Subject: interop/encryption to pgp2

From: Ingo Luetkebohle <[email-masked]>
Date: Fri, 16 Nov 2001 17:05:25 -0800

Hi,

David Shaw just pointed out that PGP2.6.2 chokes when it receives a
message that has been encrypted to a v4 key, even when it has been
encrypted to a v3 key, too. 

I can only assume that this is because public-key encrypted session
key packets allow non-RSA cipher material.  Can anybody who has a
working knowledge of the old code confirm this?

If this is the case, would it be possible to introduce a v4 packet of
that type? Would that be ignored by PGP2, so that having both v3 and
v4 public key encrypted session key packets would work with pgp2?

Ingo

---

From: Derek Atkins <[email-masked]>
Date: 16 Nov 2001 20:30:48 -0500

PGP 2.6.2 does not handle any new-style packets, even if
it's only part of a message.  If PGP 2.6.2 doesn't understand
_any_ packet, it will barf.

Basically, the only thing you can do is, if you're using -ANY-
non-RFC1991 packets, you should emit a leading "nonce" header that
declares the message to be a non-RFC1991 message.  IIRC, in PGP 5.0 we
did this via a two-byte leading sequence followed by the three ASCII
characters P, G, and P.  I'd have to go look at the code to figure out
what the leading bytes were.

-derek

Ingo Luetkebohle <[email-masked]> writes:

> --1UWUbFP1cBYEclgG
> Content-Type: text/plain; charset=us-ascii
> Content-Disposition: inline
> Content-Transfer-Encoding: quoted-printable
> 
> Hi,
> 
> encrypted to a v3 key, too.=20
> 
> --1UWUbFP1cBYEclgG
> Content-Type: application/pgp-signature
> Content-Disposition: inline
> 
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.0.6 (GNU/Linux)
> Comment: Weitere Infos: siehe http://www.gnupg.org
> 
> iD8DBQE79bfVzZDBZDStzlsRAvfoAJ9No97fDMgoVCdCIEVRPu5rV+mJuQCeJB/P
> XkZYDFmyylSMnNKMxtUNn3o=
> =5kFE
> -----END PGP SIGNATURE-----
> 
> --1UWUbFP1cBYEclgG--

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       [email-masked]                        PGP key available

---

From: Jon Callas <[email-masked]>
Date: Fri, 16 Nov 2001 20:29:05 -0800

>what the leading bytes were.

Marker Packet -- Section 5.8 of 2440.

I'll note that while OpenPGP encourages interoperating with 2.6.2, it is
not required. It is not quite deprecated, but there are weasel words in
2440 that permit "breaking" 2440 in a few cases for 2.6.2 compatibility.

So 2.6.2 compatibility will get you a golf clap, but it shouldn't stand in
the way of getting us to Draft Standard.

	Jon

	Jon

---

From: David Shaw <[email-masked]>
Date: Sat, 17 Nov 2001 01:10:45 -0500

> working knowledge of the old code confirm this?

It can also be the size of the key.  V4 RSA keys that are greater than
2048 bits long will cause PGP 2.6.2 to fail with various odd errors.
V4 RSA keys <= 2048 bits long can be mixed in with v3 keys without
causing any problems.

David

-- 
David Shaw          |  Technical Lead
<[email-masked]>  |  Enterprise Content Delivery
617-250-3028        |  Akamai Technologies