GnuPG 2.4.4 still using legacy packets?

[Bruce Walzer]

On Tue, Nov 11, 2025 at 10:44:01AM +0100, Loup Vaillant wrote:
[..]
>
>     0x88 = 0b10001000
>
> Broken down, I get:
>
>     10  : Legacy format
[...]
> The RFC {9580} states that is should not:
>
> > The Legacy packet format SHOULD NOT be used to generate new data,
> > unless the recipient is known to only support the Legacy packet
> > format. This latter case is extremely unlikely, as the Legacy packet
> > format was obsoleted by [RFC2440] in 1998.

>From RFC-2440:

>PGP 2.6.x only uses old format packets. Thus, software that
>interoperates with those versions of PGP must only use old format
>packets. If interoperability is not an issue, either format may be
>used.

No preference is expressed at all in RFC-2440. So it appears that
RFC-9580 is simply incorrect.

>From RFC-4880:

>PGP 2.6.x only uses old format packets. Thus, software that
>interoperates with those versions of PGP must only use old format
>packets.  If interoperability is not an issue, the new packet format
>is RECOMMENDED.

So RFC-9580 is also incorrect for RFC-4880 as well. I don't know the
reasoning behind RFC-9580 changing this to "SHOULD NOT" and why the
incorrect language was used. 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.

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.

LibrePGP introduces no changes from RFC-4880 with respect to this. So
in the world of GnuPG the new packet format is only "RECOMMENDED" for
cases where interoperability is not an issue.

Bruce