Add DHE_RSA support to tlslite.

third_party/tlslite/tlslite/messages.py

Index: third_party/tlslite/tlslite/messages.py
diff --git a/third_party/tlslite/tlslite/messages.py b/third_party/tlslite/tlslite/messages.py
index 532d86bb13c9977834ec1f48e7dd33306339aa3e..550b387f947119e928fbcb120306db1e6f078029 100644
--- a/third_party/tlslite/tlslite/messages.py
+++ b/third_party/tlslite/tlslite/messages.py
@@ -533,31 +533,31 @@ class ServerKeyExchange(HandshakeMsg):
         p.stopLengthCheck()
         return self
 
-    def write(self):
+    def write_params(self):
         w = Writer()
         if self.cipherSuite in CipherSuite.srpAllSuites:
             w.addVarSeq(numberToByteArray(self.srp_N), 1, 2)
             w.addVarSeq(numberToByteArray(self.srp_g), 1, 2)
             w.addVarSeq(self.srp_s, 1, 1)
             w.addVarSeq(numberToByteArray(self.srp_B), 1, 2)
-            if self.cipherSuite in CipherSuite.srpCertSuites:
-                w.addVarSeq(self.signature, 1, 2)
-        elif self.cipherSuite in CipherSuite.anonSuites:
+        elif self.cipherSuite in CipherSuite.dhAllSuites:
             w.addVarSeq(numberToByteArray(self.dh_p), 1, 2)
             w.addVarSeq(numberToByteArray(self.dh_g), 1, 2)
             w.addVarSeq(numberToByteArray(self.dh_Ys), 1, 2)
-            if self.cipherSuite in []: # TODO support for signed_params
-                w.addVarSeq(self.signature, 1, 2)
+        else:
+            assert(False)
+        return w.bytes
+
+    def write(self):
+        w = Writer()
+        w.bytes += self.write_params()
+        if self.cipherSuite in CipherSuite.certAllSuites:
+            w.addVarSeq(self.signature, 1, 2)
         return self.postWrite(w)
 
     def hash(self, clientRandom, serverRandom):
-        oldCipherSuite = self.cipherSuite
-        self.cipherSuite = None
-        try:
-            bytes = clientRandom + serverRandom + self.write()[4:]

[wtc, 2014/04/01 22:00:01]

Do you know why the original code uses [4:] after self.write()? That seems
wrong.

Do you know why the original code uses a try block?

[davidben, 2014/04/01 23:25:18]

The try/finally thing is just so the cipherSuite gets fixed no matter what
exceptions through. It's a reasonable common Python thing since you're never
really sure what might throw in a dynamic language.

As for the [4:], I think it's to strip off the handshake type and length.
write_params doesn't include it, so we don't need it.

But I'm not sure the old code worked at all anyway. It sets self.cipherSuite to
None temporarily, probably so self.signature wouldn't be added, but self.write()
doesn't write the parameters if self.cipherSuite is None. I'm pretty sure it's
always been hashing the empty string. It just didn't break because both client
and server were doing that.

-            return MD5(bytes) + SHA1(bytes)
-        finally:
-            self.cipherSuite = oldCipherSuite
+        bytes = clientRandom + serverRandom + self.write_params()
+        return MD5(bytes) + SHA1(bytes)
 
 class ServerHelloDone(HandshakeMsg):
     def __init__(self):
@@ -607,7 +607,7 @@ class ClientKeyExchange(HandshakeMsg):
                     p.getFixBytes(len(p.bytes)-p.index)
             else:
                 raise AssertionError()
-        elif self.cipherSuite in CipherSuite.anonSuites:
+        elif self.cipherSuite in CipherSuite.dhAllSuites:
             self.dh_Yc = bytesToNumber(p.getVarBytes(2))            
         else:
             raise AssertionError()