Subject: [Trans] [trans] #113 (rfc6962-bis): Add advice about the tls-feature TLS extension

From: "trans issue tracker" <[email-masked]>
Date: Wed, 04 Nov 2015 12:20:47 -0000

#113: Add advice about the tls-feature TLS extension

 RFC7633 standardizes the TLS Feature certificate extension.  This could
 potentially be included in a certificate to signal that a TLS server MUST
 send the CT TLS extension (if the TLS client indicated support for it)
 when it sends this particular certificate.  However, since this would
 prevent the use of the other SCT distribution mechanisms (embedded in
 cert; embedded in stapled OCSP response) in conjunction with this cert, it
 seems like it would be an unnecessarily limiting thing to do.

 Having said that, perhaps we could specify our own semantics for what it
 means to include the CT TLS extension number in the TLS Feature
 certificate extension - e.g. that the TLS server MUST send at least 1 SCT
 via _any_ of the supported distribution mechanisms (if the TLS client
 indicated support for the CT TLS extension).

 Tom Ritter pointed out [1] that using the TLS Feature certificate
 extension in an end-entity certificate...
 "...wouldn't solve the generic problem of letting
 a site owner dictate that CT should always be enabled for their
 domain.  The reason I'm critical of 7633 is that it only applies to a
 single certificate[0].  If I want to 'enforce' CT for a single
 certificate, via a x509 extension... I could just put the CT x509
 extension in the certificate."

 However, Tom went on to advocate using TLS Feature in CA certificates...
 "[0] Now technically where 7633 really comes into play and is very
 useful is when it's included in intermediates or (my pounding heart be
 still) - root certs.  In *that* case it would work great for requiring
 CT... but not for site owners, for certificate authorities.  A CA is
 assured that all the certs it issues will be publicly logged, and it
 can use this as a check against misissuance.  I think that's great...
 but it still doesn't help site owners. =)"

 So I suggest that we specify that...
   - CAs SHOULD NOT (or MUST NOT?) include the CT TLS extension number in
 the TLS Feature certificate extension in end-entity certificates, because
 there are (or we expect that there will be) better ways to require CT
 compliance for single certificates.
   - CAs MAY include the CT TLS extension number in the TLS Feature
 certificate extension in root/intermediate certificates, to indicate that
 CT compliance is required for all certs whose chains involve this
 root/intermediate certificate.

 Any other opinions?

 [1] https://groups.google.com/a/chromium.org/d/msg/ct-policy/AGN23TW-
 ei8/0lQXUX56BQAJ

-- 
-------------------------------------+-------------------------------------
 Reporter:                           |      Owner:  draft-ietf-trans-
  [email-masked]           |  [email-masked]
     Type:  enhancement              |     Status:  new
 Priority:  minor                    |  Milestone:
Component:  rfc6962-bis              |    Version:
 Severity:  -                        |   Keywords:
-------------------------------------+-------------------------------------

Ticket URL: <http://trac.tools.ietf.org/wg/trans/trac/ticket/113>
trans <http://tools.ietf.org/trans/>