Re: [TLS] Antw: Re: Antw: Re: Suspicious behaviour of TLS server implementations

Hubert Kario <hkario@redhat.com> Fri, 23 September 2016 12:16 UTC

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From: Hubert Kario <hkario@redhat.com>
To: tls@ietf.org
Date: Fri, 23 Sep 2016 14:16:43 +0200
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Subject: Re: [TLS] Antw: Re: Antw: Re: Suspicious behaviour of TLS server implementations
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On Friday, 23 September 2016 08:38:44 CEST Peter Gutmann wrote:
> Andreas Walz <andreas.walz@hs-offenburg.de>; writes:
> >However, where would you draw the line between "I can't" and "I don't want
> >to"?
> 
> It's one of those judgement-call things, I don't know if you can strictly
> define it but as a rule of thumb I'd say that if you encounter it during
> normal processing it's an I-can't problem while if you have to add special-
> case checks to identify it and refuse to continue it's an I-don't-want-to
> problem.

So it comes down how the code just happens to be written? I don't think that's 
a good approach for security critical code... 

I mean if you do a

while not is_empty(buffer):
   c_id = get_two_bytes_with_overflow_check(buffer)
   list_of_cipher_ids.append(c_id)

you won't need to do additional checks to see if the length is even or not.

-- 
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purky┼łova 99/71, 612 45, Brno, Czech Republic