Subject: [smime] Enveloping for the sender.

From: "Timothy J. Miller" <[email-masked]>
Date: Tue, 29 Sep 2009 08:41:58 -0500

So every S/MIME MUA I'm aware of includes the sender in the enveloped 
message's RecipientInfos.  This makes sense because people generally 
expect to read the email they send themselves.

However, yesterday I had a case where a sender had two certs issued with 
the same email address subjectAlternativeName under two different PKIs 
(don't go there).  On the system in question he had only one of these 
key pairs installed; the other was present but only as the cert (no 
private key).  The MUA, for whatever reason, used the incomplete 
identity in the envelope RecipientInfos and the user was unable to read 
his sent mail.

I'm thinking that an MUA, when enveloping an outgoing message for the 
sender, should check to make sure the sender has the private key and 
warn the user if it's not present.

While this can be addressed as a bug in the MUA (and I'll be reporting 
it), I scanned through 3850, 3851, and 5652 and I find no mention of 
this enveloping for sender behavior anywhere.  I was wondering if anyone 
felt enveloping for sender is common enough to place some minimal 
requirements on it, maybe in 3851 (I'm not sure it belongs in 5652).

-- Tim

---

From: "Timothy J. Miller" <[email-masked]>
Date: Wed, 30 Sep 2009 08:12:50 -0500

Peter Gutmann wrote:

> Isn't this a rather obscure implementation-specific issue?  If you start
> trying to enumerate every possible corner case of this kind in the spec, I
> suspect you'd get a rather large, and never-quite-finished, document.  Even
> then, how do you handle the situation where the private key is in a smart card
> that's not presently inserted in the machine, or it's CC'd to the sender's
> other email address at a location where they have the private key, or ...

I can buy that.  How about a BCP?  Is there a BCP for S/MIME?

-- Tim