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crypto/tls: don't select ECDSA ciphersuites with only an RSA certificate.

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47ec7a68b1a2 added support for ECDSA ciphersuites but didn't alter the
cipher suite selection to take that into account. Thus Go servers could
try and select an ECDSA cipher suite while only having an RSA
certificate, leading to connection failures.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/13239053
This commit is contained in:
Adam Langley 2013-09-17 13:30:36 -04:00
parent 8eaa99cd77
commit 679f6ca983
3 changed files with 77 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

51
cipher_suites.go
View File

@ -34,6 +34,19 @@ type keyAgreement interface {
generateClientKeyExchange(*Config, *clientHelloMsg, *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error)
}
const (
// suiteECDH indicates that the cipher suite involves elliptic curve
// Diffie-Hellman. This means that it should only be selected when the
// client indicates that it supports ECC with a curve and point format
// that we're happy with.
suiteECDHE = 1 << iota
// suiteECDSA indicates that the cipher suite involves an ECDSA
// signature and therefore may only be selected when the server's
// certificate is ECDSA. If this is not set then the cipher suite is
// RSA based.
suiteECDSA
)
// A cipherSuite is a specific combination of key agreement, cipher and MAC
// function. All cipher suites currently assume RSA key agreement.
type cipherSuite struct {
@ -43,31 +56,29 @@ type cipherSuite struct {
macLen int
ivLen int
ka func(version uint16) keyAgreement
// If elliptic is set, a server will only consider this ciphersuite if
// the ClientHello indicated that the client supports an elliptic curve
// and point format that we can handle.
elliptic bool
cipher func(key, iv []byte, isRead bool) interface{}
mac func(version uint16, macKey []byte) macFunction
aead func(key, fixedNonce []byte) cipher.AEAD
// flags is a bitmask of the suite* values, above.
flags int
cipher func(key, iv []byte, isRead bool) interface{}
mac func(version uint16, macKey []byte) macFunction
aead func(key, fixedNonce []byte) cipher.AEAD
}
var cipherSuites = []*cipherSuite{
// Ciphersuite order is chosen so that ECDHE comes before plain RSA
// and RC4 comes before AES (because of the Lucky13 attack).
{TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 16, 0, 4, ecdheRSAKA, true, nil, nil, aeadAESGCM},
{TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, 16, 0, 4, ecdheECDSAKA, true, nil, nil, aeadAESGCM},
{TLS_ECDHE_RSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheRSAKA, true, cipherRC4, macSHA1, nil},
{TLS_ECDHE_ECDSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheECDSAKA, true, cipherRC4, macSHA1, nil},
{TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, ecdheRSAKA, true, cipherAES, macSHA1, nil},
{TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA, 16, 20, 16, ecdheECDSAKA, true, cipherAES, macSHA1, nil},
{TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA, 32, 20, 16, ecdheRSAKA, true, cipherAES, macSHA1, nil},
{TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA, 32, 20, 16, ecdheECDSAKA, true, cipherAES, macSHA1, nil},
{TLS_RSA_WITH_RC4_128_SHA, 16, 20, 0, rsaKA, false, cipherRC4, macSHA1, nil},
{TLS_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, rsaKA, false, cipherAES, macSHA1, nil},
{TLS_RSA_WITH_AES_256_CBC_SHA, 32, 20, 16, rsaKA, false, cipherAES, macSHA1, nil},
{TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, ecdheRSAKA, true, cipher3DES, macSHA1, nil},
{TLS_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, rsaKA, false, cipher3DES, macSHA1, nil},
{TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 16, 0, 4, ecdheRSAKA, suiteECDHE, nil, nil, aeadAESGCM},
{TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, 16, 0, 4, ecdheECDSAKA, suiteECDHE | suiteECDSA, nil, nil, aeadAESGCM},
{TLS_ECDHE_RSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheRSAKA, suiteECDHE, cipherRC4, macSHA1, nil},
{TLS_ECDHE_ECDSA_WITH_RC4_128_SHA, 16, 20, 0, ecdheECDSAKA, suiteECDHE | suiteECDSA, cipherRC4, macSHA1, nil},
{TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, ecdheRSAKA, suiteECDHE, cipherAES, macSHA1, nil},
{TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA, 16, 20, 16, ecdheECDSAKA, suiteECDHE | suiteECDSA, cipherAES, macSHA1, nil},
{TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA, 32, 20, 16, ecdheRSAKA, suiteECDHE, cipherAES, macSHA1, nil},
{TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA, 32, 20, 16, ecdheECDSAKA, suiteECDHE | suiteECDSA, cipherAES, macSHA1, nil},
{TLS_RSA_WITH_RC4_128_SHA, 16, 20, 0, rsaKA, 0, cipherRC4, macSHA1, nil},
{TLS_RSA_WITH_AES_128_CBC_SHA, 16, 20, 16, rsaKA, 0, cipherAES, macSHA1, nil},
{TLS_RSA_WITH_AES_256_CBC_SHA, 32, 20, 16, rsaKA, 0, cipherAES, macSHA1, nil},
{TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, ecdheRSAKA, suiteECDHE, cipher3DES, macSHA1, nil},
{TLS_RSA_WITH_3DES_EDE_CBC_SHA, 24, 20, 8, rsaKA, 0, cipher3DES, macSHA1, nil},
}
func cipherRC4(key, iv []byte, isRead bool) interface{} {

41
handshake_server.go
View File

@ -23,10 +23,12 @@ type serverHandshakeState struct {
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.
@ -167,6 +169,16 @@ Curves:
hs.hello.nextProtos = config.NextProtos
}
if len(config.Certificates) == 0 {
return false, c.sendAlert(alertInternalError)
}
hs.cert = &config.Certificates[0]
if len(hs.clientHello.serverName) > 0 {
hs.cert = config.getCertificateForName(hs.clientHello.serverName)
}
_, hs.ecdsaOk = hs.cert.PrivateKey.(*ecdsa.PrivateKey)
if hs.checkForResumption() {
return true, nil
}
@ -181,7 +193,7 @@ Curves:
}
for _, id := range preferenceList {
if hs.suite = c.tryCipherSuite(id, supportedList, hs.ellipticOk); hs.suite != nil {
if hs.suite = c.tryCipherSuite(id, supportedList, hs.ellipticOk, hs.ecdsaOk); hs.suite != nil {
break
}
}
@ -222,7 +234,7 @@ func (hs *serverHandshakeState) checkForResumption() bool {
}
// Check that we also support the ciphersuite from the session.
hs.suite = c.tryCipherSuite(hs.sessionState.cipherSuite, c.config.cipherSuites(), hs.ellipticOk)
hs.suite = c.tryCipherSuite(hs.sessionState.cipherSuite, c.config.cipherSuites(), hs.ellipticOk, hs.ecdsaOk)
if hs.suite == nil {
return false
}
@ -264,15 +276,7 @@ func (hs *serverHandshakeState) doFullHandshake() error {
config := hs.c.config
c := hs.c
if len(config.Certificates) == 0 {
return c.sendAlert(alertInternalError)
}
cert := &config.Certificates[0]
if len(hs.clientHello.serverName) > 0 {
cert = config.getCertificateForName(hs.clientHello.serverName)
}
if hs.clientHello.ocspStapling && len(cert.OCSPStaple) > 0 {
if hs.clientHello.ocspStapling && len(hs.cert.OCSPStaple) > 0 {
hs.hello.ocspStapling = true
}
@ -282,20 +286,20 @@ func (hs *serverHandshakeState) doFullHandshake() error {
c.writeRecord(recordTypeHandshake, hs.hello.marshal())
certMsg := new(certificateMsg)
certMsg.certificates = cert.Certificate
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 = cert.OCSPStaple
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, cert, hs.clientHello, hs.hello)
skx, err := keyAgreement.generateServerKeyExchange(config, hs.cert, hs.clientHello, hs.hello)
if err != nil {
c.sendAlert(alertHandshakeFailure)
return err
@ -419,7 +423,7 @@ func (hs *serverHandshakeState) doFullHandshake() error {
hs.finishedHash.Write(certVerify.marshal())
}
preMasterSecret, err := keyAgreement.processClientKeyExchange(config, cert, ckx, c.vers)
preMasterSecret, err := keyAgreement.processClientKeyExchange(config, hs.cert, ckx, c.vers)
if err != nil {
c.sendAlert(alertHandshakeFailure)
return err
@ -601,7 +605,7 @@ func (hs *serverHandshakeState) processCertsFromClient(certificates [][]byte) (c
// tryCipherSuite returns a cipherSuite with the given id if that cipher suite
// is acceptable to use.
func (c *Conn) tryCipherSuite(id uint16, supportedCipherSuites []uint16, ellipticOk bool) *cipherSuite {
func (c *Conn) tryCipherSuite(id uint16, supportedCipherSuites []uint16, ellipticOk, ecdsaOk bool) *cipherSuite {
for _, supported := range supportedCipherSuites {
if id == supported {
var candidate *cipherSuite
@ -617,7 +621,10 @@ func (c *Conn) tryCipherSuite(id uint16, supportedCipherSuites []uint16, ellipti
}
// Don't select a ciphersuite which we can't
// support for this client.
if candidate.elliptic && !ellipticOk {
if (candidate.flags&suiteECDHE != 0) && !ellipticOk {
continue
}
if (candidate.flags&suiteECDSA != 0) != ecdsaOk {
continue
}
return candidate

22
handshake_server_test.go
View File

@ -302,6 +302,28 @@ func TestClientAuthECDSA(t *testing.T) {
}
}
// TestCipherSuiteCertPreferance ensures that we select an RSA ciphersuite with
// an RSA certificate and an ECDSA ciphersuite with an ECDSA certificate.
func TestCipherSuiteCertPreferance(t *testing.T) {
var config = *testConfig
config.CipherSuites = []uint16{TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA, TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA}
config.MaxVersion = VersionTLS11
config.PreferServerCipherSuites = true
testServerScript(t, "CipherSuiteCertPreference", tls11ECDHEAESServerScript, &config, nil)
config = *testConfig
config.CipherSuites = []uint16{TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA, TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA}
config.Certificates = []Certificate{
Certificate{
Certificate: [][]byte{testECDSACertificate},
PrivateKey: testECDSAPrivateKey,
},
}
config.BuildNameToCertificate()
config.PreferServerCipherSuites = true
testServerScript(t, "CipherSuiteCertPreference2", ecdheECDSAAESServerScript, &config, nil)
}
func TestTLS11Server(t *testing.T) {
var config = *testConfig
config.CipherSuites = []uint16{TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA}