My questions have to do with what can appear after (or with) a header
with Content-type: message/pem-clear or application/pem-encrypted.
E.g., the example on page 9 of the ID:
...
What other headers can occur with the message/pem-clear or
application/pem headers that would have to be considered to process the
mail?
Any of the legal Content- headers can occur. I don't know what a Content-Id or
Content-Description *mean* in this context, but I see no reason to prohibit
them.
For example, is the following snippet legal?
--next-part
Content-type: message/pem-clear
Content-transfer-encoding: base64
uihfduihbnfre
...
This is legal modulo one formatting error (which I corrected).
If so, then presumably one decodes the body of this part & recursively
processes it to see what it "really" is (i.e., it has its own headers &
body part). Is that correct?
Yes.
Are there other headers (besides Content-transfer-encoding:) that could
appear with the PEM-MIME Content-type headers & affect processing?
They certainly can appear; but since the currently defined content-? headers
besides Content-Type and Content-Transfer-Encoding don't have any semantics
defined that affect processing of this sort I don't see what good (or harm)
they would do.
Lets confuse things a bit further... Some interesting possibilities do arise if
you relax the restriction on the types allowed in the first part. For example:
Date: Mon, 29 Apr 93 14:36:40 -0500
From: Jim Galvin <galvin(_at_)TIS(_dot_)COM>
To: Ned Freed <ned(_at_)innosoft(_dot_)com>
Subject: Example of indirect reference to encrypted content
MIME-Version: 1.0
Content-Type: multipart/pem; boundary="PEM Boundary";
privacy=encrypted
--PEM Boundary
Content-type: Message/External-body;
name="random-pem-encrypted-file";
site="ds.internic.net"; access-type="anon-ftp";
directory="encrypted-stuff"
Content-Type: application/pem-encrypted
Content-Transfer-Encoding: base64
--PEM Boundary
Content-Type: application/pem
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-CBC,4C776432D61A9829
Originator-ID-Asymmetric: ...,09
Key-Info: RSA,...
MIC-Info: RSA-MD5,RSA,...
--PEM Boundary--
Is this useful? It lets you disassociate the content of an enhanced object from
the information about the enhancement. I really don't have enough experience in
the use of enhanced services to say if this is a winner, loser, or don't care.
I will point out that it simply isn't possible without the extra level of
indirection, since without the extra level you'd just be enhancing the
mesage/external-body stuff and not the actual content.
Ned