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Re: [Syslog] Fingerprint/handshake

"Rainer Gerhards" <rgerhards@hq.adiscon.com> Thu, 29 May 2008 07:48 UTC

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From: Rainer Gerhards <rgerhards@hq.adiscon.com>
To: "Joseph Salowey (jsalowey)" <jsalowey@cisco.com>, syslog@ietf.org
Subject: Re: [Syslog] Fingerprint/handshake
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Inline...
> -----Original Message-----
> From: Joseph Salowey (jsalowey) [mailto:jsalowey@cisco.com]
> Sent: Thursday, May 29, 2008 2:32 AM
> To: Rainer Gerhards; syslog@ietf.org
> Subject: RE: [Syslog] Fingerprint/handshake
> 
> Hi Rainer,
> 
> A TLS alert could be sent by the server indicating the error condition.
> Would this help?

That's an interesting idea. Let me give it a try. Will provide feedback when I have done this. In any case, if it turns out to be a problem with one library, we may be better of mandating that all verification is done during the handshake...

> 
> Joe
> 
> > -----Original Message-----
> > From: Rainer Gerhards [mailto:rgerhards@hq.adiscon.com]
> > Sent: Sunday, May 25, 2008 11:46 PM
> > To: Joseph Salowey (jsalowey); syslog@ietf.org
> > Subject: RE: [Syslog] Fingerprint/handshake
> >
> > Hi Joe,
> >
> > inline
> >
> > > -----Original Message-----
> > > From: Joseph Salowey (jsalowey) [mailto:jsalowey@cisco.com]
> > > Sent: Friday, May 23, 2008 8:21 PM
> > > To: Rainer Gerhards; syslog@ietf.org
> > > Subject: RE: [Syslog] Fingerprint/handshake
> > >
> > > The fingerprint check should be done where certificate validation
> > would
> > > be done.  This is typically done within the handshake itself,
> >
> > I agree to this, but have found this to be problematic with
> > some TLS libraries. Of course, that doesn't mean the standard
> > needs to change, but I would still like to provide some
> > implementation feedback.
> >
> > With GnuTLS, for example, you can do the final authentication
> > only after the handshake [1]. With NSS, it can be done during
> > the handshake. As of my understanding, OpenSSL does support
> > it after the handshake only (but I have not actually used
> > OpenSSL, this is based on my understanding after reading
> > doc). This brings me to the conclusion that, at least in some
> > environments I may be forced to delay the authentication
> > check to after the handshake.
> >
> [Joe] Its been a while since I used OpenSSL, but if I remember
> correctly
> they do have hooks in the certificate validation code.

[Rainer]
From what I have seen in the doc, this does not permit to do all checks. Most importantly, it looked like I am not able to check the fingerprint and subject name. But fortunately Martin Schütte is using openSSL for his implementation and I hope he can provide feedback on this in the not so distant future.

Rainer
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