DNSOP O. Kolkman Internet-Draft
RIPE NCC Expires: September 2, 2005R. Gieben Updates: 2541 (if approved) NLnet Labs MarchExpires: April 2, 2006 September 29, 2005 DNSSEC Operational Practices draft-ietf-dnsop-dnssec-operational-practices-04.txtdraft-ietf-dnsop-dnssec-operational-practices-05.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on SeptemberApril 2, 2005.2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document describes a set of practices for operating the DNS with security extensions (DNSSEC). The target audience is zone administrators deploying DNSSEC. The document discusses operational aspects of using keys and signatures in the DNS. It discusses issues as key generation, key storage, signature generation, key rollover and related policies. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.11.1. The Use of the Term 'key' . . . . . . . . . . . . . . . . 4 1.21.2. Time Definitions . . . . . . . . . . . . . . . . . . . . . 5 2. Keeping the Chain of Trust Intact . . . . . . . . . . . . . . 5 3. Keys Generation and Storage . . . . . . . . . . . . . . . . . 6 3.13.1. Zone and Key Signing Keys . . . . . . . . . . . . . . . . 6 22.214.171.124.1. Motivations for the KSK and ZSK Separation . . . . . . 6 3.1.27 3.1.2. KSKs for high level zonesHigh Level Zones . . . . . . . . . . . . . . 7 3.23.2. Randomness . . . . . . . . . . . . . . . . . . . . . . . . 8 3.33.3. Key Effectivity Period . . . . . . . . . . . . . . . . . . 8 3.43.4. Key Algorithm . . . . . . . . . . . . . . . . . . . . . . 9 3.53.5. Key Sizes . . . . . . . . . . . . . . . . . . . . . . . . 9 3.63.6. Private Key Storage . . . . . . . . . . . . . . . . . . . 1011 4. Signature generation, Key Rollover and Related Policies . . . 11 4.112 4.1. Time in DNSSEC . . . . . . . . . . . . . . . . . . . . . . 11 4.1.112 4.1.1. Time Considerations . . . . . . . . . . . . . . . . . 11 4.212 4.2. Key Rollovers . . . . . . . . . . . . . . . . . . . . . . 13 4.2.114 4.2.1. Zone-signing Key Rollovers . . . . . . . . . . . . . . 13 4.2.214 4.2.2. Key-signing Key Rollovers . . . . . . . . . . . . . . 17 4.2.318 4.2.3. Difference Between ZSK and KSK Rollovers . . . . . . . 18 4.2.419 4.2.4. Automated Key Rollovers . . . . . . . . . . . . . . . 19 4.320 4.3. Planning for Emergency Key Rollover . . . . . . . . . . . 19 4.3.121 4.3.1. KSK Compromise . . . . . . . . . . . . . . . . . . . . 20 4.3.221 4.3.2. ZSK Compromise . . . . . . . . . . . . . . . . . . . . 20 4.3.323 4.3.3. Compromises of Keys Anchored in Resolvers . . . . . . 20 4.423 4.4. Parental Policies . . . . . . . . . . . . . . . . . . . . 21 4.4.123 4.4.1. Initial Key Exchanges and Parental Policies Considerations . . . . . . . . . . . . . . . . . . . . 21 4.4.223 4.4.2. Storing Keys or Hashes? . . . . . . . . . . . . . . . 21 4.4.324 4.4.3. Security Lameness . . . . . . . . . . . . . . . . . . 22 4.4.424 4.4.4. DS Signature Validity Period . . . . . . . . . . . . . 2225 5. SecurityIANA Considerations . . . . . . . . . . . . . . . . . . . 23 6. Acknowledgments . .. . 25 6. Security Considerations . . . . . . . . . . . . . . . . . . . 2326 7. References . . .Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24 7.1 Normative26 8. References . . . . . . . . . . . . . . . . . . . 24 7.2 Informative References. . . . . . . 26 8.1. Normative References . . . . . . . . . . . 24 Authors' Addresses. . . . . . . . 26 8.2. Informative References . . . . . . . . . . . . . . 25 A. Terminology. . . . 27 Appendix A. Terminology . . . . . . . . . . . . . . . . . . . . . 2527 Appendix B. Zone-signing Key Rollover Howto . . . . . . . . . . . . . . . 2628 Appendix C. Typographic Conventions . . . . . . . . . . . . . . . . . . . 2629 Appendix D. Document Details and Changes . . . . . . . . . . . . . . . . . 29 D.131 D.1. draft-ietf-dnsop-dnssec-operational-practices-00 . . . . . 29 D.231 D.2. draft-ietf-dnsop-dnssec-operational-practices-01 . . . . . 29 D.331 D.3. draft-ietf-dnsop-dnssec-operational-practices-02 . . . . . 29 D.431 D.4. draft-ietf-dnsop-dnssec-operational-practices-03 . . . . . 29 D.532 D.5. draft-ietf-dnsop-dnssec-operational-practices-04 . . . . . 3032 D.6. draft-ietf-dnsop-dnssec-operational-practices-05 . . . . . 32 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33 Intellectual Property and Copyright Statements . . . . . . . . 31. . 34 1. Introduction During workshops and early operational deployment tests, operators and system administrators have gained experience about operating the DNS with security extensions (DNSSEC). This document translates these experiences into a set of practices for zone administrators. At the time of writing, there exists very little experience with DNSSEC in production environments; this document should therefore explicitly not be seen as representing 'Best Current Practices'. The procedures herein are focused on the maintenance of signed zones (i.e. signing and publishing zones on authoritative servers). It is intended that maintenance of zones such as resigningre-signing or key rollovers be transparent to any verifying clients on the Internet. The structure of this document is as follows. In Section 2 we discuss the importance of keeping the "chain of trust" intact. Aspects of key generation and storage of private keys are discussed in Section 3; the focus in this section is mainly on the private part of the key(s). Section 4 describes considerations concerning the public part of the keys. Since these public keys appear in the DNS one has to take into account all kinds of timing issues, which are discussed in Section 4.1. Section 4.2 and Section 4.3 deal with the rollover, or which,supercession, of keys. Finally Section 4.4 discusses considerations on how parents deal with their children's public keys in order to maintain chains of trust. The typographic conventions used in this document are explained in Appendix C. Since this is a document with operational suggestions and there are no protocol specifications, the RFC2119  language does not apply. This document obsoletes RFC2541  1.11.1. 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 (Public Key Cryptography ).). Therefore, this document will use the term 'key' rather loosely. Where it is written that 'a key is used to sign data' it is assumed that the reader understands that it is the private part of the key-pairkey pair that is used for signing. It is also assumed that the reader understands that the public part of the key-pairkey pair is published in the DNSKEY resource record and that it is the public part that is used in key-exchanges. 1.2key exchanges. 1.2. Time Definitions In this document we will be using a number of time related terms. The following definitions apply: o "Signature validity period" 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 specific 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. After one stopped publishing an RRSIG in a zone it may take a while before the RRSIG has expired from caches and has actually been removed from the DNS. o "Key effectivity period" The period during which a key pair is expected to be effective. This period is defined as the time between the first inception time stamp and the last expiration date of any signature made with this key, regardless of any discontinuity in the use of the key. The key effectivity period can span multiple signature validity periods. o "Maximum/Minimum Zone TTL" The maximum or minimum value of the TTLs from the complete set of RRs in a zone. Note that the minimum TTL is not the same as the MINIMUM field in the SOA RR. 2. Keeping the Chain of Trust Intact Maintaining a valid chain of trust is important because broken chains of trust will result in data being marked as Bogus (as defined in  section 5), which may cause entire (sub)domains to become invisible to verifying clients. The administrators of secured zones have to realize that their zone is, to theirverifying clients, part of a chain of trust. As mentioned in the introduction, the procedures herein are intended to ensure maintenance of zones, such as resigningre-signing or key rollovers, will be transparent to the verifying clients on the Internet. Administrators of secured zones will have to keep in mind that data published on an authoritative primary server will not be immediately seen by verifying clients; it may take some time for the data to be transferedtransferred to other secondary authoritative nameservers and clients may be fetching data from caching non-authoritative servers. In this light it is good to note that the time from master to slave is negligible when using NOTIFY and IXFR, increasing by reliance on AXFR, and more if you rely on the SOA timing parameters for zone refresh. For the verifying clients it is important that data from secured zones can be used to build chains of trust regardless of whether the data came directly from an authoritative server, a caching nameserver or some middle box. Only by carefully using the available timing parameters can a zone administrator assure that the data necessary for verification can be obtained. The responsibility for maintaining the chain of trust is shared by administrators of secured zones in the chain of trust. This is most obvious in the case of a 'key compromise' when a trade off between maintaining a valid chain of trust and replacing the compromised keys as soon as possible must be made. Then zone administrators will have to make a trade off, between keeping the chain of trust intact - thereby allowing for attacks with the compromised key - or to deliberately break the chain of trust and making secured sub domains invisible to security aware resolvers. Also see Section 4.3. 3. Keys Generation and Storage This section describes a number of considerations with respect to the security of keys. It deals with the generation, effectivity period, size and storage of private keys. 3.13.1. Zone and Key Signing Keys The DNSSEC validation protocol does not distinguish between DNSKEYs. All DNSKEYs can be used during the validation. In practice operators use Key Signing and Zone Signing Keys and use the so-called (Secure Entry Point) SEP  flag to distinguish between them during operations. The dynamics and considerations are discussed below. To make zone resigningre-signing and key rollover procedures easier to implement, it is possible to use one or more keys as Key Signing Keys (KSK). These keys will only sign the apex DNSKEY RR setRRset in a zone. Other keys can be used to sign all the RRsets in a zone and are referred to as Zone Signing Keys (ZSK). In this document we assume that KSKs are the subset of keys that are used for key exchanges with the parent and potentially for configuration as trusted anchors - the SEP keys. In this document we assume a one-to-one mapping between KSK and SEP keys and we assume the SEP flag to be set on all KSKs. 126.96.36.199.1. Motivations for the KSK and ZSK Separation Differentiating between the KSK and ZSK functions has several advantages: o No parent/child interaction is required when ZSKs are updated. o The KSK can be made stronger (i.e. using more bits in the key material). This has little operational impact since it is only used to sign a small fraction of the zone data. Also when verifying the KSK is only used to verify the zone's keyset.key set. o As the KSK is only used to sign a key set, which is most probably updated less frequently than other data in the zone, it can be stored separately from and in a safer location than the ZSK. o A KSK can have a longer key effectivity period. For almost any method of key management and zone signing the KSK is used less frequently than the ZSK. Once a key set is signed with the KSK all the keys in the key set can be used as ZSK. If a ZSK is compromised, it can be simply dropped from the key set. The new key set is then resignedre-signed with the KSK. Given the assumption that for KSKs the SEP flag is set, the KSK can be distinguished from a ZSK by examining the flag field in the DNSKEY RR. If the flag field is an odd number it is a KSK. If it is an even number it is a ZSK. 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, no interaction with the parent is needed. This allows for "Signature Validity Periods" on the order of days. The key-signing key is only to be used to sign the DNSKEY RRs in a zone. If a key-signing key is to be rolled over, there will be interactions with parties other than the zone administrator. These can include the registry of the parent zone or administrators of verifying resolvers that have the particular key configured as trusted entry points. Hence, the key effectivity period 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 planning for a key effectivity of the order of a few months so that a key rollover remains an operational routine. 188.8.131.52.2. KSKs for high level zonesHigh Level Zones Higher level zones are generally more sensitive than lower level zones. Anyone controlling or breaking the security of a zone thereby obtains authority over all of its sub domains (except in the case of resolvers that have locally configured the public key of a sub domain). Therefore, extra care should be taken with high level zones and strong keys used. The root zone is the most critical of all zones. Someone controlling or compromising the security of the root zone would control the entire DNS name space of all resolvers using that root zone (except in the case of resolvers that have locally configured the public key of a sub domain). Therefore, the utmost care must be taken in the securing of the root zone. The strongest and most carefully handled keys should be used. The root zone private key should always be kept off line. Many resolvers will start at a root server for their access to and authentication of DNS data. Securely updating the trust anchors in an enormous population of resolvers around the world will be extremely difficult. 3.23.2. Randomness Careful generation of all keys is a sometimes overlooked but absolutely essential element in any cryptographically secure system. The strongest algorithms used with the longest keys are still of no use if an adversary can guess enough to lower the size of the likely key space so that it can be exhaustively searched. Technical suggestions for the generation of random keys will be found in RFC1750 . One should carefully assess if the random number generator used during key generation adheres to these suggestions. Keys with a long effectivity period are particularly sensitive as they will represent a more valuable target and be subject to attack for a longer time than short period keys. It is strongly recommended that long term key generation occur off-line in a manner isolated from the network via an air gap or, at a minimum, high level secure hardware. 3.33.3. Key Effectivity Period For various reasons keys in DNSSEC need to be changed once in a while. The longer a key is in use, the greater the probability that it will have been compromised through carelessness, accident, espionage, or cryptanalysis. Furthermore when key rollovers are too rare an event, they will not become part of the operational habit and there is risk that nobody on-site will remember the procedure for rollover when the need is there. For Key Signing KeysFrom a purely operational perspective a reasonable key effectivity period for Key Signing Keys is 13 months, with the intent to replace them after 12 months. An intended key effectivity period of a month is reasonable for Zone Signing Keys. UsingFor a key sizes that matches these recommendationseffectivity periods see Section 3.5. As argued in Section 3.1.2 securely updating trust anchors will leadbe extremely difficult. On the other hand the "operational habit" argument does also apply to rollovers occurring frequently enoughtrust anchor reconfiguration. If a short key-effectivity period is used and the trust anchor configuration has to become part of 'operational habits';be revisited on a regular basis the procedure does not haveodds that the configuration tends to be reinvented every timeforgotten is smaller. The trade-off is against a keysystem that is replaced.so dynamic that administrators of the validating clients will not be able to follow the modifications. Key effectivity periods can be made very short, as in the order of a few minutes. But when replacing keys one has to take the considerations from Section 4.1 and Section 4.2 into account. 3.43.4. Key Algorithm There are currently three different types of algorithms that can be used in DNSSEC: RSA, DSA and elliptic curve cryptography. The latter is fairly new and still needshas yet to be standardized for usage in DNSSEC. RSA has been developed in an open and transparent manner. As the patent on RSA expired in 2000, its use is now also free. DSA has been developed by NIST. The creation of signatures is roughly done at the same speed as with RSA, but is 10 to 40 times as slow for verification .. We suggest the use of RSA/SHA-1 as the preferred algorithm for the key. The current known attacks on RSA can be defeated by making your key longer. As the MD5 hashing algorithm is showing (theoretical) cracks, we recommend the usage of SHA1.SHA-1. In 2005 some discoveries were made that SHA-1 also has some weaknesses. Currently SHA-1 is strong enough for DNSSEC. It is expected that a new hashing algorithm is rolled out, before any attack becomes practical. 3.53.5. Key Sizes When choosing key sizes, zone administrators will need to take into account how long a key will be used andused, how much data will be signed during the key publication period. It is hard to give precise recommendations but Lenstra and Verheul  suppliedperiod (See Section 8.10 of ) and, optionally, how large the following table with lower bound estimates for cryptographickey sizes. Their recommendations are based on a setsize of explicitly formulated parameter settings, combined with existing data points about cryptographic systems. For details we refer tothe original paper. Year RSA Key Sizes Year RSA Key Sizes 2000 952 2015 1613 2001 990 2016 1664 2002 1028 2017 1717 2003 1068 2018 1771 2004 1108 2019 1825 2005 1149 2020 1881 2006 1191 2021 1937 2007 1235 2022 1995 2008 1279 2023 2054 2009 1323 2024 2113 2026 2236 2025 2174 2010 1369 2027 2299 2011 1416 2028 2362 2012 1464 2029 2427 2013 1513 2014 1562 For example, should you wish your key to last three years from 2003, checkparent is. As the RSA key size values for 2006 in this table. In this casechain of trust really is "a chain", it should be at least 1191 bits. Please keepdoes not make much sense in mind that nobody can see into the future, and that these key lengths are only provided here as a guide. When determining a key sizemaking one should take into account that a large key will be slower during generation and verification. For RSA, verification, the most common operation, will vary roughly with the squareof the key size; signing will vary with the cube ofkeys in the key size length; and key generation will vary withchain several times larger then the fourth power ofothers. As always, it's the modulus length. Besides larger keys will increaseweakest link that defines the sizesstrength of the RRSIG and DNSKEY records and will therefore increase the chance of DNS UDP packet overflow.entire chain. Also see Section 3.1.1 for a discussion of how keys serving different roles (ZSK v. KSK) may need different key strengths. 3.6 Private Key Storage It is recommended that, where possible, zone private keys and the zone file master copy be kept and used in off-line, non-network connected, physically secure machines only. Periodically an application can be run to add authentication tosizes. Generating a zone by adding RRSIG and NSEC RRs. Then the augmented file can be transferred, perhaps by sneaker-net, tokey of the networked zone primary server machine. The ideal situationcorrect size is to havea one way information flowdifficult problem, RFC3766  tries to deal with that problem. Paragraph 1 of that RFC states: 1. Determine the networkattack resistance necessary to avoidsatisfy the possibilitysecurity requirements of tampering from the network. Keeping the zone master file on-line on the network and simply cycling it through an off-line signer does not do this. The on-line version could still be tampered with ifthe host it resides on is compromised. For maximum security,application. Do this by estimating the master copyminimum number of computer operations that the zone file should be off net and should not be updated based on an unsecured network mediated communication. In general keeping a zone-file off-line will not be practical and the machines on which zone files are maintainedattacker will be connectedforced to a network. Operators are advised to take security measures to shield unauthorized accessdo in order to compromise the master copy. For dynamically updated secured zones  bothsecurity of the master copysystem and then take the private keylogarithm base two of that is used to update signatures on updated RRs will need tonumber. Call that logarithm value "n". A 1996 report recommended 90 bits as a good all-around choice for system security. The 90 bit number should be increased by about 2/3 bit/year, or about 96 bits in 2005.  goes on line. 4. Signature generation, Key Rollover and Related Policies 4.1 Timeto explain how this number "n" can be used to calculate the key sizes in DNSSEC Without DNSSEC all timespublic key cryptography. This culminated in DNS are relative.the table given below (slightly modified for our purpose): +-------------+-----------+--------------+ | System | | | | requirement | Symmetric | RSA or DSA | | for attack | key size | modulus size | | resistance | (bits) | (bits) | | (bits) | | | +-------------+-----------+--------------+ | 70 | 70 | 947 | | 80 | 80 | 1228 | | 90 | 90 | 1553 | | 100 | 100 | 1926 | | 150 | 150 | 4575 | | 200 | 200 | 8719 | | 250 | 250 | 14596 | +-------------+-----------+--------------+ The SOA RR's refresh, retry and expiration timerskey sizes given are counters thatrather large. This is because these keys are used to determine the time elapsed afterresilient against a slave server synchronized (or tried to synchronize) withtrillionaire attacker. Assuming this rich attacker will not attack your key and that the key is rolled over once a master server. The Timeyear, we come to Live (TTL)the following recommendations about KSK sizes; 1024 bits low value domains, 1300 for medium value and 2048 for the SOA RR minimum TTL parameter  are used to determine how long a forwarder should cache data after it has been fetched from an authoritative server. By usinghigh value domains. Whether a signature validity period, DNSSEC introducesdomain is of low, medium, high value depends solely on the notionviews of an absolute time inthe DNS. Signatureszone owner. One could for instance view leaf nodes in DNSSEC have an expiration date after whichthe signature is markedDNS as invalid and the signed data is to be considered Bogus. 4.1.1 Time Considerations Becauseof low value and TLDs or the expirationroot zone of signatures, onehigh value. The suggested key sizes should considerbe safe for the following: o We suggestnext 5 years. As ZSKs can be rolled over more easily (and thus more often) the Maximum Zone TTL of your zone data tokey sizes can be a fractionmade smaller. But as said in the introduction of your signature validity period. Ifthis paragraph, making the TTL would be of similar order asZSKs' key sizes too small (in relation to the signature validity period, then all RRsets fetched duringKSKs' sizes) doesn't make much sense. Try to limit the validity period would be cached untildifference in size to about 100 bits. Note that nobody can see into the signature expiration time.future, and that these key sizes are only provided here as a guide. Further information can be found in  and Section 7.17.5 of  suggests. It should be noted thought that "the resolver may use the time remaining before expiration of is already considered overly optimistic about what key sizes are considered safe. One final note concerning key sizes. Larger keys will increase the signature validity periodsizes of a signed RRset as an upper bound for the TTL". As a result query load on authoritative servers would peak at signature expiration time, as this is alsothe time at whichRRSIG and DNSKEY records simultaneously expire from caches. To avoid query load peaks we suggestand will therefore increase the TTL on allchance of DNS UDP packet overflow. Also the RRs intime it takes to validate and create RRSIGs increases with larger keys, so don't needlessly double your key sizes. 3.6. Private Key Storage It is recommended that, where possible, zone toprivate keys and the zone file master copy be at leastkept and used in off-line, non-network connected, physically secure machines only. Periodically an application can be run to add authentication to a few times smaller than your signature validity period. o We suggestzone by adding RRSIG and NSEC RRs. Then the signature publication periodaugmented file can be transferred. When relying on dynamic update to manage a signed zone , be aware that at least one maximum TTL smaller thanprivate key of the signature validity period. Resigning azone shortly before the end ofwill have to reside on the signature validity period may cause simultaneous expiration of data from caches.master server. This in turn may lead to peaks inkey is only as secure as the load on authoritative servers. o We suggestamount of exposure the minimum zone TTL to be long enoughserver receives to both fetchunknown clients and verify allthe RRs insecurity of the authentication chain. A low TTLhost. Although not mandatory one could cause two problems: 1. During validation, some data may expire beforeadminister the validation is complete.DNS in the following way. The validator should be able to keep all data, untilmaster that processes the dynamic updates is completed. This applies to all RRs needed to completeunavailable from generic hosts on the chain of trust: DSs, DNSKEYs, RRSIGs, andInternet, it is not listed in the final answers i.e.NS RR set, although it's name appears in the SOA RRs MNAME field. The nameservers in the NS RR set thatare able to receive zone updates through NOTIFY, IXFR, AXFR or an out-of-band distribution mechanism. This approach is returned forknown as the initial query. 2. Frequent verification causes load on recursive nameservers. Data at delegation points, DSs, DNSKEYs and RRSIGs benefit from caching."hidden master" setup. The TTL on those should be relatively long. o Slave servers will needideal situation is to be ablehave a one way information flow to fetch newly signed zones well before the RRSIGs inthe zone served bynetwork to avoid the slave server pass their signature expiration time. When a slave server is outpossibility of sync with itstampering from the network. Keeping the zone master file on-line on the network and data in a zone is signed by expired signaturessimply cycling it may be better for the slave server not to give out any answer. Normally a slave server that is not able to contact a master server forthrough an extended period will expire a zone. When that happens the zone willoff-line signer does not respond on queries.do this. The time of expiration is set inon-line version could still be tampered with if the SOA record andhost it resides on is relative to the last successful refresh betweencompromised. For maximum security, the master and the slave server. There exists no coupling between the signature expirationcopy of RRSIGs inthe zone file should be off net and the expire parameter in the SOA. If the server servesshould not be updated based on an unsecured network mediated communication. In general keeping a DNSSEC zone than it may well happen that the signatures expire well beforezone-file off-line will not be practical and the SOA expiration timer counts downmachines on which zone files are maintained will be connected to zero. It is not possiblea network. Operators are advised to take security measures to shield unauthorized access to completely prevent this from happening by tweakingthe SOA parameters. However,master copy. For dynamically updated secured zones  both the effects can be minimized wheremaster copy and the SOA expiration timeprivate key that is equal or smaller than the signature validity period. The consequence of an authoritative server not being ableused to update a zone, whilst that zone includes expired signatures, is that non-secure resolverssignatures on updated RRs will continueneed to be able to resolve data served by the particular slave servers while security aware resolvers will experience problems because of answers being marked as Bogus. We suggest theon-line. 4. Signature generation, Key Rollover and Related Policies 4.1. Time in DNSSEC Without DNSSEC all times in DNS are relative. The SOA RRs refresh, retry and expiration timer being approximately one third or one fourth oftimers are counters that are used to determine the signature validity period. It will allow problemstime elapsed after a slave server synchronized (or tried to synchronize) with transfers from thea master serverserver. The Time to be noticed beforeLive (TTL) value and the actual signature time out. We also suggest that operators of nameservers that supply secondary services develop 'watch dogs'SOA RR minimum TTL parameter  are used to spot upcomingdetermine how long a forwarder should cache data after it has been fetched from an authoritative server. By using a signature expirationsvalidity period, DNSSEC introduces the notion of an absolute time in zones they slave,the DNS. Signatures in DNSSEC have an expiration date after which the signature is marked as invalid and take appropriate action. When determiningthe value forsigned data is to be considered Bogus. 4.1.1. Time Considerations Because of the expiration parameterof signatures, one has to takeshould consider the following into account: What arefollowing: o We suggest the chances that all my secondary zones expire; How quickly can I reach an administratorMaximum Zone TTL of secondary serversyour zone data to loadbe a valid zone? All these arguments are not DNSSEC specific but may influence the choicefraction of your signature validity intervals. 4.2 Key Rollovers A DNSSEC keyperiod. 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. Section 7.1 of  suggests that "the resolver may use the time remaining before expiration of the signature validity period of a signed RRset as an upper bound for the TTL". As a result query load on authoritative servers would peak at signature expiration time, as this is also the time at which records simultaneously expire from caches. To avoid query load peaks we suggest the TTL on all the RRs in your zone to be at least a few times smaller than your signature validity period. o We suggest the publication period of a signature end at least one maximum TTL duration before the end of the signature's validity period. Re-signing a zone shortly before the end of the signature validity period may cause simultaneous expiration of data from caches. This in turn may lead to peaks in the load on authoritative servers. o We suggest the minimum zone TTL to be long enough to both fetch and verify all the RRs in the trust chain. In workshop environments it has been demonstrated  that a low TTL (under 5 to 10 minutes) caused disruptions because of the following two problems: 1. During validation, some data may expire before the validation is complete. The validator should be able to keep all data, until is completed. This applies to all RRs needed to complete the chain of trust: DSs, DNSKEYs, RRSIGs, and the final answers i.e. the RRset 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. o Slave servers will need to be able to fetch newly signed zones well before the RRSIGs in the zone served by the slave server pass their signature expiration time. When a slave server is out of sync with its master and data in a zone is signed by expired signatures it may be better for the slave server not to give out any answer. Normally a slave server that is not able to contact a master server for an extended period will expire a zone. When that happens the server will respond differently to queries for that zone. Some servers issues SERVFAIL while others turn off the 'AA' bit in the answers. The time of expiration is set in the SOA record and is relative to the last successful refresh between the master and the slave server. There exists no coupling between the signature expiration of RRSIGs in the zone and the expire parameter in the SOA. If the server serves a DNSSEC zone than it may well happen that the signatures expire well before the SOA expiration timer counts down to zero. It is not possible to completely prevent this from happening by tweaking the SOA parameters. However, the effects can be minimized where the SOA expiration time is equal or shorter than the signature validity period. The consequence of an authoritative server not being able to update a zone, whilst that zone includes expired signatures, is that non-secure resolvers will continue to be able to resolve data served by the particular slave servers while security aware resolvers will experience problems because of answers being marked as Bogus. We suggest the SOA expiration timer being approximately one third or one fourth of the signature validity period. It will allow problems with transfers from the master server to be noticed before the actual signature time out. We also suggest that operators of nameservers that supply secondary services develop 'watch dogs' to spot upcoming signature expirations in zones they slave, and take appropriate action. When determining the value for the expiration parameter one has to take the following into account: What are the chances that all my secondary zones expire; How quickly can I reach an administrator of secondary servers to load a valid zone? All these arguments are not DNSSEC specific but may influence the choice of your signature validity intervals. 4.2. Key Rollovers A DNSSEC key cannot be used forever (see Section 3.3). Soused forever (see Section 3.3). So key rollovers -- or supercessions, as they are sometimes called -- are a fact of life when using DNSSEC. Zone administrators who are in the process of rolling their keys have to take into account that data 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 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 Bogus. 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 Bogus. 4.2.1. Zone-signing Key Rollovers For zone-signing key rollovers there are two ways to make sure that during the rollover data still cached can be verified with the new key rollovers --sets or supercessions, as they are sometimes called --newly generated signatures can be verified with the keys still in caches. One schema, described in Section 184.108.40.206, uses double signatures; the other uses key pre-publication (Section 220.127.116.11). The pros, cons and recommendations are described in Section 18.104.22.168. 22.214.171.124. Pre-publish Key Rollover This section shows how to perform a factZSK rollover without the need to sign all the data in a zone twice - the so-called "pre-publish rollover".This method has advantages in the case of a key compromise. If the old key is compromised, the new key has already been 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. initial new DNSKEY new RRSIGs DNSKEY removal SOA0 SOA1 SOA2 SOA3 RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2) RRSIG11(SOA3) 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) initial: Initial version of the zone: DNSKEY 1 is the key-signing key. DNSKEY 10 is used to sign all the data of the zone, the zone-signing key. new DNSKEY: DNSKEY 11 is introduced into the key set. Note that no signatures are generated with this key yet, but this does not secure against brute force attacks on the public key. The minimum duration of life when using DNSSEC. Zone administrators who are inthis pre-roll phase is the processtime it takes for the data to propagate to the authoritative servers plus TTL value of rolling their keys havethe key set. new RRSIGs: At the "new RRSIGs" stage (SOA serial 2) DNSKEY 11 is used to take into account thatsign the data publishedin previous versions of theirthe zone still livesexclusively (i.e. all the signatures from DNSKEY 10 are removed from the zone). DNSKEY 10 remains published in caches. When deploying DNSSEC, this becomes an important consideration; ignoringthe key set. This way data that may be inwas loaded into caches may lead to loss of service for clients. The most pressing examplefrom version 1 of this is whenthe zone material signedcan still be verified with an oldkey sets fetched from version 2 of the zone. The minimum time that the key set including DNSKEY 10 is to be published is being validated by a resolver which does not havethe oldtime that it takes for zone key cached. Ifdata from the previous version of the zone to expire from old key is no longer present incaches i.e. the current zone,time it takes for this validation fails, marking the data Bogus. Alternatively, an attempt could be madezone to validatepropagate to all authoritative servers plus the Maximum Zone TTL value of any of the data whichin the previous version of the zone. DNSKEY removal: DNSKEY 10 is removed from the zone. The key set, now only containing DNSKEY 1 and DNSKEY 11 is signedre-signed with a newthe DNSKEY 1. The above scheme can be simplified by always publishing the "future" key against an oldimmediately after the rollover. The scheme would look as follows (we show two rollovers); the future key that livesis introduced in "new DNSKEY" as DNSKEY 12 and again a local cache, also resultingnewer one, numbered 13, in data being marked Bogus. 4.2.1 Zone-signing Key Rollovers For zone-signing key rollovers there are two ways to make sure"new DNSKEY (II)": initial new RRSIGs new DNSKEY SOA0 SOA2 SOA3 RRSIG10(SOA0) RRSIG11(SOA2) RRSIG11(SOA3) DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY10 DNSKEY10 DNSKEY11 DNSKEY11 DNSKEY11 DNSKEY12 RRSIG1(DNSKEY) RRSIG1 (DNSKEY) RRSIG1(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY) new RRSIGs (II) new DNSKEY (II) SOA4 SOA5 RRSIG12(SOA4) RRSIG12(SOA5) DNSKEY1 DNSKEY1 DNSKEY11 DNSKEY12 DNSKEY12 DNSKEY13 RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG12(DNSKEY) RRSIG12(DNSKEY) Note that duringthe rollover data still cached can be verified withkey introduced in the new"new DNSKEY" phase is not used for production yet; the private key sets or newly generated signaturescan thus be verified with the keys still in caches. One schema, describedstored in Section 126.96.36.199, uses double signatures; the other uses key pre-publication (Section 188.8.131.52). The pros, consa physically secure manner and recommendations are described in Section 184.108.40.206. 220.127.116.11 Pre-publish key setdoes not need to be 'fetched' every time a zone needs to be signed. 18.104.22.168. Double Signature Zone-signing Key Rollover This section shows how to perform a ZSK key rollover without the need to sign allusing the data in adouble zone twice - the so-called "pre-publish rollover".This method has advantages in the case of a key compromise. Ifdata signature scheme, aptly named "double sig rollover". During the old key is compromised,"new DNSKEY" stage the new key has already been distributed inversion of the DNS. Thezone administrator is then ablefile will need to quickly switchpropagate to the new keyall authoritative servers and remove the compromised key fromthe zone. Another major advantage isdata 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 foundexists in Appendix B. normal pre-roll roll after(distant) caches will need to expire, requiring at least the maximum Zone TTL. initial new DNSKEY DNSKEY removal SOA0 SOA1 SOA2 SOA3RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2) RRSIG11(SOA3) DNSKEY1RRSIG11(SOA1) DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY10 DNSKEY10 DNSKEY10DNSKEY11 DNSKEY11 DNSKEY11 RRSIG1 (DNSKEY) RRSIG1 (DNSKEY)RRSIG1(DNSKEY) RRSIG1 (DNSKEY)RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY) normal:initial: Initial Version 0of the zone: DNSKEY 1 is the key-signing key. DNSKEY 10 is used to sign all the data of the zone, the zone- signing key. pre-roll: DNSKEY 11 is introduced into the key set. Note that no signatures are generated with this key yet, but this does not secure against brute force attacks on the publiczone-signing 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 of the key set. This equates to two times the Maximum Zone TTL. roll:new DNSKEY: At the rollover"New DNSKEY" stage (SOA serial 2)1) DNSKEY 11 is used to sign the data inintroduced into the zone exclusively (i.e.key set and all the signatures from DNSKEY 10 are removed from the zone). DNSKEY 10 remains published in the key set. This waydata that was loaded into caches from version 1 ofin the zone can still be verifiedis signed with key sets fetched from version 2 of the zone. The minimum time that the key set includingDNSKEY 10 isand DNSKEY 11. The rollover period will need to be published is the time that it takes for zoneexist until all data from the previousversion 0 of the zone to expirehas expired from old caches i.e. the time it takes for this zone to propagate to all authoritative servers plusremote caches. This will take at least the Maximummaximum Zone TTL value of anyof the data in the previousversion 0 of the zone. after:DNSKEY removal: DNSKEY 10 is removed from the zone. All the signatures from DNSKEY 10 are removed from the zone. The key set, now only containing DNSKEY 1 and DNSKEY 1111, is resignedre-signed with theDNSKEY 1. At every instance, RRSIGs from the previous version of the zone can be verified with the DNSKEY RRset from the current version and the other way around. The above schemedata from the current version can be simplified by always publishingverified with the "future" key immediately afterdata from the rollover.previous version of the zone. The scheme would look as follows (we show two rollovers);duration of the future key is introduced in "after" as DNSKEY 12"new KEY" phase and again a newer one, numbered 13,the period between rollovers should be at least the "Maximum Zone TTL". Making sure that the "new DNSKEY" phase lasts until the signature expiration time of the data in "2nd after": normal roll after SOA0 SOA2 SOA3 RRSIG10(SOA0) RRSIG11(SOA2) RRSIG11(SOA3) DNSKEY1 DNSKEY1 DNSKEY1 DNSKEY10 DNSKEY10 DNSKEY11 DNSKEY11 DNSKEY11 DNSKEY12 RRSIG1(DNSKEY) RRSIG1 (DNSKEY) RRSIG1(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY) 2nd roll 2nd after SOA4 SOA5 RRSIG12(SOA4) RRSIG12(SOA5) DNSKEY1 DNSKEY1 DNSKEY11 DNSKEY12 DNSKEY12 DNSKEY13 RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG12(DNSKEY) RRSIG12(DNSKEY)version 0 of the zone is recommended. This way all caches are cleared of the old signatures. However, this date could be considerably longer than the Maximum Zone TTL, making the rollover a lengthy procedure. Note that in this example we assumed that the keyzone was not modified during the rollover. New data can be introduced afterin the rolloverzone as long as it is signed with both keys. 22.214.171.124. Pros and Cons of the Schemes Pre-publish-key set rollover: This rollover does not used for production yet;involve signing the privatezone data twice. Instead, before the actual rollover, the new key can thus be storedis published in a physically secure mannerthe key set and does not need to be 'fetched' every time athus available for cryptanalysis attacks. A small disadvantage is that this process requires four steps. Also the pre-publish scheme involves more parental work when used for KSK rollovers as explained in Section 4.2.3. Double signature rollover: The drawback of this signing scheme is that during the rollover the number of signatures in your zone needs todoubles, this may be signed. 126.96.36.199 Double Signature Zone-signingprohibitive if you have very big zones. An advantage is that it only requires three steps. 4.2.2. Key-signing Key Rollover This section shows how to performRollovers For the rollover of a ZSKkey-signing key rollover usingthe double zone data signature scheme, aptly named "double sig rollover". Duringsame considerations as for the rollover stage the new versionof the zone file will need to propagatea zone-signing key apply. However we can use a double signature scheme to all authoritative servers and the dataguarantee that existsold data (only the apex key set) in (distant)caches will need to expire, requiring at leastcan be verified with a new key set and vice versa. Since only the maximum Zone TTL. normal roll afterkey set is signed with a KSK, zone size considerations do not apply. initial new DNSKEY DS change DNSKEY removal Parent: SOA0 --------> SOA3 --------> RRSIGpar(SOA0) --------> RRSIGpar(SOA3) --------> DS1 --------> DS2 --------> RRSIGpar(DS) --------> RRSIGpar(DS) --------> Child: SOA0 SOA1 --------> SOA2 RRSIG10(SOA0) RRSIG10(SOA1) RRSIG11(SOA2) RRSIG11(SOA1) DNSKEY1--------> RRSIG10(SOA2) DS1 --------> --------> DNSKEY1 DNSKEY1 --------> DNSKEY2 DNSKEY2 --------> DNSKEY10 DNSKEY10 DNSKEY11 DNSKEY11 RRSIG1(DNSKEY) RRSIG1(DNSKEY) RRSIG1(DNSKEY)--------> DNSKEY10 RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) --------> RRSIG2 (DNSKEY) RRSIG2 (DNSKEY) --------> RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG11(DNSKEY) RRSIG11(DNSKEY) normal: Version 0--------> RRSIG10(DNSKEY) initial: Initial version of the zone: DNSKEY 1 is the key-signing key. DNSKEY 10 is usedzone. The parental DS points to sign all the data of the zone, the zone- signing key. roll: AtDNSKEY1. Before the rollover stage (SOA serial 1) DNSKEY 11 is introduced into the key set and all the data instarts the zone is signed with DNSKEY 10 and DNSKEY 11. The rollover periodchild will needhave to exist until all data from version 0 of the zone has expired from remote caches. This will take at leastverify what the maximum ZoneTTL of version 0is of the zone. after: DNSKEY 10DS RR that points to DNSKEY1 - it is removed fromneeded during the zone. Allrollover and we refer to the signatures from DNSKEY 10 are removed fromvalue as TTL_DS. new DNSKEY: During the zone."new DNSKEY" phase the zone administrator generates a second KSK, DNSKEY2. The key set, now only containing DNSKEY 11,is resigned with DNSKEY 1. At every instance, RRSIGs from the previous version of the zone can be verified with the DNSKEY RRset fromprovided to the current versionparent and the other way around. The data from the current version can be verified with the data from the previous version of the zone. The duration ofchild will have to wait until a new DS RR has been generated that points to DNSKEY2. After that DS RR has been published on all servers authoritative for the rollover phase andparent's zone, the period between rollovers should bezone administrator has to wait at least the "Maximum Zone TTL". MakingTTL_DS to make sure that the rollover phase lasts until the signature expiration time ofold DS RR has expired from caches. DS change: The parent replaces DS1 with DS2. DNSKEY removal: DNSKEY1 has been removed. The scenario above puts the data in version 0responsibility for maintaining a valid chain of trust with the zonechild. It also is recommended. This way all caches are cleared of the old signatures. However, this date could be considerably longer than the Maximum Zone TTL, makingbased on the rollover a lengthy procedure. Note that in this example we assumedpremises that the zone was not modified duringparent only has one DS RR (per algorithm) per zone. An alternative mechanism has been considered. Using an established trust relation, the rollover. New datainteraction can be introduced in the zone as long as it is signed with both keys. 188.8.131.52 Prosperformed in-band, and Consthe removal of the Schemes Pre-publish-key set rollover: This rollover does not involve signingkeys by the zone data twice. Instead, beforechild can possibly be signaled by the actual rollover,parent. In this mechanism there are periods where there are two DS RRs at the new key is published inparent. Since at the key set and thus available for cryptanalysis attacks. A small disadvantage is that this process requires four steps. Alsomoment of writing the pre-publish scheme involves more parental work when usedprotocol for KSK rollovers as explained in Section 4.2. Double signature rollover: The drawbackthis interaction has not been developed, further discussion is out of scope for this signing scheme isdocument. 4.2.3. Difference Between ZSK and KSK Rollovers Note that during the rollover the number of signaturesKSK rollovers and ZSK rollovers are different in your zone doubles, this may be prohibitive if you have very big zones. An advantage isthe sense that it onlya KSK rollover requires three steps. 4.2.2 Key-signing Key Rollovers Forinteraction with the rolloverparent (and possibly replacing of a key-signing keytrust anchors) and the same considerations asensuing delay while waiting for theit. A zone-key rollover of a zone-signing key apply. However wecan use abe handled in two different ways: pre-publish (Section Section 184.108.40.206) and double signature scheme(Section Section 220.127.116.11). As the KSK is used to guarantee that old data (onlyvalidate the apex key set) in caches can be verified with a newkey set and vice versa. Since onlybecause the key setKSK is signed with a KSK, zone size considerations donot apply. normal roll after SOA0 SOA1 SOA2 RRSIG10(SOA0) RRSIG10(SOA1) RRSIG10(SOA2) DNSKEY1 DNSKEY1 DNSKEY2 DNSKEY2 DNSKEY10 DNSKEY10 DNSKEY10 RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG2(DNSKEY) RRSIG2 (DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) normal: Version 0changed during a ZSK rollover, a cache is able to validate the new key set of the zone. The pre-publish method would work for a KSK rollover. The record that are to be pre-published are the parental DS points to DNSKEY1. BeforeRRs. The pre-publish method has some drawbacks. We first describe the rollover startsscheme and then indicate these drawbacks. initial new DS new DNSKEY DS/DNSKEY removal Parent: SOA0 SOA1 --------> SOA3 RRSIGpar(SOA0) RRSIGpar(SOA1) --------> RRSIGpar(SOA3) DS1 DS1 --------> DS2 DS2 --------> RRSIGpar(DS) RRSIGpar(DS) --------> RRSIGpar(DS) Child: SOA0 --------> SOA1 SOA1 RRSIG10(SOA0) --------> RRSIG10(SOA1) RRSIG10(SOA1) --------> DNSKEY1 --------> DNSKEY2 DNSKEY2 --------> DNSKEY10 --------> DNSKEY10 DNSKEY10 RRSIG1 (DNSKEY) --------> RRSIG2(DNSKEY) RRSIG2 (DNSKEY) RRSIG10(DNSKEY) --------> RRSIG10(DNSKEY) RRSIG10(DNSKEY) When the child will have to verify what the TTL is of the DS RR that pointszone wants to DNSKEY1 -roll it is needed during the rollover and we refer tonotifies the value as TTL_DS. roll: Duringparent during the rollover"new DS" phase and submits the zone administrator generates a second KSK, DNSKEY2. Thenew key is provided(or the corresponding DS) to the parent. The parent publishes DS1 and the child will haveDS2, pointing to wait until aDNSKEY1 and DNSKEY2 respectively. During the rollover ("new DNSKEY" phase), which can take place as soon as the new DS RR has been generated that points to DNSKEY2. After that DS RR has been published on all servers authoritative for the parent's zone,set propagated through the zone administrator has to wait at least TTL_DS to make sure thatDNS, the old DS RR has expired from caches. after:child replaces DNSKEY1 has been removed. The scenario above puts the responsibility for maintaining a valid chain of trustwith the child. It also is based on the premisesDNSKEY2. Immediately after ("DS/DNSKEY removal" phase) that it can notify the parent only has one DS RR (per algorithm) per zone. An alternative mechanism has been considered. Using an established trust relation,that the interactionold DS record can be performed in-band, and the removaldeleted. The drawbacks of this scheme are that during the keys by"new DS" phase the child can possibly be signaled byparent cannot verify the parent. In this mechanism there are periods where there are two DS RRs atmatch between the parent. Since atDS2 RR and DNSKEY2 using the moment of writingDNS -- as DNSKEY2 is not yet published. Besides, we introduce a "security lame" key (See Section 4.4.3). Finally the protocol for thischild-parent interaction has not been developed further discussion is outconsists of scope for this document. 4.2.3 Difference Between ZSK and KSKtwo steps. The "double signature" method only needs one interaction. 4.2.4. Automated Key Rollovers Note that KSK rollovers andAs keys must be renewed periodically, there is some motivation to automate the rollover process. Consider that: o ZSK rollovers are different.easy to automate as only the child zone is involved. o A zone-keyKSK rollover canneeds interaction between the parent and child. Data exchange is needed to provide the new keys to the parent, consequently, this data must be handledauthenticated and integrity must be guaranteed in two different ways: pre-publish (Section Section 18.104.22.168)order to avoid attacks on the rollover. o All time and double signature (SectionTTL considerations presented in Section 22.214.171.124). As4.2 apply to an automated rollover. 4.3. 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. When the KSKprivate material of one of your keys is compromised it can be used to validatefor as long as a valid trust chain exists. An trust chain remains intact for: o as long as a signature over the compromised key set and becausein the KSKtrust chain is not changed duringvalid, o as long as a ZSK rollover,parental DS RR (and signature) points to the compromised key, o as long as the key is anchored in a resolver and is used as a cachestarting point for validation. (This is able to validategenerally the newhardest to update.) While an trust chain to your compromised key setexists, your name-space is vulnerable to abuse by anyone who has obtained illegitimate possession of the zone. The pre-publish method would work for a KSK rollover. The record that arekey. Zone operators have to be pre-published aremake a trade off if the parental DS RRs. The pre-publish method has some drawbacks. We first describeabuse of the rollover scheme and then indicate these drawbacks. normal pre-roll roll after Parent: SOA0 SOA1 SOA2 SOA3 RRSIGpar(SOA0) RRSIGpar(SOA1) RRSIGpar(SOA2) RRSIGpar(SOA3) DS1 DS1 DS1 DS2 DS2 DS2 RRSIGpar(DS) RRSIGpar(DS) RRSIGpar(DS) RRSIGpar(DS) Child: SOA0 SOA0 SOA1 SOA1 RRSIG10(SOA0) RRSIG10(SOA0) RRSIG10(SOA1) RRSIG10(SOA1) DNSKEY1 DNSKEY1 DNSKEY2 DNSKEY2 DNSKEY10 DNSKEY10 DNSKEY10 DNSKEY10 RRSIG1 (DNSKEY) RRSIG1 (DNSKEY) RRSIG2(DNSKEY) RRSIG2 (DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) RRSIG10(DNSKEY) Whencompromised key is worse than having data in caches that cannot be validated. If the childzone wantsoperator chooses to roll it notifies the parent duringbreak the pre-roll phase and submitstrust chain to the newcompromised key, data in caches signed with this key tocannot be validated. However, if the parent. The parent publishes DS1 and DS2, pointingzone administrator chooses to DNSKEY1 and DNSKEY2 respectively. Duringtake the rollover, whichpath of a regular roll-over, the malicious key holder can take placespoof data so that it appears to be valid. 4.3.1. KSK Compromise A zone containing a DNSKEY RRset with a compromised KSK is vulnerable as soonlong as the newcompromised KSK is configured as trust anchor or a parental DS points to it. A compromised KSK can be used to sign the key set propagated throughof an attackers zone. That zone could be used to poison the DNS,DNS. Therefore when the child replaces DNSKEY1 with DNSKEY2. Immediately after that it can notifyKSK has been compromised, the parent thattrust anchor, or the old DS record canparental DS, should be deleted. The drawbacks of these scheme are that duringreplaced as soon as possible. It is local policy whether to break the pre-roll phasetrust chain during the parent cannot verifyemergency rollover. The trust chain would be broken when the match betweencompromised KSK is removed from the DS RR and DNSKEY2 usingchild's zone while the DNS. Besides, we introduceparent still has a "security lame"DS record Section 4.4.3. Finallypointing to the child-parent interaction consists of two steps. The "double signature" method only needs one interaction. 4.2.4 Automated Key Rollovers As keys must be renewed periodically,compromised KSK. (The assumption is that there is some motivation to automateonly one DS at the rollover process. Consider that: o ZSK rolloversparent if there are easy to automate as onlymultiple DSs this does not apply -- however the local zonechain of trust of this particular key is involved. o A KSK rollover needs interaction betweenbroken). Note that an attacker's zone still uses the parentcompromised KSK and child. Data exchange is needed to providethe new keys topresence of a parental DS would cause the parent, consequently, thisdata must be authenticated and integrity must be guaranteedin order to avoid attacks onthe rollover. o All time and TTL considerations presented in Section 4.2 applythis zone to an automated rollover. 4.3 Planning for Emergency Key Rollover This section deals with preparation for a possibleappear as valid. Removing the compromised key compromise. Our advice iswould cause the attacker's zone to haveappear as valid and the child's zone as bogus. Therefore we advise not to remove the KSK before the parent has a documented procedure ready for whenDS to a key compromise is suspected or confirmed. Whennew KSK in place. 126.96.36.199. Keeping the private materialChain of oneTrust Intact If we follow this advice the timing of your keysthe replacement of the KSK is somewhat critical. The goal is to remove the compromised it can be used for as long as a valid authentication chain exists. An authentication chain remains intact for: oKSK as longsoon as athe new DS RR is available at the parent. And also make sure that the signature made with a new KSK over the compromisedkey set with the compromised KSK in it expires just after the authentication chain is valid, o as long as a parentalnew DS RR (and signature) points toappears at the compromised key, o as long asparent. Thus removing the key is anchoredold cruft in a resolver andone swoop. The procedure is usedas follows: 1. Introduce a starting point for validation. (This is generallynew KSK into the hardest to update.) While an authentication chain to your compromisedkey exists, your name-space is vulnerable to abuse by anyone who has obtained illegitimate possession ofset, keep the key.Zone operators have to make a trade off ifcompromised KSK in the abuse ofkey set. 2. Sign the compromisedkey set, with a short validity interval. The validate interval should expire shortly after the DS is worse than having dataexpected to appear in caches that cannot be validated. Ifthe zone operator chooses to breakparent and the authentication chain toold DSs have expired from caches. 3. Upload the compromised key, data in caches signed withDS for this new key cannot be validated. However, if the zone administrator choosesto takethe pathparent. 4. Follow the procedure of athe regular roll- over,KSK rollover: Wait for the malicious key holder can spoof data so that it appears to be valid. Note that this kind of attack is more likelyDS to occurappear in a localized partthe authoritative servers and then wait as long as the TTL of the network topology i.e. downstream from whereold DS RRs. If necessary re-sign the spoof takes place. 4.3.1 KSK CompromiseDNSKEY RRset and modify/extend the expiration time. 5. When the KSKnew DS has beenappeared, remove the compromised DNSKEY RR from the zone and re-sign the parent must be notified as soon as possible using secure means. Thekey set using your "normal" validity interval. An additional danger of a key compromise is that the zone should be resigned as soon as possible. Care mustcompromised key could be takenused to not break the authentication chain. The local zone can only be resigned with the new KSK after the parent's zone has created and reloaded its zone withfacilitate a legitimate DNSKEY/DS rollover and/or nameserver changes at the DS created fromparent. When that happens the new KSK. Before this update takes place it woulddomain may be best to drop the security statusin dispute. An authenticated out of band and secure notify mechanism to contact a zone all together: theparent removesis needed in this case. 188.8.131.52. Breaking the DSChain of Trust There are two methods to break the chain of trust. The first method causes the child atzone to appear as 'bogus' to validating resolvers. The other causes the nextthe child zone to appear as 'insecure'. These are described below. The child zone update. After thatreplaces the child can be made secure again. An additional danger ofcurrent KSK with a new one and resigns the key compromise is thatset. Next it sends the compromisedDS of the new key can be usedto facilitate a legitimate DNSKEY/DS and/or nameserver rollover atthe parent. When that happensOnly after the domain can beparent has placed the new DS in dispute.the zone, the child's chain of trust is repaired. An authenticated outalternative method of band and secure notify mechanism to contact a parentbreaking the chain of trust is needed in this case. 4.3.2by removing the DS RRs from the parent zone altogether. As a result the child zone would become insecure. 4.3.2. ZSK Compromise Primarily because there is no parental interaction required when a ZSK is compromised, the situation is less severe than with witha KSK compromise. The zone must still be resignedre-signed 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. However, one has to take into account that just as with a normal rollover the immediate disappearance fromof the old compromised key may lead to verification problems. The pre- publication scheme as discussed above (Section Section 184.108.40.206) minimizes such problems. 220.127.116.11.3. Compromises of Keys Anchored in Resolvers A key can also be pre-configured in resolvers. For instance, if DNSSEC is successfully deployed the root key may be pre-configured in most security aware resolvers. If trust-anchor keys are compromised, the resolvers using these keys 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. End-users faced with the task of updating an anchored key should always validate the new key. New keys should be authenticated out of the DNS, for example, looking them up on an SSL secured announcement website. 4.44.4. Parental Policies 18.104.22.168.1. Initial Key Exchanges and Parental Policies Considerations The initial key exchange is always subject to the policies set by the parent (or its registry).parent. 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. I.e. there is no implicit need in DNSSEC to make the authentication process stronger than it was in DNS. 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 chances of user error. A parental DNSKEY download tool can make use of the SEP bit  to select the proper key from a DNSSEC key set; thereby reducing the chance that the wrong DNSKEY is sent. It can validate the self-signature over a key; thereby verifying the ownership of the private key material. Fetching the DNSKEY from the DNS ensures that the chain of trust remains intact once the parent publishes the DS RR indicating the child is secure. Note: the off-band verification is still needed when the key-material is fetched via the DNS. The parent can never be sure whether the DNSKEY RRs have been spoofed or not. 22.214.171.124.2. Storing Keys or Hashes? When designing a registry system one should consider which of the DNSKEYs and/or the corresponding DSs to store. Since a child zone might wish to have a DS published using a message digest algorithm not yet understood by the registry, the registry can't count on being able to generate the DS record from a raw DNSKEY. Thus, we recommend that registry systemsystems at least support storing DS records. It may also be useful to store DNSKEYs, since having them may help during troubleshooting and, so long as the child's chosen message digest is supported, the overhead of generating DS records from them is minimal. Having an out-of-band mechanism, such as a Whois database,registry directory (e.g. Whois), to find out which keys are used to generate DS Resource Records for specific owners and/or zones may also help with troubleshooting. The storage considerations also relate to the design of the customer interface and the method by which data is transferedtransferred between registrant and registry; Will the child zone owneradministrator be able to upload DS RRs with unknown hash algorithms or does the interface only allowsallow DNSKEYs? In the registry-registrar model one can use the DNSSEC EPP protocol extensions  which allows transfer of DS RRs and optionally DNSKEY RRs. 126.96.36.199.3. Security Lameness Security Lameness is defined as what happens when a parent has a DS RR pointing to a non-existing DNSKEY RR. During key exchangeWhen this happens the child's zone may be marked as "Bogus" by verifying DNS clients. As part of a comprehensive delegation check the parent should make surecould, at key exchange time, verify that the child's key is actually configured in the DNS before publishingDNS. However if a DS RR in its zone. Failureparent does not understand the hashing algorithm used by child the parental checks are limited to do so could causeonly comparing the child's zone being marked as Bogus.key id. Child zones should be very careful removing DNSKEY material, specifically SEP keys, for which a DS RR exists. Once a zone is "security lame", a fix (e.g. removing a DS RR) will take time to propagate through the DNS. 188.8.131.52.4. DS Signature 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(s). A signature validity period that is too short introduces the possibility that a zone is marked Bogus 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 operator unavailability during weekends shows the need for DS signature validity periods longer than 2 days. We recommend thean absolute minimum for a DS signature validity period of a few days. The maximum signature validity period of the DS record depends on how long child zones are willing to be vulnerable after a key compromise. Other considerations, such as how oftenOn the zone is (re)signed can also be taken into account. We consider aother hand shortening the DS signature validity period of around one weekinterval increases the operational risk for the parent. Therefore the parent may have policy to beuse a goodsignature validity interval that is considerably longer than the child would hope for. A compromise between the operational constraints of the parent and minimizing damage for the child.child may result in a DS signature validity period somewhere between the order of a week to order of months. In addition to the signature validity period, which sets a lower bound on the amountnumber of times the zone owner will need to sign the zone data and which sets an upper bound to the time a child is vulnerable after key compromise, there is the TTL value on the DS RRs. By loweringShortening the TTL,TTL means that the authoritative servers will see more queries,queries. But on the other handhand, a lowshort TTL lowers the persistence of DS RRSets in caches thereby increases the speed with which newupdated DS RRsRRSets propagate through the DNS. As argued in Section 4.1.1, the TTL should be a fraction of the signature validity period.5. IANA Considerations This overview document introduces no new IANA considerations. 6. Security Considerations DNSSEC adds data integrity to the DNS. This document tries to assess the operational considerations to maintain a stable and secure DNSSEC service. Not taking into account the 'data propagation' properties in the DNS will cause validation failures and may make secured zones unavailable to security aware resolvers. 6.7. Acknowledgments Most of the ideas in this draft were the result of collective efforts during workshops, discussions and try outs. At the risk of forgetting individuals who were the original contributors of the ideas we would like to acknowledge people who were actively involved in the compilation of this document. In random order: Rip Loomis, Olafur Gudmundsson, Wesley Griffin, Michael Richardson, Scott Rose, Rick van Rein, Tim McGinnis, Gilles Guette Olivier Courtay, Sam Weiler, Jelte Jansen andJansen, Niall O'Reilly.O'Reilly, Holger Zuleger, Ed Lewis, Hilarie Orman and Peter Koch. Some material in this document has been shamelessly copied from RFC2541  by Donald Eastlake. Mike StJohns designed the key exchange between parent and child mentioned in the last paragraph of Section 4.2.2 Section 4.2.4 was supplied by G. Guette and O. Courtay. Emma Bretherick, Adrian Bedford and Lindy Foster corrected many of the spelling and style issues. Kolkman and Gieben take the blame for introducing all miscakes(SIC). 7.Kolkman was employed by the RIPE NCC while working on this document. 8. References 7.18.1. Normative References  Kolkman, O., Schlyter, J., and E. Lewis, "Domain Name System KEY (DNSKEY) Resource Record (RR) Secure Entry Point (SEP) Flag", RFC 3757, May 2004.  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005. 7.28.2. Informative References  Eastlake, D., Crocker, S., and J. Schiller, "Randomness Recommendations for Security", RFC 1750, December 1994.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Eastlake, D., "Secure Domain Name System Dynamic Update", RFC 2137, April 1997.  Andrews, M., "Negative Caching of DNS Queries (DNS NCACHE)", RFC 2308, March 1998.  Eastlake, D., "DNS Security Operational Considerations", RFC 2541, March 1999.  Gudmundsson, O., "Delegation Signer (DS) Resource Record (RR)", RFC 3658, December 2003.  Orman, H. and P. Hoffman, "Determining Strengths For Public Keys Used For Exchanging Symmetric Keys", BCP 86, RFC 3766, April 2004.  Hollenbeck, S., "Domain Name System (DNS) Security Extensions Mapping for the Extensible Provisioning Protocol (EPP)", draft-hollenbeck-epp-secdns-07 (work in progress), March 2005.  Lenstra, A. and E. Verheul, "Selecting Cryptographic Key Sizes", The Journal of Cryptology 14 (255-293), 2001.  Schneier, B., "Applied Cryptography: Protocols, Algorithms, and Source Code in C", 1996. Authors' Addresses Olaf M. Kolkman RIPE NCC Singel 256 Amsterdam 1016 AB The Netherlands Phone: +31 20 535 4444 Email: firstname.lastname@example.org URI: http://www.ripe.net/ Miek Gieben NLnet Labs Kruislaan 419 Amsterdam 1098 VA The Netherlands Email: email@example.com URI: http://www.nlnetlabs.nl Rose, S., "NIST DNSSEC workshop notes", June 2001. 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 given a more elaborate explanation of the meaning. Note that these explanations should not be seen as authoritative. Anchored Key: A DNSKEY configured in resolvers around the globe. This key is hard to update, hence the term anchored. Bogus: Also see Section 5 of . An RRset in DNSSEC is marked "Bogus" when a signature of a RRset does not validate against a DNSKEY. Key-Signing Key or KSK: A Key-Signing Key (KSK) is a key that is used exclusively for signing the apex key set. The fact that a key is a KSK is only relevant to the signing tool. Key size: The term 'key size' can be substituted by 'modulus size' throughout the document. It is mathematical more correct to use modulus size, but as this is a document directed at operators we feel more at ease with the term key size. Private and Public Keys: DNSSEC secures the DNS through the use of public key cryptography. Public key cryptography is based on the existence of two (mathematical related) keys, a public key and a private key. The public keys are published in the DNS by use of the DNSKEY Resource Record (DNSKEY RR). Private keys should remain private. Key Rollover: A key rollover (also called key supercession in some environments) is the act of replacing one key pair by another at the end of a key effectivity period. Secure Entry Point key or SEP Key: A KSK that has a parental DS record pointing to it. Note: thisit or is configured as a trust anchor. Although not required nor enforced inby the protocol we recommend that the protocol. ASEP Key with no parental DSflag  is security lame.set on these keys. Singing the Zone File: The term used for the event where an administrator joyfully signs its zone file while producing melodic sound patterns. 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. Zone-Signing Key or 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. Zone Administrator: The 'role' that is responsible for signing a zone and publishing it on the primary authoritative server. 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 caches here follows the "HOWTO". Step 0: The preparation: Create two keys and publish both in your key set. 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. The protocol does not provide for attributes to mark a key as active or published. This is something you have to do on your own, through the use of a notebook or key management tool. Step 1: Determine expiration: At the beginning of the rollover make a note of the highest expiration time of signatures in your zone file created with the current key marked as "active". Wait until the expiration time marked in Step 1 has passed 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,DNSKEYx, where x is a number,number or an identifier, 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","A1, A2", specifying the RRset containing two "A" records. This could again be abbreviated to just "A". Signature notation: Signatures are denoted as RRSIGx(RRset), which means that RRset is signed with DNSKEYx. Zone representation: Using the above notation we have simplified the representation of a signed zone by leaving out all unnecessary details such as the names and by representing all data by "SOAx" SOA representation: SOA'sSOAs are represented as SOAx, where x is the serial number. Using this notation the following signed zone: example.net. 60086400 IN SOA ns.example.net. bert.example.net. ( 10 ; serial 45086400 ; refresh (7 minutes 30 seconds) 600(1 day) 7200 ; retry (10 minutes) 345600(2 hours) 3600000 ; expire (4 days) 300(1000 hours) 172800 ) ; minimum (5 minutes) ) 600(2 days) 86400 RRSIG SOA 5 2 60086400 20130522213204 ( 20130422213204 14 example.net. cmL62SI6iAX46xGNQAdQ... ) 60086400 NS a.iana-servers.net. 60086400 NS b.iana-servers.net. 60086400 RRSIG NS 5 2 60086400 20130507213204 ( 20130407213204 14 example.net. SO5epiJei19AjXoUpFnQ ... ) 360086400 DNSKEY 256 3 5 ( EtRB9MP5/AvOuVO0I8XDxy0... ) ; key id = 14 360086400 DNSKEY 256257 3 5 ( gsPW/Yy19GzYIY+Gnr8HABU... ) ; key id = 15 360086400 RRSIG DNSKEY 5 2 360086400 20130522213204 ( 20130422213204 14 example.net. J4zCe8QX4tXVGjV4e1r9... ) 360086400 RRSIG DNSKEY 5 2 360086400 20130522213204 ( 20130422213204 15 example.net. keVDCOpsSeDReyV6O... ) 60086400 RRSIG NSEC 5 2 60086400 20130507213204 ( 20130407213204 14 example.net. obj3HEp1GjnmhRjX... ) a.example.net. 60086400 IN TXT "A label" 60086400 RRSIG TXT 5 3 60086400 20130507213204 ( 20130407213204 14 example.net. IkDMlRdYLmXH7QJnuF3v... ) 60086400 NSEC b.example.com. TXT RRSIG NSEC 60086400 RRSIG NSEC 5 3 60086400 20130507213204 ( 20130407213204 14 example.net. bZMjoZ3bHjnEz0nIsPMM... ) ... is reduced to the following representation: 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 document is published. $Id: draft-ietf-dnsop-dnssec-operational-practices.xml,v 184.108.40.206 2005/03/21 15:51:41 dnssec Exp $ D.1D.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. D.2D.2. draft-ietf-dnsop-dnssec-operational-practices-01 changed the definition of "Bogus" to reflect the one in the protocol draft. Bad to Bogus Style and spelling corrections KSK - SEP mapping made explicit. Updates from Sam Weiler added D.3D.3. draft-ietf-dnsop-dnssec-operational-practices-02 Style and errors corrected. Added Automatic rollover requirements from I-D.ietf-dnsop-key- rollover-requirements. D.4D.4. draft-ietf-dnsop-dnssec-operational-practices-03 Added the definition of Key effectivity period and used that term instead of Key validity period. Modified the order of the sections, based on a suggestion by Rip Loomis. Included parts from RFC2541 . Most of its ground was already covered. This document obsoletes RFC2541 . Section 3.1.2 deserves some review as it in contrast to RFC2541 does _not_ give recomendations about root-zone keys. added a paragraph to Section 4.4.4 D.5D.5. draft-ietf-dnsop-dnssec-operational-practices-04 Somewhat more details added about the pre-publish KSK rollover. Also moved that subsection down a bit. Editorial and content nits that came in during wg last call were fixed. D.6. draft-ietf-dnsop-dnssec-operational-practices-05 Applied some another set of comments that came in _after_ the the WGLC. Applied comments from Hilarie Orman and made a referece to RFC 3766. Deleted of a lot of key-length discussion and took over the recommendations from RFC 3766. Reworked all the heading of the rollover figures Authors' Addresses Olaf M. Kolkman NLnet Labs Kruislaan 419 Amsterdam 1098 VA The Netherlands Email: firstname.lastname@example.org URI: http://www.nlnetlabs.nl Miek Gieben NLnet Labs Kruislaan 419 Amsterdam 1098 VA The Netherlands Email: email@example.com URI: http://www.nlnetlabs.nl Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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