Subject: Re: filenames of encrypted attachments visible ? How hard would it be to hide?

From: Adrian von Bidder <[email-masked]>
Date: Mon, 5 Jan 2004 14:31:50 +0100

[sorry. ralf, of course I meant to answer to the lists]

On Monday 05 January 2004 14:06, Ralf Hauser wrote:
> To my understanding,
>
> If I send a message with attachments, the attachment filename is visible
> without cryptanalysis.
> Would it be hard to give the encrypted file a random name and only upon
> decryption, give it back its real name?
>
> http://www.ietf.org/rfc/rfc2440.txt doesn't appear state anything on this
> issue.
>
> Isn't that kind of giving away information that could be easily protected -
> or did I miss something?

Hi,

You did miss rfc3156 (PGP/MIME). The structure of these (encrypted) emails is:

============================
From: whatever
To: whatever
Subject: whatever
Date: whatever
Content-Type: multipart/encrypted;
  protocol="application/pgp-encrypted";
  boundary="Boundary-02=_5Plx/pJ9Yq8C9E0"

--Boundary-02=_5Plx/pJ9Yq8C9E0
Content-Type: application/pgp-encrypted

Version: 1

--Boundary-02=_5Plx/pJ9Yq8C9E0
Content-Type: application/octet-stream

--Boundary-02=_5Plx/pJ9Yq8C9E0--

============================

And the encrypted part is again a full MIME message, with attachments and all. 
So the only relevant bits that go over the wire unencrypted are From/To 
(unavoidable to the extent of the email addresses) and the Subject (I have a 
proposal that could address this cooking slowly, I think I posted it in some 
places a few months ago).

Greetings
-- vbi

-- 
<Knghtbrd> joeyh now has a terminal at the couch?
<Knghtbrd> That guy is wired, I swear  =3D>
<doogie> Knghtbrd: laptop
<doogie> and I don't mean the cats.

---

From: "Brian G. Peterson" <[email-masked]>
Date: Mon, 5 Jan 2004 07:40:49 -0600 (CST)

Ralf Hauser said:
> Rgds
> 	Ralf

Ralf,

This is totally an implementation detail.

Many mail programs that integrate PGP or GnuPG already *do* obfuscate the
filename, calling it encrypted.dat.asc or data.asc or
somerandomstring.asc.  If the asc file has an embedded filename, any
OpenPGP compatible client should be able to retrieve the file name upon
decryption.

There are times when knowing the filenmae may be more important than
obfuscating it for security reasons.  The reverse is most certainly true
as well.

In my opinion, it should probably be left as an implementation detail for
each OpenPGP compatible mail client to decide on.

Regards,

   - Brian

---

From: "Ralf Hauser" <[email-masked]>
Date: Mon, 5 Jan 2004 14:06:54 +0100

To my understanding,

Rgds
	Ralf

Sample use case: Some investment banker uses PGP and sends around an
attachment with the name "UnfriendlyTakeoverOfListedCorpXYZ.doc.asc" - isn't
that kind of an invitation to insiders?
Sure, it wouldn't be hard to rename the file before sending, but this kind
of negligence is happening all over... and I hope applications like gpg/pgp
could eventually become fool-proof/fail-safe to this level?