Re: [pkix] Last Call: draft-ietf-pkix-tamp (Trust Anchor ManagementProtocol(TAMP)) to Proposed Standard

["Denis Pinkas"<[e-mail]>]

Carl,

You said: "the current protocol is able to accommodate the web browser model and 
does so for the existing path processing constraints defined in RFC 5280, i.e., 
name constraints, certificate policies and certificate policy constraints".

Unfortunately, this is not the case. Applying "name constraints, certificate policies 
and certificate policy constraints" as defined in RFC 5280 is not sufficient to accommodate 
the web browser model.

The web browser model controls characteristics which only apply to leaf certificates, 
in practice EKU (Extended Key Usages) and OIDs of Certication Policies.

You claim that this feature could be provided as an extension to the protocol. 
This is an acknowledgment that the current document does not currently support the web browser model.

The current draft is in fact covering three use cases, none of them is correctly addressing the web browser model.

Should an extension be defined, it would be difficult to use, since extensions, as supported in the draft, 
mandate to use two separate operations: to set the initial content of a trust anchor and then to modify it 
afwterwards using a TAMPUpdate operation (which is solely able to use extensions).

The initial content of a Trust Anchor is defined by:

    TrustAnchorChoice ::= CHOICE {
        certificate  Certificate,
        tbsCert      [1] EXPLICIT TBSCertificate,
        taInfo       [2] EXPLICIT TrustAnchorInfo }

None of these options, include an extension field. 

Only the TAMP update operation includes an extension field:

    TBSCertificateChangeInfo  ::=  SEQUENCE  {
      serialNumber         CertificateSerialNumber OPTIONAL,
      signature            [0] AlgorithmIdentifier OPTIONAL,
      issuer               [1] Name OPTIONAL,
      validity             [2] Validity OPTIONAL,
      subject              [3] Name OPTIONAL,
      subjectPublicKeyInfo [4] SubjectPublicKeyInfo,
      exts                 [5] EXPLICIT Extensions OPTIONAL  }


Using a change function to add information is not the right way to proceed.

The protocol is unable to support the sending of a full description of a trust anchor, 
including the support of extensions, all in a single exchange.

As said in the PKIX list, this can be done in a single step. Proposals have been posted to demonstrate how it could be done.
It has been responded that the proposal was correctly adressing the issue in principle, but the editors were not willing 
to make a change which was considered as a major change to the initial proposal.

Another major issue for this draft is that it is unable to tell for which usage (e.g. for which application or which purpose) 
each trust anchor may be used.

All these issues led me to propose that this document proceeds on the EXPERIMENTAL track, 
thus leaving room for a STANDARD protocol adressing the needs of the Internet community 
when using X.509 self-signed certificates associated with metadata. 

Denis  
De : pkix-bounces 
À : denis.pinkas,ietf 
Date : 2010-01-25, 16:20:06
Sujet : Re: [pkix] Last Call: draft-ietf-pkix-tamp (Trust Anchor ManagementProtocol(TAMP)) to Proposed Standard


Denis,
As we have discussed on the PKIX mailing list, the current protocol is able to accommodate the web browser model and does so for the existing path processing constraints defined in RFC 5280, i.e., name constraints, certificate policies and certificate policy constraints.  The problem you are referring to is really with the current EKU extension, which is not processed across a certification path.  Were one to define an EKU variant that has path processing semantics, TAMP would convey this information just fine.  Other specifications have defined extensions for inclusion in trust anchors to extend the RFC 5280 set, including RFC 3779 and CCC.  Something similar is appropriate for this purpose.
Carl
From: [e-mail] [mailto:[e-mail]] On Behalf Of Denis Pinkas
Sent: Monday, January 25, 2010 3:49 AM
To: ietf
Cc: pkix
Subject: Re: [pkix] Last Call: draft-ietf-pkix-tamp (Trust Anchor ManagementProtocol (TAMP)) to Proposed Standard
The current protocol has severe limitations.
They have been pointed during the last call at the PKIX WG level, but the protocol 
has not been modified to address them.The end result has only been to add text 
to explain the limitations without removing these limitations.
See section 3: "When using these structures without any additional extension, 
for which purposes the trust anchor info shall be used to verify 
certification paths needs to be locally defined; this means that different 
usages for the same or different trust anchors placed in the same TAS 
are not possible either.
One way to have different usages for different trust anchors without 
using extensions is to use a different TAS for every different usage".
The consequences are as follows:
All web browser providers currently use a different model to manage trust anchors. 
They are able to associate different key usages for every leaf certificate 
with any trust anchor (all placed in the same trust anchor store). This can be done 
in a single operation.
Furthermore, with the introduction of EV SSL Certificates 
(i.e. Extended Validation SSL certificates) the Certification Policy OIDs of 
leaf certificates that fulfills the requirements of EV SL certificates 
are added to the trust anchor to which the EV SSL certificate relates.
This means that supporting the web browser model mandates to be able to add 
key usages (e.g. EKU extended key usages) for leaf certificates 
as well as Certification Policies for leaf certificates.
This is not possible with the proposed protocol.
As a consequence, the current protocol is unable to accomodate the web browser model.
Since the protocol seems to be sufficient for another community 
(but not to the Internet community), it is proposed to place this document 
on the EXPERIMENTAL track rather than on the standards track.
Denis
Date : 2010-01-14, 18:34:14
Sujet : [pkix] Last Call: draft-ietf-pkix-tamp (Trust Anchor Management Protocol (TAMP)) toProposed Standard
The IESG has received a request from the Public-Key Infrastructure 
(X.509) WG (pkix) to consider the following document:

- 'Trust Anchor Management Protocol (TAMP) '
   <draft-ietf-pkix-tamp-05.txt> as a Proposed Standard

This document includes a downref to draft-ietf-pkix-new-asn1, which
is under consideration by the IESG for publication as an Informational RFC.
This document updates ASN.1 modules for PKIX specifications to conform to
the 2002 version of ASN.1, but makes no changes to the bits on the wire.
The community is specifically requested to consider whether down refs
to draft-ietf-pkix-new-asn1 are appropriate in the general case, 
in addition to the specific case of draft-ietf-pkix-tamp.

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
[e-mail] mailing lists by 2010-01-28. Exceptionally, 
comments may be sent to [e-mail] instead. In either case, please 
retain the beginning of the Subject line to allow automated sorting.

The file can be obtained via
http://www.ietf.org/internet-drafts/draft-ietf-pkix-tamp-05.txt


IESG discussion can be tracked via
https://datatracker.ietf.org/public/pidtracker.cgi?command=view_id&dTag=17760&rfc_flag=0

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