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Network Working Group                                          B. Laurie
Internet-Draft                                                   Nominet
Expires: December 16, 2006                                 June 14, 2006


                      Distributing Keys for DNSSEC
                draft-laurie-dnssec-key-distribution-02

Status of this Memo

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   This Internet-Draft will expire on December 16, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   Until DNSSEC is fully deployed, so-called "islands of trust" will
   exist.  This will lead to a large number of keys with no method
   within DNSSEC to manage the keys.  This proposal seeks to address
   that issue using existing mechanisms to allow cross-signing of root
   (i.e. roots of islands) keys.  This cross-signing of keys creates a
   non-hierarchical web of trust which permits the efficient gathering
   and validation of trust anchors.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Island CAs  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Key Signing . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Publication of Certificates . . . . . . . . . . . . . . . . . . 4
   5.  Location of Island Publication URL  . . . . . . . . . . . . . . 4
   6.  Use of Certificates . . . . . . . . . . . . . . . . . . . . . . 4
   7.  Verification of Certificates  . . . . . . . . . . . . . . . . . 5
   8.  Variations  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   9.  Security Non-issues . . . . . . . . . . . . . . . . . . . . . . 5
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   11. Requirements notation . . . . . . . . . . . . . . . . . . . . . 6
   12. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     13.1.  Normative References . . . . . . . . . . . . . . . . . . . 6
     13.2.  Informative References . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9
































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1.  Introduction

   When DNSSEC signatures are validated the validators will follow a
   chain of authority from a pre-configured trust anchor to the data
   that is to be validated.  The DNSSEC protocol (RFC 4033 [RFC4033],
   RFC 4034 [RFC4034] and RFC 4035 [RFC4035]) clearly describes how
   these chains of trust are to be established but does not address the
   issue of the distribution of the trust anchors.

   This document describes how an X.509 based public key infrastructure
   can be used to bootstrap the configuratation of a set of trust
   anchors.  SEP keys are stored in certificates that are signed by the
   registries' Certificate Authorities.  The system allows registries to
   indicate levels of trust which allows for prudent cross-signing.

   The Certificate Authority and the certificates are discussed in
   Section 2 and Section 3.  Section 4 and Section 5 describe how the
   certificates are published.  Section 6 describes how the certificates
   are used to establish the trust-anchors.

   In this document the term secure entry point (SEP) key is used to
   describe the (sub)set of public key(s) that is intended as a secure
   entry point into the zone [RFC3757].  The term Island of security, or
   island for short, is used for a zone for which one of the SEP keys
   are used as a trust-anchor and which is therefore the start of a
   chain of authority.


2.  Island CAs

   The root of each island will publish an X.509 CA certificate.  This
   will be a long-term, self-signed certificate, known as the Island
   Root CA (IRCA).  This CA will then be used to create two subsidiary
   CAs, each with a shorter expiry, known as the High Assurance Island
   CA and the Low Assurance Island CA.  The High and Low Assurance CA
   certificates will each contain an X.509v3 extension indicating their
   role.

   Each island will have a set of requirements for cross-signing, one
   for low assurance and one for high assurance.  The reason for having
   two is to allow cross-signing of keys that the island's operators do
   not have high confidence in without exposing them to accusations of
   insufficient prudence.


3.  Key Signing

   Each island will issue a certificate signed by the Island Root CA for



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   each of its own SEPs.  The public key in the certificate will be the
   same public key as used by the SEP.

   For each other island that meets the island's requirements for cross-
   signing, the island will issue a certificate for their IRCA signed by
   either the Low or High Assurance Island CA, as appropriate.  That is,
   the certificate will have the same subject name and public key as the
   IRCA being signed, but the issuer will be one of this island's
   subsidiary CAs.  This could be done using the cross-certification
   protocol from RFC 2510 [RFC2510]

   Each certificate issued will contain an X.509v3 extension with the
   name of the domain associated with the signed public key.


4.  Publication of Certificates

   Each island will maintain a URL (known as the Island Publication URL
   or IPU) where all current certificates issued by any of its CAs are
   available.  This URL may also have a collection of certificates
   issued by other island CAs and also the CA certificates themselves of
   other islands.  Note, however, that the presence of a certificate
   does not indicate any kind of trust in it - that is done purely by
   the certificate signatures.


5.  Location of Island Publication URL

   The location of each IPU will be held in the IRCA using an X.509v3
   certificate extension registered for the purpose.


6.  Use of Certificates

   A resolver wishing to bootstrap its collection of trust anchors need
   only choose a small set of IRCAs to trust (or, with luck, a single
   one).  Once it has done so, it can extract the IPU from the CA
   certificate, use HTTP to retrieve the certificate collection
   available there, check their (chained) signatures, extract the public
   keys from the certificates and use these as the initial set of SEPs
   for the domains named in the certificates.

   Once the initial set of certificates has been retrieved, this process
   can be followed recursively for other IRCAs retrieved.  Also, the set
   of trusted IRCAs could be expanded to include some or all of the
   retrieved IRCAs.

   After the set of trusted trust anchors have been established, in-band



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   mechanisms can be used to keep them up to date.  If for some reason
   the set of trust anchors becomes too stale to update (for example,
   because the device has been offline for an extended period), then the
   process can be repeated from the start.


7.  Verification of Certificates

   Once the collection of certificates is complete, the resolver uses
   the trusted IRCAs to verify the certificate of each SEP.  Because of
   the use of cross-certification, the X.509 verification must be
   capable of trying multiple paths to verification, as specified in RFC
   3280 [RFC3280].

   Users may choose to restrict the verification path, for example by
   requiring certificate chains to be below some length, or not
   permitting verification through Low Assurance CAs.

   Once the set of verified SEPs has been established, then the public
   keys are extracted from each one and associated as trust anchors for
   DNSSEC with the corresponding domain.


8.  Variations

   Instead of a URL, the certificate could contain a domain name and
   socket number.

   Certificates could be published in the DNS [I-D.ietf-dnsext-
   rfc2538bis].

   Rather than using X.509 for signing, OpenPGP [RFC2440] could be used
   instead.


9.  Security Non-issues

   Note that DNSSEC is not required to secure the domain names used for
   certificate retrieval, since the signature of the selected IRCA(s)
   will be sufficient to validate the retrieved certificates.


10.  Acknowledgements

   Thanks to Olaf Kolkman for comments on early drafts and Russ Housley
   for explaining how to use X.509 the way I wanted to.





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11.  Requirements notation

   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 [RFC2119].


12.  Security Considerations


13.  References

13.1.  Normative References

   [I-D.ietf-dnsext-rfc2538bis]
              Josefsson, S., "Storing Certificates in the Domain Name
              System (DNS)", draft-ietf-dnsext-rfc2538bis-09 (work in
              progress), October 2005.

   [RFC2440]  Callas, J., Donnerhacke, L., Finney, H., and R. Thayer,
              "OpenPGP Message Format", RFC 2440, November 1998.

   [RFC2510]  Adams, C. and S. Farrell, "Internet X.509 Public Key
              Infrastructure Certificate Management Protocols",
              RFC 2510, March 1999.

   [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
              X.509 Public Key Infrastructure Certificate and
              Certificate Revocation List (CRL) Profile", RFC 3280,
              April 2002.

13.2.  Informative References

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2418]  Bradner, S., "IETF Working Group Guidelines and
              Procedures", BCP 25, RFC 2418, September 1998.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",



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              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.














































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Author's Address

   Ben Laurie
   Nominet
   17 Perryn Road
   London  W3 7LR
   England

   Phone: +44 (20) 8735 0686
   Email: ben@algroup.co.uk









































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Intellectual Property Statement

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Copyright Statement

   Copyright (C) The Internet Society (2006).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




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