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Versions: 00                                                            
INTERNET-DRAFT                                       DNSIND Key Rollover
UPDATES RFC 1996                                              April 1999
                                                    Expires October 1999

             Domain Name System (DNS) Security Key Rollover
             ------ ---- ------ ----- -------- --- --------

                  Donald E. Eastlake 3rd, Mark Andrews

Status of This Document

   This draft, file name draft-ietf-dnsind-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 working group
   mailing list <namedroppers@internic.net> or to the authors.

   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.  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.''

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at


   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 will be necessary for
   this to be practical and is specified herein.

   [Note: this draft has been moved to dnsind from dnssec as part of the
   ongoing combination of these working groups.  It would have been
   draft-ietf-dnssec-rollover-01.txt otherwise.]

D. Eastlake 3rd, M. Andrews                                     [Page 1]

INTERNET-DRAFT                 April 1999            DNSSEC Key Rollover

Table of Contents

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

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

      1. Introduction............................................3
      2. Key Rollover Scenario...................................3
      3. Rollover Operation......................................5
      3.1 Rollover to Parent.....................................5
      3.2 Rollover to Children...................................6
      4. Secure Zone Cuts and Joinders...........................7
      5. Security Considerations.................................8
      6. IANA Considerations.....................................9

      Authors Address...........................................10
      Expiration and File Name..................................11

D. Eastlake 3rd, M. Andrews                                     [Page 2]

INTERNET-DRAFT                 April 1999            DNSSEC Key Rollover

1. Introduction

   The Domain Name System (DNS) [RFC 1034, 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 [RFC 2535].

   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
   [RFC 2541].

   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 hundred of thousands of new signatures on
   the existing child public keys to the child zones.

   It will be impractical to handle such update volumes manually on a
   case by case basis.  The bulk of such key rollover updates must be

   The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED",  and "MAY"
   in this document are to be interpreted as described in [RFC 2119].

2. Key Rollover Scenario

   Although DNSSEC provides for the storage of other keys in the DNS for
   other 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.  Similarly, old parent
   SIGs should be retained for a short time after a parent KEY(s) roll
   over and new parent SIGs have been installed.

D. Eastlake 3rd, M. Andrews                                     [Page 3]

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   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/SIG RRsets due to
   simultaneous expiration of SIGs everywhere in the DNS.  But these
   assumptions do not hold.  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 generally be left due to
   clock skew, RR retention by applications, and the like.  Retaining
   old KEYs for a while after rolling over to new KEYs will be necessary
   in practical cases.

   Assume a middle zone with a secure parent and a secure child 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 middle zone.  (These RRs may also
   exist at the leaf node for this zone in its parent if the parent
   chooses to store them there.) The contents of the middle zone and the
   zone KEY RRs of its secure child will have SIGs under the old key.

   The middle 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.  The signature on both is needed so the
   old KEY can be retain for the period it might be needed to
   authenticate old SIGs.  The middle zone 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 its zone.  Finally, it
   needs to give new SIG RRs to its child that cover its KEY RRs so it
   must signal its children to ask for such SIG RRs.


       p.x     KEY      P1     p.x     KEY      P1     p.x     KEY      P1
       p.x     SIG(KEY) P1     p.x     SIG(KEY) P1     p.x     SIG(KEY) P1
       p.x     SIG(KEY) GP     p.x     SIG(KEY) GP     p.x     SIG(KEY) GP

       m.p.x   KEY      M1     m.p.x   KEY      M2     m.p.x   KEY      M2
       m.p.x   SIG(KEY) P1     m.p.x   KEY      M1     m.p.x   SIG(KEY) P1
       m.p.x   SIG(KEY) M1     m.p.x   SIG(KEY) P1     m.p.x   SIG(KEY) M2
                               m.p.x   SIG(KEY) M2

       c.m.p.x KEY      C1     c.m.p.x KEY      C1     c.m.p.x KEY      C1
       c.m.p.x SIG(KEY) M1     c.m.p.x SIG(KEY) M2     c.m.p.x SIG(KEY) M2
       c.m.p.x SIG(KEY) C1     c.m.p.x SIG(KEY) M1     c.m.p.x SIG(KEY) C1
                               c.m.p.x SIG(KEY) C1

         p = parent, m = middle, c = child, GP = grandparent key
         P* = parent key, M* = middle zone key, C* = child key

D. Eastlake 3rd, M. Andrews                                     [Page 4]

INTERNET-DRAFT                 April 1999            DNSSEC Key Rollover

3. Rollover Operation

   Rollover operations use a DNS request syntactically identical to the
   UPDATE request [RFC 2136] (except that the operation code is ROLLOVER
   which is equal to (TBD)) and use a new form of NOTIFY [RFC 1996].
   Considerations for such requests to the parent and children of a zone
   are givens below.

   All rollover operations involve significant amounts of cryptographic
   calculations.  Appropriate rate limiting SHOULD be applied to avoid
   denial of service attacks.

   [This draft does not consider cross-certification key rollover.]

3.1 Rollover to Parent

   A zone rolling over its KEY RRset sends an upward ROLLOVER request to
   its parent.  Actually, it will normally do two upward ROLLOVERs, one
   for a combined KEY RRset of its old and new KEYs and one for just its
   new KEY RRset, as discussed above.

   The server selection algorithm in [RFC 2136] section 4 should be
   used.  A child needs to be configured with or determine the name of
   its parent but SHOULD NOT remember the location of its parent other
   than via normal DNS caching of address RRs so that rollover will
   continue to work if its parent servers are moved.

   The ROLLOVER request Zone should be specified as the parent zone.
   The request Update section has the new 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 child SIG or SIGs are the
   requested inception and expiration times for the new parent SIG(s).
   The "prerequisites" section has the old child KEY RRset with the
   parent SIG (see next paragraph).

   An upward ROLLOVER request MUST be signed and if not signed a BADAUTH
   response generated. The signature MUST be under the previous zone
   KEY, so the parent can validate it, or under a valid TSIG key
   [draft-ietf-dnsind-tsig-*.txt] arranged with the parent.  Including
   the "prerequisite" section as specified above enables a parent that
   keeps no record of its children's KEYs to still authenticate a
   child's ROLLOVER request based on the old child KEY because the
   parent is presented with its own SIG on the old KEY.

   If the ROLLOVER command is erroneous or violates parental policy, an
   Error response is returned.  If a parent retains copies of its
   children's KEYs, it may use that knowledge to validate ROLLOVER

D. Eastlake 3rd, M. Andrews                                     [Page 5]

INTERNET-DRAFT                 April 1999            DNSSEC Key Rollover

   request SIGs and ignore the "prerequisites" section.

   If the ROLLOVER command is OK and the parent can sign online, its
   response MAY include the new parent SIG(s) in the response Update
   section.  This response MUST be sent to the originator of the

   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.

   ROLLOVER response messages MUST always include the actual parent's
   SOA signed with a key the child should recognize in the Additional
   Information section (see section 4 below).

   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).  There
   are several reasons for sending the ROLLOVER response regardless of
   whether the new SIG RR(s) were sent in the original response.  One is
   to provide an indication to the operators of the zone in the event
   someone is trying to hijack the zone.  Another is that this maximizes
   the probability of the response getting through.

   Although the parent zone need not hold or serve the child's key, if
   it does the ROLLOVER command REQUEST SHOULD NOT automatically 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

   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 of future
   authoritative existence to the controller of the child private key
   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

3.2 Rollover to Children

   When a secure 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).  The
   parent simply notifIES the child via a rollover NOTIFY [RFC 1996]

D. Eastlake 3rd, M. Andrews                                     [Page 6]

INTERNET-DRAFT                 April 1999            DNSSEC Key Rollover

   that the parent KEY(s) have changed.  The child then proceeds to do
   an upward ROLLOVER request, as described in 3.1 above to obtain the
   new parental SIG(s).

   A rollover NOTIFY is a NOTIFY request [RFC 1996] that has a QTYPE of
   SIG and the owner name of the child zone.  The answer section has the
   current parent SOA signed by a key the child will know (see section

   A rollover NOTIFY MUST be signed and if not signed a BADAUTH response
   generated. The signature MUST be under the previous parental zone
   KEY, so the child can validate it, or under a valid TSIG key [draft-
   ietf-dnsind-tsig-*.txt] negotiated between parent and child.

   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 same 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
   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.  As with all rollover operations, care
   should be taken to rate limit these messages so prevent them being
   used to facilitate a denial of service attack.

   Once the message has been sent (or suppressed if so configured) to
   the child zone's administrator the master server for the child zone
   is free to respond to the rollover NOTIFY request.

4. Secure Zone Cuts and Joinders

   There are two other events that have some similarity to key rollover.

   The first is when a secure zone the is more than one level deep has a
   zone cut introduced inside it.  For example, assume zone example.com
   has a.b.c.example.com, d.b.c.example.com and e.example.com in it.  A
   zone cut could be introduced such that b.c.example.com became a
   separate child zone of example.com.  A real world exampe would be a
   company that structures its DNS as host.branch.company.example.  It
   might start out will all of these names in one zone but later decide
   to delegate all or some of the branches to branch zone file

D. Eastlake 3rd, M. Andrews                                     [Page 7]

INTERNET-DRAFT                 April 1999            DNSSEC Key Rollover

   The second is when a secure zone absorbs a child zone eliminating a
   zone cut.  This is simply the inverse of the previous paragraph.

   From the point of view of the parent zone above the splitting zone or
   above the upper of the two combining zones, there is no change.

   When a zone is split by introducing a cut, the newly created child
   must be properly configured.

   However, from the point of view of a child of the splitting zone
   which becomes a grandchild or a grandchild that becomes a child due
   to joinder, there is a change in parent name.  Therefore, in general,
   there is a change in parent KEY(s).  Unless the entity that handles
   rollovers for the zone whose parent name has changed is appropriately
   updated, future automated rollover will fail because it will be sent
   to the old parent.

   For this reason and so that other consistency checks can be made, the
   parent SOA and SIG(SOA) are always included in the Answer section of
   rollover NOTIFY requests and in ROLLOVER responsess.  For automated
   rollover to the new cut or joined state to work, these SOAs must be
   signed with old KEY(s) of the former parent so the signatures can be
   validated by the zone whose parent name is changing.  In the case of
   a joinder, if the private key of the pinched out middle zone is not
   available, then manual update of the former grandchild, now child,
   will be necessary.  In the case of introducing a cut, operational
   coordination with the former parent, now grandparent, signing the
   initial updates to the former child, now grandchild, will be needed
   to automate the reconfiguration of the zones.

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,

   A ROLLOVER request can be authenticated by request SIG(s)under the
   old zone KEY(s) of the requestor [RFC 2535].  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-dnsind-tsig-*.txt].  (TSIG
   security could be used to rollover a zone to unsecured and to

D. Eastlake 3rd, M. Andrews                                     [Page 8]

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   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

6. IANA Considerations

   The DNS operation code (TBD) is assigned to ROLLOVER.  There are no
   other IANA considerations in this document.

D. Eastlake 3rd, M. Andrews                                     [Page 9]

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   [RFC 1034] - "Domain names - concepts and facilities", P.
   Mockapetris, 11/01/1987.

   [RFC 1035] - "Domain names - implementation and specification", P.
   Mockapetris, 11/01/1987.

   [RFC 1996] - "A Mechanism for Prompt Notification of Zone Changes
   (DNS NOTIFY)", P. Vixie, August 1996.

   [RFC 2119] - "Key words for use in RFCs to Indicate Requirement
   Levels", S.  Bradner. March 1997.

   [RFC 2136] - "Dynamic Updates in the Domain Name System (DNS
   UPDATE)", P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound. April


   [RFC 2535] - "Domain Name System Security Extensions", D. Eastlake.
   March 1999.

   [RFC 2541] - "DNS Security Operational Considerations", D. Eastlake.
   March 1999.

Authors Address

   Donald E. Eastlake 3rd
   65 Sindegan Hill Road, RR #1
   Carmel, NY 10512

   Telephone:   +1 914-276-2668 (h)
                +1 914-784-7913 (w)
   FAX:         +1 914-784-3833 (w)
   EMail:       dee3@us.ibm.com

   Mark Andrews
   Internet Software Consortium
   1 Seymour Street
   Dundas Valley, NSW 2117

   Telephone:   +61-2-9871-4742
   Email:       marka@isc.org

D. Eastlake 3rd, M. Andrews                                    [Page 10]

INTERNET-DRAFT                 April 1999            DNSSEC Key Rollover

Expiration and File Name

   This draft expires in October 1999.

   Its file name is draft-ietf-dnsind-rollover-00.txt.

D. Eastlake 3rd, M. Andrews                                    [Page 11]