Please find attached a draft of the Web PKI Trust Models document.
I plan to review the document in the meeting tomorrow. Iñigo and I would
appreciate any comments on the document plan and the content.
Thanks,
Bruce Morton
+1 613.270.3743
Internet Engineering Task Force I. Barreira, Ed.
Internet-Draft Izenpe
Intended status: BCP B. Morton, Ed.
Expires: May 4, 2013 Entrust
October 31, 2012
Trust models of the Web PKI
draft-webpki-trustmodel-00
Abstract
This is one of a set of drafts that document the operation of the Web
PKI. It describes common variants of the Web PKI trust model
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 4, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
1.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Basic trust model . . . . . . . . . . . . . . . . . . . . . . . 5
3. Trust model variants . . . . . . . . . . . . . . . . . . . . . 5
3.1. Certificate-using product adopts root store . . . . . . . . 5
3.2. Certificate-using product uses OS root store . . . . . . . 5
3.3. Certificate-using product uses Trust Service Status
List Issued by Recognised Authorities . . . . . . . . . . . 5
3.4. Certificate holder certificates issued by root CA . . . . . 6
3.5. One root CA cross-certifies another root CA . . . . . . . . 6
3.6. Issuing CA is an affiliate . . . . . . . . . . . . . . . . 6
3.7. Registration authority is an affiliate . . . . . . . . . . 6
3.8. Root CA is operated by a government . . . . . . . . . . . . 7
3.9. Certificate user directly trusts issuing CA key . . . . . . 7
3.10. Certificate user directly trusts certificate holder key . . 7
3.11. Certificate holder operates issuing CA . . . . . . . . . . 7
3.12. Certificate holder sources management of issuing CA . . . . 7
3.13. Certificate holder manages RA . . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
6. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Definitions
Certificate: The public key of a user, together with some other
information, rendered unforgeable by encipherment with the private
key of the certification authority which issued it.
Certification Authority (CA) - Authority trusted by one or more
users to create and assign certificates.
Certificate holder - A natural or legal person who is identified
as the subject in a certificate.
Certificate policy: A named set of rules that indicates the
applicability of a certificate to a particular community and/or
class of application with common security requirements.
Certification Practice Statement (CPS): A statement of the
practices that a Certification Authority employs in issuing,
managing, revoking and renewing or re-keying certificates.
Certificate subject - The certificate holder as represented in the
certificate.
Certificate user - A natural person who operates a certificate
using product.
Certificate-using product - A product that evaluates a certificate
or certificate chain and adjusts its behavior according to the
result.
End entity: A certificate subject which uses its public key for
purposes other than signing certificates.
Intermediate CA - A CA that issues certificates to issuing CAs
and/or other intermediate CAs.
Issuing CA - A CA that issues certificates to certificate holders.
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Policy management authority - A natural or legal person who
administers the certificate policy by which one or more
certification authorities operate.
Public-key infrastructure (PKI) - is a system for the creation,
storage, and distribution of certificates which are used to verify
that a particular public key belongs to a certain entity.
Relying party: A user or agent that relies on the data in a
certificate in making decisions.
Registration authority (RA): An entity that is responsible for
identification and authentication of certificate subjects, but
that does not sign or issue certificates (i.e., an RA is delegated
certain tasks on behalf of a CA).
Root certificate - is either an unsigned public key certificate or
a self-signed certificate that identifies the Root Certificate
Authority (CA). A root certificate is part of a public key
infrastructure scheme.
Root CA - The trust anchor for the digital certificate is the Root
Certificate Authority (CA). A CA whose public key is included in
a root store.
Root store - A set of certification authority public keys that is
embedded in a certificate-using product.
Self-signed certificate: A certificate for one CA signed by that
CA.
Trust anchor - is an authoritative entity represented via a public
key and associated data.
Trust model - The roles, and the relationships between those
roles, that are relevant to the management and evaluation of
certificates.
Trust service - Service which enhances trust and confidence in
electronic transactions.
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2. Basic trust model
In the basic Web PKI trust model, a certificate-using product
includes a root store that contains one or more root certification
authority public keys, each of which is under the control of a CA and
managed in conformance with the certificate policy prescribed and
administered by the certificate using product supplier. Each such
root certification authority issues a certificate to one or more
issuing CAs that are under the control of the same commercial CA.
Each issuing CA accepts and responds to certificate requests from one
or more certificate applicants via one or more registration
authorities that are under the control of the same CA. If the
request is granted, then the certificate applicant becomes a
certificate holder. The role of the registration authority is to
confirm the accuracy of the information provided in the certificate
request.
The certificate user implicitly accepts the policy of the policy
management authority by choosing to use a particular certificate-
using product.
All functions of the CA are subject to the audit process prescribed
by the certificate policy.
3. Trust model variants
There are several variants of the basic trust model in common use.
3.1. Certificate-using product adopts root store
In this variant, the supplier of the certificate-using product adopts
the policies of other suppliers by copying their root stores, without
seeking independent evidence of conformance.
3.2. Certificate-using product uses OS root store
In this variant, the certificate-using product does not use its own
root store. Instead, it uses the platform operating system root
store and certificate processing functions to evaluate the
certificate holder's certificate. It may then checks that the
certificate subject's domain name matches that requested by the
certificate user.
3.3. Certificate-using product uses Trust Service Status List Issued by
Recognised Authorities
In this variant, one or more authorities (e.g. EU national
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regulatory authorities) provide a list of CAs which have been
assessed for trustworthiness for specific purposes (e.g. web sites
meeting EU regulations), called the Trust Service Status List (TSSL).
3.4. Certificate holder certificates issued by root CA
Some legacy situations demand that the certificate holder certificate
be issued directly by the root CA, without the involvement of
intermediate or issuing CAs. This model is now deprecated, but the
practice will remain in effect indefinitely.
3.5. One root CA cross-certifies another root CA
A small but significant portion of the certificate-using products in
active use does not possess the capability to be updated in the
field. Consequently, these products do not accept certificates
issued by CAs that came into existence after they were first
deployed. Although their certificates are accepted by newer products
and ones that can be updated in the field, newer CAs operate at a
disadvantage to older CAs, and they commonly address this
disadvantage by having their public key cross-certified by an older
CA.
Because the cross-certified root CA is also recognized directly by a
policy management authority, it operates in accordance with the
requirements of that certificate policy, regardless of any
requirements placed upon it by the contract between it and the cross-
certifying root CA.
3.6. Issuing CA is an affiliate
The issuing CA may operate at arm's length to the root CA.
The issuing CA's behavior is governed by its contract with the root
CA, which commonly stipulates adherence to the policies of the policy
management authority.
3.7. Registration authority is an affiliate
The registration authority may operate at arm's length to the issuing
CA.
The registration authority's behavior is governed by its contract
with the issuing CA.
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3.8. Root CA is operated by a government
In the case where the root CA is operated by a government department,
the policy authority may relax the requirement for a fully-
independent third-party audit, relying instead upon an audit
conducted in accordance with the government's own internal audit
process.
3.9. Certificate user directly trusts issuing CA key
The certificate-using product may allow the certificate user to
designate a CA key as trusted, a priori, for the purpose of
evaluating certificate holder certificates.
3.10. Certificate user directly trusts certificate holder key
The certificate-using product may allow the certificate user to
designate a certificate holder key as trusted, a priori.
3.11. Certificate holder operates issuing CA
A certificate holder may operate its own issuing CA. Typically, the
certificate holder is approved to issue certificates only within a
specific region of the name-space, and this limitation is enforced by
contract.
The root CA may use the RFC 5280 [RFC5280] name constraints
certificate extension to limit the region of the name-space in which
the issuing CA can issue valid certificates.
3.12. Certificate holder sources management of issuing CA
A root CA may host an issuing CA on behalf of a certificate holder.
Typically, the certificate holder is approved to issue certificates
only within a specific region of the name-space, and this limitation
is enforced by the host root CA. Examination of the certificate
chain would indicate that the issuing CA was owned and operated by
the certificate holder.
3.13. Certificate holder manages RA
An issuing CA may host a registration authority on behalf of a
certificate holder. Typically, the certificate holder is approved to
issue certificates only within a specific region of the name-space,
and this limitation is enforced by the host issuing CA. Examination
of the certificate chain would indicate that the registration
authority was owned and operated by the issuing CA.
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4. IANA Considerations
This memo includes no request to IANA.
5. Security Considerations
The trust models described here exhibit several vulnerabilities that
could adversely affect the reliability of the authentication they
provide. The first concerns the naming of certificate holders. The
second concerns controllability and observability of issued
certificates.
Certificate holder names with any of the following characteristics
can be used in an impersonation attack.
o homographic name
o mixed-alphabet name
o name that contains a string termination character
o non-unique name (e.g. an internal server name)
With the exception of non-unique names, CAs in the Web PKI are
required to screen out requests for certificates with any of these
characteristics. CAs are required to phase out the practice of
issuing non-unique names by 2016.
Technically, unless constrained by an upstream CA to issue
certificates only in a specific region of the name-space, any CA in
the Web PKI can issue an apparently legitimate certificate for any
name, whether or not the legitimate holder of that name is aware of
or approves the issuance. Furthermore, the legitimate holder of that
name may not discover that such a certificate has been issued.
In the event of a compromise of a root CA, its key is blacklisted by
certificate-using products by means of a software update. This has
the effect of invalidating every otherwise-valid certificate that
chains to that root, whether or not it was issued while the
compromise existed. This step would have a severe impact upon the CA
and its certificate holders; a step not likely to be taken without
very careful deliberation and (perhaps) hesitation.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
Authors' Addresses
Inigo Barreira (editor)
Izenpe
C/Beato Tomas de Zumarraga 71, 1o. 01008 Vitoria-Gasteiz. Spain
Phone: +34 945067705
Email: [email protected]
Bruce Morton (editor)
Entrust
1000 Innovation Drive. Ottawa, Ontario. Canada K2K 3E7
Email: [email protected]
Barreira & Morton Expires May 4, 2013 [Page 9]
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