To tell you the truth, I've never liked smime-type, and it wasn't my doing.
I think that lgl put this in.
If I had to take a stab at it, I would characterize it as being a shortcut
hint to present to the client, and if it is inaccurate, it should have no
effect on processing. So if you wanted to provide an icon to indicate the
message type, without tearing through the contents, this would be your boy.
Now, I think that only RFC2633 profiles any smime-type (with the exception
of signed-receipt in ESS). If I had to summarize what went in the value and
when to change the value, I would say "whenever there is significant client
benefit".
I think that the micalg parameter in RFC1847 is in somewhat the same boat --
it's meant to be a hint, the values aren't really well specified, and you
just expect the worst and work it out in processing.
Blake
-----Original Message-----
From: Jim Schaad [mailto:jimsch5(_at_)home(_dot_)com]
Sent: Friday, July 06, 2001 1:40 AM
To: Ietf-Smime (E-mail)
Subject: SMIME-TYPE question
I have a general question that I once knew the answer for but am no longer
sure that is the case.
The SMIME-TYPE attribute was defined so that a mime-level processor could
have some idea of the content type without having to pull apart the message
and look at the contentHint attribute or the innermost eContent. (Or at
least that is what I remember it as being for.) This being the case, what
is the correct value of smime-type on a triple wrapped message with a
signedReceipt as the content? It is signed-data or signed-receipt. Should
the answer change if the inner mime-layers were to be omitted (relevant for
the X.400 case).
Does the answer change if you have an encrypted receipt (i.e. E(S(Receipt)))
What is the correct value of smime-type now? signedReceipt or
encrypted-data? Again does the answer change if the mime layer were to be
omitted.
Signed-receipt means that the top level processor knows what is going to
happen before it gets there and can make intellegent decisions.
Signed-Data is "correct" because the encapsulated content contained in this
SignedData object is id-data or MIME content.
NOTE: For the simple case of data (or MIME) content the question is
accedemic as signed-data and encrypted-data both imply data content.
My original answer was the the correct answer is that signed-receipt should
be propigated up over all of the layers, but I don't find any statements
about this in either the message or ESS RFCs.
jim