Re: [openpgp] Backwards compatibility

Werner Koch <wk@gnupg.org> Wed, 25 October 2023 15:56 UTC

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From: Werner Koch <wk@gnupg.org>
To: Justus Winter <justus@sequoia-pgp.org>
Cc: Paul Wouters <paul@nohats.ca>, openpgp@ietf.org
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In-Reply-To: <87lebrvst1.fsf@europ.lan> (Justus Winter's message of "Wed, 25 Oct 2023 13:35:06 +0200")
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Subject: Re: [openpgp] Backwards compatibility
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On Wed, 25 Oct 2023 13:35, Justus Winter said:

> In the following attack, a SEIPD packet (type 18) was downgraded to a
> SED packet (type 9), effectively stripping the authentication bits,
> making the encryption container malleable.  Key space separation would
> have prevented this.

For the records: This is a red herring.  If you require authenticated
(but non-signed) data you will reject classic packets of type 9 or at
least show a prominet warning.  Mangling authenticated encryption
packets (type 18) into classic encryption packets (type 9) does not
change anything here - your packet will be rejected.



Salam-Shalom,

   Werner

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