[openpgp] padding packet as first packet in a packet sequence

"Neal H. Walfield" <neal@walfield.org> Thu, 01 December 2022 10:23 UTC

Date: Thu, 01 Dec 2022 11:23:17 +0100
Message-ID: <87sfhz4e3u.wl-neal@walfield.org>
From: "Neal H. Walfield" <neal@walfield.org>
To: IETF OpenPGP WG <openpgp@ietf.org>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (Gojō) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset="US-ASCII"
Archived-At: <https://mailarchive.ietf.org/arch/msg/openpgp/eT16eI0MF8ZrUcKU24rwv6VO0c4>
Subject: [openpgp] padding packet as first packet in a packet sequence
Precedence: list

> 5.14.  Padding Packet (Tag 21)
>
>     The Padding packet contains random data...
>
>     Such a packet MUST be ignored when received.

> 11.4.  Detached Signatures
>
>    In addition, a marker packet (Section 5.8) and a padding packet
>    (Section 5.14) can appear anywhere in the sequence.

The padding packet doesn't contain much identifying information
(perhaps 8 bits: the two hard-wired high bits, and the 6-bit packet
tag?).  This makes fingerprint files quite difficult.  Ideally, a
program, like file(1), should be able to look at the first few
kilobytes of data, and quickly identify its format.  This is also
important for an OpenPGP implementation to avoid wasting cycles.

I think the draft should be changed to forbid the padding packet from
being the first packet in a packet sequence.  Something like:

  the padding packet MUST NOT occur as the first packet in a packet
  sequence.

Alternative, I propose fixing the first few (4? 8?) bytes of the
padding packet to some value specified by the standard.

Neal

[openpgp] padding packet as first packet in a pac… Neal H. Walfield
Re: [openpgp] padding packet as first packet in a… Daniel Kahn Gillmor
Re: [openpgp] padding packet as first packet in a… Ángel