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
other documents at any time. It is not appropriate to use Internet-
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
1id-abstracts.txt listing contained in the Internet-Drafts Shadow
Directories on ds.internic.net (East USA), ftp.isi.edu (West USA),
nic.nordu.net (North Europe), ftp.nis.garr.it (South Europe),
munnari.oz.au (Pacific Rim), or ftp.is.co.za (Africa).
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.
Donald E. Eastlake 3rd [Page 1]
INTERNET-DRAFT Indirect KEY RRs
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]
INTERNET-DRAFT Indirect KEY RRs
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]
INTERNET-DRAFT Indirect KEY RRs
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-
Donald E. Eastlake 3rd [Page 4]
INTERNET-DRAFT Indirect KEY RRs
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
Donald E. Eastlake 3rd [Page 5]
INTERNET-DRAFT Indirect KEY RRs
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]
INTERNET-DRAFT Indirect KEY RRs
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]
