EAP-TLS, session resumption and OCSP

[Arran Cudbard-Bell]

> On Mar 3, 2017, at 7:12 AM, Alan DeKok <aland at deployingradius.com> wrote:
> 
> On Mar 3, 2017, at 4:34 AM, Stefan Winter <stefan.winter at restena.lu> wrote:
>> One of the things we observed is that if an authentication uses TLS
>> session resumption, the server does not re-check the OCSP state of the
>> client cert that was used to login initially.
> 
>  Yes.  The OCSP checks are done in an OpenSSL callback when the certificate is first received.  During session resumption there's no certificate used, so no OpenSSL callback.

It's fixed in >= v3.1.x.  Although the client doesn't provide the certificate, the certificate is still available.

Unfortunately the OpenSSL callback infrastructure doesn't allow re-checking the certificate chain, so something had to be hacked together to do that manually (see tls_validate_client_cert_chain).

> 
>> Looking at the TLS-Client-Cert-* attributes which get restored from
>> session cache, it looks like it could be easy to do that though - the
>> serial number of the cert is saved; and the OCSP responder URL maybe
>> isn't but could be. And with both pieces of information, another OCSP
>> check can be run even on a resumed session.
> 
>  Yes.

See above.

>> A related question: how is the cache lifetime determined? When config
>> sets it to 24 hours, is that 24 hours after the initial, full,
>> authentication, or is that lifetime refreshed with every re-auth,
>> meaning the cache expires after 24 hours of non-use?
> 
>  The cached session information will expire after 24 hours.  When a session is resumed, the old information is deleted, and a new entry is created.

Yes.

> 
>> If the latter, a revoked user could perpetually prolong his account
>> lifetime even if OCSP wouldn't want to let him.
> 
>  So long as you keep letting him in, yes.

Only in <= v3.0.x.

>> Also, something we didn't check but that just now comes to my mind: does
>> the server check the expiry time of the cert on a resumed session?
> 
>  Hmm... I'll have to check that.  I'm not sure.

In >= v3.1.x yes, in < v3.1.x probably maybe not.

-Arran
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