Re: [openpgp] incomplete/confusing guidance around "Hash" Armor header for cleartext signing framework

Werner Koch <> Fri, 19 March 2021 06:50 UTC

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From: Werner Koch <>
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Subject: Re: [openpgp] incomplete/confusing guidance around "Hash" Armor header for cleartext signing framework
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On Thu, 18 Mar 2021 22:59, brian m. carlson said:

> I agree that MD5 is right out.  If we expect implementations to need
> this to process a message correctly, then it should be mandatory, since
> if someone really wants to use MD5, they should be fine declaring that
> up front.  Practically, though, nobody will want to use MD5 for that

You can't do that for existisng data and thus we need to allow such a
default.  New messages should of course not be created using MD5 and
thus for all practical reasons SHA256 will show up there.  In any case
this is mostly irrelevant because what we have here is basically a
one-pass signature packet.  It needs to be matched against the signature
anyway and for the signature we have rules what algorithm may be used
(for new messages).

> interesting about the integrity of the message, so everyone will need to
> declare a hash.


> computational power.  I don't have a strong preference as to what we do,
> but I would like to leave the former possibility open because it
> drastically simplifies fast one-pass streaming implementations,
> especially if the clearsigned data is large.




Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.