full-disclosure - Re: Firefox 2.0.x: tracking unsuspecting users using TLS client certificates

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Date: Fri, 07 Sep 2007 20:45:05 +0200
From: Erik Tews <e_tews@....informatik.tu-darmstadt.de>
To: Arshad Noor <arshad.noor@...ongauth.com>
Cc: full-disclosure@...ts.grok.org.uk, dev-security@...ts.mozilla.org,
	dev-tech-crypto@...ts.mozilla.org
Subject: Re: Firefox 2.0.x: tracking unsuspecting
	users	using TLS client	certificates

Am Freitag, den 07.09.2007, 10:04 -0400 schrieb Arshad Noor:
> Alex,
> 
> Do you presume that the websites in the domains that you intend
> to track users will install the self-signed CA certificate that
> issued the client-certificate to the unsuspecting user?  If not,
> how will the browser know which client certificate to send to 
> the website during client-auth?  And what happens to the users

In TLS, the Server can for example request that the Cert was issued by a
certain CA, to select from multiple installed certificates.

> who do not have have client-certs issued by this CA when they
> attempt to connect to the site?

From RFC4346: If no suitable certificate is available, the client SHOULD
send a certificate message containing no certificates.  That is, the
certificate_list structure has a length of zero.  If client
authentication is required by the server for the handshake to continue,
it may respond with a fatal handshake failure alert.

So the connection can still be continued.

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