Subject: [saag] RFC5280 + DNS name constraints

From: Nikos Mavrogiannopoulos <[email-masked]>
Date: Wed, 25 Mar 2015 16:12:42 +0100

Hello,
 The text for DNS name constraints in RFC5280 [0] is the following:

   "DNS name restrictions are expressed as host.example.com.  Any DNS
   name that can be constructed by simply adding zero or more labels to
   the left-hand side of the name satisfies the name constraint.  For
   example, www.host.example.com would satisfy the constraint but
   host1.example.com would not."

My interpretation of it is that name constraints are domain names of
the form of "name.example.com", "example.com", "com", etc.

However, I got a report that are several certificates with constraints
expressed in the following format ".example.com", ".com", and that
gnutls is the only implementation which doesn't honor these
constraints. Allegedly openssl and NSS are two implementations which
accept this type of constraints. Reading the text above, it is not
apparent to me why ".example.com" would be acceptable at all as a DNS
name constraint.

Is my interpretation of the text above correct? Do you know if that
definition of name constraints has been superseded by another document
which includes the '.'?

regards,
Nikos

[0]. http://tools.ietf.org/html/rfc5280#section-4.2.1.10

---

From: Viktor Dukhovni <[email-masked]>
Date: Wed, 25 Mar 2015 15:26:11 +0000

> apparent to me why ".example.com" would be acceptable at all as a DNS

IIRC the "." form is an interoperability concession for some CAs
that have issued certicates with name constraints of that form.

IIRC the "." prefix is by analogy with name constraints for URIs,
but is not defined for DNS names in any standard.

This was added to OpenSSL somewhat recently.

    http://rt.openssl.org/Ticket/Display.html?id=3562

-- 
	Viktor.