One document matched: draft-schlyter-pkix-dns-02.txt
Differences from draft-schlyter-pkix-dns-01.txt
PKIX Working Group J. Schlyter
Internet-Draft Carlstedt Research &
Expires: December 9, 2002 Technology
L. Johansson
Stockholm University
June 10, 2002
DNS as X.509 PKIX Certificate Storage
draft-schlyter-pkix-dns-02
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on December 9, 2002.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
A major problem facing PKIX deployment and implementation is the
problem of constructing certificate paths for input to the path
validation algorithm. This draft describes the use of the DNS as a
certificate store and it's implication for path validation in PKIX.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Storing PKIX certificates in DNS . . . . . . . . . . . . . . . . 3
3. Certificate lookup algorithm . . . . . . . . . . . . . . . . . . 4
4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
A major problem facing PKIX deployment and implementation is the
problem of constructing certificate paths for input to the path
validation algorithm described in RFC 2459 [2]. This problem can be
solved by successively looking at the issuerAltName extension of each
certificate and using the information found there together with a
storage and transport protocol for certificates to find a set of
candidate certificates associated with the issuerAltName.
Using the CERT RR [5] a certificate can be published using DNS. This
draft describes the use of DNS as a certificate store and it's
implication for path validation in PKIX.
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 [1].
2. Storing PKIX certificates in DNS
A PKIX certificate is published in DNS using the CERT RR [5] for a
given domain name which SHOULD be equal to the dnsName component of
the subjectAltName extension in the certificate. Multiple
certificates may be present for each domain name and all SHOULD have
the same subject DN. If the domain name does not match the dnsName
component of the subjectAltName extension the client SHOULD notify
the user of this and allow the user to decide weather to allow the
use of the certificate or not.
When constructing a certificate path for validation the client MAY
use the AuthorityKeyIdentifier and SubjectKeyIdentifier extensions to
select the (set of) certificates to use.
There are a few important cases when multiple CA certificates are
published in CERT RRs for given domain name:
Multiple certificates each signed by another member of the same
set. This situation occurs when a self-signed certificate issues
a certificate under the same DN (for the purpose of adding policy
for instance).
Multiple certificates, either self-signed or issued by another CA,
with different validity periods.
Root key roll-over as described in section 2.4 of RFC 2510 [3]
where exactly 4 certificates would be published using DNS.
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3. Certificate lookup algorithm
Given a certificate with a non-empty issuerAltName extension of type
dnsName, perform a DNS lookup of the corresponding domain name with
the class IN and type CERT. For each of the certificates returned
that are of type PKIX, implementations SHOULD verify that the
subjectAltName in the certificate contains a component of type
dnsName with the same domain name as the one where the certificate
was published using the DNS.
If a certificate obtained by this algorithm is a self-signed
certificate and was successfully verified by DNSSEC [4], the user
SHOULD be given the opportunity to use this certificate as a trust
anchor.
The result of this algorithm is a set of of certificates suitable for
input to the PKIX path validation algorithm.
4. Example
Client A talks TLS to server B and receives a certificate chain
ending in a cert (X) with issuerAltName:dnsName set to
ca.example.com.
Client A does path validation on the chain and is unable to find X
in its list of trusted roots.
Client A queries the DNS for the CERT record for ca.example.com
and receives a set of certificates.
Client A looks for X in the set of certificates. If found, and
depending on local configuration, A trusts the certificate for use
as a TLS client trust anchor and adds it to the list of trusted
roots.
Path validation now succeeds.
5. Security Considerations
This document describes a mechanism for automated download of
certificates from DNS with special provision for bridging trust
between a PKIX PKI and DNSSEC. However, if only self-signed end-
entity PKIX certificates are published using DNS the benefits of PKIX
policy and key usage management is lost.
The benefit of this mechanism is a potential for added protection of
certificate trust anchors in common use on the Internet by leveraging
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DNSSEC infrastructure.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Housley, R., Ford, W., Polk, T. and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and CRL Profile", RFC
2459, January 1999.
[3] Adams, C. and S. Farrell, "Internet X.509 Public Key
Infrastructure Certificate Management Protocols", RFC 2510,
March 1999.
[4] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[5] Eastlake, D. and O. Gudmundsson, "Storing Certificates in the
Domain Name System (DNS)", RFC 2538, March 1999.
Authors' Addresses
Jakob Schlyter
Carlstedt Research & Technology
Stora Badhusgatan 18-20
Goteborg SE-411 21
Sweden
EMail: jakob@crt.se
URI: http://www.crt.se/~jakob/
Leif Johansson
Stockholm University
IT and Media Unit
Frescati Hagvag 8
Stockholm SE-106 91
Sweden
Phone: +46 8 16 45 41
EMail: leifj@it.su.se
URI: http://www.it.su.se
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Appendix A. Acknowledgements
The author gratefully acknowledges, in no particular order, the
contributions of the following persons:
Martin Fredriksson
Niklas Hallqvist
Edward Lewis
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Full Copyright Statement
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
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