Re: Last Call: <draft-ietf-lamps-eai-addresses-05.txt> (Internationalized Email Addresses in X.509 certificates) to Proposed Standard

Viktor Dukhovni <ietf-dane@dukhovni.org> Thu, 09 February 2017 22:39 UTC

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Date: Thu, 9 Feb 2017 22:39:51 +0000
From: Viktor Dukhovni <ietf-dane@dukhovni.org>
To: ietf@ietf.org
Subject: Re: Last Call: <draft-ietf-lamps-eai-addresses-05.txt> (Internationalized Email Addresses in X.509 certificates) to Proposed Standard
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On Thu, Feb 09, 2017 at 04:33:44PM -0500, Russ Housley wrote:

> RFC 5280 says:
> 
>    A name constraint for Internet mail addresses MAY specify a
>    particular mailbox, all addresses at a particular host, or all
>    mailboxes in a domain.  To indicate a particular mailbox, the
>    constraint is the complete mail address.  For example,
>    "root@example.com" indicates the root mailbox on the host
>    "example.com".  To indicate all Internet mail addresses on a
>    particular host, the constraint is specified as the host name.  For
>    example, the constraint "example.com" is satisfied by any mail
>    address at the host "example.com".  To specify any address within a
>    domain, the constraint is specified with a leading period (as with
>    URIs).  For example, ".example.com" indicates all the Internet mail
>    addresses in the domain "example.com", but not Internet mail
>    addresses on the host "example.com”.
> 
> I think you are talking about constraints on addresses at a particular
> host and constraints on mailboxes in a domain, but not constraints on a
> particular mailbox.  Please correct me is I got that wrong.

Primarily, but not exclusively.  In the case that an issuer CA is
constrainted to a specific rfc822Name, it should not be possible
to evade that constraint by using the same (all-ASCII) address as
an SmtpUtf8Name.

> I think you are suggesting that any A-label in the rfc822Name be converted
> to a U-label, and the result is used to constrain the SmtpUtf8Name.

No.  I am *not* suggesting *any* conversions.  If a CA has rfc822Name
constraints and no SmptUtf8Name constraints, and the rfc822Name
constraints limit the CA to "example.com", ".example.com", or as
you suggest above, a particular set of explicit rfc822Name addresses,
my suggestion is that it MUST NOT be able to issue SmtpUtf8Name altnames
that violate those constraints.  For example:

    * CA is constrained to permitted subtree rfc822Name: example.com
	- can issue SmtpUtfName: виктор@example.com
	- cannot issue SmtpUtf8Name: виктор@example.net

In the current form of the draft both would be allowed, the second
is a clear violation of the principle of least surprise (and the
policy of the parent CA that created the name constraint).

> If people like your suggestion, then a constraint for a particular mailbox
> will still require a SmtpUtf8Name, so I think the mechanism described in
> the draft is needed.  It would just be used in combination with the above.

As to particular addresses, again:


    * CA is constrained to permitted subtree rfc822Name: viktor@example.com
	- cannot SmtpUtfName: виктор@example.com
	- cannot issue SmtpUtf8Name: виктор@example.net

In the current form of the draft both would be allowed, in clear
violation of the name constraint on the permitted email addresses.

-- 
	Viktor.