R. Moskowitz, ICSA Labs Internet Draft Document: <draft-moskowitz-hip-arch-02.txt> February 2001 Host Identity Payload Architecture 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 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. Table of Contents 1. Abstract...........................................................2 2. Conventions used in this document..................................2 3. Introduction.......................................................2 4. Background.........................................................3 5. The Host Identity..................................................4 5.1. Host Identity....................................................5 5.2. Host Identity Tag (HIT)..........................................5 5.2.1. Storing HIT in DNS.............................................6 5.3. Host Assigning Authority (HAA) field.............................6 5.4. Local Scope Identity (LSI).......................................7 5.5. Security Parameter Index (SPI)...................................7 5.6. Difference between an LSI and the SPI............................7 6. Using the Host Identity............................................8 7. Mobility via HIP...................................................8 8. HIP and NATs.......................................................9 8.1. HIP and TCP Checksum.............................................9 9. HIP Policies......................................................10 10. Benefits of HIP..................................................10 11. Security Considerations..........................................11 Moskowitz 1 Host Identity Payload Architecture February 2001 11.1. HITs used in ACLs..............................................13 11.2. Non-security Considerations....................................13 12. IANA Considerations..............................................13 13. ICANN Considerations.............................................14 14. References.......................................................14 15. Acknowledgments..................................................14 16. Author's Address.................................................15 17. Copyright Statement..............................................15 1. Abstract This memo describes the reasoning behind proposing a new namespace, the Host Identity, and a payload, between the Internetworking and Transport layers, the Host layer, to carry this identity. Herein is presented the basics of the current namespaces, strengths and weaknesses, and how a new namespace will add completeness to them. This new namespace's roles in the protocols are defined. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC-2119]. 3. Introduction The Internet has created two namespaces: Internet Protocol (IP) addresses, and Domain Name Services (DNS) names. These two namespaces have a set of features and abstractions that have powered the Internet to what it is today. They also have a number of weaknesses. Basically, since they are all we have, we try and do too much with them. Semantic overloading and functionality extensions have greatly complicated these namespaces. The Host Identity (HI) namespace fills an important gap between the IP and DNS namespaces. The HI is cryptographic in its nature; it is the public key of an asymmetric key-pair. It is assigned to each host, or technically it's networking kernel or stack. Each host will have at least one HI, which can either be public (e.g. published in DNS), or anonymous. Client systems will tend to have both public and anonymous HIs. Although the HI can be used in many authentication systems, its principle design calls out for a new protocol header (HIP)_and exchange [HIP] that will support trust between systems, enhance mobility and dynamic IP renumbering, aid in protocol translation/transition, and greatly reduce Denial Of Service (DOS) attacks. Moskowitz 2 Host Identity Payload Architecture February 2001 4. Background The Internet is built from three principle components: Computing platforms, Packet transport (i.e. internetworking) infrastructure, and Services (applications). The Internet exists to service two principle components: People and Robotic processes (silicon based people, if you will). All these components need to be named in order to interact in a scalable manner. There are two principle namespaces in use in the Internet for these components: IP numbers, and Domain Names. Email and SIP addresses are really only an extension of Domain Names. IP numbers are a confounding of two namespaces ('confounding' is a term used in statistics to discuss to metrics that were merged into one with a gain in indexing, but a loss in informational value), the name of the networking interfaces and the routing direction vector. IP numbers name networking interfaces, and typically only when the interface is connected to the network. Originally IP numbers had long-term significance. Today, the vast number of interfaces uses ephemeral and/or non-unique IP numbers. That is ever time the interface is connected to the network, it is assigned an IP number. Further the transport layers are coupled to the IP addresses. Neither can evolve separately from the other. IPng deliberations were framed by concerns of requiring a TCPng effort as well. Domain Names provide hierarchically assigned names for some computing platforms and some services. Each hierarchy is delegated from the level above; there is no anonymity in Domain Names. Email addresses provide naming for both carbon and silicon based people. Email addresses are extensions of Domain Names, only in so far as a named service is responsible for managing a person's mail. There is some anonymity in Email addresses. There are three critical deficiencies with the current namespaces. Dynamic readdressing cannot be directly managed. Anonymity is not provided in a consistent, trustable manner. And authentication for systems and datagrams is not provided. All because computing platforms are not well named with the current namespaces. A namespace for computing platforms can be used in end-to-end operations independent of the evolution of the internetworking layer and across the many internetworking layers. This could support rapid readdressing of the internetworking layer either from mobility or renumbering. If this namespace is cryptographically based, it can also provide authentication services for IPsec. If this namespace is locally created without requiring registration, it can provide anonymity. Moskowitz 3 Host Identity Payload Architecture February 2001 Such a namespace (for computing platforms) should have the following characteristics: It is applied to the IP 'kernel'. The IP kernel is the 'component' between services and the packet transport infrastructure. It should fully decouple the Internetworking layer from the higher layers. It should replace all occurrences of IP addresses within applications (like in the TCB). This may require API changes. It should not mandate any infrastructure. Deployment must come from the bottom up, in a pairwise deployment. It should be fixed length, for easy inclusion in datagrams and programming interfaces (e.g the TCB). It should be affordable when used in protocols. This is primarily a packet size issue. There is also a computational concern in affordablity. It MUST be statistically globally unique. 64 bits is inadequate (1% chance of collision in a population of 640M); thus approximately 128 bits should be used. It should have a localized abstraction so that it can be used in existing protocols and APIs. It SHOULD be locally created. This can provide anonymity at the cost of making resolvability very difficult. Sometimes it MAY contain a delegation component. This is the cost of resolvability. It SHOULD provide authentication services. This is a preferred function. It should be long lived, but replaceable at any time. This impacts access control lists; short lifetimes will tend to result in tedious list maintenance or require a namespace infrastructure for central control of access lists. This new namespace will be called the Host Identity. It will require its own protocol layer (the Host Identity Payload), between the Internetworking and Transport layers. It will be based on Public Key Cryptography to supply authentication services. Properly designed, it can deliver all of the above stated requirements. 5. The Host Identity Moskowitz 4 Host Identity Payload Architecture February 2001 The Host Identity represents a statistically globally unique name for naming any system with an IP stack. This identity is normally associated, but not limited to, an IP stack. A system can have multiple identities, some 'well known', some anonymous. A system may self assert its identity, or may use a third-party authenticator like DNSSEC, PGP, or X.509 to 'notarize' the identity assertion. DNSSEC is the MUST implement authenticator for the Host Identity. Although the Host Identity can be any name that can claim 'statistically globally unique', a public key of a 'public key' pair makes the best Host Identity. As documented in the Host Identity Payload (HIP) protocol [HIP], a public key based HI can authenticate the HIP packets and protect them for man-in-the-middle attacks. And since authenticated datagrams are MANDITORY to provide much of HIP's DOS protection, the Diffie-Hellman exchange in HIP has to be authenticated. Thus only public key HI and authenticated datagrams SHOULD be supported. The non-cryptographic forms of HI and HIP are presented to complete the theory of HI, but SHOULD NOT be implemented as they could produce worst DOS attacks than the internet has without HI. 5.1. Host Identity Host Identity adds two main features to Internet protocols. The first is a decoupling of the internetworking and transport layers. This decoupling will allow for independent evolution of the two layers. Additionally it can provide end-to-end services over multiple internetworking realms. The second feature is host authentication. If the Host Identity is a public key, this key can be used to authenticate security protocols like IPsec. The preferred structure of the Host Identity is that of a public key pair. DSA is the MUST implement algorithm for any implementation supporting public keys for the Host Identity. Any other Internet naming convention MAY be used for the Host Identity. However, these should only be used in situations of high trust - low risk. That is any place where host authentication is not needed (no risk of host spoofing) and no use of IPsec. The Host Identity is never directly used in any Internet protocol. It may be stored in various DNS or LDAP directories as identified in the HIP architecture and it is passed in the HIP payload. If the Host Identity is a public key, it SHOULD be stored in a DNS KEY RR with the protocol set to HIP. A Host Identity Tag (HIT) is used in protocols to represent the Host Identity. Another representation of the Host Identity, the Local Scope Identity (LSI) can also be used in protocols and APIs. LSI's advantage over HIT is its size; its disadvantage is its local scope. 5.2. Host Identity Tag (HIT) Moskowitz 5 Host Identity Payload Architecture February 2001 The Host Identity Tag is a 128 bit field. There are two advantages of using a hash over the actual Identity in protocols. First its fix length makes for easier protocol coding and also better manages the packet size cost of this technology. Secondly, it presents a consistent format to the protocol whatever underlying identity technology is used. When the Host Identity is a public key, HIT functions much like the SPI does in IPsec. However, instead of being an arbitrary 32-bit value that, in combination with the destination IP address and security protocol (ESP), uniquely identifies the Security Association for a datagram, HIT identifies the public key that can validate the packet authentication. HIT SHOULD be unique in the whole IP universe. If there is more than one public key for a HIT, the HIT acts as a hint for the correct public key to use. There are two formats for HIT. Bit 0 is used to differentiate the formats. If Bit 0 is zero, then the rest of HIT is a 127 bits of a Hash of the key. For example, if the Identity is DSA, these bits are the least significant 127 bits of the SHA-1 [FIPS-180-1] hash of the DSA public key Host Identity. If Bit 0 is one, then the next 63 bits is the Host Assigning Authority (HAA) field, and only the last 64 bits come from a hash of the Host Identity. This format for HIT is recommended for 'well known' systems. It is possible to support a resolution mechanism for these names in directories like DNS. Another use of HAA is in policy controls. The birthday paradox sets a bound for the expectation of collisions. It is based on the square root of the number of values. A 64-bit hash, then, would put the chances of a collision at 50-50 with 2^32 hosts (4 billion). A 1% chance of collision would occur in a population of 640M and a .001% collision chance in a 20M population. A 128 bit hash will have the same .001% collision chance in a 9x10^16 population. 5.2.1. Storing HIT in DNS The HIT SHOULD be stored in DNS. The exception to this is anonymous identities. The HIT is stored in a new KEY RR. The HIT KEY RR will have all flags set to ZERO, its protocol set to HIP, and algorithm set to HIT128. The 'public key' field of the HIT KEY RR will be the 128 bit HIT. 5.3. Host Assigning Authority (HAA) field The 63 bits of HAA supports two levels of delegation. The first is a registered assigning authority (RAA). The second is a registered identity (RI, commonly a company). The RAA is 23 bits with values assign sequentially by ICANN. The RI is 40 bits, also assigned Moskowitz 6 Host Identity Payload Architecture February 2001 sequentially but by the RAA. This can be used to create a resolution mechanism in the DNS. For example if FOO is RAA number 100 and BAR is FOO's 50th registered identity, and if 1385D17FC63961F5 is the hash of the key for www.foo.com, then by using DNS Binary Labels [DNSBIN] there could be a reverse lookup record like: \[x1385D17FC63961F5/64].\[x32/40].\[x64/23].HIT.int IN PTR www.foo.com. 5.4. Local Scope Identity (LSI) LSIs are 32 bit localized representations of a Host Identity. The purpose of an LSI is to facilitate using Host Identities in existing protocols and APIs. The owner of the Host Identity does not set its own LSI; each host selects its partner's 32 bit representation for a Host Identity. It MUST be random. The risk of collisions is too great (1% in a population of 10,000). Since the LSI only has meaning to the host, its generation is a local policy issue. One method for LSI creation that meets these criteria, would be to concatenate the HIT with a 32 bit random number, hash this (using SHA1), and then use the high order 32 bits as the LSI. Examples of how LSIs can be used include: as the address in a FTP command and as the address in a socket call. Thus LSIs act as a bridge for Host Identity into old protocols and APIs. 5.5. Security Parameter Index (SPI) SPIs are used in ESP to index into the security association negotiated in HIP. The ESP SPIs have added significance when used with HIP; they are a compressed representation of the HIT in every packet. Thus they MAY be used by intermediary systems in providing services like address mapping. A system does not set its own SPI; each host selects its partner's SPI. It MUST be random. The risk of collisions is too great (1% in a population of 10,000). A different SPI MUST be used for each HIP exchange with a particular host; this is to avoid a replay attack. Additionally, when a host rekeys, the SPI MUST change. One method for SPI creation that meets these criteria, would be to concatenate the HIT with a 32 bit random number, hash this (using SHA1), and then use the high order 32 bits as the SPI. 5.6. Difference between an LSI and the SPI There is a subtle difference between an LSI and a SPI. Moskowitz 7 Host Identity Payload Architecture February 2001 The LSI is relatively longed lived. A system selects its peer's LSI and SHOULD reuse a previous LSI for a HIT during a HIP exchange. The LSI ONLY appears in the 3rd and 4th HIP packets (each system providing the other with its LSI). The LSI is used anywhere in system processes where IP addresses have traditionally have been used, like in TCBs and FTP port commands. The SPI is short-lived. It changes with each HIP exchange and with a HIP rekey. A system notifies its peer of the SPI to use in ESP packets sent to it. Since the SPI is in all but the first two HIP packets, it can be used in intermediary systems to assist in address remapping. 6. Using the Host Identity There are a number of ways that Host Identity can be used in Internet Protocols. The first is to use it in IKE [IKE]. HIT can be used in Main Mode. For this, the Host Identity MUST be a Public Key, and an appropriate Main Mode authentication (e.g. DSA signature) used. The LSI of the HIT can replace the usage of IP addresses in IKE. An appropriate ISAKMP [ISAKMP] payload will be needed to accommodate the Host Identity and HIT. These additions to IKE would produce a mode of operation for IKE that could traverse a NAT. This, coupled with ESP transport mode, would produce a NAT friendly IPsec mode (note that the NATs can alter none of the data within the ESP). Another, and perhaps more powerful mode is a new, lightweight, protocol that will allow for one host to convey its Host Identity to another host. This Host Identity Protocol will enable two hosts to exchange Host Identity and related information and rapidly establish an ESP Security Association. It will lack the fine-grain controls of IKE and some of IKE's security features (like identity protection). 7. Mobility via HIP As HIP decouples the Transport from the Internetworking layer, and binds the Transport to the Host Identity (through actually either the HIT or LSI), HIP can provide for a HIT degree of Internetworking 'mobility' at a very low infrastructure cost. HIP Internetworking Mobility includes IP address changes (via any method) to either the initiator or responder. Thus a system is considered mobile if its IP address can change dynamically for any reason like PPP, DHCP, IPv6 TLA reassignments, or a NAT remapping its translation. Initiator address changes are rather straightforward. A responder CAN just accept a HIP or an ESP (whose SPI is an LSI) packet from any address and totally ignore the address for anything more than transmitting return packets. An initiator MAY send a HIP readdress packet to inform the responder of the new location of the initiator. Moskowitz 8 Host Identity Payload Architecture February 2001 This is especially helpful for those situations where the responder is sending data periodically to the initiator (that is starting a connection after the initial connection). Responder mobility is slightly more involved. The initiator has to know where the responder is to start the HIP exchange. HIP need not rely on Dynamic DNS for this function, but will use a rendezvous server. The DNS address for the responder will be the address of the rendezvous server. The responder will keep the rendezvous server continuously updated with its IP address. The rendezvous server simply forwards the initial HIP packet from the initiator to the responder at its current location. All further packets are between the initiator and responder, and responder mobility is handled just like initiator mobility. There is very little activity on the rendezvous server, responder address updates and initial HIP packet forwarding, thus one server can support a large number of potential responders. The responders MUST trust the rendezvous server to properly maintain its HIT and IP address mapping. The responder keeps its address current on the rendezvous server by setting up a HIP based SA with the rendezvous server and sending it HIP Readdress packets. The rendezvous server MUST have the responder's Host Identity from a trusted third party (manual, DNSSEC, etc.) to avoid attacks against its HIT and IP address mapping on behalf of the responder. Further, a rendezvous server will permit two mobile systems to use HIP without any extraneous infrastructure, including DNSSEC if they have a method other than a DNS query to get each other's HI and HIT. 8. HIP and NATs With HIP, the Transport is bound to the LSI; thus a connection between two hosts can traverse many addressing realm boundaries, typically implemented with Network Address Translation (NAT) technology. For a HIP based flow, the NAT needs only track the mapping of the HIT or SPI to an IP address. Many HITs can map to a single IP address on a NAT, simplifying connections on address poor NAT interfaces. The NAT can gain much of its knowledge from the HIP packets themselves, however some NAT configuration MAY be necessary. The NAT systems CANNOT touch the datagrams within the ESP envelope, thus application specific address translation MUST be done in the end systems. HIP provides for 'Distributed NAT', and uses the LSI as a place holder for embedded IP addresses. See the HIP Implementation document [HIPIMPL] for details. 8.1. HIP and TCP Checksum A HIP implementation CANNOT trust the TCP checksum. There is no way for a host to know if any of the IP addresses in the IP header are the addresses used to calculate the TCP Checksum. Thus ALL HIP Moskowitz 9 Host Identity Payload Architecture February 2001 implementations MUST recalculate the TCP Checksum after removing the ESP envelope. 9. HIP Policies There are a number of variables that will influence the HIP exchanges that each host must support. All HIP implementations MUST support at least 2 HIs, one to publish in DNS and one for anonymous usage. Although anonymous HIs will be rarely used as responder HIs, they will be common for initiators. Support for multiple HIs is recommended. Many initiators would want to use a different HI for different responders. The implementations SHOULD provide for an ACL of initiator HIT to responder HIT. This Access Control List (ACL) SHOULD also include preferred transform and local lifetimes. For HITs with HAAs, wildcarding SHOULD be supported. Thus if a Community of Interest, like Banking gets an RAA, a single ACL could be used. A global wildcard would represent the general policy to be used. Policy selection would be from most specific to most general. Responders would need a similar ACL, representing which hosts they accept HIP exchanges, and the preferred transform and local lifetimes. Wildcarding SHOULD be support supported for this ACL also. 10. Benefits of HIP In the beginning, the network (i.e. IP) layer had the following four "classic" invariants: Non-mutable: The NLP sent is the NLP received (ignoring such things as hop count fields---actually the only interesting things are the two addresses). Non-mobile: The NLP doesn't change during the course of an "association". Reversible: A return NLP can always be formed by reversing the source and destination addresses. Omniscient: Each host knows what NLP a partner host can use to send packets to it. Actually, the fourth can be inferred from 1 and 3, but it is worth mentioning for reasons that will be obvious soon if not already. In the current "post-classic" world, we are trying intentionally to get rid of the second invariant (both for mobility and for multihoming), and we have been forced to give up the first and the fourth. RSIP [RSIP] is an attempt to reinstate the fourth invariant Moskowitz 10 Host Identity Payload Architecture February 2001 without the first invariant. IPv6 is an attempt to reinstate the first invariant. Few systems on the Internet have DNS names, or more specifically, Fully Qualified Domain Names (FQDN). FQDN names (and their extensions as email names) are Application Layer names; more frequently naming processes than a particular system. This is why most systems on the internet are not registered in DNS; they do not have processes of interest to other Internet hosts. DNS names are indirect references to IP addresses. This only demonstrates the interrelationship of the networking and application layers. DNS, as the Internet's only deployed, distributed, database is also the repository of other namespaces, due in part to DNSSEC and KEY records. Although each namespace can be stretched (IP with v6, DNS with KEY records), neither can adequately provide for host authentication or act as a separation between Internetworking and Transport layers. The Host Identity (HI) namespace fills an important gap between the IP and DNS namespaces. An interesting thing about the HI is that it actually allows one to give-up all but the 3rd Network Layer invariant. That is to say, as long as the Network Layer Protocol (NLP) is reversible, then things work ok because HIP takes care of host identification, and reversibility allows one to get a packet back to one's partner host. You don't care if the NLP changes in transit (mutable) and you don't care what NLP the partner is using (non-omniscient). Since all systems can have a Host Identity, every system can have an entry in the DNS. The mobility features in HIP make it attractive to trusted 3rd parties to offer rendezvous servers. 11. Security Considerations HIP takes advantage of the new Host Identity paradigm to provide secure authentication of hosts and provide a fast key exchange for IPsec ESP. HIP also attempts to limit the exposure of the host to various denial-of-service (DOS) and man-in-the-middle (MITH) attacks. In so doing, HIP itself is subject to its own DOS and MITM attacks that potentially could be more damaging to a host's ability to conduct business as usual. The Security Association for ESP is indexed by the SPI and HIT, not the SPI and IP address. HIP enabled ESP is IP address independent. This might seem to make it easier for an attacker, but ESP with replay protection is already as well protected as possible, and the removal of the IP address as a check should not increase the exposure of ESP to DOS attacks. Denial-of-service attacks take advantage of the cost of start of state for a protocol on the responder compared to the 'cheapness' on Moskowitz 11 Host Identity Payload Architecture February 2001 the initiator. HIP makes no attempt to increase the cost of the start of state on the initiator, but makes an effort to reduce the cost to the responder. This is done by having the responder start the 3-way cookie exchange instead of the initiator, making the HIP protocol 4 packets long. There are more details on this process in the HIP protocol document [HIP]. HIP optionally supports opportunistic negotiation. That is, if a host receives a start of transport without a HIP negotiation, it can attempt to force a HIP exchange before accepting the connection. This has the potential for DOS attacks against both hosts. If the method to force the start of HIP is expensive on either host, the attacker need only spoof a TCP SYN. This would put both systems into the expensive operations. HIP avoids this attack by having the responder send a simple HIP packet that it can build at HI selection time. Since this packet is fixed and easily spoofed the initiator only reacts to it if it has just started a connection to the responder. Man-in-the-middle attacks are difficult to defend against, without third-party authentication. A skillful MITM could easily handle all parts of HIP; but HIP indirectly provides the following protection from a MITM attack. If the responder's HI is retrieved from a signed DNS zone by the initiator, the initiator can use this to validate the signed HIP packets. Likewise, if the initiator's HI is in a secure DNS zone, the responder can retrieve it and validate the signed HIP packets. However, since an initiator may choose to use an anonymous HI, it knowingly risks a MITM attack. The responder may choose not to accept a HIP exchange with an anonymous initiator. Since not all hosts will ever support HIP, ICMP 'Destination Protocol Unreachable' are to be expected and present a DOS attack. Against an initiator, the attack would look like the responder does not support HIP, but shortly after receiving the ICMP message, the initiator would receive a valid HIP packet. Thus to protect against this attack, an initiator should not react to an ICMP message until a reasonable delta time to get the real responder's HIP packet. A similar attack against the responder is more involved. Another MITM attack is simulating a responder's rejection of a HIP initiation. This is a simple ICMP Host Unreachable, Administratively Prohibited message. A HIP packet was not used because it would either have to have unique content, and thus difficult to generate, resulting in yet another DOS attack, or just as spoofable as the ICMP message. The defense against this MITM attack is for the responder to wait a reasonable time period to get a valid HIP packet. If one does not come, then the Initiator has to assume that the ICMP message is valid. Since this is the only point in the HIP exchange where this ICMP message is appropriate, it can be ignored at any other point in the exchange. Moskowitz 12 Host Identity Payload Architecture February 2001 11.1. HITs used in ACLs It is expected that HITs will be used in ACLs. Firewalls will use HITs to control egress and ingress to networks, with an assurance difficult to achieve today. [add here wildcarding] There has been considerable bad experience with distributed ACLs that contain public key related material, for example with SSH. If the owner of the key needs to revoke it for any reason, the task of finding all locations where the key is held in an ACL may be impossible. If the reason for the revocation is due to private key theft, this could be a serious issue. A host can keep track of all of its partners that might use its HIT in an ACL by logging all remote HITs. It should only be necessary to log responder hosts. With this information, the host can notify the various hosts about the change to the HIT. There has been no attempt here to develop a secure method (like in CMP and CMC) to issue the HIT revocation notice. NATs, however, are transparent to the HIP aware systems by design. Thus the host many find it difficult to notify any NAT that is using a HIT in an ACL. Since most systems will know of the NATs for their network, there should be a process by which they can notify these NATs of the change of the HIT. This is MANDITORY for systems that function as responders behind a NAT. In a similar vein, if a host is notified of a change in a HIT of an initiator, it should notify its NAT of the change. In this manner, NATs will get updated with the HIT change. 11.2. Non-security Considerations The definition of the Host Identity states that the HI need not be a public key. That the HI could be any value; for example an FQDN. This document does not describe how to support a non-cryptographic HI. Such a HI would still offer the services of the LSI for NAT traversal. It would carry the LSIs in an ESP that had neither privacy nor authentication (ESP EMPTY). Since this mode of HIP would offer so little additional functionality for so much addition to the IP kernel, it has not been defined in this document. Given how little public key cryptography HIP requires, HIP SHOULD only be implemented using public key Host Identities. 12. IANA Considerations The IANA considerations for HIP are covered in the Host Identity payload document [HIP]. Moskowitz 13 Host Identity Payload Architecture February 2001 13. ICANN Considerations ICANN will need to set up the HIT.int zone and accredit the registered assigning authorities (RAA) for HAA field. With 21 bits, ICANN can allocate just over 2M registries. 14. References [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [HIP], Moskowitz, R., "Host Identity Payload", draft-ietf-moskowitz- hip-02.txt, January 2001. [ESP], Kent, S., and Atkinson, R., "IP Encapsulating Security Payload", RFC 2406, November 1998. [RSIP], [FIPS-180-1], NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995. http://csrc.nist.gov/fips/fip180-1.txt (ascii) http://csrc.nist.gov/fips/fip180-1.ps (postscript) [DNSBIN], Crawford, M., "Binary Labels in the Domain Name System", RFC 2673, August 1999. [IKE], Harkins, D., and Carrel, D., "The Internet Key Exchange", RFC 2409, November 1998. [ISAKMP], Maughan, D., Schertler, M., Schneider, M., and Turner, J., "Internet Security Association and Key Management Protocol", RFC 2408, November 1998. [HIPIMPL], Moskowitz, R., "Host Identity Payload Implementation", draft-ietf-moskowitz-hip-impl-01.txt, January 2001. 15. Acknowledgments The drive to create HIP came to being after attending the MALLOC meeting at IETF 43. It has matured considerably since the early drafts thanks to extensive input from IETFers. Most importantly, its design goals are articulated and are different from other efforts in this direction. Particular mention goes to the members of the NameSpace Research Group of the IRTF. Noel Chiappa provided the framework for LSIs and Kieth Moore the impetuous to provide resolvability. Steve Deering provided encouragement to keep working, as a solid proposal can act as a proof of ideas for a research group. Paul Francis provided much of the layering architectural text. Many others contributed; extensive security tips were provided by Steve Bellovin. Rob Austein kept the DNS Moskowitz 14 Host Identity Payload Architecture February 2001 parts on track. Rodney Thayer and Hugh Daniels provide extensive feedback. John Gilmore kept me challenged to provide something of value. I hope I have. 16. Author's Address Robert Moskowitz ICSA Labs 1200 Walnut Bottom Rd. Carlisle, PA 17013 Email: rgm@icsa.net 17. Copyright Statement Copyright (c) The Internet Society (2001). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Moskowitz 15