[1.4.0] hidden recipient vs. ID 00000000

[Florian Weimer]

* David Shaw:

> On Fri, Jan 28, 2005 at 08:48:48PM +0100, Bernd Eckenfels wrote:
>> On Fri, Jan 28, 2005 at 03:56:40PM +0100, Janos.Farkas-lists+priv-#RVXrkLgxX70*-gpg-dev at lists.xeon.eu.org wrote:
>> > On 2005-01-27 at 15:07:33, David Shaw wrote:
>> > > Try the attached patch.  It changes the "no keyid" case to all FFs
>> > > instead of zeroes.  All FFs is as good as all zeroes here, especially
>> > > since all zeroes is reserved.
>> > 
>> > It's definitely less disturbing now, thanks! :)
>> 
>> Is all-FF keyid a valid one? If yes this patch does not make it any better.
>> Ie. it makes normal handling worse. Special values and in-band signalling
>> sux pretty often.
>
> All-FF and All-00 are both valid.  All-00 is overloaded to mean
> "anonymous recipient" on top of its usual meaning.
>
> There is a small problem since a V3 key that isn't RSA is illegal
> according to the spec.  Quite literally, they have *no* key IDs.  So
> how should it be represented?  The old code represented it as all-00.
> The new code represents it as all-FF.  Pick a value.  They all have
> problems.

All-0 is not a valid V3 key ID because its LSB is not set.  All-1 is
theoretically valid, but rather unlikely (it imposes rather strict
requirements on the lower bits in both prime factors).