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

[Ben Laurie <[e-mail]>]

On Thu, Jan 1, 2009 at 11:17 AM, Peter Gutmann
<[e-mail]> wrote:
>
> Mike <[e-mail]> writes:
> >There is a simple fix -- a CA can just reorder the extensions prior to
> >issuing a certificate.
>
> That's actually a nice fix, but unfortunately not universally applicable: for
> some types of signed data (e.g. S/MIME attributes) the DER rules require
> sorting the encoded extensions, so there's only one valid order for them (and
> some applications actually check for this, so you have to do it or sig checks
> will start failing).

Surely the whole point of DER is that there's only one correct way to
encode any particular certificate?

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