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

Peter Gutmann <pgut001@cs.auckland.ac.nz> Fri, 23 September 2016 08:38 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Andreas Walz <andreas.walz@hs-offenburg.de>
Thread-Topic: Antw: Re: Antw: Re: [TLS] Suspicious behaviour of TLS server implementations
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Date: Fri, 23 Sep 2016 08:38:44 +0000
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Subject: Re: [TLS] Antw: Re: Antw: Re: Suspicious behaviour of TLS server implementations
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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.

Using again the example of "Couldn't connect to Amazon because no suitable
encryption was available", if the server or client accidentally memset()s the
cipher suite block to 0xDEADBEEF then you've run into an I-can't-continue
problem, while if the length fields don't quite match up (the MUST NOT that
was cited at the start of this thread), something that you wouldn't even
notice unless you added special-case code to check for it, then it's an I-
don't-want-to-continue problem.

Peter.