Subject: Re: Issues with S/MIME Message Specification

From: [email-masked] (Peter Gutmann)
Date: Wed, 19 May 1999 07:08:52 (NZST)

[Recipient list trimmed somewhat]

"Robert R. Jueneman" <[email-masked]> writes:

>Finally, somewhere in these documents there is a statement regarding the
>advisability of including the content encryption key encrypted in the
>originator's public key, but despite rereading the documents multiple
>times I can't find that text again.  As I recall, the text said that this
>SHOULD be done.  I would argue that this should be changed to MUST, for I
>can't imagine a situation where the originator of an encrypted message
>would not want to be able to read his own message, 

Given that anyone who wants to re-read their own messages will keep a copy 
stored locally, why on earth would they go through the complex encrypt->
decrypt process just to read what they've written?  I think even the presence
of SHOULD is too restrictire for this, it's purely a matter for the sender to
decide and doesn't really have any place in MSG - for the majority of users
all it'll do is double the number of keys available for attack.  Anyone who 
needs sent-mail revocation and whatnot desperately enough can go use X.400 
for their mail.

Peter.

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From: William Whyte <[email-masked]>
Date: Tue, 18 May 1999 20:33:57 +0100

> >SHOULD be done....
> of SHOULD is too restrictire for this, 
> ...
> Anyone who 

Not quite right. If you're using (for example) Outlook, the message
that's stored in your Sent Mail box is the message that was actually
sent. You need to have encrypted it to yourself to be able to read
it subsequently.

William

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From: [email-masked] (Peter Gutmann)
Date: Wed, 19 May 1999 08:55:10 (NZST)

[SHOULD -> MUST for encrypt-to-self]

It's probably unnecessary to mention that there should have been a smiley 
after the X.400 comment in my previous message... another reason why
saying anything on the use of encrypt-to-self is a bad thing is that it 
assumes that S/MIME mail will only ever be sent by humans.  There are all
sorts of protocols and messaging systems being built around S/MIME, for
many of these encrypt-to-self is completely illogical or even dangerous
(consider its use in medical EDI (HL7) messaging systems where the message 
indicates that the sender has been diagnosed with some terminal illness, 
that's something you definitely don't want the sender to stumble across 
unless they've been prepared for it).  This is really a matter for users
to decide, and not something which the standard should comment on.

Peter.

---

From: "Jim Schaad (Exchange)" <[email-masked]>
Date: Tue, 18 May 1999 14:41:58 -0700

Finally, somewhere in these documents there is a statement regarding the
advisability of including the content encryption key encrypted in the
originator's public key, but despite rereading the documents multiple
times I can't find that text again.  As I recall, the text said that this
SHOULD be done.  I would argue that this should be changed to MUST, for I
can't imagine a situation where the originator of an encrypted message
would not want to be able to read his own message, for example in an
outgoing or Sent-Mail queue. He might need to be able to decrypted, and
even retract it in order to resend it with modifications.  It would not be
reasonable to rely on the originator to bcc herself to gain this
capability -- it ought to be required by the spec.

[Jim Schaad]  This was a requested functionality by a group of people and is
there for a reason.  One situation in which this would be the case is human
rights workers sending encrypted mail to the home office.  They do not want
the local police to be able to read the mail by stealing the machine and key
or by force.

jim schaad

---

From: "Bob Jueneman" <[email-masked]>
Date: Tue, 18 May 1999 16:03:21 -0600

Jim,

I still can't find the comment, so maybe I'm remembering something from an 
e-mail exchange or something -- is the statement included somewhere, or 
not?

I can't tell from your message which functionality was requested --
that the self-encrypted message be included, or not. Or were you
referring to a request to Microsoft, rather than to the IETF?

In any case, although I value the human rights worker's cause,
and also the whistle blower's, etc., there is another set of values
that also needs to be addressed at the same time, and that is the
need for either the business or the user to be able to recover
encrypted messages, of various but legitimate purposes.

One set of values doesn't necessarily trump the other -- they need
to be debated on their merits.

(Again, apologies if this issue was thrashed to death without my having 
seen it go by.)

Bob

>>> "Jim Schaad (Exchange)" <[email-masked]> 05/18/99 03:41PM >>>

jim schaad