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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
// The handshake goroutine reads handshake messages from the record processor
// and outputs messages to be written on another channel. It updates the record
// processor with the state of the connection via the control channel. In the
// case of handshake messages that need synchronous processing (because they
// affect the handling of the next record) the record processor knows about
// them and either waits for a control message (Finished) or includes a reply
// channel in the message (ChangeCipherSpec).
import (
"crypto/hmac"
"crypto/rc4"
"crypto/rsa"
"crypto/subtle"
"crypto/x509"
"io"
"os"
)
type cipherSuite struct {
id uint16 // The number of this suite on the wire.
hashLength, cipherKeyLength int
// TODO(agl): need a method to create the cipher and hash interfaces.
}
var cipherSuites = []cipherSuite{
{TLS_RSA_WITH_RC4_128_SHA, 20, 16},
}
func (c *Conn) serverHandshake() os.Error {
config := c.config
msg, err := c.readHandshake()
if err != nil {
return err
}
clientHello, ok := msg.(*clientHelloMsg)
if !ok {
return c.sendAlert(alertUnexpectedMessage)
}
vers, ok := mutualVersion(clientHello.vers)
if !ok {
return c.sendAlert(alertProtocolVersion)
}
c.vers = vers
c.haveVers = true
finishedHash := newFinishedHash()
finishedHash.Write(clientHello.marshal())
hello := new(serverHelloMsg)
// We only support a single ciphersuite so we look for it in the list
// of client supported suites.
//
// TODO(agl): Add additional cipher suites.
var suite *cipherSuite
for _, id := range clientHello.cipherSuites {
for _, supported := range cipherSuites {
if supported.id == id {
suite = &supported
break
}
}
}
foundCompression := false
// We only support null compression, so check that the client offered it.
for _, compression := range clientHello.compressionMethods {
if compression == compressionNone {
foundCompression = true
break
}
}
if suite == nil || !foundCompression {
return c.sendAlert(alertHandshakeFailure)
}
hello.vers = vers
hello.cipherSuite = suite.id
t := uint32(config.time())
hello.random = make([]byte, 32)
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(config.rand(), hello.random[4:])
if err != nil {
return c.sendAlert(alertInternalError)
}
hello.compressionMethod = compressionNone
if clientHello.nextProtoNeg {
hello.nextProtoNeg = true
hello.nextProtos = config.NextProtos
}
finishedHash.Write(hello.marshal())
c.writeRecord(recordTypeHandshake, hello.marshal())
if len(config.Certificates) == 0 {
return c.sendAlert(alertInternalError)
}
certMsg := new(certificateMsg)
certMsg.certificates = config.Certificates[0].Certificate
finishedHash.Write(certMsg.marshal())
c.writeRecord(recordTypeHandshake, certMsg.marshal())
if config.AuthenticateClient {
// Request a client certificate
certReq := new(certificateRequestMsg)
certReq.certificateTypes = []byte{certTypeRSASign}
// An empty list of certificateAuthorities signals to
// the client that it may send any certificate in response
// to our request.
finishedHash.Write(certReq.marshal())
c.writeRecord(recordTypeHandshake, certReq.marshal())
}
helloDone := new(serverHelloDoneMsg)
finishedHash.Write(helloDone.marshal())
c.writeRecord(recordTypeHandshake, helloDone.marshal())
var pub *rsa.PublicKey
if config.AuthenticateClient {
// Get client certificate
msg, err = c.readHandshake()
if err != nil {
return err
}
certMsg, ok = msg.(*certificateMsg)
if !ok {
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("could not parse client's certificate: " + err.String())
}
certs[i] = cert
}
// TODO(agl): do better validation of certs: max path length, name restrictions etc.
for i := 1; i < len(certs); i++ {
if err := certs[i-1].CheckSignatureFrom(certs[i]); err != nil {
c.sendAlert(alertBadCertificate)
return os.ErrorString("could not validate certificate signature: " + err.String())
}
}
if len(certs) > 0 {
key, ok := certs[0].PublicKey.(*rsa.PublicKey)
if !ok {
return c.sendAlert(alertUnsupportedCertificate)
}
pub = key
c.peerCertificates = certs
}
}
// Get client key exchange
msg, err = c.readHandshake()
if err != nil {
return err
}
ckx, ok := msg.(*clientKeyExchangeMsg)
if !ok {
return c.sendAlert(alertUnexpectedMessage)
}
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 MD5SHA1 digest of all preceeding
// 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
// posession 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 {
return c.sendAlert(alertUnexpectedMessage)
}
digest := make([]byte, 36)
copy(digest[0:16], finishedHash.serverMD5.Sum())
copy(digest[16:36], finishedHash.serverSHA1.Sum())
err = rsa.VerifyPKCS1v15(pub, rsa.HashMD5SHA1, digest, certVerify.signature)
if err != nil {
c.sendAlert(alertBadCertificate)
return os.ErrorString("could not validate signature of connection nonces: " + err.String())
}
finishedHash.Write(certVerify.marshal())
}
preMasterSecret := make([]byte, 48)
_, err = io.ReadFull(config.rand(), preMasterSecret[2:])
if err != nil {
return c.sendAlert(alertInternalError)
}
err = rsa.DecryptPKCS1v15SessionKey(config.rand(), config.Certificates[0].PrivateKey, ckx.ciphertext, preMasterSecret)
if err != nil {
return c.sendAlert(alertHandshakeFailure)
}
// We don't check the version number in the premaster secret. For one,
// by checking it, we would leak information about the validity of the
// encrypted pre-master secret. Secondly, it provides only a small
// benefit against a downgrade attack and some implementations send the
// wrong version anyway. See the discussion at the end of section
// 7.4.7.1 of RFC 4346.
masterSecret, clientMAC, serverMAC, clientKey, serverKey :=
keysFromPreMasterSecret11(preMasterSecret, clientHello.random, hello.random, suite.hashLength, suite.cipherKeyLength)
cipher, _ := rc4.NewCipher(clientKey)
c.in.prepareCipherSpec(cipher, hmac.NewSHA1(clientMAC))
c.readRecord(recordTypeChangeCipherSpec)
if err := c.error(); err != nil {
return err
}
if hello.nextProtoNeg {
msg, err = c.readHandshake()
if err != nil {
return err
}
nextProto, ok := msg.(*nextProtoMsg)
if !ok {
return c.sendAlert(alertUnexpectedMessage)
}
finishedHash.Write(nextProto.marshal())
c.clientProtocol = nextProto.proto
}
msg, err = c.readHandshake()
if err != nil {
return err
}
clientFinished, ok := msg.(*finishedMsg)
if !ok {
return c.sendAlert(alertUnexpectedMessage)
}
verify := finishedHash.clientSum(masterSecret)
if len(verify) != len(clientFinished.verifyData) ||
subtle.ConstantTimeCompare(verify, clientFinished.verifyData) != 1 {
return c.sendAlert(alertHandshakeFailure)
}
finishedHash.Write(clientFinished.marshal())
cipher2, _ := rc4.NewCipher(serverKey)
c.out.prepareCipherSpec(cipher2, hmac.NewSHA1(serverMAC))
c.writeRecord(recordTypeChangeCipherSpec, []byte{1})
finished := new(finishedMsg)
finished.verifyData = finishedHash.serverSum(masterSecret)
c.writeRecord(recordTypeHandshake, finished.marshal())
c.handshakeComplete = true
c.cipherSuite = TLS_RSA_WITH_RC4_128_SHA
return nil
}