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INTERNET-DRAFT                                       DNSSEC Key Rollover
UPDATES RFC 1996                                           December 2000
                                                       Expires June 2001

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

                  Mark Andrews, Donald E. Eastlake 3rd

Status of This Document

   This draft is intended to be become a Proposed Standard RFC.
   Distribution of this document is unlimited. Comments should be sent
   to the Domain Name Server Operations working group mailing list
   <dnsop@cafax.se> or to the authors.

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.  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

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

   [Note: The previous versions of this draft included draft-ietf-
   dnsind-rollover-*.txt and draft-ietf-dnssec-rollover-*.txt.]

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

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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...................................7
      4. Secure Zone Cuts and Joinders...........................8
      5. Security Considerations.................................9
      6. IANA Considerations.....................................9


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

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

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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 a few
   percent 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 need 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.

M. Andrews, D. Eastlake 3rd                                     [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, rounding, 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 secure 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 sign the zone, but for this
   scenario, we will simply assume it is one KEY RR.  The old KEY RR and
   two SIG RRs, one signed by the parent and one signed by the zone
   itself, 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 this middle zone and
   the zone KEY RRs of its secure child will have SIGs under the old

   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 a
   parental signature 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
   the child's KEY RRs so it must signal its children to ask for such
   SIG RRs.

   The table below illustrates what happens during this rollover

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

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       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

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 variation of NOTIFY [RFC
   1996].  Considerations are given 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
   for the retrieval of SRV RRs [RFC 2782] using the service name (tbd)
   to determine which host(s) to which the ROLLOVER request is sent.  A
   child needs to be configured with or determine the name of its

   The ROLLOVER request Zone should be specified in the Zone section.

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

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   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 a SIG(0) using the
   previous zone KEY, so the parent can validate it, or be under a valid
   TSIG key [RFC 2845] 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
   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 in a reasonable length of time, 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, in the Additional
   Information section, the actual parent's SOA signed with a key the
   child should recognize (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 host determined as
   follows: the server selection algorithm defined in RFC 2136, Section 
   4, for updates to the child zone is used to fetch SRV RRs for service
   name (tbd).  This ROLLOVER reqeust contains the KEY RR set 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

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

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   it does, the ROLLOVER command request MAY automatically update the
   parent zone.

   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, may 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 a very 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 children via a rollover NOTIFY [RFC 1996]
   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 [RFC
   2845] negotiated between parent and child.

   The rollover NOTIFY MUST be send by using the the nameserver
   selection algorithm defined in RFC 2136, Section 4, to fetch SRV RRs
   for the (tbd) named service.  Servers for the child zone receiving a
   rollover NOTIFY query will forward the rollover NOTIFY in the same
   manner as an UPDATE is forwarded except that they will forward using
   SRV RRs as above.

   Unless the rollover server for the zone master 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

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

INTERNET-DRAFT               December 2000           DNSSEC Key Rollover

   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 example 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

   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 the
   normal case, 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 rollovers will fail because
   they 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.

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

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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.

   Alternatively, if there is a prior arrangement between a child and a
   parent, ROLLOVER requests and responses can be secured and
   authenticated using TSIG [RFC 2845].

   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
   is 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.

   The Service Name (TBD) is assigned to the DNS key rollover service.

   There are no other IANA considerations in this document.

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

INTERNET-DRAFT               December 2000           DNSSEC Key Rollover


   [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.

   [RFC 2782] - "A DNS RR for specifying the location of services (DNS
   SRV)", A.  Gulbrandsen, P. Vixie, L. Esibov. February 2000.

   [RFC 2845] - "Secret Key Transaction Authentication for DNS (TSIG)",
   P. Vixie, O. Gundmundsson, D. Eastlake, B. Wellington.  May 2000.

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

INTERNET-DRAFT               December 2000           DNSSEC Key Rollover

Authors Address

   Donald E. Eastlake 3rd
   155 Beaver Street
   Milford, MA 01757 USA

   Telephone:   +1 508-261-5434 (w)
                +1 508-634-2066 (h)
   FAX:         +1 508-261-4447 (w)
   EMail:       Donald.Eastlake@motorola.com

   Mark Andrews
   Nominum, Inc.
   1 Seymour Street
   Dundas Valley, NSW 2117

   Telephone:   +61-2-9871-4742
   Email:       Mark.Andrews@nominum.com

Expiration and File Name

   This draft expires in June 2001

   Its file name is draft-ietf-dnsop-rollover-01.txt.

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

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