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Re: [saag] [Cfrg] Further MD5 breaks: Creating a rogue CAcertificate

Paul Hoffman <paul.hoffman@vpnc.org> Thu, 01 January 2009 17:20 UTC

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Date: Thu, 01 Jan 2009 09:20:00 -0800
To: Ben Laurie <benl@google.com>, Peter Gutmann <pgut001@cs.auckland.ac.nz>
From: Paul Hoffman <paul.hoffman@vpnc.org>
Cc: ietf-pkix@imc.org, mike-list@pobox.com, cfrg@irtf.org, saag@ietf.org, ietf-smime@imc.org
Subject: Re: [saag] [Cfrg] Further MD5 breaks: Creating a rogue CAcertificate
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At 3:06 PM +0000 1/1/09, Ben Laurie wrote:
>Surely the whole point of DER is that there's only one correct way to
>encode any particular certificate?

Not so "surely". The SEQUENCE for extensions does not say what order they should be in.

>So, either extensions must be sorted, or changing their order changes
>their meaning. Either way, nothing can be reordered.

Wrong on both counts. Each extension has stand-alone semantics, and they can be in any order.

However, this is irrelevant for the MD5 break discussion, as is clearly shown in the paper.

--Paul Hoffman, Director
--VPN Consortium
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