Re: [TLS] MITM Attacks on Client Authentication after Resumption

mrex@sap.com (Martin Rex) Mon, 03 March 2014 19:37 UTC

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To: Dr Stephen Henson <lists@drh-consultancy.co.uk>
Date: Mon, 3 Mar 2014 20:37:37 +0100 (CET)
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From: mrex@sap.com (Martin Rex)
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Archived-At: http://mailarchive.ietf.org/arch/msg/tls/zNtKp3H59Hd7tWRvh399TZK5tbE
Cc: tls@ietf.org
Subject: Re: [TLS] MITM Attacks on Client Authentication after Resumption
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Dr Stephen Henson wrote:
> 
> If the client checks the hostname against the certificate whenever a
> certificate is presented[2] then additionally the attacker needs a certificate
> with the same hostname as the attacked server.
> 
> 2. This isn't always the case. Some applications check the hostname only after
> the handshake has completed.

An application client that is using a TLS library _without_ callbacks,
and requests a blocking TLS handshake to be performed, will only get to
see the server certificate after the handshake has completed.

While the X.509 cert chain validation might be performed in-band
by the TLS stack, the rfc2818 Section 3.1 server endpoint
identification is left up to the application caller.


-Martin