On 10/22/2012 07:08 PM, [email protected] wrote: > Cannot secure the https (SSL) connection to sso.ncl.edu.tw port 443; > [IO(gnutls): Key usage > violation in certificate has been detected.].
I think the "key usage violation" here is that the server wants to
negotiate only a diffie-hellman cipher suite and the key is marked only
as legitimate for:
Key Usage (critical):
Key encipherment.
Data encipherment.
I'm able to connect cleanly if i instruct the client to not try to
negotiate DHE-RSA cipher suites.
gnutls-cli --priority NORMAL:-DHE-RSA sso.ncl.edu.tw
The server administrators should not have their server
(Apache-Coyote/1.1?) configured to negotiate DHE cipher suites if their
key is not marked with the keyAgreement flag.
See:
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.
So this is a bug in their server configuration (and possibly in the
non-gnutls clients which continue with the TLS session in the face of an
invalid certificate for the selected key exchange method, i they choose
a diffie-hellman ciphersuite), but not a bug in gnutls.
hth,
--dkg
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