Hi, Bruce. On 11/11/2025 12:11, Bruce Walzer via Gnupg-users wrote:
No preference is expressed at all in RFC-2440. So it appears that RFC-9580 is simply incorrect.
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So RFC-9580 is also incorrect for RFC-4880 as well.
It is neither accurate nor helpful to use the term "incorrect". None of these documents claim correctness, they are merely specifications. That means that they can and will differ; it does not mean that any of them are more "correct" than any other. All that you can say is that some of them are more recent than others.
I don't know the reasoning behind RFC-9580 changing this to "SHOULD NOT" and why the incorrect language was used.
Surely the reason is obvious? It is desirable in general to gracefully sunset legacy formats. As you have pointed out already, the specification changed between RFC2440 and RFC4880, to explicitly prefer the newer format (with caveats). RFC9580 merely strengthens the language again to more strongly prefer the newer format. This seems to me to be a natural evolution of the spec.
You would probably have to ask on the appropriate mailing list to find out if anyone from that faction still knows, is still around, and is interested enough to answer your question.
This backhanded snark is unbecoming of you, Bruce. The authors of RFC9580 are named individuals - three of whom currently work on PGP software, and one of those (Niibe) works on GnuPG. Your insinuation that RFC9580 was written by shadowy, disinterested figures is an insult to its authors, and you should consider issuing an apology.
For reference, the relevant mailing list is [email protected] (https://mailarchive.ietf.org/arch/browse/openpgp/)
There doesn't seem to be any practical reason to use a new packet header if the packet tag is less than 16. Otherwise you *have* to use a new packet header.
The practical reason is that the implementers want the ability (eventually) to drop support for the legacy format. This can't be done if today's software is still generating it. Considering that all RFC2440-compatible software (i.e. anything written in the last 25 years) MUST implement the modern format, any software that cannot read it is so far out of date that it doesn't support any modern cryptography either (for example, it won't support MDC) so is not safe for use anyway, other than to read prehistoric archives.
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