
INTERNET-DRAFT                                          Indirect KEY RRs
                                                           November 1997
                                                        Expires May 1998



               Indirect KEY RRs in the Domain Name System
               -------- --- --- -- --- ------ ---- ------

                         Donald E. Eastlake 3rd



Status of This Document

   This draft, file name draft-ietf-dnssec-indirect-key-01.txt, is
   intended to be become a Proposed Standard RFC.  Distribution of this
   document is unlimited. Comments should be sent to the DNSSEC mailing
   list <dns-security@tis.com> or to the author.

   This document is an Internet-Draft.  Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and its working groups.  Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months.  Internet-Drafts may be updated, replaced, or obsoleted by
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   Drafts as reference material or to cite them other than as a
   ``working draft'' or ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
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Abstract

   RFC 2065 defines a means for storing cryptogrpahic public keys in the
   Domain Name System.  An additional code point is defined for the KEY
   resource record (RR) algorithm field to indicate that the key itself
   is not stored in the KEY RR but is pointed to by the KEY RR.
   Encodings to indicate different types of key and pointer formats are
   specified.








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Table of Contents

      Status of This Document....................................1
      Abstract...................................................1

      Table of Contents..........................................2

      1. Introduction............................................3

      2. The Indirect KEY RR Algorithm...........................4
      2.1 The Target Type Field..................................4
      2.2 The Target Algorithm Field.............................5
      2.3 The Hash Fields........................................5

      3. Performance Considerations..............................7
      4. Security Considerations.................................7

      References.................................................8
      Author's Address...........................................8
      Expiration and File Name...................................8
































Donald E. Eastlake 3rd                                          [Page 2]


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1. Introduction

   The Domain Name System (DNS) security extensions [RFC 2065] provide
   for the general storage of public keys in the domain name system via
   the KEY resource record (RR).  These KEY RRs are used in support of
   DNS security and may be used to support other security protocols.
   KEY RRs can be associated with users, zones, and hosts or other end
   entities named in the DNS.

   For reasons given below, in many cases it will be desireable to store
   a key or keys elsewhere and merely point to it from the KEY RR.
   Indirect key storage makes it possible to point to a key service via
   a URL, to have a compact pointer to a larger key or set of keys, to
   point to a certificate either inside DNS [see draft-ietf-dnssec-
   certs-*.txt] or outside the DNS, and where appropriate, to store a
   key or key set applicable to many DNS entries in some place and point
   to it from those entries.

   However, to simplify DNSSEC implementation, this technique MUST NOT
   be used for KEY RRs used in for verification in DNSSEC.
































Donald E. Eastlake 3rd                                          [Page 3]


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2. The Indirect KEY RR Algorithm

   Domain Name System (DNS) KEY Resource Record (RR) [RFC 2065]
   algorithm number 252 is defined as the indirect key algorithm.  This
   algorithm MAY NOT be used for zone keys in support of DNS security.
   All KEYs used in DNSSEC validation must be stored directly in the
   DNS.

   When the algorithm byte of a KEY RR has thae value 252, the "public
   key" portion of the RR is formated as follows:

                        1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          target type          |  target alg.  |   hash type   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   hash size   |             hash (variable size)              /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-/
   |                                                               /
   /                    pointer (varible size)                     /
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|



2.1 The Target Type Field

   Target type specifies the type of the key containing data being
   pointed at.

   Target types 0 and 65535 are reserved.

   Target type 1 indicates that the pointer is a domain name from which
   KEY RRs [RFC 2065] should be retrieved.  Name compression in the
   pointer field is prohibited.

   Target type 2 indicates that the pointer is a null terminated
   character string which is a URL [RFC 1738].  For exisiting data
   transfer URL schemes, such as ftp, http, shttp, etc., the data is the
   same as the public key portion of a KEY RR.  (New URL schmes may be
   defined which return multiple keys.)

   Target type 2 indicates that the pointer is a domain name from which
   CERT RRs [draft-ietf-dnssec-certs-*.txt] should be retrieved.  Name
   compression in the pointer field is prohibiited.

   Target type 3 indicates that the pointer is a null terminated
   character string which is a URL [RFC 1738].  For exisiting data
   transfer URL schemes, such as ftp, http, shttp, etc., the data is the
   same as the entire RDATA portion of a CERT RR [draft-ietf-dnssec-


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   certs-*.txt].  (New URL schmes may be defined which return multiple
   such data blocks.)

   Target type 4 indicates that the pointer is a null terminated
   character string which is a URL [RFC 1738].  For exisiting data
   transfer URL schemes, such as ftp, http, shttp, etc., the data is a
   PKCS#1 format key.  (New URL schmes may be defined which return
   multiple keys.)

   The target types  5 through 255 are available for assignment by IANA.

   Target type 256 through 511 (i.e., 256 + n) indicate that the pointer
   is a null terminated character string which is a URL [RFC 1738]. For
   exisiting data transfer URL schemes, such as ftp, http, shttp, etc.,
   the data is a certificate of the type indicated by a CERT RR [draft-
   ietf-dnssec-certs-*.txt] certificate type of n.  That is, target
   types 257, 258, and 259 are PKIX, SPKI, and PGP certificates and
   target types 509 and 510 are URL and OID private certificate types.
   (New URL schmes may be defined which return multiple such
   certificates.)

   Target types 512 through 65534 are available for assignment by IANA.



2.2 The Target Algorithm Field

   The algorithm field is as defined in RFC 2065.  if non-zero, it
   specifies the algorithm type of the target key or keys pointed.  If
   zero, it does not specify what algorithm the target key or keys apply
   to.



2.3 The Hash Fields

   If the indirecting KEY RR is retrieved from an appropriately secure
   DNS zone with a resolver implementing DNS security, then there would
   be a high level of confidence in the entire value of the KEY RR
   including any direct keys. This may or may not be true of any
   indirect key pointed to.  If that key is embodied in a certificate or
   retrieved via a secure protocol such as SHTTP, it may also be secure.
   But an indirecting KEY RR could, for example, simply have an FTP URL
   pointing to a binary key stored elsewhere, the retrieval of which
   would not be secure.

   The hash option in algorithm 252 KEY RRs provides a means of
   extending the security of the indirecting KEY RR to the actual key
   material pointed at.  By inclduing a hash in a secure indirecting RR,
   this secure hash can be checked against the hash of the actual keying


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   material

         Type  Hash Algorithm
         ----  --------------
            0  indicates no hash present
            1  MD5  [RFC 1321]
            2  SHA-1
            3  RIPEMD
        4-254  available for assignment
          255  reserved

   The hash size field is an unsigned octet count of the hash size.  For
   some hash algorithms it may be fixed by the algorithm choice but this
   will not always be the case.  For example, hash size is used to
   distinguish between RIPEMD-128 (16 octets) and RIPEMD-160 (20
   octets).  If the hash algorithm is 0, the hash size MUST be zero and
   no hash octets are present.

   The hash field itself is variable size with its length specified by
   the hash size field.
































Donald E. Eastlake 3rd                                          [Page 6]


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3. Performance Considerations

   With current public key technology, an indirect key will sometimes be
   shorter than the keying material it points at.  This may improve DNS
   permformace in the retrieval of the initial KEY RR.  However, an
   additional retrieval step then needs to be done to get the actualy
   keying material which must be added to the overall time to get the
   public key.



4. Security Considerations

   The indirecting step of using an indirect KEY RR adds complexity and
   additional steps where security could go wrong.  If the indirect key
   RR was retrieved from a zone that was insecure for the resolver, you
   have no security.  If the indirect key RR, although secure itself,
   point to a key which can not be securely retrieved and is not
   validatated by a secure hash in the indirect key RR, you have no
   security.
































Donald E. Eastlake 3rd                                          [Page 7]


INTERNET-DRAFT                                          Indirect KEY RRs


References

   PKCS#1

   RFC 1034 - P. Mockapetris, "Domain Names - Concepts and Facilities",
   STD 13, November 1987.

   RFC 1035 - P. Mockapetris, "Domain Names - Implementation and
   Specifications", STD 13, November 1987.

   RFC 1321 - R. Rivest, "The MD5 Message-Digest Algorithm", April 1992.

   RFC 1738 - T. Berners-Lee, L. Masinter & M.  McCahill, "Uniform
   Resource Locators (URL)", December 1994.

   RFC 2065 - D. Eastlake, C. Kaufman, "Domain Name System Security
   Extensions", 01/03/1997.

   draft-ietf-dnssec-certs-*.txt



Author's Address

   Donald E. Eastlake 3rd
   CyberCash, Inc.
   318 Acton Street
   Carlisle, MA 01741 USA

   Telephone:   +1 978 287 4877
                +1 703 620-4200 (main office, Reston, VA)
   FAX:         +1 978 371 7148
   EMail:       dee@cybercash.com



Expiration and File Name

   This draft expires May 1998.

   Its file name is draft-ietf-dnssec-indirect-key-01.txt.











Donald E. Eastlake 3rd                                          [Page 8]

