Add DHE_RSA support to tlslite.

third_party/tlslite/tlslite/tlsconnection.py

 # Authors: 
 #   Trevor Perrin
 #   Google - added reqCAs parameter
 #   Google (adapted by Sam Rushing and Marcelo Fernandez) - NPN support
 #   Dimitris Moraitis - Anon ciphersuites
 #   Martin von Loewis - python 3 port
 #
 # See the LICENSE file for legal information regarding use of this file.
 
 """
 MAIN CLASS FOR TLS LITE (START HERE!).
 """
 
 import socket
 from .utils.compat import formatExceptionTrace
 from .tlsrecordlayer import TLSRecordLayer
 from .session import Session
 from .constants import *
 from .utils.cryptomath import getRandomBytes
 from .errors import *
 from .messages import *
 from .mathtls import *
 from .handshakesettings import HandshakeSettings
 from .utils.tackwrapper import *
 
 
+class KeyExchange(object):
+    def __init__(self, cipherSuite, clientHello, serverHello, privateKey):

[wtc, 2014/04/02 19:11:29]

Nit: it would be nice to document what privateKey is. This is only ambiguous
when the server has two key pairs. In that case I think this privateKey should
be the DH private key rather than the signing private key.

[wtc, 2014/04/02 19:13:46]

Sorry, I forgot to update this comment. I believe in that case this privateKey
should be the signing private key.

[davidben, 2014/04/03 18:45:48]

Done.

+        self.cipherSuite = cipherSuite
+        self.clientHello = clientHello
+        self.serverHello = serverHello
+        self.privateKey = privateKey
+
+    def makeServerKeyExchange():

[wtc, 2014/04/02 19:11:29]

Nit: document what this method returns, and what it means for this method to
return None.

[davidben, 2014/04/03 18:45:48]

Done.

+        raise NotImplementedError()
+    def processClientKeyExchange(clientKeyExchange):

[wtc, 2014/04/02 19:11:29]

Nit: document what this method returns (the premaster secret).

[davidben, 2014/04/03 18:45:48]

Done.

+        raise NotImplementedError()
+
+

[wtc, 2014/04/02 19:11:29]

Nit: use only one blank line here and before line 27?

[davidben, 2014/04/03 18:45:48]

Done. Although this code doesn't seem to be very consistent. :-)

+class RSAKeyExchange(KeyExchange):
+    def makeServerKeyExchange(self):
+        return None
+
+    def processClientKeyExchange(self, clientKeyExchange):
+        premasterSecret = self.privateKey.decrypt(\
+            clientKeyExchange.encryptedPreMasterSecret)
+
+        # On decryption failure randomize premaster secret to avoid
+        # Bleichenbacher's "million message" attack
+        randomPreMasterSecret = getRandomBytes(48)
+        versionCheck = (premasterSecret[0], premasterSecret[1])
+        if not premasterSecret:

[wtc, 2014/04/02 19:11:29]

Hmm... On line 51 we already dereferenced premasterSecret[0] and
premasterSecret[1], before checking premasterSecret is not null and has at least
two elements. This seems wrong.

It seems that the code should read:

    # On decryption failure randomize premaster secret to avoid
    # Bleichenbacher's "million message" attack
    randomPreMasterSecret = getRandomBytes(48)
    if not premasterSecret:
        premasterSecret = randomPreMasterSecret
    elif len(premasterSecret)!=48:
        premasterSecret = randomPreMasterSecret
    else:
        versionCheck = (premasterSecret[0], premasterSecret[1])
        if versionCheck != self.clientHello.client_version:
            #Tolerate buggy IE clients
            if versionCheck != self.serverHello.server_version:
                premasterSecret = randomPreMasterSecret
    return premasterSecret

[davidben, 2014/04/03 18:45:48]

Haha. I guess that code never actually worked then. Done.

+            premasterSecret = randomPreMasterSecret
+        elif len(premasterSecret)!=48:
+            premasterSecret = randomPreMasterSecret
+        elif versionCheck != self.clientHello.client_version:
+            #Tolerate buggy IE clients
+            if versionCheck != self.serverHello.server_version:
+                premasterSecret = randomPreMasterSecret
+        return premasterSecret
+
+def _hexStringToNumber(s):
+    s = s.replace(" ", "").replace("\n", "")
+    if len(s) % 2 != 0:
+        raise ValueError("Length is not even")
+    return bytesToNumber(bytearray(s.decode("hex")))
+
+class DHE_RSAKeyExchange(KeyExchange):
+    # 2048-bit MODP Group (RFC 3526, Section 3)
+    dh_p = _hexStringToNumber("""
+FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
+29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
+EF9519B3 CD3A431B 302B0A6D F25F1437 4FE1356D 6D51C245
+E485B576 625E7EC6 F44C42E9 A637ED6B 0BFF5CB6 F406B7ED
+EE386BFB 5A899FA5 AE9F2411 7C4B1FE6 49286651 ECE45B3D
+C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8 FD24CF5F
+83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
+670C354E 4ABC9804 F1746C08 CA18217C 32905E46 2E36CE3B
+E39E772C 180E8603 9B2783A2 EC07A28F B5C55DF0 6F4C52C9
+DE2BCBF6 95581718 3995497C EA956AE5 15D22618 98FA0510
+15728E5A 8AACAA68 FFFFFFFF FFFFFFFF""")

[wtc, 2014/04/02 19:11:29]

Nit: should lines 71-81 be indented?

[davidben, 2014/04/03 18:45:48]

*shrug* It does actually change what's in the string, but it doesn't really
matter I guess; _hexStringToNumber is going to strip it all away anyway. But I
suppose if I wanted to be really faithful to the string in the RFC, lines 70 and
71 should be merged.

+    dh_g = 2
+
+    # RFC 3526, Section 8.
+    strength = 160
+
+    def makeServerKeyExchange(self):
+        # Per RFC 3526, Section 1, the exponent should have double the entropy
+        # of the strength of the curve.
+        self.dh_Xs = bytesToNumber(getRandomBytes(self.strength * 2 / 8))
+        dh_Ys = powMod(self.dh_g, self.dh_Xs, self.dh_p)
+
+        serverKeyExchange = ServerKeyExchange(self.cipherSuite)
+        serverKeyExchange.createDH(self.dh_p, self.dh_g, dh_Ys)
+        serverKeyExchange.signature = self.privateKey.sign(
+            serverKeyExchange.hash(self.clientHello.random,
+                                   self.serverHello.random))
+        return serverKeyExchange
+
+    def processClientKeyExchange(self, clientKeyExchange):
+        dh_Yc = clientKeyExchange.dh_Yc
+
+        # First half of RFC 2631, Section 2.1.5.

[wtc, 2014/04/02 19:11:29]

Nit: Add "Validate the client's public key."

This DH group doesn't have a 'q' (subprime) parameter, so we can't do the second
half of the public key validation. Perhaps that check is not necessary for this
group.

[davidben, 2014/04/03 18:45:48]

Done.

+        if not 2 <= dh_Yc <= self.dh_p - 1:
+            raise TLSLocalAlert(AlertDescription.illegal_parameter,
+                                "Suspicious dh_Yc value")

[wtc, 2014/04/02 19:11:29]

Nit: Suspicious => Invalid

[davidben, 2014/04/03 18:45:48]

Done.

+
+        S = powMod(dh_Yc, self.dh_Xs, self.dh_p)
+        return numberToByteArray(S)
+
 class TLSConnection(TLSRecordLayer):
     """
     This class wraps a socket and provides TLS handshaking and data
     transfer.
 
     To use this class, create a new instance, passing a connected
     socket into the constructor.  Then call some handshake function.
     If the handshake completes without raising an exception, then a TLS
     connection has been negotiated.  You can transfer data over this
     connection as if it were a socket.
@@ skipping 456 matching lines @@
 
     def _clientSendClientHello(self, settings, session, srpUsername,
                                 srpParams, certParams, anonParams, 
                                 serverName, nextProtos, reqTack):
         #Initialize acceptable ciphersuites
         cipherSuites = [CipherSuite.TLS_EMPTY_RENEGOTIATION_INFO_SCSV]
         if srpParams:
             cipherSuites += CipherSuite.getSrpAllSuites(settings)
         elif certParams:
             cipherSuites += CipherSuite.getCertSuites(settings)
+            # Client DHE_RSA not supported.

[wtc, 2014/04/02 19:11:29]

Nit: Add "TODO" to this comment.

[davidben, 2014/04/03 18:45:48]

Done.

+            # cipherSuites += CipherSuite.getDheCertSuites(settings)
         elif anonParams:
             cipherSuites += CipherSuite.getAnonSuites(settings)
         else:
             assert(False)
 
         #Initialize acceptable certificate types
         certificateTypes = settings._getCertificateTypes()
             
         #Either send ClientHello (with a resumable session)...
         if session and session.sessionID:
@@ skipping 684 matching lines @@
         # Perform the SRP key exchange
         clientCertChain = None
         if cipherSuite in CipherSuite.srpAllSuites:
             for result in self._serverSRPKeyExchange(clientHello, serverHello, 
                                     verifierDB, cipherSuite, 
                                     privateKey, certChain):
                 if result in (0,1): yield result
                 else: break
             premasterSecret = result
 
-        # Perform the RSA key exchange
-        elif cipherSuite in CipherSuite.certSuites:
+        # Perform the RSA or DHE_RSA key exchange
+        elif (cipherSuite in CipherSuite.certSuites or
+              cipherSuite in CipherSuite.dheCertSuites):
+            if cipherSuite in CipherSuite.certSuites:
+                keyExchange = RSAKeyExchange(cipherSuite,
+                                             clientHello,
+                                             serverHello,
+                                             privateKey)
+            elif cipherSuite in CipherSuite.dheCertSuites:
+                keyExchange = DHE_RSAKeyExchange(cipherSuite,
+                                                 clientHello,
+                                                 serverHello,
+                                                 privateKey)
+            else:
+                assert(False)
             for result in self._serverCertKeyExchange(clientHello, serverHello, 
-                                        certChain, privateKey,
+                                        certChain, keyExchange,
                                         reqCert, reqCAs, cipherSuite,
                                         settings, ocspResponse):
                 if result in (0,1): yield result
                 else: break
             (premasterSecret, clientCertChain) = result
 
         # Perform anonymous Diffie Hellman key exchange
         elif cipherSuite in CipherSuite.anonSuites:
             for result in self._serverAnonKeyExchange(clientHello, serverHello, 
                                         cipherSuite, settings):
@@ skipping 40 matching lines @@
                                 sessionCache, anon, tlsIntolerant, fallbackSCSV):
         #Initialize acceptable cipher suites
         cipherSuites = []
         if verifierDB:
             if certChain:
                 cipherSuites += \
                     CipherSuite.getSrpCertSuites(settings)
             cipherSuites += CipherSuite.getSrpSuites(settings)
         elif certChain:
             cipherSuites += CipherSuite.getCertSuites(settings)
+            cipherSuites += CipherSuite.getDheCertSuites(settings)
         elif anon:
             cipherSuites += CipherSuite.getAnonSuites(settings)
         else:
             assert(False)
 
         #Tentatively set version to most-desirable version, so if an error
         #occurs parsing the ClientHello, this is what we'll use for the
         #error alert
         self.version = settings.maxVersion
 
@@ skipping 195 matching lines @@
         u = makeU(N, A, B)
 
         #Calculate premaster secret
         S = powMod((A * powMod(v,u,N)) % N, b, N)
         premasterSecret = numberToByteArray(S)
         
         yield premasterSecret
 
 
     def _serverCertKeyExchange(self, clientHello, serverHello, 
-                                serverCertChain, privateKey,
+                                serverCertChain, keyExchange,
                                 reqCert, reqCAs, cipherSuite,
                                 settings, ocspResponse):
-        #Send ServerHello, Certificate[, CertificateRequest],
-        #ServerHelloDone
+        #Send ServerHello, Certificate[, ServerKeyExchange]
+        #[, CertificateRequest], ServerHelloDone
         msgs = []
 
         # If we verify a client cert chain, return it
         clientCertChain = None
 
         msgs.append(serverHello)
         msgs.append(Certificate(CertificateType.x509).create(serverCertChain))
         if serverHello.status_request:
             msgs.append(CertificateStatus().create(ocspResponse))
+        serverKeyExchange = keyExchange.makeServerKeyExchange()

[wtc, 2014/04/02 19:11:29]

Nit: the function call you use to create the ServerKeyExchange message is
different from how the other messages are created. The other messages are all
created with a .create() method call on the message class.

I don't know how hard it is to follow that pattern.

[davidben, 2014/04/03 18:45:48]

Hrm. Yeah, I'm not sure we can follow that pattern very well and still allow
keyExchange to decide whether or not to send a ServerKeyExchange. I didn't want
to duplicate _serverCertKeyExchange for every key exchange mechanism; if
anything, probably the other _server*KeyExchange functions should get adapted to
that interface. The constructor probably will need changing through.

+        if serverKeyExchange is not None:
+            msgs.append(serverKeyExchange)
         if reqCert and reqCAs:
             msgs.append(CertificateRequest().create(\
                 [ClientCertificateType.rsa_sign], reqCAs))
         elif reqCert:
             msgs.append(CertificateRequest())
         msgs.append(ServerHelloDone())
         for result in self._sendMsgs(msgs):
             yield result
 
         #From here on, the client's messages must have the right version
@@ skipping 38 matching lines @@
                 raise AssertionError()
 
         #Get ClientKeyExchange
         for result in self._getMsg(ContentType.handshake,
                                   HandshakeType.client_key_exchange,
                                   cipherSuite):
             if result in (0,1): yield result
             else: break
         clientKeyExchange = result
 
-        #Decrypt ClientKeyExchange
-        premasterSecret = privateKey.decrypt(\
-            clientKeyExchange.encryptedPreMasterSecret)
-
-        # On decryption failure randomize premaster secret to avoid
-        # Bleichenbacher's "million message" attack
-        randomPreMasterSecret = getRandomBytes(48)
-        versionCheck = (premasterSecret[0], premasterSecret[1])
-        if not premasterSecret:
-            premasterSecret = randomPreMasterSecret
-        elif len(premasterSecret)!=48:
-            premasterSecret = randomPreMasterSecret
-        elif versionCheck != clientHello.client_version:
-            if versionCheck != self.version: #Tolerate buggy IE clients
-                premasterSecret = randomPreMasterSecret
+        #Process ClientKeyExchange
+        try:
+            premasterSecret = \
+                keyExchange.processClientKeyExchange(clientKeyExchange)
+        except TLSLocalAlert, e:
+            for result in self._sendError(e.description, e.message):

[wtc, 2014/04/02 19:11:29]

Nit: rename |e| to |alert|?

[davidben, 2014/04/03 18:45:48]

Done.

+                yield result
 
         #Get and check CertificateVerify, if relevant
         if clientCertChain:
             if self.version == (3,0):
                 masterSecret = calcMasterSecret(self.version, premasterSecret,
                                          clientHello.random, serverHello.random)
                 verifyBytes = self._calcSSLHandshakeHash(masterSecret, b"")
             elif self.version in ((3,1), (3,2)):
                 verifyBytes = self._handshake_md5.digest() + \
                                 self._handshake_sha.digest()
@@ skipping 227 matching lines @@
             except TLSAlert as alert:
                 if not self.fault:
                     raise
                 if alert.description not in Fault.faultAlerts[self.fault]:
                     raise TLSFaultError(str(alert))
                 else:
                     pass
             except:
                 self._shutdown(False)
                 raise