testing a signed message..

Simon Fowler simon at himi.org
Fri Feb 28 10:59:07 EST 2003

On Fri, Feb 28, 2003 at 10:11:11AM +1100, Michael James wrote:
> The area where perhaps I have some learning to do
>  is my attitude to attachments.
> I use attachments when I want the file attached
>  to have an existence independent of the mail that carries it.
> eg: Here is: a photo of you, my latest script, your phone bill, etc
> Chuck the wrapping, keep the attachment.
> On my old mac disk space is limited,
>  so I am not happy about attachments accumulating
>  in a directory hidden within the mailer,
>  I want to file them properly or delete them.
> So, as a configuration option I choose to have them put on the desktop.
Two things . . .

Firstly, MIME doesn't say anything about the existence of an
attatchment independant of the main message: all it specifies is a
general purpose way of encoding arbitrary collections of files into
a single FC822 message. A lot of mailers use MIME for things like
alternate html and text versions of a message, and other things like
that.  Attatching a PGP signature via PGP-MIME seems quite
reasonable to me, and certainly an improvement over an inline
signature (how do you automatically check an inline signature? You
have to look at the content of the message for a certain magic
sequence of characters.  How does that differ from MIME? MIME does
it in a well defined standard that mail readers /alredy know/).

Secondly, I think you'll find the attatchments are already
'accumulating in a directory hidden within the mailer' - MIME
encoded messages are just plain boring old RFC822 format emails, and
the whole thing will get saved to the mailbox (at least, with sane
MUAs - all bets are off with things like Outlook). Eudora stores its
mail locally in mbox files, which will contain the whole text of the
original message, attatchments included. Automatically saving them
to the desktop just creates a second copy, taking up even more of
your disk space . . .

> Then GPG implement a system where an increasing percentage of mails
>  spew out a signature that has no relevance independent of the mail.
> To others it's as annoying as Outlook enabling vcards by default.
Actually, it was mutt that started PGP-MIME, and it's been slowly
picked up by other MUAs. 

> On all non-GPG aware mailers
>  (call them broken if you will, but that's most mailers)
>  it requires special case handling, (or a filter that eudora doesn't have)
>  to say, "Whoa, signature; chuck it".
The whole point of PGP-MIME is that basically /all/ MUAs are MIME
aware, whereas very few are aware of inlined PGP signatures. Every
MUA I've seen will handle MIME attatchments it doesn't explicitly
know about quite sanely: they'll do nothing, until you tell them to.
It doesn't require any special cases, just a sane default behaviour.
/That/ seems to be where your problem arises - you've set Eudora up
so that it doesn't handle MIME messages sanely. It'd be much more
sensible to default to doing nothing with attatchments unless you
explicitly save them (whether to the desktop or somewhere else). And
remember, even if you don't do anything about them the moment they
come in, they'll still be there in the original message - you won't
lose anything.

> GPG signatures are ascii,  and don't seem to include return or spaces
>  wouldn't they be better in a header?
> X-GPG-signature: 
> iD8DBQE+Xn+hWzq7BJucGyIRArm5AKDTbWgmhhqK0GxdbZ8nLxRRN054/gCgpewG
> f7YZVQiO73VnJmzNAxuZsZc=
> =+clI
That'd probably work, though I imagine it has issues as well (if
only because it's potentially ambiguous in the case of a multipart
message - which part is the signature for?). Regardless, there's a
well established standard out there that works sanely with any MIME
aware MUA - we /should/ be using it. After all, that's what
standards are for.

Also, you probably /want/ signatures to be at least a little bit
intrusive - otherwise it's too easy to ignore them, or to miss an
important detail that might indicate some kind of problem (does the
key that signed the message give the same name as the message, for
example). This kind of thing /needs/ human intervention, because
machines are too stupid to deal with human trust relationships and
all their deceptions. At least with PGP-MIME the signature /is/
seperate from the original message, so you can choose to ignore it
completely if you want . . .

> If you don't like this mail, just hit delete. It will be gone.
> Every bit of it. Wonderful. See what I mean?
Same goes for any of the signed messages I deal with. The only thing
stopping it from working for you is your default MIME handling.


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