INTERNET-DRAFT Donald E. Eastlake 3rd
CyberCash, Inc.
Expires September 1998 March 1998
Detached Domain Name System (DNS) Information
-------- ------ ---- ------ ----- -----------
Donald E. Eastlake 3rd
Status of This Document
This draft, file name draft-ietf-dnssec-ddi-05.txt, is intended to be
become a Proposed Standard RFC. Distribution of this document is
unlimited. Comments should be sent to the DNS Security Working Group
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,
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Donald E. Eastlake 3rd [Page 1]
INTERNET-DRAFT Detached DNS Information March 1998
Abstract
A standard format is defined for representing detached DNS
information. This is anticipated to be of use for storing
information retrieved from the Domain Name System (DNS), including
security information, in archival contexts or contexts not connected
to the Internet.
Table of Contents
Status of This Document....................................1
Abstract...................................................2
Table of Contents..........................................2
1. Introduction............................................3
2. General Format..........................................4
2.1 Binary Format..........................................4
2.2. Text Format...........................................6
3. Usage Example...........................................7
4. Security Considerations.................................7
References.................................................8
Author's Address...........................................8
Expiration and File Name...................................8
Donald E. Eastlake 3rd [Page 2]
INTERNET-DRAFT Detached DNS Information March 1998
1. Introduction
The Domain Name System (DNS) is a replicated hierarchical distributed
database system [RFC 1034, 1035] that can provide highly available
service. It provides the operational basis for Internet host name to
address translation, automatic SMTP mail routing, and other basic
Internet functions. The DNS has been extended as described in
[draft-ietf-dnssec-secext2-*.txt] to permit the general storage of
public cryptographic keys in the DNS and to enable the authentication
of information retrieved from the DNS though digital signatures.
The DNS was not originally designed for storage of information
outside of the active zones and authoritative master files that are
part of the connected DNS. However there may be cases where this is
useful, particularly in connection with archived security
information.
Donald E. Eastlake 3rd [Page 3]
INTERNET-DRAFT Detached DNS Information March 1998
2. General Format
The formats used for detached Domain Name System (DNS) information
are similar to those used for connected DNS information. The primary
difference is that elements of the connected DNS system (unless they
are an authoritative server for the zone containing the information)
are required to count down the Time To Live (TTL) associated with
each DNS Resource Record (RR) and discard them (possibly fetching a
fresh copy) when the TTL reaches zero. In contrast to this, detached
information may be stored in a off-line file, where it can not be
updated, and perhaps used to authenticate historic data or it might
be received via non-DNS protocols long after it was retrieved from
the DNS. Therefore, it is not practical to count down detached DNS
information TTL and it may be necessary to keep the data beyond the
point where the TTL (which is defined as an unsigned field) would
underflow. To preserve information as to the freshness of this
detached data, it is accompanied by its retrieval time.
Whatever retrieves the information from the DNS must associate this
retrieval time with it. The retrieval time remains fixed thereafter.
When the current time minus the retrieval time exceeds the TTL for
any particular detached RR, it is no longer a valid copy within the
normal connected DNS scheme. This may make it invalid in context for
some detached purposes as well. If the RR is a SIG (signature) RR it
also has an expiration time. Regardless of the TTL, it and any RRs
it signs can not be considered authenticated after the signature
expiration time.
2.1 Binary Format
The standard binary format for detached DNS information is as
follows:
Donald E. Eastlake 3rd [Page 4]
INTERNET-DRAFT Detached DNS Information March 1998
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| first retrieval time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR count | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Resource Records (RRs) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| next retrieval time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RR count | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Resource Records (RRs) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ ... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| hex 20 |
+-+-+-+-+-+-+-+-+
Retrieval time - the time that the immediately following information
was obtained from the connected DNS system. It is an unsigned
number of seconds since the start of 1 January 1970, GMT, ignoring
leap seconds, in network (big-endian) order. Note that this time
can not be before the initial proposal of this standard.
Therefore, the initial byte of an actual retrieval time,
considered as an unsigned quantity, will be larger than 20 hex.
The end of detached DNS information is indicated by a "retrieval
time" field initial byte equal to 20 hex. Use of a "retrieval
time" field with a leading unsigned byte less than 20 in binary
detached DNS information is reserved for future use. It may
indicate a different format. The present format will run out of
bits during the year 2106. Retrieval times will not generally be
32 bit aligned with respect to each other due to the variable
length nature of RRs.
RR count - an unsigned integer number (with bytes in network order)
of following resource records retrieved at the preceding retrieval
time.
Resource Records - the actual data which is in the same format as if
it were being transmitted in a DNS response. In particular, name
compression via pointers is permitted with the origin at the
beginning of the particular detached information data section,
just after the RR count.
Donald E. Eastlake 3rd [Page 5]
INTERNET-DRAFT Detached DNS Information March 1998
2.2. Text Format
The standard text format for detached DNS information is as
prescribed for zone master files [RFC 1035] except that the $INCLUDE
control entry is prohibited and the new $DATE entry is required
(unless the information set is empty). $DATE is followed by the date
and time that the following information was obtained from the DNS
system as described for retrieval time in section 2.1 above. It is
in the text format YYYYMMDDHHMMSS where YYYY is the year, the first
MM is the month number (01-12), DD is the day of the month (01-31),
HH is the hour in 24 hours notation (00-23), the second MM is the
minute (00-59), and SS is the second (00-59). Thus a $DATE must
appear before the first RR and at every change in retrieval time
through the detached information.
Donald E. Eastlake 3rd [Page 6]
INTERNET-DRAFT Detached DNS Information March 1998
3. Usage Example
A document might be authenticated by a key retrieved from the DNS in
a KEY resource record (RR). To later prove the authenticity of this
document, it would be desirable to preserve the KEY RR for that
public key, the SIG RR signing that KEY RR, the KEY RR for the key
used to authenticate that SIG, and so on through SIG and KEY RRs
until a well known trusted key is reached, perhaps the key for the
DNS root or some third party authentication service. (In some cases
these KEY RRs will actually be sets of KEY RRs with the same owner
and class because SIGs actually sign such record sets.)
This information could be preserved as a set of detached DNS
information blocks.
4. Security Considerations
The entirety of this document concerns a means to represent detached
DNS information. Such detached resource records may be security
relevant and/or secured information as described in [draft-ietf-
dnssec-secext2-*.txt]. The detached format provides no overall
security for sets of detached information or for the association
between retrieval time and information. This can be provided by
wrapping the detached information format with some other form of
signature. However, if the detached information is accompanied by
SIG RRs, its validity period is indicated in those SIG RRs so the
retrieval time might be of secondary importance.
Donald E. Eastlake 3rd [Page 7]
INTERNET-DRAFT Detached DNS Information March 1998
References
[RFC 1034] - Domain Names - Concepts and Facilities, P. Mockapetris,
November 1987.
[RFC 1035] - Domain Names - Implementation and Specifications, P.
Mockapetris, November 1987.
[draft-ietf-dnssec-secext2-*.txt] - Domain Name System Security
Extensions, D. Eastlake.
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, Virginia)
Fax: +1 978 371 7148
email: dee@cybercash.com
Expiration and File Name
This draft expires September 1998.
Its file name is draft-ietf-dnssec-ddi-05.txt.
Donald E. Eastlake 3rd [Page 8]
