Re: [pkix] Clarification on "zero" hash value in SigPolicyHash (CAdES)

Peter Gutmann <pgut001@cs.auckland.ac.nz> Wed, 17 July 2019 03:28 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Stefan Santesson <stefan@aaa-sec.com>, Niklas Matthies <pkix@nmhq.net>, "pkix@ietf.org" <pkix@ietf.org>
Thread-Topic: [pkix] Clarification on "zero" hash value in SigPolicyHash (CAdES)
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Date: Wed, 17 Jul 2019 03:28:10 +0000
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Subject: Re: [pkix] Clarification on "zero" hash value in SigPolicyHash (CAdES)
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Stefan Santesson <stefan@aaa-sec.com>; writes:

>To assign a specific meaning to one out of all possible but syntactically
>valid hash values, is exactly the type of specification work that leads to
>implementation errors and security vulnerabilities.

How would it lead to implementation errors and security vulns?  It's a value
that's guaranteed to not match anything while requiring zero changes to
existing code, what sort of implementation error would it lead to?

Peter.