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Network Working Group J. Schlyter
Internet-Draft Carlstedt Research &
Expires: May 11, 2002 Technology
November 10, 2001
Storing application public keys in the DNS
draft-schlyter-appkey-01.txt
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
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
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 11, 2002.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document specifies a new DNS RR type for applications to store
public keys in. Experience with DNSSEC has indicated that mixing DNS
keys and application keys is a bad idea in many regards. The new RR
expands certain fields based on experience from early DNSSEC
deployment.
Schlyter Expires May 11, 2002 [Page 1]
Internet-Draft Application public keys in DNS November 2001
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The APPKEY resource record . . . . . . . . . . . . . . . . . 3
2.1 The APPKEY RDATA format . . . . . . . . . . . . . . . . . . 4
2.1.1 The protocol field . . . . . . . . . . . . . . . . . . . . . 4
2.1.2 Version number octet . . . . . . . . . . . . . . . . . . . . 4
2.1.3 Algorithm number specification . . . . . . . . . . . . . . . 5
2.2 Text representation of APPKEY RRs . . . . . . . . . . . . . 5
2.3 Owner names for APPKEY RRs . . . . . . . . . . . . . . . . . 5
3. Applicability Statement . . . . . . . . . . . . . . . . . . 5
4. Security considerations . . . . . . . . . . . . . . . . . . 5
5. IANA considerations . . . . . . . . . . . . . . . . . . . . 5
References . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . 7
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
Full Copyright Statement . . . . . . . . . . . . . . . . . . 8
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1. Introduction
The Domain Name System Security Extensions (DNSSEC) as described in
RFC 2535 [4] specifies the KEY resource record (RR). The KEY RR is
specified for use both for storing keys used by the DNSSEC
infrastructure itself and for storing keys used by non-DNSSEC
infrastructure applications (e.g. TLS [2], email and IPsec). The
issues with combining these two uses in one RR are further discussed
in draft-ietf-dnsext-restrict-key-for-dnssec-00 [11].
The protocol field in the KEY RR is only 8-bit and thus limited to
256 different protocols. As there is no way of separating different
version of a specific protocol, incompatible versions of a single
protocol requires multiple protocol values. A larger protocol field
together with the possibility to specify a version of the protocol
could solve this issue.
The KEY RR includes a flag field that specifies key usage, what kind
of entity the key is associated with and various other flags. As
this kind of information often is application dependent and a common
specification that covers all kinds of different flags that an
application might need is hard to do, the usability of this field is
questionable.
A problem with multiple applications storing their public keys at a
single owner name and thus creating a very large RR set has been
identified. A possible solution for this could be to use a generic
protocol value [10] indicating that the actual protocol used is
indicated in the owner name using a SRV-like encoding. Although this
would indeed solve the problem with large RR sets when querying for
an application key, it could also make the protocol field lose its
value in practice as new applications would not require a new
protocol value. The author believes that combining unique protocol
values with SRV-like encode of protocol would be a better solution,
solving both the issue with large RR sets and a large number of
possible applications.
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. The APPKEY resource record
The APPKEY resource record (RR) is used to store a application public
key that is associated with a Domain Name System (DNS) name.
The RR type code for the APPKEY RR is TBA.
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An APPKEY RR is, like any other RR, authenticated by a SIG RR.
2.1 The APPKEY RDATA format
The RDATA for an APPKEY RR consists of a protocol field, a version
number octet, the algorithm number octet and the public key itself.
The format is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| protocol | version | algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /
/ public key /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
The meaning of the APPKEY RR owner name, protocol field, version
number octet and algorithm number octet are described in the sections
below. The format of the public key is algorithm dependent.
APPKEY RRs do not specify their validity period but their
authenticating SIG RR(s) do as described in RFC 2535 [4].
2.1.1 The protocol field
The protocol field specifies what protocol the public key is to be
used for. The following values of the protocol field are available:
Value Protocol
----- --------
0x0000 reserved
0x0001 - 0xFEFF available for assignment by IANA
0xFF00 - 0xFFFE experimental uses
0xFFFF any protocol
0xFFFF indicates that the key can be used in connection with any
protocol. Use of this value is discouraged and the use of unique
protocol values for different protocols is encouraged.
2.1.2 Version number octet
The version number octet is defined by the protocol specified in the
protocol field. It is up to the application implementing the
specified protocol to interpret the value of this octet.
Any document specifying how a protocol uses APPKEY MUST specify how
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to specify and interpret the version number octet.
2.1.3 Algorithm number specification
The algorithm number used is the same as defined for the KEY RR
described in RFC 2535 [4].
2.2 Text representation of APPKEY RRs
The RDATA portion of an APPKEY RR has the protocol field, version
number octet and algorithm number octet represented as unsigned
integers.
The public key fields is represented in base 64 [9] and may be
divided up into any number of white space separated substrings, down
to single base 64 digits, which are concatenated to obtain the full
public key. These substrings can span lines using the standard
parenthesis notation. Note that although the public key field may
have internal sub-fields, these do not appear in the master file
representation.
2.3 Owner names for APPKEY RRs
The owner name of the APPKEY RR is defined per application. This can
be, but is not limited to, the domain name of the host the
application is running at (e.g. host.example.com) or a name matching
the SRV RR [6] for the service (e.g. _ssh._tcp.host.example.com).
3. Applicability Statement
The APPKEY resource record (RR) are only intended for storage of
public keys - private keys MUST NOT be stored in an APPKEY RR.
The APPKEY RR is not intended for storage of certificates and a
separate certificate RR, defined in RFC 2538 [5], has been developed
for that purpose.
4. Security considerations
Public keys from an APPKEY RR, SHOULD NOT be trusted unless the
APPKEY was authenticated by a trusted SIG RR. Applications that do
not validate the signatures by themselves are advised to use TSIG [7]
or SIG(0) [8] to protect the transport between themselves and the
name server doing the signature validation.
5. IANA considerations
IANA needs to allocate a RR type code for APPKEY from the standard RR
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type space.
Protocol values 0x0000 and 0xFFFF are reserved.
Protocol values 0x0001 through 0xFEFF are allocated based on
"Specification Required" as defined in RFC 2434 [3].
XXX should the protocol values be divided into different ranges for
IETF Standard Action, IETF consensus and Specification Required ?
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and
P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January
1999.
[3] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.
[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.
[6] Gulbrandsen, A., Vixie, P. and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[7] Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington,
"Secret Key Transaction Authentication for DNS (TSIG)", RFC
2845, May 2000.
[8] Eastlake, D., "DNS Request and Transaction Signatures (
SIG(0)s)", RFC 2931, September 2000.
[9] Josefsson, S., "Base Encodings", work in progress draft-
josefsson-base-encoding-02, May 2001.
[10] Lewis, E., "DNS KEY Resource Record Generic Protocol Value",
work in progress draft-lewis-dnsext-key-genprot-00, July 2001.
[11] Massey, D. and S. Rose, "Limiting the Scope of the KEY Resource
Record", work in progress draft-ietf-dnsext-restrict-key-for-
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dnssec-00, November 2001.
Author's Address
Jakob Schlyter
Carlstedt Research & Technology
Stora Badhusgatan 18-20
Goteborg SE-411 21
Sweden
EMail: jakob@crt.se
URI: http://www.crt.se/~jakob/
Appendix A. Acknowledgements
The author gratefully acknowledges, in no particular order, the
contributions of the following persons:
Olafur Gudmundsson
Olaf Kolkman
Edward Lewis
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Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
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English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
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"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Schlyter Expires May 11, 2002 [Page 8]