Bug#691213: ncl.edu.tw vs, gnutls

[jidanni at jidanni.org]

OK. (I wonder how all the big name browsers deal with it.)

>>>>> "DKG" == Daniel Kahn Gillmor <dkg at fifthhorseman.net> writes:

DKG> On 10/22/2012 07:08 PM, jidanni at jidanni.org wrote:
>> Cannot secure the https (SSL) connection to sso.ncl.edu.tw port 443; [IO(gnutls): Key usage
>> violation in certificate has been detected.].

DKG> I think the "key usage violation" here is that the server wants to
DKG> negotiate only a diffie-hellman cipher suite and the key is marked only
DKG> as legitimate for:

DKG> 		Key Usage (critical):
DKG> 			Key encipherment.
DKG> 			Data encipherment.


DKG> I'm able to connect cleanly if i instruct the client to not try to
DKG> negotiate DHE-RSA cipher suites.

DKG>    gnutls-cli --priority NORMAL:-DHE-RSA sso.ncl.edu.tw

DKG> The server administrators should not have their server
DKG> (Apache-Coyote/1.1?) configured to negotiate DHE cipher suites if their
DKG> key is not marked with the keyAgreement flag.

DKG> See:

DKG>  https://tools.ietf.org/html/rfc5280#page-31

>>> The keyAgreement bit is asserted when the subject public key is
>>> used for key agreement.  For example, when a Diffie-Hellman key is
>>> to be used for key management, then this bit is set.

DKG> So this is a bug in their server configuration (and possibly in the
DKG> non-gnutls clients which continue with the TLS session in the face of an
DKG> invalid certificate for the selected key exchange method, i they choose
DKG> a diffie-hellman ciphersuite), but not a bug in gnutls.

DKG> hth,

DKG> 	--dkg