INTERNET-DRAFT DNSSEC Key Rollover
October 1998
Expires April 1999
Domain Name System (DNS) Security Key Rollover
------ ---- ------ ----- -------- --- --------
Donald E. Eastlake 3rd, Mark Andrews
Status of This Document
This draft, file name draft-ietf-dnssec-rollover-00.txt, is intended
to be become a Proposed Standard RFC. Distribution of this document
is unlimited. Comments should be sent to the DNS security mailing
list <dns-security@tis.com> or to the authors.
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 view the entire list of current Internet-Drafts, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern
Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific
Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).
Abstract
Practical deployment of Domain Name System (DNS) security with good
cryptologic practice will involve large volumes of key rollover
traffic. A standard format and protocol for such messages is
specified.
D. Eastlake 3rd, M. Andrews [Page 1]
INTERNET-DRAFT October 1998 DNSSEC Key Rollover
Table of Contents
Status of This Document....................................1
Abstract...................................................1
Table of Contents..........................................2
1. Introduction............................................3
2. Key Rollover Scenarios..................................3
3. Rollover Operation......................................4
3.1 Rollover to Parent.....................................4
3.2 Rollover to Children...................................5
4. Rollover NOTIFY.........................................6
5. Security Considerations.................................7
References.................................................8
Authors Address............................................8
Expiration and File Name...................................9
D. Eastlake 3rd, M. Andrews [Page 2]
INTERNET-DRAFT October 1998 DNSSEC Key Rollover
1. Introduction
The Domain Name System (DNS) [RFC 1034, RFC 1035] is the global
hierarchical replicated distributed database system for Internet
addressing, mail proxy, and other information. The DNS has been
extended to include digital signatures and cryptographic keys as
described in [draft-ietf-dnssec-secext2-*].
The principle security service provided for DNS data is data origin
authentication. The owner of each zone signs the data in that zone
with a private key known only to the zone owner. Anyone that knows
the corresponding public key can then authenticate that zone data is
from the zone owner. To avoid having to preconfigure resolvers with
all zone's public keys, keys are stored in the DNS with each zone's
key signed by its parent (if the parent is secure).
To obtain high levels of security, keys must be periodically changed,
or "rolled over". The longer a private key is used, the more likely
it is to be compromised due to cryptanalysis, accident, or treachery
[draft-ietf-dnssec-secops-*.txt].
In a widely deployed DNS security system, the volume of update
traffic will be large. Just consider the .com zone. If only 10% of
its children are secure and change their keys only once a year, you
are talking about hundreds of thousands of new child public keys that
must be securely sent to the .com manager to sign and return with
their new parent signature. And when .com rolls over its private
key, it will needs to send hundreds of thousands of new signatures on
the existing child public keys to the child zones.
The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"
in this document are to be interpreted as described in RFC 2119.
2. Key Rollover Scenarios
Although DNSSEC provides for the storage of other keys in the DNS for
a variety of purposes, DNSSEC zone keys are included solely for the
purpose of being retrieved to authenticate DNSSEC signatures. Thus,
when a zone key is being rolled over, the old public key should be
left in the zone, along with the addition of the new public key, for
as long as it will reasonably be needed to authenticate old
signatures that have been cached or are held by applications. If
DNSSEC were universally deployed and all DNS server's clocks were
synchronized and zone transfers were instantaneous etc., it might be
possible to avoid ever having duplicate old/new KEY RRsets but they
will be necessary in practical cases. Security aware DNS servers
decrease the TTL of secure RRs served as the expiration of their
authenticating SIG(s) approaches but some dithered fudge must
D. Eastlake 3rd, M. Andrews [Page 3]
INTERNET-DRAFT October 1998 DNSSEC Key Rollover
generally be left due to clock skew and to avoid massive load on
large zones due to the signatures on their entire contents expiring
simultaneously.
Assume a zone with a secure parent and secure children wishes to role
over its KEY RRset. This RRset would probably be one KEY RR per
crypto algorithm used to secure the zone, but for this scenario, we
will simply assume it is one KEY RR. The old KEY RR and two SIG RRs
will exist at the apex of the zone and these RRs may also exist at
the leaf node for this zone in its parent. The contents of the zone
and the zone KEY RRs of its secure children will have SIGs under the
old key.
The zone owner needs to communicate with its parent to obtain a new
parental signature covering both the old and new KEY RRs and covering
just the new KEY RR. It would probably want to obtain these in
advance so that it can install them at the right time along with its
new SIG RRs covering the content of the zone. Finally, it needs to
give new SIG RRs to its children that cover their KEY RRs if it has
these, or signal its children to ask for such SIG RRs.
3. Rollover Operation
Rollover operations use a DNS request syntactically identical to the
UPDATE request [RFC 2136] except that the operation is ROLLOVER which
is equal to TBD. Considerations for such request to the parent and
children of a zone are given in the subsections.
[This draft does not currently consider cross-certification key
rollover.]
3.1 Rollover to Parent
A zone rolling over its KEY RRset sends a ROLLOVER command to the
parent. The Zone should be specified as the parent zone and no
Prerequisites are included. The Update section has the KEY RRset on
which the parent signature is requested along with the requesting
zone's SIG(s) under its old KEY(s) as RRs to be added to the parent
zone. The inception and expiration times in this SIG are the
requested inception and expiration times for the parent SIG.
If the ROLLOVER command is erroneous or violates parental policy, an
Error response is returned.
If the ROLLOVER command is OK and the parent can sign online, its
response may include the new parent SIG(s) in the Update section.
D. Eastlake 3rd, M. Andrews [Page 4]
INTERNET-DRAFT October 1998 DNSSEC Key Rollover
This response MUST be sent to the originator of the request.
If the parent can not sign online, it should return a response with
an empty Update section and queue the SIG(s) calculation request.
This response MUST be sent to the originator of the request.
Regardless of whether the server has sent the new signatures above,
it MUST, once it has calculated the new SIG(s), send a ROLLOVER to
the child zone using the DNS port (53) and the server selection
algorithm defined in RFC 2136, Section 4. This ROLLOVER reqeust
contains the KEY RRset that triggered it and the new SIG(s). This
downward ROLLOVER request is distinguished from those in Section 3.2
below in that the Zone section is the parental zone.
The reason for sending the ROLLOVER request regardless of whether the
new SIG RR(s) were sent in the original response is to provide an
indication to the operators of the zone in the event someone is
trying to hijack the zone.
Although the parent zone need not hold or serve the child's key, the
ROLLOVER command MUST NOT actually update the parent zone. A later
UPDATE command can be used to actually put the new KEY into the
parent zone if desired and supported by parent policy.
This document does not cover the question of parental policy on key
rollovers. Parents may have restrictions on how far into the future
they will sign KEY RRsets, what algorithms or key lengths they will
support, might require payment for the service, etc. The signing of
a future KEY by a parent is, to some extent a granting to the
controller of the child private key of future authoritative existence
even if the child zone ownership should change. The only effective
way of invalidating such future signed child public keys would be for
the parent to roll over its key(s), which might be an expensive
operation.
3.2 Rollover to Children
When a zone is going to rollover its key(s), it needs to re-sign the
zone keys of any secure children under its new key(s).
If the parent holds the KEY RRset for the child (whether or not it
actually serves it from the parent zone), it can simply do a ROLLOVER
request to to child specifying the child as the Zone in the request
and the new SIG(KEY)s to be added in the Update section. The
inception and expiration times in the SIG(s) indicate the time during
which the parent will be utilizing the new parent key. It is up to
the child when and how it adds the new parental SIG(s). The ROLLOVER
request may optionally indicate the deletion of old parental SIG(s)
D. Eastlake 3rd, M. Andrews [Page 5]
INTERNET-DRAFT October 1998 DNSSEC Key Rollover
but SHOULD only do so if the corresponding key is being withdrawn by
the parent in advance of the expiration time in the old SIG(s). It
is up to the child when and how it deletes the old parental SIG(s).
Even if the expiration of the old SIG(s) equals the inception time of
the new SIG(s), the child should serve both signatures for a fudge
time to account for clock skew.
A ROLLOVER request is used instead of an UPDATE because serves may
wish to support ROLLOVER via special techniques, such as notification
to the operator, even when they have not implemented UPDATE. With
adequate advance notice, even manual cut and paste editing of the
master file and restarting of a DNS server process could work.
If the parent does not retain knowledge of the child KEY RRset, then
the parent simply notifies the child via a ROLLOVER NOTIFY (see
Section 4 below) that the parent KEY(s) have changed. The child then
proceeds to do an upward ROLLOVER request to obtain the new parental
SIG(s). (This requires that a different method, such as TSIG, be
used to secure such ROLLOVER requests since we are assuming the
parent does not have authoritative knowledge of the child public key.
See Section 5 below.)
The NOTIFY technique MAY also be used by parents who retain knowledge
of their children's KEY RRsets.
4. Rollover NOTIFY
A ROLLOVER NOTIFY informs a child zone that the parent zone want it
to resubmit its keys for resigning.
A ROLLOVER NOTIFY MUST be signed and if not signed a BADAUTH response
generated.
A ROLLOVER NOTIFY is a NOTIFY reqeust [RFC 1996] that has a QTYPE of
SIG and the owner name of the child zone. The answer section is
empty.
The ROLLOVER NOTIFY can be sent to any of the nameservers for the
child using the nameserver selection algorithm defined in RFC 2136,
Section 4.
Nameservers for the child zone receiving a ROLLOVER NOTIFY query will
forward the ROLLOVER NOTIFY in the saem manner as an UPDATE is
forwarded.
Unless the master server is configured to initiate an automatic
ROLLOVER it MUST seek to inform its operators that a ROLLOVER NOTIFY
request has been received. This could be done by a number of methods
D. Eastlake 3rd, M. Andrews [Page 6]
INTERNET-DRAFT October 1998 DNSSEC Key Rollover
including generating a log message, generating an email request to
the child zone's SOA RNAME or any other method defined in the
server's configuration for the zone. The default should be to send
mail to the zone's SOA RNAME. Care should be taken to rate limit
these message so prevent them being used to facilitate a denial of
service attack.
Once the message has been sent (or suppressed) to the child zone's
administrator the master server for the child zone is free to respond
to the ROLLOVER NOTIFY request.
5. Security Considerations
The security of ROLLOVER or UPDATE requests is essential, otherwise
false children could steal parental authorization or a false parent
could cause a child to install an invalid signature on its zone key,
etc.
A ROLLOVER request can be authentication by request SIG(s)under the
old zone KEY(s) of the requestor [draft-ietf-dnssec-secext2-*.txt].
The response SHOULD have transaction SIG(s) under the old zone KEY(s)
of the responder. (This public key security could be used to
rollover a zone to the unsecured state but at that point it would
generally not be possible to roll back without manual intervention.)
Alternatively, if there is a prior arrangement between a child and a
parent, ROLLOVER requests and responses can be secured and
authenticated using TSIG [draft-ietf-dnssec-tsig-*.txt]. (TSIG
security could be used to rollover a zone to unsecured and to
rollover an unsecured zone to the secured state.)
A server that implements online signing SHOULD have the ability to
black list a zone and force manual processing or demand that a
particular signature be used to generate the ROLLOVER request. This
it to allow ROLLOVER to be used even after a private key has been
compromised.
D. Eastlake 3rd, M. Andrews [Page 7]
INTERNET-DRAFT October 1998 DNSSEC Key Rollover
References
[RFC 1034] - P. Mockapetris, "Domain names - concepts and
facilities", 11/01/1987.
[RFC 1035] - P. Mockapetris, "Domain names - implementation and
specification", 11/01/1987.
[RFC 1996] - P. Vixie, "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", August 1996.
[RFC 2136] - Dynamic Updates in the Domain Name System (DNS UPDATE).
P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound. April 1997.
[draft-ietf-dnsind-tsig-*.txt]
[draft-ietf-dnssec-update2-*.txt]
[draft-ietf-dnssec-secext2-*.txt]
[draft-ietf-dnssec-secops-*.txt]
Authors Address
Donald E. Eastlake 3rd
IBM
318 Acton Street
Carlisle, MA 01741 USA
Telephone: +1 978-287-4877
+1 914-784-7913
FAX: +1 978-371-7148
EMail: dee3@us.ibm.com
Mark Andrews
Internet Software Consortium
1 Seymour Street
Dundas Valley, NSW 2117
AUSTRALIA
Telephone: +61-2-9871-4742
Email: marka@isc.org
D. Eastlake 3rd, M. Andrews [Page 8]
INTERNET-DRAFT October 1998 DNSSEC Key Rollover
Expiration and File Name
This draft expires in April 1999.
Its file name is draft-ietf-dnssec-rollover-00.txt.
D. Eastlake 3rd, M. Andrews [Page 9]
