[cabfpub] Ballot 105 Technical Constraints for Subordinate Certificate Authorities yielding broader and safer PKI adoption.

Dean Coclin Dean_Coclin at symantec.com
Thu Jul 25 20:22:17 UTC 2013


Symantec votes ABSTAIN but would like to offer the following commentary for
the benefit of all:

 

In an ideal world, technical constraints would enhance security of the CA
trust model, but we fall far short of the ideal in two areas:

1)      Apple currently offers no support for constraints, and has not
indicated any plans to add that support in the future

2)      As Erwann's email pointed out, there are important differences in
how different platforms interpret technical constraints.

 

Dean Coclin

 

From: public-bounces at cabforum.org [mailto:public-bounces at cabforum.org] On
Behalf Of Steve Roylance
Sent: Monday, July 22, 2013 3:28 AM
To: public at cabforum.org
Cc: Stephen Davidson
Subject: [cabfpub] Ballot 105 - Technical Constraints for Subordinate
Certificate Authorities yielding broader and safer PKI adoption.

 

Dear all,

 

As we made some slight modifications to the Wiki version last week to add
clarity and address final concerns I'm sending out the agreed modified
version as an e-mail (which matches the Wiki) so that people can vote based
on the e-mail version for their own records.

 

Steve

 

 

Ballot 105 - Technical Constraints for Subordinate Certificate Authorities
yielding broader and safer PKI adoption.

Steve Roylance made the following motion, and Gervase Markham from Mozilla
and Stephen Davidson from Quovadis endorsed it:

Motion Begins

EFFECTIVE IMMEDIATELY, this ballot provides clarity to the language covering
external audits for Subordinate CAs, removing ambiguity as well as providing
better alignment of the Baseline Requirements to the Mozilla CA Root program
where the subject is already covered and accepted by the wider PKI
community. In addition, the proposal sets out to aid wider and broader PKI
adoption by Subordinate CAs by defining the use of Technical Constraints and
highlighting how additional barriers to adoption within the guidelines can
be optional when using Name Constraints, specifically the requirement for
'OCSP Good' responses originally proposed in Ballot 100. We propose amending
the Baseline Requirements Guidelines as follows:

Section 1 - Scope (Adding scope)

These Requirements are applicable to all Certification Authorities within a
chain of trust. They are to be flowed down from the Root Certification
Authority through successive Subordinate Certification Authorities.

Section 4 - Definitions (Additional Definition)

Technically Constrained Subordinate CA Certificate: A Subordinate CA
certificate which uses a combination of Extended Key Usage settings and Name
Constraint settings to limit the scope within which the Subordinate CA
Certificate may issue Subscriber or additional Subordinate CA Certificates.

Section 9.2.7 Other Subject Attributes (Moving to 9.2.8)

Section 9.2.7 Subject Information - Subordinate CA Certificates (Adding a
new section)

By issuing a Subordinate CA Certificate, the CA represents that it followed
the procedure set forth in its Certificate Policy and/or Certification
Practice Statement to verify that, as of the Certificate's issuance date,
all of the Subject Information was accurate.

Section 9.4 Validity Period (Clarifying the Validity Period for Subscriber
Certificates)

Was:-

9.4 Validity Period

Certificates issued after the Effective Date MUST have a Validity Period no
greater than 60 months. Except as provided for below, Certificates issued
after 1 April 2015 MUST have a Validity Period no greater than 39 months.
Beyond 1 April 2015, CAs MAY continue to issue Certificates with a Validity
Period greater than 39 months but not greater than 60 months provided that
the CA documents that the Certificate is for a system or software that:

Amended to:-

9.4 Validity Period

9.4.1 Subscriber Certificates

Subscriber Certificates issued after the Effective Date MUST have a Validity
Period no greater than 60 months. Except as provided for below, Subscriber
Certificates issued after 1 April 2015 MUST have a Validity Period no
greater than 39 months. Beyond 1 April 2015, CAs MAY continue to issue
Subscriber Certificates with a Validity Period greater than 39 months but
not greater than 60 months provided that the CA documents that the
Certificate is for a system or software that:

9.5 Subscriber Public Key (Alignment of Key checking for all certificates)

9.5 Public Key

9.7 Additional Technical Requirement (Moving to Section 9.8)

9.7 Technical Constraints in Subordinate CA Certificates via Name
Constraints & EKU (New section)

9.7 Technical Constraints in Subordinate CA Certificates via Name
Constraints & EKU

For a Subordinate CA Certificate to be considered Technically Constrained,
the certificate MUST include an Extended Key Usage (EKU) extension
specifying all extended key usages that the Subordinate CA Certificate is
authorized to issue certificates for. The anyExtendedKeyUsage KeyPurposeId
MUST NOT appear within this extension. If the Subordinate CA Certificate
includes the id-kp-serverAuth extended key usage, then the Subordinate CA
Certificate MUST include the Name Constraints X.509v3 extension with
constraints on dNSName, iPAddress and DirectoryName as follows:-

(a) For each dNSName in permittedSubtrees, the CA MUST confirm that the
Applicant has registered the dNSName or has been authorized by the domain
registrant to act on the registrant's behalf in line with the verification
practices of section 11.1

(b) For each iPAddress range in permittedSubtrees, the CA MUST confirm that
the Applicant has been assigned the iPAddress range or has been authorized
by the assigner to act on the assignee's behalf.

(c) For each DirectoryName in permittedSubtrees the CA MUST confirm the
Applicants and/or Subsidiary's Organizational name and location such that
end entity certificates issued from the subordinate CA Certificate will be
in compliancy with section 9.2.4 and 9.2.5.

If the Subordinate CA Certificate is not allowed to issue certificates with
an iPAddress, then the Subordinate CA Certificate MUST specify the entire
IPv4 and IPv6 address ranges in excludedSubtrees. The Subordinate CA
Certificate MUST include within excludedSubtrees an iPAddress GeneralName of
8 zero octets (covering the IPv4 address range of 0.0.0.0/0). The
Subordinate CA Certificate MUST also include within excludedSubtrees an
iPAddress GeneralName of 32 zero octets (covering the IPv6 address range of
::0/0). Otherwise, the Subordinate CA Certificate MUST include at least one
iPAddress in permittedSubtrees.

A decoded example for issuance to the domain and sub domains of example.com
by organization :- Example LLC, Boston, Massachusetts, US would be:-

   X509v3 Name Constraints:

   Permitted:

                   DNS:example.com 

                   DirName: C=US, ST=MA, L=Boston, O=Example LLC

   Excluded:

                   IP:0.0.0.0/0.0.0.0 

                   IP:0:0:0:0:0:0:0:0/0:0:0:0:0:0:0:0

If the Subordinate CA is not allowed to issue certificates with dNSNames,
then the Subordinate CA Certificate MUST include a zero-length dNSName in
excludedSubtrees. Otherwise, the Subordinate CA Certificate MUST include at
least one dNSName in permittedSubtrees.

Section 11.1.1 Authorization by Domain Name Registrant (Adding
clarification)

Note: FQDNs may be listed in Subscriber Certificates using dNSNames in the
subjectAltName extension or in Subordinate CA Certificates via dNSNames in
permittedSubtrees within the Name Constraints extension.

Section 11.1.2 Authorization for an IP Address (Adding clarification)

Note: IPAddresses may be listed in Subscriber Certificates using IPAddress
in the subjectAltName extension or in Subordinate CA Certificates via
IPAddress in permittedSubtrees within the Name Constraints extension.

Section 13.2.6 Response for non-issued certificates (Amending applicability)

Was:-

13.2.6 Response for non-issued certificates

If the OCSP responder receives a request for status of a certificate that
has not been issued, then the responder SHOULD NOT respond with a "good"
status. The CA SHOULD monitor the responder for such requests as part of its
security response procedures. Effective 1 August 2013, OCSP responders MUST
NOT respond with a "good" status for such certificates.

Amended to:-

13.2.6 Response for non-issued certificates

If the OCSP responder receives a request for status of a certificate that
has not been issued, then the responder SHOULD NOT respond with a "good"
status. The CA SHOULD monitor the responder for such requests as part of its
security response procedures. Effective 1 August 2013, OCSP responders for
CAs which are not Technically Constrained in line with Section 9.7 MUST NOT
respond with a "good" status for such certificates.

Section 17 Audit (Clarification notes added to the section heading)

Certificates that are capable of being used to issue new certificates MUST
either be Technically Constrained in line with section 9.7 and audited in
line with section 17.9 only, or Unconstrained and fully audited in line with
all remaining requirements from section 17. A Certificate is deemed as
capable of being used to issue new certificates if it contains an X.509v3
basicConstraints extension, with the cA boolean set to true and is therefore
by definition a Root CA Certificate or a Subordinate CA Certificate.

Section 17.9 Regular Quality Assessment of Technically Constrained
Subordinate CAs (New Section)

During the period in which a Technically Constrained Subordinate CA issues
Certificates, the CA which signed the Subordinate CA SHALL monitor adherence
to the CA's Certificate Policy and the Subordinate CA's Certification
Practice Statement. On at least a quarterly basis, against a randomly
selected sample of the greater of one certificate or at least three percent
of the Certificates issued by the Subordinate CA, during the period
commencing immediately after the previous audit sample was taken, the CA
shall ensure all applicable Baseline Requirements are met.

Appendix B - Certificate Extensions (Normative) (Clarify F and add G)

Was:-

F. nameConstraints (optional) If present, this extension SHOULD be marked
critical*.

* Non-critical Name Constraints are an exception to RFC 5280 that MAY be
used until the Name Constraints extension is supported by Application
Software Suppliers whose software is used by a substantial portion of
Relying Parties worldwide.

Amended to:-

F. nameConstraints (optional) If present, this extension SHOULD be marked
critical*.

* Non-critical Name Constraints are an exception to RFC 5280 (4.2.1.10),
however, they MAY be used until the Name Constraints extension is supported
by Application Software Suppliers whose software is used by a substantial
portion of Relying Parties worldwide.

G. extkeyUsage (optional) For Subordinate CA Certificates to be Technically
constrained in line with section 9.8, then either the value id-kp-serverAuth
[RFC5280] or id-kp-clientAuth [RFC5280] or both values MUST be present**.
Other values MAY be present.  If present, this extension SHOULD be marked
non-critical.

** Generally Extended Key Usage will only appear within end entity
certificates (as highlighted in RFC 5280 (4.2.1.12)), however, Subordinate
CAs MAY include the extension to further protect relying parties until the
use of the extension is consistent between Application Software Suppliers
whose software is used by a substantial portion of Relying Parties
worldwide.

The review period for this ballot shall commence on July 15th, 2013 and will
close on July 22nd, 2013. Unless the motion is withdrawn during the review
period, the voting period will start immediately thereafter and will close
at July 29, 2013. Votes must be cast by posting an on-list reply to this
thread.

Motion Ends

A vote in favor of the motion must indicate a clear 'yes' in the response. A
vote against must indicate a clear 'no' in the response. A vote to abstain
must indicate a clear 'abstain' in the response. Unclear responses will not
be counted. The latest vote received from any representative of a voting
member before the close of the voting period will be counted. Voting members
are listed here:  <http://www.cabforum.org/forum.html>
http://www.cabforum.org/forum.html In order for the motion to be adopted,
two thirds or more of the votes cast by members in the CA category and one
half or more of the votes cast by members in the browser category must be in
favor. Also, at least seven members must participate in the ballot, either
by voting in favor, voting against, or abstaining.

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