + err.String())
		}
		certs[i] = cert
	}

	for i := 1; i < len(certs); i++ {
		if !certs[i].BasicConstraintsValid || !certs[i].IsCA {
			c.sendAlert(alertBadCertificate)
			return os.ErrorString("intermediate certificate does not have CA bit set")
		}
		// KeyUsage status flags are ignored. From Engineering
		// Security, Peter Gutmann:
		// A European government CA marked its signing certificates as
		// being valid for encryption only, but no-one noticed. Another
		// European CA marked its signature keys as not being valid for
		// signatures. A different CA marked its own trusted root
		// certificate as being invalid for certificate signing.
		// Another national CA distributed a certificate to be used to
		// encrypt data for the country’s tax authority that was marked
		// as only being usable for digital signatures but not for
		// encryption. Yet another CA reversed the order of the bit
		// flags in the keyUsage due to confusion over encoding
		// endianness, essentially setting a random keyUsage in
		// certificates that it issued. Another CA created a
		// self-invalidating certificate by adding a certificate policy
		// statement stipulating that the certificate had to be used
		// strictly as specified in the keyUsage, and a keyUsage
		// containing a flag indicating that the RSA encryption key
		// could only be used for Diffie-Hellman key agreement.

		if err := certs[i-1].CheckSignatureFrom(certs[i]); err != nil {
			c.sendAlert(alertBadCertificate)
			return os.ErrorString("could not validate certificate signature: " + err.String())
		}
	}

	// TODO(rsc): Find certificates for OS X 10.6.
	if c.config.RootCAs != nil {
		root := c.config.RootCAs.FindParent(certs[len(certs)-1])
		if root == nil {
			c.sendAlert(alertBadCertificate)
			return os.ErrorString("could not find root certificate for chain")
		}
		if err := certs[len(certs)-1].CheckSignatureFrom(root); err != nil {
			c.sendAlert(alertBadCertificate)
			return os.ErrorString("could not validate signature from expected root: " + err.String())
		}
	}

	pub, ok := certs[0].PublicKey.(*rsa.PublicKey)
	if !ok {
		return c.sendAlert(alertUnsupportedCertificate)
	}

	c.peerCertificates = certs

	if serverHello.certStatus {
		msg, err = c.readHandshake()
		if err != nil {
			return err
		}
		cs, ok := msg.(*certificateStatusMsg)
		if !ok {
			return c.sendAlert(alertUnexpectedMessage)
		}
		finishedHash.Write(cs.marshal())

		if cs.statusType == statusTypeOCSP {
			c.ocspResponse = cs.response
		}
	}

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

	transmitCert := false
	certReq, ok := msg.(*certificateRequestMsg)
	if ok {
		// We only accept certificates with RSA keys.
		rsaAvail := false
		for _, certType := range certReq.certificateTypes {
			if certType == certTypeRSASign {
				rsaAvail = true
				break
			}
		}

		// For now, only send a certificate back if the server gives us an
		// empty list of certificateAuthorities.
		//
		// RFC 4346 on the certificateAuthorities field:
		// A list of the distinguished names of acceptable certificate
		// authorities.  These distinguished names may specify a desired
		// distinguished name for a root CA or for a subordinate CA; thus,
		// this message can be used to describe both known roots and a
		// desired authorization space.  If the certificate_authorities
		// list is empty then the client MAY send any certificate of the
		// appropriate ClientCertificateType, unless there is some
		// external arrangement to the contrary.
		if rsaAvail && len(certReq.certificateAuthorities) == 0 {
			transmitCert = true
		}

		finishedHash.Write(certReq.marshal())

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

	shd, ok := msg.(*serverHelloDoneMsg)
	if !ok {
		return c.sendAlert(alertUnexpectedMessage)
	}
	finishedHash.Write(shd.marshal())

	var cert *x509.Certificate
	if transmitCert {
		certMsg = new(certificateMsg)
		if len(c.config.Certificates) > 0 {
			cert, err = x509.ParseCertificate(c.config.Certificates[0].Certificate[0])
			if err == nil && cert.PublicKeyAlgorithm == x509.RSA {
				certMsg.certificates = c.config.Certificates[0].Certificate
			} else {
				cert = nil
			}
		}
		finishedHash.Write(certMsg.marshal())
		c.writeRecord(recordTypeHandshake, certMsg.marshal())
	}

	ckx := new(clientKeyExchangeMsg)
	preMasterSecret := make([]byte, 48)
	preMasterSecret[0] = byte(hello.vers >> 8)
	preMasterSecret[1] = byte(hello.vers)
	_, err = io.ReadFull(c.config.Rand, preMasterSecret[2:])
	if err != nil {
		return c.sendAlert(alertInternalError)
	}

	ckx.ciphertext, err = rsa.EncryptPKCS1v15(c.config.Rand, pub, preMasterSecret)
	if err != nil {
		return c.sendAlert(alertInternalError)
	}

	finishedHash.Write(ckx.marshal())
	c.writeRecord(recordTypeHandshake, ckx.marshal())

	if cert != nil {
		certVerify := new(certificateVerifyMsg)
		var digest [36]byte
		copy(digest[0:16], finishedHash.serverMD5.Sum())
		copy(digest[16:36], finishedHash.serverSHA1.Sum())
		signed, err := rsa.SignPKCS1v15(c.config.Rand, c.config.Certificates[0].PrivateKey, rsa.HashMD5SHA1, digest[0:])
		if err != nil {
			return c.sendAlert(alertInternalError)
		}
		certVerify.signature = signed

		finishedHash.Write(certVerify.marshal())
		c.writeRecord(recordTypeHandshake, certVerify.marshal())
	}

	suite := cipherSuites[0]
	masterSecret, clientMAC, serverMAC, clientKey, serverKey :=
		keysFromPreMasterSecret11(preMasterSecret, hello.random, serverHello.random, suite.hashLength, suite.cipherKeyLength)

	cipher, _ := rc4.NewCipher(clientKey)

	c.out.prepareCipherSpec(cipher, hmac.NewSHA1(clientMAC))
	c.writeRecord(recordTypeChangeCipherSpec, []byte{1})

	finished := new(finishedMsg)
	finished.verifyData = finishedHash.clientSum(masterSecret)
	finishedHash.Write(finished.marshal())
	c.writeRecord(recordTypeHandshake, finished.marshal())

	cipher2, _ := rc4.NewCipher(serverKey)
	c.in.prepareCipherSpec(cipher2, hmac.NewSHA1(serverMAC))
	c.readRecord(recordTypeChangeCipherSpec)
	if c.err != nil {
		return c.err
	}

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

	verify := finishedHash.serverSum(masterSecret)
	if len(verify) != len(serverFinished.verifyData) ||
		subtle.ConstantTimeCompare(verify, serverFinished.verifyData) != 1 {
		return c.sendAlert(alertHandshakeFailure)
	}

	c.handshakeComplete = true
	c.cipherSuite = TLS_RSA_WITH_RC4_128_SHA
	return nil
}