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Versions: 00 01 02 03 04 05 06 07 08 RFC 4641

DNSOP                                                         O. Kolkman
Internet-Draft                                                  RIPE NCC
Expires: March 1, 2004                                         R. Gieben
                                                              NLnet Labs
                                                          September 2003


                      DNSSEC Operational Practices
          draft-ietf-dnsop-dnssec-operational-practices-00.txt

Status of this Memo

   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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at http://
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on March 1, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   This document intends to describe a set of practices for operating a
   DNSSEC aware enviroment. Its target audience is zone administrators
   who are deploying DNSSEC and need a guide to help them chose sensible
   values for DNSSEC parameters. Is also discusses operational matters
   like key rollovers, KSK and ZSK considerations and more.









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Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
   1.1   The use of the term 'key'  . . . . . . . . . . . . . . . . .  3
   2.    Time in DNSSEC . . . . . . . . . . . . . . . . . . . . . . .  3
   2.1   Time definitions . . . . . . . . . . . . . . . . . . . . . .  3
   2.2   Time considerations  . . . . . . . . . . . . . . . . . . . .  4
   3.    Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.1   Motivations for the KSK and ZSK functions  . . . . . . . . .  6
   3.2   Key security considerations  . . . . . . . . . . . . . . . .  7
   3.3   Key rollovers  . . . . . . . . . . . . . . . . . . . . . . .  8
   3.3.1 Zone-signing key rollovers . . . . . . . . . . . . . . . . .  9
   3.3.2 Key-signing key rollovers  . . . . . . . . . . . . . . . . . 12
   4.    Planning for emergency key rollover. . . . . . . . . . . . . 13
   4.1   KSK compromise . . . . . . . . . . . . . . . . . . . . . . . 13
   4.2   ZSK compromise . . . . . . . . . . . . . . . . . . . . . . . 14
   4.3   Compromises of keys anchored in resolvers  . . . . . . . . . 14
   5.    Parental policies. . . . . . . . . . . . . . . . . . . . . . 14
   5.1   Initial key exchanges and parental policies
         considerations.  . . . . . . . . . . . . . . . . . . . . . . 14
   5.2   Storing keys so hashes can be regenerated  . . . . . . . . . 15
   5.3   Security lameness checks.  . . . . . . . . . . . . . . . . . 15
   5.4   SIG DS validity period.  . . . . . . . . . . . . . . . . . . 15
   6.    Security considerations  . . . . . . . . . . . . . . . . . . 16
   7.    Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . 16
         Normative References . . . . . . . . . . . . . . . . . . . . 16
         Informative References . . . . . . . . . . . . . . . . . . . 16
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17
   A.    Terminology  . . . . . . . . . . . . . . . . . . . . . . . . 17
   B.    Zone-signing key rollover howto  . . . . . . . . . . . . . . 18
   C.    Typographic conventions  . . . . . . . . . . . . . . . . . . 19
   D.    Document Details and Changes . . . . . . . . . . . . . . . . 20
   D.1   draft-ietf-dnsop-dnssec-operational-practices-00 . . . . . . 21
         Intellectual Property and Copyright Statements . . . . . . . 22

















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1. Introduction

   During workshops and early operational deployment tests, operators
   and system administrators gained knowledge about operating DNSSEC
   aware DNS services. This document describes these practices.

   The structure of the document is as follows. It starts with
   discussing some of the considerations with respect to timing
   parameters of DNS in relation to DNSSEC (Section 2). Aspects of key
   management such as key rollover schemes are described in Section 3.
   Emergency rollover considerations are addressed in Section 4. The
   Typographic conventions used in this document are explained in
   Appendix C.

   Since this is a document with operational suggestions and there is no
   protocol specifications the RFC2119 [5] language does not apply.

1.1 The use of the term 'key'

   It is assumed that the reader is familiar with the concept of
   asymmetric keys on which DNSSEC is based. Therefore this document
   will use the term key rather loosely. Wherever we write that 'a key
   is used to sign data' it is assumed that the reader knows that it is
   the private part of the key-pair that is used for signing. It is also
   assumed that the reader will know that the public part of the
   key-pair is published in the DNSKEY resource record and that it is
   the public part of a key-pair that is used in key-exchanges.

2. Time in DNSSEC

   Without DNSSEC all times in DNS are relative. The SOA's refresh,
   retry and expiration timers are counters that are being used to
   determine the time elapsed after a slave server synced (or tried to
   sync) with a master server. The TTL value and the SOA minimum TTL
   parameter [6] are used to to determine how long a forwarder should
   cache data after it has been fetched from an authoritative server.
   DNSSEC introduces the notion of an absolute time in the DNS.
   Signatures in DNSSEC have an expiration date after which the
   signature is invalid and the signed data is to be considered BAD.

2.1 Time definitions

   In this document we will be using a number of time related terms.
   Within the context of this document the following definitions apply:

   o  "Signature validity period"





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         The period that a signature is valid. It starts at the time
         specified in the signature inception field of the RRSIG RR and
         ends at the time specified in the expiration field of the RRSIG
         RR.

   o  "Signature publication period"

         Time after which a signature made with a key is replaced with a
         new signature made with the same key. This replacement takes
         place by publishing the relevant RRSIG in the master zone file.
         If a signature is published on time T0 and a new signature is
         published on time T1, the signature publication period is T1 -
         T0. If all signatures are refreshed at zone (re)signing then
         the signature publication period is equal to the period between
         two consecutive zone signing operations.

   o  "Key publication period"

         The period for which the public part of the key is published in
         the DNS. The public part of the key can be published in the DNS
         while it has not yet been used to sign data. As soon as a
         public key is published a brute force attack can be attempted
         to recover the private key. Publishing the public key in
         advance (and not signing any data with it) does not guard
         against this attack.

         [Editor's Note: We don't use this term in the doc yet, is it
         needed elsewhere and handy to define here? No:1 Yes:0]

   o  "Maximum/Minimum Zone TTL"

         The maximum or minimum value of all the TTLs in a zone.


2.2 Time considerations

   Because of the expiration of signatures one should consider the
   following.

   o  The Maximum zone TTL of your zone data should be a fraction of
      your signature validity period.

         If the TTL would be of similar order as the signature validity
         period then all RRsets fetched during the validity period would
         be cached until the signature expiration time.  As a result
         query behavior might become bursty.





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         We suggest the TTL on all the RRs in your zone to be at least
         an order of magnitude smaller than your signature validity
         period.

   o  The signature publication period should at least be one maximum
      TTL smaller than the signature validity period.

         If a zone is resigned shortly before the end of the signature
         validity period this may cause simultaneous expiration of data
         from caches which leads to bursty query behavior and increase
         the load on authoritative servers.

   o  The Minimum zone TTL should be long enough to fetch and verify all
      the RRs in the authentication chain.

            1. During validation, some data may expire before validation
            is complete. The validator should be able to keep all the
            data, until validation is complete. This applies to all data
            in the chain of trust: DSs, DNSKEYs, RRSIGs, and the final
            answers i.e. the RR that is returned for the initial query.

            2. Frequent verification causes load on recursive
            nameservers. Data at delegation points, DSs, DNSKEYs and
            RRSIGs benefit from caching. The TTL on those should be
            relatively long.

         We have seen events where data needed for verification of an
         authentication chain had expired from caches.

         We suggest the TTL on DNSKEY and DSs to be at least of the
         order 10 minutes to an hour and all the other RRs in your zone
         to be at least 30 seconds. These are absolute minimum, we
         recommend zone administrators to chose longer ones.

         [Editor's Note: this observation could be implementation
         specific. We are not sure if we should leave this item]

   o  Slave servers will need to be able to fetch newly signed zones
      well before the data expires from your zone.

         If a properly implemented slave server is not able to contact a
         master server for an extended period the data will at some
         point expire and the slave server will not hand out any data.
         If the server serves a DNSSEC zone than it may well happen that
         the signatures expire well before the SOA expiration timer
         counted down to zero. It is not possible to fully prevent this
         from happening by tweaking the SOA parameters. But the effects
         can be minimized if the SOA expiration time is of the same of



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         order of magnitude as or smaller than the signature validity
         period.

         When a zone cannot be updated while signatures in that zone
         have expired non-secure resolvers will continue to be able to
         resolve the data served by the particular slave servers. Only
         security aware resolvers that receive data with expired
         signatures will experience problems.

         We suggest the SOA expiration timer being approximately one
         third or one fourth of the signature validity period.

         We also suggest that operators of nameservers with slave zones
         develop watchdogs to be able to spot these upcoming signature
         expirations in slave zones, so that appropriate action can be
         taken.

   o  [Editor's Note: Need examples here]


3. Keys

3.1 Motivations for the KSK and ZSK functions

   Delegation Signer [7] introduced the concept of key-signing and
   zone-signing keys.The Key-signing-flag [4] introduced the concept of
   a key with the Secure Entry Point flag set; a key that is the first
   key from the zone when following an authentication chain. When using
   a key-signing key with the SEP flag set (the parent has a DS RR
   pointing to that DNSKEY) and when using zone-signing keys without the
   SEP flag set (a practice which we recommend ) one can use the
   following operational procedures.

   The zone-signing key can be used to sign all the data in a zone on a
   regular basis. When a zone-signing key is to be rolled over no
   interactions with the parent is needed. This allows for relatively
   short "Signature Validity Periods" (order of days).

   The key-signing key (with the SEP flag set) is only to be used to
   sign the Key RR set from the zone apex. If a key-signing key is to be
   rolled over, there will be interactions with parties other than the
   zone maintainer such as the registry of the parent zone or
   administrators of verifying resolvers that have the particular key
   configured as trusted entry points. Hence, the "Key Usage Time" of
   these keys can and should be made much longer. Although, given a long
   enough key, the "Key Usage Time" can be on the order of years we
   suggest to plan for a "Key Usage Time" of the order of a few months
   so that a key rollover remains an operational routine.



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3.2 Key security considerations

   In RFC2541 [2] a number of considerations with respect to the
   security of keys are described. That document deals with the
   generation, lifetime, size and storage of private keys.

   In Section 3 of RFC2541 [2], Eastlake does have some suggestions: 13
   months for long-lived keys and 36 days for transaction keys but
   suggestions for key sizes are not made.

   If we read the long-lived key being a key that is used as key-signing
   key and transaction keys being zone signing keys, then these
   recommendations are good starting points for an operational
   procedure. These recommendations will lead to rollovers occurring
   frequently enough so that they can become part of 'operational
   habits' and the procedure does not have to be reinvented every time a
   key is replaced.

   When choosing a key sizes, zone administrators will need to take into
   account how long a key will be used and how much data will be signed
   during the key publication period. It is hard to give precise
   recommendations but Lenstra and Verheul [9] supplied the following
   table with lower bound estimates for cryptographic key sizes. Their
   recommendations are based on a set of explicitly formulated parameter
   settings, combined with existing data points about cryptosystems. For
   details we refer to the original paper.

        Year            RSA key sizes   Elliptic Curve Key Size
        2000            952                     132
        2001            990                     135
        2002            1028                    139
        2003            1068                    140
        2004            1108                    143

        2005            1149                    147
        2006            1191                    148
        2007            1235                    152
        2008            1279                    155
        2009            1323                    157


        2010            1369                    160
        2011            1416                    163
        2012            1464                    165
        2013            1513                    168
        2014            1562                    172

        2015            1613                    173



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        2016            1664                    177
        2017            1717                    180
        2018            1771                    181
        2019            1825                    185


        2020            1881                    188
        2021            1937                    190
        2022            1995                    193
        2023            2054                    197
        2024            2113                    198

        2025            2174                    202
        2026            2236                    205
        2027            2299                    207
        2028            2362                    210
        2029            2427                    213

   Suppose you want your key to last 3 years and the current year is
   2003. Add 3 to 2003 equals 2006 and read of the sizes: 1191 for
   asymmetric keys and 148 bits for elliptic curve keys.

   Note that adding only a "handful of bits" to the key size will
   increase the key's resistance against brute force attacks.

3.3 Key rollovers

   Key rollovers are a fact of life when using DNSSEC. A DNSSEC key
   cannot be used forever (see RFC2541 [2] and Section 3.2 ).  Zone
   maintainers who are in the process of rolling their keys have to take
   into account that data they have published in previous versions of
   their zone still lives in caches. When deploying DNSSEC this becomes
   an important consideration; ignoring data that may be in caches may
   lead to loss of service for clients.

   The most pressing example of this is when zone material which is
   signed with an old key is being validated by a resolver which does
   not have the old zone key cached. If the old key is no longer present
   in the current zone, this validation fails, marking the data BAD.
   Alternatively, an attempt could be made to validate data which is
   signed with a new key against an old key that lives in a local cache,
   also resulting in data being marked BAD.

   To appreciate the situation one could think of a number of
   authoritative servers that may not be instantaneously running the
   same version of a zone and a security aware non-recursive resolver
   that sits behind security aware caching forwarders.




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   Note that KSK rollovers and ZSK rollovers are different. A zone-key
   rollover can be handled in two different way: pre-publish and
   [Editors note: ref please] double-sig. The pre-publish technique
   works because the key-signing key stays the same during this ZSK
   rollover. With this KSK a cache is able to validate the new keyset of
   a zone. With a KSK rollover a cache can not validate the new keyset,
   because it does not trust the new KSK.

   [Editors note: This needs more verbose explanation, nobody will
   appreciate the situation just yet. Help with text and examples is
   appreciated]

3.3.1 Zone-signing key rollovers

   For zone-signing key rollovers there are two ways to make sure that
   during the rollover the data still in caches can be verified with the
   new keysets or the newly generated signatures can be verified with
   the keys still in caches. One schema uses double signatures, it is
   described in Section 3.3.1.1, the other uses key pre-publication
   (Section 3.3.1.2). The pros, cons and recommendations are described
   in Section 3.3.1.3.

3.3.1.1 A double signature zone-signing key rollover

   This section shows how to perform a ZSK key rollover using the double
   zone data signature scheme.

   During the rollover stage the new version of the zone file will need
   to propagate to all authoritative servers and the data that exists in
   (distant) caches will need to expire, this will take at least the
   maximum Zone TTL .

       normal              roll              after

       SOA0                SOA1              SOA2
       RRSIG10(SOA0)       RRSIG10(SOA1)     RRSIG11(SOA2)
                           RRSIG11(SOA1)

       DNSKEY1             DNSKEY1           DNSKEY1
       DNSKEY10            DNSKEY10          DNSKEY11
                           DNSKEY11
       RRSIG1(DNSKEY)      RRSIG1(DNSKEY)    RRSIG1(DNSKEY)
       RRSIG10(DNSKEY)     RRSIG10(DNSKEY)   RRSIG11(DNSKEY)
                           RRSIG11(DNSKEY)







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   normal: Version 0 of the zone: DNSKEY 1 is a key-signing key. DNSKEY
      10 is used to sign all the data of the zone, it is the
      zone-signing key.

   roll: At the rollover stage (SOA serial 1) DNSKEY 11 is introduced
      into the keyset and all the data in the zone is signed with DNSKEY
      10 and DNSKEY 11. The rollover period will need to exist until all
      data from version 0 of the zone has expired from remote caches.
      This will take at least the Maximum Zone TTL of the version 0 of
      the zone.

   after: DNSKEY 10 is removed from the zone. All the signatures from
      DNSKEY 10 are removed from the zone. The keyset, now only
      containing DNSKEY 11 is resigned with the DNSKEY 1.

   At every instance the data from the previous version of the zone can
   be verified with the key from the current version. And vice verse,
   the data from the current version can be verified with the data from
   the previous version of the zone. The duration of the rollover phase
   and the period between rollovers should be at least the "Maximum Zone
   TTL".

   To be on the safe side one could make sure that the rollover phase
   lasts until the signature expiration time of the data in version 0 of
   the zone. But this date could be considerable longer than the Maximum
   Zone TTL, making the rollover a lengthly procedure.

   Note that in this example we assumed that the zone did not get
   modified during the rollover. New data can be introduced in the zone
   as long as it is signed with both keys.

3.3.1.2 Pre-publish keyset rollover

   This section shows how to perform a ZSK rollover without the need to
   sign all the data in a zone twice. We recommend this method because
   it has advantages in the case of key compromises. If the old key gets
   compromised the new key is already distributed in the DNS. The zone
   administrator is then able to quickly switch to the new key and
   remove the compromised key from the zone. Another major advantage is
   that the zone size does not double, as is the case with the double
   signature ZSK rollover. A small "HOWTO" for this kind of rollover can
   be found in Appendix B.

       normal          pre-roll         roll            after

       SOA0            SOA1             SOA2            SOA3
       RRSIG10(SOA0)   RRSIG10(SOA1)    RRSIG11(SOA2)   RRSIG11(SOA3)




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       DNSKEY1         DNSKEY1          DNSKEY1         DNSKEY1
       DNSKEY10        DNSKEY10         DNSKEY10        DNSKEY11
                       DNSKEY11         DNSKEY11
       RRSIG1 (DNSKEY) RRSIG1 (DNSKEY)  RRSIG1(DNSKEY)  RRSIG1 (DNSKEY)
       RRSIG10(DNSKEY) RRSIG10(DNSKEY)  RRSIG11(DNSKEY) RRSIG11(DNSKEY)


   normal: Version 0 of the zone: DNSKEY 1 is a key-signing key. DNSKEY
      10 is used to sign all the data of the zone, its the zone-signing
      key.

   pre-roll: DNSKEY 11 is introduced in the keyset. Note that no
      signatures are generated with this key yet, but this will not
      prevent brute force attacks on the public key. The minimum
      duration of this pre-roll phase is the time it takes for the data
      to propagate to the authoritative servers plus TTL value on the
      keyset. This would boil down to two times the Maximum Zone TTL.

   roll:

      At the rollover stage (SOA serial 1) DNSKEY 11 is used to sign the
      data in the zone (exclusively i.e. all the signatures from DNSKEY
      10 are removed from the zone.). DNSKEY 10 remains published in the
      keyset. This way data that was loaded into caches from version 1
      of the zone can still be verified with key sets fetched from
      version 2 of the zone.

      The minimum time that the keyset that includes DNSKEY 10 is to be
      published is the time that it takes for zone data from the
      previous version of the zone to expire from old caches i.e. the
      time it takes for this zone to propagate to all authoritative
      servers plus the Maximum Zone TTL value of any of the data in the
      previous version of the zone.

   after: DNSKEY 10 is removed from the zone. The keyset, now only
      containing DNSKEY 11 is resigned with the DNSKEY 1.

   The above scheme can be simplified a bit by always publishing the
   "future" key immediately after the rollover. The scheme would look
   like this (we show 2 rollovers); the future key is introduced in
   "after" as DNSKEY 12 and again a newer one, numbered 13, in "2nd
   after":


       normal          roll            after           2nd roll        2nd after

       SOA0            SOA2            SOA3            SOA4            SOA5
       RRSIG10(SOA0)   RRSIG11(SOA2)   RRSIG11(SOA3)   RRSIG12(SOA4)   RRSIG12(SOA5)



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       DNSKEY1         DNSKEY1         DNSKEY1         DNSKEY1         DNSKEY1
       DNSKEY10        DNSKEY10        DNSKEY11        DNSKEY11        DNSKEY12
       DNSKEY11        DNSKEY11        DNSKEY12        DNSKEY12        DNSKEY13
       RRSIG1(DNSKEY)  RRSIG1 (DNSKEY) RRSIG1(DNSKEY)  RRSIG1(DNSKEY)  RRSIG1(DNSKEY)
       RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY) RRSIG12(DNSKEY) RRSIG12(DNSKEY)


   Note that the key introduced after the rollover is not used for
   production yet; the private key can thus be stored in a physically
   secure manner and does not need to be 'fetched' every time a zone
   needs to be signed.

   This scheme has the benefit that the key that is intended for future
   use, can immediately be used during an emergency rollover under the
   assumption that it was stored in a physically secure manner.

3.3.1.3 Pros and cons of the schemes

   A double signature rollover: The drawback of this signing scheme is
      that during the rollover the number of signatures in your zone
      doubles, which may be prohibitive if you have very big zones. An
      advantage is that it only requires three steps.

   Prepublish-keyset rollover: This rollover does not involve signing
      the zone data twice. Instead, just before the actual rollover the
      new key is published in the keyset and thus available for
      cryptanalysis attacks. A small disavantage is that this process
      requires four steps. Also the prepublish scheme is useless for
      KSKs as explained in Section 3.3.


3.3.2 Key-signing key rollovers

   For the rollover of a key-signing key the same considerations as for
   the rollover of a zone-signing key apply. However we can use a double
   signature scheme to guarantee that old data (only the apex keyset) in
   caches can be verified with a new keyset and vice versa. Since only
   the keyset is signed with a KSK, size considerations do not apply.


       normal          roll            after

       SOA0            SOA1            SOA2
       RRSIG10(SOA0)   RRSIG10(SOA1)   RRSIG10(SOA2)

       DNSKEY1         DNSKEY1         DNSKEY2
                       DNSKEY2
       DNSKEY10        DNSKEY10        DNSKEY10



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       RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG2(DNSKEY)
                       RRSIG2 (DNSKEY)
       RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY)


4. Planning for emergency key rollover.

   This section deals with preparation for a possible key compromise.
   Our advice is to have a documented procedure ready for when a key
   compromise is suspected or confirmed.

   [Editors note: We are much in favor of a rollover tactic that keeps
   the authentication chain intact as long as possible. This has as a
   result that one has to take all the regular rollover properties into
   account.]

   When the private material of one of your keys is compromised it can
   be used by 'blackhats' for as long as a valid authentication chain
   exists.  A authentication chain remains intact for:

      as long as a signature over the compromised key in the
      authentication chain is valid,

      as long as a parental DS RR (and signature) points to the
      compromised key,

      as long as the key is anchored in a resolver and is used as a
      starting point for validation. (This is the hardest to update.)

   While an authentication chain to your compromised key exists your
   name-space is vulnerable to abuse by the "blackhat". Zone operators
   have to make a trade off if the abuse of the compromised key is worse
   than having data in caches that cannot be validated. If the zone
   operator chooses to break the authentication chain to the compromised
   key, data in caches signed with this key can not be validated. On the
   other hand if the zone administrator chooses to take the path of a
   regular roll-over the "blackhat" can spoof data so that it appears to
   be valid, note that this kind of attack will usually be localized in
   the Internet topology.


4.1 KSK compromise

   When the KSK has been compromised the parent must be notified as soon
   as possible and through secure means. The keyset of the zone should
   be resigned as soon as possible. Care must be taken to not break the
   authentication chain. The local zone can only be resigned with the
   new KSK after the parent's zone has been updated with the new KSK.



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   Before this update takes place it would be best to drop the security
   status of a zone all together: the parent removes the DS of the child
   at the next zone update.  After that the child can be made secure
   again. An additional danger of a key compromise is that the
   compromised key can be used to facilitate a legitemate DNSKEY/DS and/
   or nameserver rollover at the parent. When that happens the domain
   can be in dispute. An out of band and secure notify mechanism to
   contact a parent is needed in this case.

4.2 ZSK compromise

   Mainly because there is no parental interaction required when a ZSK
   is compromised the situation is less severe than with with a KSK
   compromise.  The zone must still be resigned with a new ZSK as soon
   as possible. As this is a local operation and requires no
   communication between the parent and child this can be achieved
   fairly quickly. One has to take into account though that just as with
   a normal rollover the immediate disappearance from the old
   compromised key may lead to verification problems. The
   pre-publication scheme as discussed above minimizes that problem.

4.3 Compromises of keys anchored in resolvers

   A key can also be pre-configured in resolvers. If DNSSEC is rolled
   out as planned the root key should be pre-configured in every secure
   aware resolver on the planet. [Editors Note: add more about
   authentication of a newly received resolver key]

   If that key is compromised all the resolvers should be notified of
   this fact. Zone administrators may consider setting up a mailing list
   to communicate the fact that a SEP key is about to be rolled over.
   This communication will of course need to be authenticated e.g. by
   using digital signatures.

5. Parental policies.

5.1 Initial key exchanges and parental policies considerations.

   The initial key exchange is always subject to the policies set by the
   parent (or its registry). When designing a key exchange policy one
   should take into account that the authentication and authorization
   mechanisms used during a key exchange should be as strong as the
   authentication and authorization mechanisms used for the exchange of
   delegation information between parent and child.

   Using the DNS itself as the source for the actual DNSKEY material
   with an off-band check on the validity of the DNSKEY has the benefit
   that it reduces the changes of operator error. A parental DNSKEY



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   download tool can make use of the SEP bit [4] to select the proper
   key from a DNSSEC keyset; thereby reducing the change that the wrong
   DNSKEY is sent. It can validate the self-signature over a key;
   thereby verifying the ownership of the private key material. Besides,
   by fetching the DNSKEY from the DNS one can be sure that the child
   will not become invisible once the parent indicates the child is
   secure by publishing the DS RR.

   Note: the off-band verification is still needed when the keymaterial
   is fetched by a tool. The parent can not be sure if the DNSKEY RRs
   where not spoofed.

5.2 Storing keys so hashes can be regenerated

   When designing a registry system one should consider if the DNSKEYs
   or the corresponding DSs are stored. Storing DNSKEYs will help during
   troubleshooting while the overhead of calculating DS records from
   them is minimal.

   Having a out-of-band mechanism, such as a WHOIS database, to find out
   which keys are used to generate DS Resource Records for specific
   owners may also help with troubleshooting.

5.3 Security lameness checks.

   Security lameness is defined as the event that a parent has a DS
   Resource Record that points to a non-existing DNSKEY RR. At key
   exchange a parent should make sure that the childs key is actually
   configured in the DNS before publishing a DS RR in its zone. Failure
   to do so would render the child's zone marked "BAD".

   Child zones should be very careful removing DNSKEY material,
   specifically SEP keys, for which a DS RR exist.

   Once a zone is "security lame" a fix (e.g. by removing a DS RR) will
   take time to propagate through the DNS.

5.4 SIG DS validity period.

   Since the DS can be replayed as long as it has a valid signature a
   short signature validity period over the DS minimizes the time a
   child is vulnerable in the case of a compromise of the child's KSK.
   A signature validity period that is too short introduces the
   possibility that a zone is marked BAD in case of a configuration
   error in the signer; there may not be enough time to fix the problems
   before signatures expire.  Something as mundane as weekends show the
   need for a DS signature lifetimes longer than 2 days. We recommend
   the minimum for a DS signature validity period to be about a few



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   days.

   The maximum signature lifetime of the DS record depends on how long
   child zones are willing to be vulnerable after a key compromise. We
   consider a signature validity period of the order of one week a good
   compromise between the operational constraints of the parent and
   minimizing damage for the child.

6. Security considerations

   DNSSEC adds data integrity to the DNS. This document tries to assess
   considerations to operate a stable and secure DNSSEC service.

7. Acknowledgments

   We, the folk mentioned as authors, only acted as editors. Most of the
   ideas in this draft where the result of collective efforts during
   workshops and discussions and try outs.

   At the risk of forgetting individuals who where the original
   contributors of the ideas we like to acknowledge people who where
   actively involved in the compilation of this document. In
   alphabetical order: Olafur Gudmundsson, Wesley Griffin, Michael
   Richardson, Scott Rose, Rick van Rein, Tim McGinnis.

   Kolkman and Gieben take the blame for all mistakes.

Normative References

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

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

   [3]  Lewis, E., "DNS Security Extension Clarification on Zone
        Status", RFC 3090, March 2001.

   [4]  Lewis, E., Kolkman, O. and J. Schlyter, "KEY RR Key-Signing Key
        (KSK) Flag", draft-ietf-dnsext-keyrr-key-signing-flag-06 (work
        in progress), February 2003.

Informative References

   [5]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [6]  Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", RFC



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        2308, March 1998.

   [7]  Gudmundsson, O., "Delegation Signer Resource Record",
        draft-ietf-dnsext-delegation-signer-13 (work in progress), March
        2003.

   [8]  Arends, R., "Protocol Modifications for the DNS Security
        Extensions", draft-ietf-dnsext-dnssec-protocol-01 (work in
        progress), March 2003.

   [9]  Lenstra, A. and E. Verheul, "Selecting Cryptographic Key Sizes",
        The Journal of Cryptology 14 (255-293), 2001.


Authors' Addresses

   Olaf M. Kolkman
   RIPE NCC
   Singel 256
   Amsterdam  1016 AB
   NL

   Phone: +31 20 535 4444
   EMail: olaf@ripe.net
   URI:   http://www.ripe.net/


   Miek Gieben
   NLnet Labs
   Kruislaan 419
   Amsterdam  1098 VA
   NL

   EMail: miek@nlnetlabs.nl
   URI:   http://www.nlnetlabs.nl

Appendix A. Terminology

   In this document there is some jargon used that is defined in other
   documents. In most cases we have not copied the text from the
   documents defining the terms but give a more elaborate explanation of
   the meaning. Note that these explanations should not be seen as
   authoritative.

   Private and Public Keys: DNSSEC secures the DNS through the use of
      public key cryptography. Public key cryptography is based on the
      existence of 2 keys, a public key and a private key. The public
      keys are published in the DNS by use of the DNSKEY Resource Record



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      (DNSKEY RR). Private keys are supposed to remain private i.e.
      should not be exposed to parties not-authorized to do the actual
      signing.

   Signer: The system that has access to the private key material and
      signs the Resource Record sets in a zone. A signer may be
      configured to sign only parts of the zone e.g. only those RRsets
      for which existing signatures are about to expire.

   KSK: A Key-Signing key (KSK) is a key that is used for exclusively
      signing the apex keyset.  The fact that a key is a KSK is only
      relevant to the signing tool.

   ZSK: A Zone signing key (ZSK) is a key that is used for signing all
      data in a zone.  The fact that a key is a ZSK is only relevant to
      the signing tool.

   BAD: [Editors Note: a reference here] A RRset in DNSSEC is marked
      "bad" when a signature of a RRset does not validate against the
      DNSKEY. Even is the key itself was not marked BAD. BAD data is not
      cached.

   Singing the Zone File: The term used for the event where an
      administrator joyfully signs its zone file while producing melodic
      sound patterns.


Appendix B. Zone-signing key rollover howto

   Using the pre-published signature scheme and the most conservative
   method to assure oneself that data does not live in distant caches
   here follows the "HOWTO". [WES: has some comments about this]

      STEP 0, the preparation: Create two keys and publish them both in
      your keyset.  Mark one of the keys as "active" and the other as
      "published". Use the "active" key for signing your zone data.
      Store the private part of the "published" key, preferably
      off-line.

      STEP 1, determine expiration: At the beginning of the rollover:
      make a note of the highest expiration time of signatures in your
      zonefile created with the current key currently marked as
      "active".

      Wait until the expiration time marked in STEP 1






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      STEP 2  Then start using the key that was marked as "published" to
      sign your data i.e. mark it as "active". Stop using the key that
      was marked as "active", mark it as "rolled".

      STEP 3: It is safe to engage in a new rollover (STEP 1) after at
      least one "signature validity period".


Appendix C. Typographic conventions

   The following typographic conventions are used in this document:

   Key notation: A key is denoted by KEYx, where x is a number, x could
      be thought of as the key id.

   RRset notations: RRs are only denoted by the type all other
      information, owner, class, rdata and TTL is left out. Thus:
      example.com 3600 IN A 192.168.1.1 is reduced to: A. RRsets are a
      list of RRs. A example of this would be: A1,A2, specifying the
      RRset containing two A records. This could again be abreviated to
      just: A.

   Signature notation: Signatures are denoted as SIGx(RRset), which
      means that RRset is signed with KEYx.

   Zone representation: Using the above notation we have simplify the
      representation of a signed zone by leaving out all unneeded
      details such as the names and by just representing all data by
      "SOAx"

   SOA representation: Soa's are represented as SOA x, where x is the
      serial number.

   Using this notation the following zone :


   example.net.      600     IN SOA  ns.example.net. ernie.example.net. (
                                     10         ; serial
                                     450        ; refresh (7 minutes 30 seconds)
                                     600        ; retry (10 minutes)
                                     345600     ; expire (4 days)
                                     300        ; minimum (5 minutes)
                                     )
                     600     RRSIG   SOA 5 2 600 20130522213204 (
                                     20130422213204 14 example.net.
                                     cmL62SI6iAX46xGNQAdQ... )
                     600     NS      a.iana-servers.net.
                     600     NS      b.iana-servers.net.



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                     600     RRSIG   NS 5 2 600 20130507213204 (
                                     20130407213204 14 example.net.
                                     SO5epiJei19AjXoUpFnQ ... )
                     3600    DNSKEY  256 3 5 (
                                     EtRB9MP5/AvOuVO0I8XDxy0...
                                     ) ; key id = 14
                     3600    DNSKEY  256 3 5 (
                                     gsPW/Yy19GzYIY+Gnr8HABU...
                                     ) ; key id = 15
                     3600    RRSIG   DNSKEY 5 2 3600 20130522213204 (
                                     20130422213204 14 example.net.
                                     J4zCe8QX4tXVGjV4e1r9... )
                     3600    RRSIG   DNSKEY 5 2 3600 20130522213204 (
                                     20130422213204 15 example.net.
                                     keVDCOpsSeDReyV6O... )
                     600     NSEC    a.example.net. NS SOA TXT RRSIG DNSKEY NSEC
                     600     RRSIG   NSEC 5 2 600 20130507213204 (
                                     20130407213204 14 example.net.
                                     obj3HEp1GjnmhRjX... )
   a.example.net.    600     IN TXT  "A label"
                     600     RRSIG   TXT 5 3 600 20130507213204 (
                                     20130407213204 14 example.net.
                                     IkDMlRdYLmXH7QJnuF3v... )
                     600     NSEC    b.example.com. TXT RRSIG NSEC
                     600     RRSIG   NSEC 5 3 600 20130507213204 (
                                     20130407213204 14 example.net.
                                     bZMjoZ3bHjnEz0nIsPMM... )

                     ...


    is reduced to the following represenation:

       SOA10
       RRSIG14(SOA10)

       DNSKEY14
       DNSKEY15

       RRSIG14(KEY)
       RRSIG15(KEY)

    The rest of the zone data has the same signature as the SOA record,
   i.e a RRSIG created with DNSKEY 14.

Appendix D. Document Details and Changes

   This section is to be removed by the RFC editor if and when the



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   document is published.

   $Header: /var/cvs/dnssec-key/
   draft-ietf-dnsop-dnssec-operational-practices.xml,v 1.5 2003/10/10
   09:49:07 dnssec Exp $

D.1 draft-ietf-dnsop-dnssec-operational-practices-00

   Submission as working group document. This document is a modified and
   updated version of draft-kolkman-dnssec-operational-practices-00.









































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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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