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Network Working Group                                      B. WellingtonRequest for Comments: 3007                                       NominumUpdates:2535,2136                                        November 2000Obsoletes:2137Category: Standards TrackSecure Domain Name System (DNS) Dynamic UpdateStatus of this Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2000).  All Rights Reserved.Abstract   This document proposes a method for performing secure Domain Name   System (DNS) dynamic updates.  The method described here is intended   to be flexible and useful while requiring as few changes to the   protocol as possible.  The authentication of the dynamic update   message is separate from later DNSSEC validation of the data.  Secure   communication based on authenticated requests and transactions is   used to provide authorization.   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 inRFC 2119 [RFC2119].1 - Introduction   This document defines a means to secure dynamic updates of the Domain   Name System (DNS), allowing only authorized sources to make changes   to a zone's contents.  The existing unsecured dynamic update   operations form the basis for this work.   Familiarity with the DNS system [RFC1034,RFC1035] and dynamic update   [RFC2136] is helpful and is assumed by this document.  In addition,   knowledge of DNS security extensions [RFC2535], SIG(0) transaction   security [RFC2535,RFC2931], and TSIG transaction security [RFC2845]   is recommended.Wellington                  Standards Track                     [Page 1]

RFC 3007                 Secure Dynamic Update             November 2000   This document updates portions ofRFC 2535, in particularsection3.1.2, andRFC 2136.  This document obsoletesRFC 2137, an alternate   proposal for secure dynamic update, due to implementation experience.1.1 - Overview of DNS Dynamic Update   DNS dynamic update defines a new DNS opcode and a new interpretation   of the DNS message if that opcode is used.  An update can specify   insertions or deletions of data, along with prerequisites necessary   for the updates to occur.  All tests and changes for a DNS update   request are restricted to a single zone, and are performed at the   primary server for the zone.  The primary server for a dynamic zone   must increment the zone SOA serial number when an update occurs or   before the next retrieval of the SOA.1.2 - Overview of DNS Transaction Security   Exchanges of DNS messages which include TSIG [RFC2845] or SIG(0)   [RFC2535,RFC2931] records allow two DNS entities to authenticate DNS   requests and responses sent between them.  A TSIG MAC (message   authentication code) is derived from a shared secret, and a SIG(0) is   generated from a private key whose public counterpart is stored in   DNS.  In both cases, a record containing the message signature/MAC is   included as the final resource record in a DNS message.  Keyed   hashes, used in TSIG, are inexpensive to calculate and verify.   Public key encryption, as used in SIG(0), is more scalable as the   public keys are stored in DNS.1.3 - Comparison of data authentication and message authentication   Message based authentication, using TSIG or SIG(0), provides   protection for the entire message with a single signing and single   verification which, in the case of TSIG, is a relatively inexpensive   MAC creation and check.  For update requests, this signature can   establish, based on policy or key negotiation, the authority to make   the request.   DNSSEC SIG records can be used to protect the integrity of individual   RRs or RRsets in a DNS message with the authority of the zone owner.   However, this cannot sufficiently protect the dynamic update request.   Using SIG records to secure RRsets in an update request is   incompatible with the design of update, as described below, and would   in any case require multiple expensive public key signatures and   verifications.Wellington                  Standards Track                     [Page 2]

RFC 3007                 Secure Dynamic Update             November 2000   SIG records do not cover the message header, which includes record   counts.  Therefore, it is possible to maliciously insert or remove   RRsets in an update request without causing a verification failure.   If SIG records were used to protect the prerequisite section, it   would be impossible to determine whether the SIGs themselves were a   prerequisite or simply used for validation.   In the update section of an update request, signing requests to add   an RRset is straightforward, and this signature could be permanently   used to protect the data, as specified in [RFC2535].  However, if an   RRset is deleted, there is no data for a SIG to cover.1.4 - Data and message signatures   As specified in [RFC3008], the DNSSEC validation process performed by   a resolver MUST NOT process any non-zone keys unless local policy   dictates otherwise.  When performing secure dynamic update, all zone   data modified in a signed zone MUST be signed by a relevant zone key.   This completely disassociates authentication of an update request   from authentication of the data itself.   The primary usefulness of host and user keys, with respect to DNSSEC,   is to authenticate messages, including dynamic updates.  Thus, host   and user keys MAY be used to generate SIG(0) records to authenticate   updates and MAY be used in the TKEY [RFC2930] process to generate   TSIG shared secrets.  In both cases, no SIG records generated by   non-zone keys will be used in a DNSSEC validation process unless   local policy dictates.   Authentication of data, once it is present in DNS, only involves   DNSSEC zone keys and signatures generated by them.1.5 - Signatory strength   [RFC2535,section 3.1.2] defines the signatory field of a key as the   final 4 bits of the flags field, but does not define its value.  This   proposal leaves this field undefined.  Updating [RFC2535], this field   SHOULD be set to 0 in KEY records, and MUST be ignored.2 - Authentication   TSIG or SIG(0) records MUST be included in all secure dynamic update   messages.  This allows the server to verifiably determine the   originator of a message.  If the message contains authentication in   the form of a SIG(0), the identity of the sender (that is, the   principal) is the owner of the KEY RR that generated the SIG(0).  If   the message contains a TSIG generated by a statically configuredWellington                  Standards Track                     [Page 3]

RFC 3007                 Secure Dynamic Update             November 2000   shared secret, the principal is the same as or derived from the   shared secret name.  If the message contains a TSIG generated by a   dynamically configured shared secret, the principal is the same as   the one that authenticated the TKEY process; if the TKEY process was   unauthenticated, no information is known about the principal, and the   associated TSIG shared secret MUST NOT be used for secure dynamic   update.   SIG(0) signatures SHOULD NOT be generated by zone keys, since   transactions are initiated by a host or user, not a zone.   DNSSEC SIG records (other than SIG(0)) MAY be included in an update   message, but MUST NOT be used to authenticate the update request.   If an update fails because it is signed with an unauthorized key, the   server MUST indicate failure by returning a message with RCODE   REFUSED.  Other TSIG, SIG(0), or dynamic update errors are returned   as specified in the appropriate protocol description.3 - Policy   All policy is configured by the zone administrator and enforced by   the zone's primary name server.  Policy dictates the authorized   actions that an authenticated principal can take.  Policy checks are   based on the principal and the desired action, where the principal is   derived from the message signing key and applied to dynamic update   messages signed with that key.   The server's policy defines criteria which determine if the key used   to sign the update is permitted to perform the requested updates.  By   default, a principal MUST NOT be permitted to make any changes to   zone data; any permissions MUST be enabled though configuration.   The policy is fully implemented in the primary zone server's   configuration for several reasons.  This removes limitations imposed   by encoding policy into a fixed number of bits (such as the KEY RR's   signatory field).  Policy is only relevant in the server applying it,   so there is no reason to expose it.  Finally, a change in policy or a   new type of policy should not affect the DNS protocol or data format,   and should not cause interoperability failures.3.1 - Standard policies   Implementations SHOULD allow access control policies to use the   principal as an authorization token, and MAY also allow policies to   grant permission to a signed message regardless of principal.Wellington                  Standards Track                     [Page 4]

RFC 3007                 Secure Dynamic Update             November 2000   A common practice would be to restrict the permissions of a principal   by domain name.  That is, a principal could be permitted to add,   delete, or modify entries corresponding to one or more domain names.   Implementations SHOULD allow per-name access control, and SHOULD   provide a concise representation of the principal's own name, its   subdomains, and all names in the zone.   Additionally, a server SHOULD allow restricting updates by RR type,   so that a principal could add, delete, or modify specific record   types at certain names.  Implementations SHOULD allow per-type access   control, and SHOULD provide concise representations of all types and   all "user" types, where a user type is defined as one that does not   affect the operation of DNS itself.3.1.1 - User types   User types include all data types except SOA, NS, SIG, and NXT.  SOA   and NS records SHOULD NOT be modified by normal users, since these   types create or modify delegation points.  The addition of SIG   records can lead to attacks resulting in additional workload for   resolvers, and the deletion of SIG records could lead to extra work   for the server if the zone SIG was deleted.  Note that these records   are not forbidden, but not recommended for normal users.   NXT records MUST NOT be created, modified, or deleted by dynamic   update, as their update may cause instability in the protocol.  This   is an update toRFC 2136.   Issues concerning updates of KEY records are discussed in the   Security Considerations section.3.2 - Additional policies   Users are free to implement any policies.  Policies may be as   specific or general as desired, and as complex as desired.  They may   depend on the principal or any other characteristics of the signed   message.4 - Interaction with DNSSEC   Although this protocol does not change the way updates to secure   zones are processed, there are a number of issues that should be   clarified.Wellington                  Standards Track                     [Page 5]

RFC 3007                 Secure Dynamic Update             November 20004.1 - Adding SIGs   An authorized update request MAY include SIG records with each RRset.   Since SIG records (except SIG(0) records) MUST NOT be used for   authentication of the update message, they are not required.   If a principal is authorized to update SIG records and there are SIG   records in the update, the SIG records are added without   verification.  The server MAY examine SIG records and drop SIGs with   a temporal validity period in the past.4.2 - Deleting SIGs   If a principal is authorized to update SIG records and the update   specifies the deletion of SIG records, the server MAY choose to   override the authority and refuse the update.  For example, the   server may allow all SIG records not generated by a zone key to be   deleted.4.3 - Non-explicit updates to SIGs   If the updated zone is secured, the RRset affected by an update   operation MUST, at the completion of the update, be signed in   accordance with the zone's signing policy.  This will usually require   one or more SIG records to be generated by one or more zone keys   whose private components MUST be online [RFC3008].   When the contents of an RRset are updated, the server MAY delete all   associated SIG records, since they will no longer be valid.4.4 - Effects on the zone   If any changes are made, the server MUST, if necessary, generate a   new SOA record and new NXT records, and sign these with the   appropriate zone keys.  Changes to NXT records by secure dynamic   update are explicitly forbidden.  SOA updates are allowed, since the   maintenance of SOA parameters is outside of the scope of the DNS   protocol.5 - Security Considerations   This document requires that a zone key and possibly other   cryptographic secret material be held in an on-line, network-   connected host, most likely a name server.  This material is at the   mercy of host security to remain a secret.  Exposing this secret puts   DNS data at risk of masquerade attacks.  The data at risk is that in   both zones served by the machine and delegated from this machine.Wellington                  Standards Track                     [Page 6]

RFC 3007                 Secure Dynamic Update             November 2000   Allowing updates of KEY records may lead to undesirable results,   since a principal may be allowed to insert a public key without   holding the private key, and possibly masquerade as the key owner.6 - Acknowledgements   The author would like to thank the following people for review and   informative comments (in alphabetical order):   Harald Alvestrand   Donald Eastlake   Olafur Gudmundsson   Andreas Gustafsson   Bob Halley   Stuart Kwan   Ed Lewis7 - References   [RFC1034]  Mockapetris, P., "Domain Names - Concepts and Facilities",              STD 13,RFC 1034, November 1987.   [RFC1035]  Mockapetris, P., "Domain Names - Implementation and              Specification", STD 13,RFC 1035, November 1987.   [RFC2136]  Vixie (Ed.), P., Thomson, S., Rekhter, Y. and J. Bound,              "Dynamic Updates in the Domain Name System",RFC 2136,              April 1997.   [RFC2137]  Eastlake, D., "Secure Domain Name System Dynamic Update",RFC 2137, April 1997.   [RFC2535]  Eastlake, G., "Domain Name System Security Extensions",RFC 2535, March 1999.   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake, D. and B.              Wellington, "Secret Key Transaction Signatures for DNS              (TSIG)",RFC 2845, May 2000.   [RFC2930]  Eastlake, D., "Secret Key Establishment for DNS (TKEY              RR)",RFC 2930, September 2000.   [RFC2931]  Eastlake, D., "DNS Request and Transaction Signatures              (SIG(0)s)",RFC 2931, September 2000.   [RFC3008]  Wellington, B., "Domain Name System Security (DNSSEC)              Signing Authority",RFC 3008, November 2000.Wellington                  Standards Track                     [Page 7]

RFC 3007                 Secure Dynamic Update             November 20008 - Author's Address   Brian Wellington   Nominum, Inc.   950 Charter Street   Redwood City, CA 94063   Phone: +1 650 381 6022   EMail: Brian.Wellington@nominum.comWellington                  Standards Track                     [Page 8]

RFC 3007                 Secure Dynamic Update             November 20009.  Full Copyright Statement   Copyright (C) The Internet Society (2000).  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   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "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.Wellington                  Standards Track                     [Page 9]