--- 1/draft-ietf-hip-rfc4423-bis-02.txt 2011-09-07 22:14:31.142132641 +0200 +++ 2/draft-ietf-hip-rfc4423-bis-03.txt 2011-09-07 22:14:31.242132222 +0200 @@ -1,19 +1,19 @@ Network Working Group R. Moskowitz Internet-Draft Verizon -Obsoletes: 4423 (if approved) February 25, 2011 +Obsoletes: 4423 (if approved) September 1, 2011 Intended status: Standards Track -Expires: August 29, 2011 +Expires: March 4, 2012 Host Identity Protocol Architecture - draft-ietf-hip-rfc4423-bis-02 + draft-ietf-hip-rfc4423-bis-03 Abstract This memo describes a new namespace, the Host Identity namespace, and a new protocol layer, the Host Identity Protocol, between the internetworking and transport layers. Herein are presented the basics of the current namespaces, their strengths and weaknesses, and how a new namespace will add completeness to them. The roles of this new namespace in the protocols are defined. @@ -30,21 +30,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." - This Internet-Draft will expire on August 29, 2011. + This Internet-Draft will expire on March 4, 2012. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -69,88 +69,95 @@ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Terms common to other documents . . . . . . . . . . . . . . 5 2.2. Terms specific to this and other HIP documents . . . . . . . 5 3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. A desire for a namespace for computing platforms . . . . . . 7 4. Host Identity namespace . . . . . . . . . . . . . . . . . . 9 4.1. Host Identifiers . . . . . . . . . . . . . . . . . . . . . . 10 - 4.2. Storing Host Identifiers in DNS . . . . . . . . . . . . . . 10 + 4.2. Host Identity Hash (HIH) . . . . . . . . . . . . . . . . . . 10 4.3. Host Identity Tag (HIT) . . . . . . . . . . . . . . . . . . 11 - 4.4. Host Identity Hash (HIH) . . . . . . . . . . . . . . . . . . 11 - 4.5. Local Scope Identifier (LSI) . . . . . . . . . . . . . . . . 11 + 4.4. Local Scope Identifier (LSI) . . . . . . . . . . . . . . . . 11 + 4.5. Storing Host Identifiers in Directories . . . . . . . . . . 12 5. New stack architecture . . . . . . . . . . . . . . . . . . . 12 5.1. Transport associations and end-points . . . . . . . . . . . 13 6. End-host mobility and multi-homing . . . . . . . . . . . . . 13 6.1. Rendezvous mechanism . . . . . . . . . . . . . . . . . . . . 14 6.2. Protection against flooding attacks . . . . . . . . . . . . 14 - 7. HIP and IPsec . . . . . . . . . . . . . . . . . . . . . . . 15 + 7. HIP and ESP . . . . . . . . . . . . . . . . . . . . . . . . 15 8. HIP and MAC Security . . . . . . . . . . . . . . . . . . . . 16 - 9. HIP and NATs . . . . . . . . . . . . . . . . . . . . . . . . 16 + 9. HIP and NATs . . . . . . . . . . . . . . . . . . . . . . . . 17 9.1. HIP and Upper-layer checksums . . . . . . . . . . . . . . . 17 - 10. Multicast . . . . . . . . . . . . . . . . . . . . . . . . . 17 - 11. HIP policies . . . . . . . . . . . . . . . . . . . . . . . . 17 + 10. Multicast . . . . . . . . . . . . . . . . . . . . . . . . . 18 + 11. HIP policies . . . . . . . . . . . . . . . . . . . . . . . . 18 12. Benefits of HIP . . . . . . . . . . . . . . . . . . . . . . 18 12.1. HIP's answers to NSRG questions . . . . . . . . . . . . . . 19 13. Changes from RFC 4423 . . . . . . . . . . . . . . . . . . . 21 14. Security considerations . . . . . . . . . . . . . . . . . . 21 14.1. HITs used in ACLs . . . . . . . . . . . . . . . . . . . . . 23 - 14.2. Non-security considerations . . . . . . . . . . . . . . . . 23 + 14.2. Alternative HI considerations . . . . . . . . . . . . . . . 24 15. IANA considerations . . . . . . . . . . . . . . . . . . . . 24 16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 24 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 17.1. Normative References . . . . . . . . . . . . . . . . . . . . 25 - 17.2. Informative references . . . . . . . . . . . . . . . . . . . 25 + 17.2. Informative references . . . . . . . . . . . . . . . . . . . 26 Author's Address . . . . . . . . . . . . . . . . . . . . . . 27 1. Introduction The Internet has two important global namespaces: Internet Protocol (IP) addresses and Domain Name Service (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 proposed Host Identity namespace fills an important gap between - the IP and DNS namespaces. The Host Identity namespace consists of - Host Identifiers (HI). A Host Identifier is cryptographic in its - nature; it is the public key of an asymmetric key-pair. Each host - will have at least one Host Identity, but it will typically have more - than one. Each Host Identity uniquely identifies a single host, - i.e., no two hosts have the same Host Identity. The Host Identity, - and the corresponding Host Identifier, can either be public (e.g. - published in the DNS), or unpublished. Client systems will tend to - have both public and unpublished Identities. + the IP and DNS namespaces. A Host Identity conceptually refers to a + computing platform, and there may be multiple such Host Identities + per computing platform (because the platform may wish to present a + different identity to different communicating peers). The Host + Identity namespace consists of Host Identifiers (HI). There is + exactly one Host Identifier for each Host Identity. While this text + later talks about non-cryptographic Host Identifiers, the + architecture focuses on the case in which Host Identifiers are + cryptographic in nature. Specifically, the Host Identifier is the + public key of an asymmetric key-pair. Each Host Identity uniquely + identifies a single host, i.e., no two hosts have the same Host + Identity. If two or more computing platforms have the same Host + Identifier, then they are instantiating a distributed host. The Host + Identifier can either be public (e.g. published in the DNS), or + unpublished. Client systems will tend to have both public and + unpublished Host Identifiers. There is a subtle but important difference between Host Identities and Host Identifiers. An Identity refers to the abstract entity that is identified. An Identifier, on the other hand, refers to the concrete bit pattern that is used in the identification process. Although the Host Identifiers could be used in many authentication systems, such as IKEv2 [RFC4306], the presented architecture introduces a new protocol, called the Host Identity Protocol (HIP), and a cryptographic exchange, called the HIP base exchange; see also Section 7. The HIP protocols provide for limited forms of trust between systems, enhance mobility, multi-homing and dynamic IP renumbering, aid in protocol translation / transition, and reduce certain types of denial-of-service (DoS) attacks. When HIP is used, the actual payload traffic between two HIP hosts is - typically, but not necessarily, protected with IPsec. The Host - Identities are used to create the needed IPsec Security Associations - (SAs) and to authenticate the hosts. When IPsec is used, the actual - payload IP packets do not differ in any way from standard IPsec + typically, but not necessarily, protected with ESP. The Host + Identities are used to create the needed ESP Security Associations + (SAs) and to authenticate the hosts. When ESP is used, the actual + payload IP packets do not differ in any way from standard ESP protected IP packets. Much has been learned about HIP since [RFC4423] was published. This document expands Host Identities beyond use to enable IP connectivity and security to general interhost secure signalling at any protocol layer. The signal may establish a security association between the hosts, or simply pass information within the channel. 2. Terminology @@ -202,26 +209,27 @@ | | | | Host Identity | An abstract concept assigned to a 'computing | | | platform'. See 'Host Identifier', below. | | | | | Host Identity | A name space formed by all possible Host | | namespace | Identifiers. | | | | | Host Identity | A protocol used to carry and authenticate Host | | Protocol | Identifiers and other information. | | | | - | Host Identity | A 128-bit datum created by taking a cryptographic | - | Tag | hash over a Host Identifier. | - | | | | Host Identity | The cryptograhic hash used in creating the Host | | Hash | Identity Tag from the Host Identity. | | | | + | Host Identity | A 128-bit datum created by taking a cryptographic | + | Tag | hash over a Host Identifier plus bits to identify | + | | which hash used. | + | | | | Host | A public key used as a name for a Host Identity. | | Identifier | | | | | | Local Scope | A 32-bit datum denoting a Host Identity. | | Identifier | | | | | | Public Host | A published or publicly known Host Identfier used | | Identifier | as a public name for a Host Identity, and the | | and Identity | corresponding Identity. | | | | @@ -245,27 +253,25 @@ named in order to interact in a scalable manner. Here we concentrate on naming computing platforms and packet transport elements. There are two principal namespaces in use in the Internet for these components: IP numbers, and Domain Names. 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, HTTP, and SIP addresses all reference Domain Names. - IP numbers are a confounding of two namespaces, the names of a host's - networking interfaces and the names of the locations ('confounding' - is a term used in statistics to discuss metrics that are merged into - one with a gain in indexing, but a loss in informational value). The - names of locations should be understood as denoting routing direction - vectors, i.e., information that is used to deliver packets to their - destinations. + The IP addressing namespace has been overloaded to name both + interfaces (at layer-3) and endpoints (for the endpoint-specific part + of layer-3, and for layer-4). In their role as interface names, IP + addresses are sometimes called "locators" and serve as an endpoint + within a routing topology. 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 use ephemeral and/or non-unique IP numbers. That is, every time an interface is connected to the network, it is assigned an IP number. In the current Internet, the transport layers are coupled to the IP addresses. Neither can evolve separately from the other. IPng deliberations were strongly shaped by the decision that a @@ -288,23 +293,23 @@ because of mobility, rehoming, or renumbering. If the namespace for computing platforms is based on public-key cryptography, it can also provide authentication services. If this namespace is locally created without requiring registration, it can provide anonymity. Such a namespace (for computing platforms) and the names in it should have the following characteristics: - o The namespace should be applied to the IP 'kernel'. The IP kernel - is the 'component' between applications and the packet transport - infrastructure. + o The namespace should be applied to the IP 'kernel' or stack. The + IP stack is the 'component' between applications and the packet + transport infrastructure. o The namespace should fully decouple the internetworking layer from the higher layers. The names should replace all occurrences of IP addresses within applications (like in the Transport Control Block, TCB). This may require changes to the current APIs. In the long run, it is probable that some new APIs are needed. o The introduction of the namespace should not mandate any administrative infrastructure. Deployment must come from the bottom up, in a pairwise deployment. @@ -325,22 +330,23 @@ were obtained. For 64 bits, this number is roughly 4 billion. A hash size of 64 bits may be too small to avoid collisions in a large population; for example, there is a 1% chance of collision in a population of 640M. For 100 bits (or more), we would not expect a collision until approximately 2**50 (1 quadrillion) hashes were generated. o The names should have a localized abstraction so that it can be used in existing protocols and APIs. - o It must be possible to create names locally. This can provide - anonymity at the cost of making resolvability very difficult. + o It must be possible to create names locally. When such names are + not published, this can provide anonymity at the cost of making + resolvability very difficult. * Sometimes the names may contain a delegation component. This is the cost of resolvability. o The namespace should provide authentication services. o The names 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. @@ -353,24 +359,24 @@ designed, it can deliver all of the above stated requirements. 4. Host Identity namespace A name in the Host Identity namespace, a Host Identifier (HI), represents a statistically globally unique name for naming any system with an IP stack. This identity is normally associated with, but not limited to, an IP stack. A system can have multiple identities, some 'well known', some unpublished or 'anonymous'. A system may self- assert its own identity, or may use a third-party authenticator like - DNSSEC [RFC2535], PGP, or X.509 to 'notarize' the identity assertion. - It is expected that the Host Identifiers will initially be - authenticated with DNSSEC and that all implementations will support - DNSSEC as a minimal baseline. + DNSSEC [RFC2535], PGP, or X.509 to 'notarize' the identity assertion + to another namespace. It is expected that the Host Identifiers will + initially be authenticated with DNSSEC and that all implementations + will support DNSSEC as a minimal baseline. In theory, any name that can claim to be 'statistically globally unique' may serve as a Host Identifier. However, in the authors' opinion, a public key of a 'public key pair' makes the best Host Identifier. As will be specified in the Host Identity Protocol Base EXchange (BEX) [RFC5201-bis] specification, a public-key-based HI can authenticate the HIP packets and protect them for man-in-the-middle attacks. Since authenticated datagrams are mandatory to provide much of HIP's denial-of-service protection, the Diffie-Hellman exchange in HIP BEX has to be authenticated. Thus, only public-key HI and @@ -385,112 +391,112 @@ challenges. 4.1. Host Identifiers Host Identity adds two main features to Internet protocols. The first is a decoupling of the internetworking and transport layers; see Section 5. 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. Because the Host Identifier is a public key, this - key can be used for authentication in security protocols like IPsec. + key can be used for authentication in security protocols like ESP. The only completely defined structure of the Host Identity is that of a public/private key pair. In this case, the Host Identity is referred to by its public component, the public key. Thus, the name representing a Host Identity in the Host Identity namespace, i.e., the Host Identifier, is the public key. In a way, the possession of the private key defines the Identity itself. If the private key is possessed by more than one node, the Identity can be considered to be a distributed one. Architecturally, any other Internet naming convention might form a usable base for Host Identifiers. However, non-cryptographic names 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. However, at least for interconnected + spoofing) and no use of ESP. However, at least for interconnected networks spanning several operational domains, the set of environments where the risk of host spoofing allowed by non- cryptographic Host Identifiers is acceptable is the null set. Hence, the current HIP documents do not specify how to use any other types of Host Identifiers but public keys. The actual Host Identities are never directly used in any Internet protocols. The corresponding Host Identifiers (public keys) may be stored in various DNS or LDAP directories as identified elsewhere in this document, and they are passed in the HIP base exchange. A Host Identity Tag (HIT) is used in other protocols to represent the Host Identity. Another representation of the Host Identities, the Local Scope Identifier (LSI), can also be used in protocols and APIs. -4.2. Storing Host Identifiers in DNS +4.2. Host Identity Hash (HIH) - The public Host Identifiers should be stored in DNS; the unpublished - Host Identifiers should not be stored anywhere (besides the - communicating hosts themselves). The (public) HI along with the - supported HIHs are stored in a new RR type. This RR type is defined - in HIP DNS Extension [I-D.ietf-hip-rfc5205-bis]. + The Host Identity Hash is the cryptographic hash used in producing + the HIT from the HI. It is also the hash used through out the HIP + protocol for consistancy and simplicity. It is possible to for the + two Hosts in the HIP exchange to use different hashes. - Alternatively, or in addition to storing Host Identifiers in the DNS, - they may be stored in various kinds of Public Key Infrastructure - (PKI). Such a practice may allow them to be used for purposes other - than pure host identification. + Multiple HIHs within HIP are needed to address the moving target of + creation and eventual compromise of cryptographic hashes. This + significantly complicates HIP and offers an attacker an additional + downgrade attack that is mitigated in the HIP protocol. 4.3. Host Identity Tag (HIT) A Host Identity Tag is a 128-bit representation for a Host Identity. - It is created by taking a cryptographic hash over the corresponding - Host Identifier. There are two advantages of using a hash over using - the Host Identifier in protocols. Firstly, its fixed length makes - for easier protocol coding and also better manages the packet size - cost of this technology. Secondly, it presents the identity in a - consistent format to the protocol independent of the cryptographic - algorithms used. + It is created from an HIH and other information, like an IPv6 prefix + and a hash identifier. There are two advantages of using the HIT + over using the Host Identifier in protocols. Firstly, its fixed + length makes for easier protocol coding and also better manages the + packet size cost of this technology. Secondly, it presents the + identity in a consistent format to the protocol independent of the + cryptographic algorithms used. There can be multiple HITs per Host Identifier when multiple hashes are supported. An Initator may have to initially guess which HIT to use for the Responder, typically based on what it perfers, until it learns the appropriate HIT through the HIP exchange. In the HIP packets, the HITs identify the sender and recipient of a packet. Consequently, a HIT should be unique in the whole IP universe as long as it is being used. In the extremely rare case of a single HIT mapping to more than one Host Identity, the Host Identifiers (public keys) will make the final difference. If there is more than one public key for a given node, the HIT acts as a hint for the correct public key to use. -4.4. Host Identity Hash (HIH) - - The Host Identity Hash is the cryptographic hash used in producing - the HIT from the HI. It is also the hash used through out the HIP - protocol for consistancy and simplicity. It is possible to for the - two Hosts in the HIP exchange to use different hashes. - - Multiple HIHs within HIP are needed to address the moving target of - creation and eventual compromise of cryptographic hashes. This - significantly complicates HIP and offers an attacker an additional - downgrade attack that is mitigated in the HIP protocol. - -4.5. Local Scope Identifier (LSI) +4.4. Local Scope Identifier (LSI) An LSI is a 32-bit localized representation for a Host Identity. The purpose of an LSI is to facilitate using Host Identities in existing protocols and APIs. LSI's advantage over HIT is its size; its disadvantage is its local scope. Examples of how LSIs can be used include: as the address in an FTP command and as the address in a socket call. Thus, LSIs act as a bridge for Host Identities into IPv4-based protocols and APIs. LSIs also make it possible for some IPv4 applications to run over an IPv6 network. +4.5. Storing Host Identifiers in Directories + + The public Host Identifiers should be stored in DNS; the unpublished + Host Identifiers should not be stored anywhere (besides the + communicating hosts themselves). The (public) HI along with the + supported HIHs are stored in a new RR type. This RR type is defined + in HIP DNS Extension [I-D.ietf-hip-rfc5205-bis]. + + Alternatively, or in addition to storing Host Identifiers in the DNS, + they may be stored in various other directories (e.g. LDAP, DHT) or + in a Public Key Infrastructure (PKI). Such a practice may allow them + to be used for purposes other than pure host identification. + 5. New stack architecture One way to characterize Host Identity is to compare the proposed new architecture with the current one. As discussed above, the IP addresses can be seen to be a confounding of routing direction vectors and interface names. Using the terminology from the IRTF Name Space Research Group Report [nsrg-report] and, e.g., the unpublished Internet-Draft Endpoints and Endpoint Names [chiappa-endpoints], the IP addresses currently embody the dual role of locators and end-point identifiers. That is, each IP address @@ -502,31 +508,32 @@ In the HIP architecture, the end-point names and locators are separated from each other. IP addresses continue to act as locators. The Host Identifiers take the role of end-point identifiers. It is important to understand that the end-point names based on Host Identities are slightly different from interface names; a Host Identity can be simultaneously reachable through several interfaces. The difference between the bindings of the logical entities are illustrated in Figure 1. - Service ------ Socket Service ------ Socket - | | + Transport ---- Socket Transport ------ Socket + association | association | | | | | | | End-point | End-point --- Host Identity \ | | \ | | \ | | \ | | Location --- IP address Location --- IP address + Figure 1 5.1. Transport associations and end-points Architecturally, HIP provides for a different binding of transport- layer protocols. That is, the transport-layer associations, i.e., TCP connections and UDP associations, are no longer bound to IP addresses but to Host Identities. It is possible that a single physical computer hosts several logical @@ -552,21 +559,21 @@ reassignments, or a NAT device remapping its translation. Likewise, a system is considered multi-homed if it has more than one globally routable IP address at the same time. HIP links IP addresses together, when multiple IP addresses correspond to the same Host Identity, and if one address becomes unusable, or a more preferred address becomes available, existing transport associations can easily be moved to another address. When a node moves while communication is already on-going, address changes are rather straightforward. The peer of the mobile node can - just accept a HIP or an integrity protected IPsec packet from any + just accept a HIP or an integrity protected ESP packet from any address and ignore the source address. However, as discussed in Section 6.2 below, a mobile node must send a HIP readdress packet to inform the peer of the new address(es), and the peer must verify that the mobile node is reachable through these addresses. This is especially helpful for those situations where the peer node is sending data periodically to the mobile node (that is re-starting a connection after the initial connection). 6.1. Rendezvous mechanism @@ -616,70 +623,68 @@ A credit-based authorization approach Host Mobility with the Host Identity Protocol [I-D.ietf-hip-rfc5206-bis] can be used between hosts for sending data prior to completing the address tests. Otherwise, if HIP is used between two hosts that fully trust each other, the hosts may optionally decide to skip the address tests. However, such performance optimization must be restricted to peers that are known to be trustworthy and capable of protecting themselves from malicious software. -7. HIP and IPsec +7. HIP and ESP - The preferred way of implementing HIP is to use IPsec to carry the + The preferred way of implementing HIP is to use ESP to carry the actual data traffic. As of today, the only completely defined method - is to use IPsec Encapsulated Security Payload (ESP) to carry the data + is to use ESP Encapsulated Security Payload (ESP) to carry the data packets [I-D.ietf-hip-rfc5202-bis]. In the future, other ways of transporting payload data may be developed, including ones that do not use cryptographic protection. In practice, the HIP base exchange uses the cryptographic Host Identifiers to set up a pair of ESP Security Associations (SAs) to enable ESP in an end-to-end manner. This is implemented in a way that can span addressing realms. While it would be possible, at least in theory, to use some existing cryptographic protocol, such as IKEv2 together with Host Identifiers, to establish the needed SAs, HIP defines a new protocol. There are a number of historical reasons for this, and there are also a few architectural reasons. First, IKE (and IKEv2) were not designed with middle boxes in mind. As adding a new naming layer allows one to potentially add a new forwarding layer (see Section 9, below), it is - very important that the HIP protocols are friendly towards any middle - boxes. + very important that the HIP provides mechanisms for middlebox + authentication. Second, from a conceptual point of view, the IPsec Security Parameter Index (SPI) in ESP provides a simple compression of the HITs. This does require per-HIT-pair SAs (and SPIs), and a decrease of policy granularity over other Key Management Protocols, such as IKE and - IKEv2. In particular, the current thinking is limited to a situation - where, conceptually, there is only one pair of SAs between any given - pair of HITs. In other words, from an architectural point of view, - HIP only supports host-to-host (or endpoint-to-endpoint) Security - Associations. If two hosts need more pairs of parallel SAs, they - should use separate HITs for that. However, future HIP extensions - may provide for more granularity and creation of several ESP SAs - between a pair of HITs. + IKEv2. In other words, from an architectural point of view, HIP only + supports host-to-host (or endpoint-to-endpoint) Security + Associations. - Since HIP is designed for host usage, not for gateways or so called - Bump-in-the-Wire (BITW) implementations, only ESP transport mode is - supported. An ESP SA pair is indexed by the SPIs and the two HITs - (both HITs since a system can have more than one HIT). The SAs need - not to be bound to IP addresses; all internal control of the SA is by - the HITs. Thus, a host can easily change its address using Mobile - IP, DHCP, PPP, or IPv6 readdressing and still maintain the SAs. - Since the transports are bound to the SA (via an LSI or a HIT), any - active transport is also maintained. Thus, real-world conditions + Originally, as HIP is designed for host usage, not for gateways or so + called Bump-in-the-Wire (BITW) implementations, only ESP transport + mode is supported. An ESP SA pair is indexed by the SPIs and the two + HITs (both HITs since a system can have more than one HIT). The SAs + need not to be bound to IP addresses; all internal control of the SA + is by the HITs. Thus, a host can easily change its address using + Mobile IP, DHCP, PPP, or IPv6 readdressing and still maintain the + SAs. Since the transports are bound to the SA (via an LSI or a HIT), + any active transport is also maintained. Thus, real-world conditions like loss of a PPP connection and its re-establishment or a mobile handover will not require a HIP negotiation or disruption of transport services [Bel1998]. + It should be noted that there are already BITW implementations. This + is still consistant to the SA bindings above. + Since HIP does not negotiate any SA lifetimes, all lifetimes are local policy. The only lifetimes a HIP implementation must support are sequence number rollover (for replay protection), and SA timeout. An SA times out if no packets are received using that SA. Implementations may support lifetimes for the various ESP transforms. 8. HIP and MAC Security The IEEE 802 standards have been defining MAC layered security. Many of these standards use EAP [RFC3748] as a Key Management System (KMS) @@ -711,61 +716,67 @@ [RFC2766]. In a network environment where identification is based on the IP addresses, identifying the communicating nodes is difficult when NAT is used. With HIP, the transport-layer end-points are bound to the Host Identities. Thus, a connection between two hosts can traverse many addressing realm boundaries. The IP addresses are used only for routing purposes; they may be changed freely during packet traversal. For a HIP-based flow, a HIP-aware NAT or NAT-PT system tracks the - mapping of HITs, and the corresponding IPsec SPIs, to an IP address. + mapping of HITs, and the corresponding ESP SPIs, to an IP address. The NAT system has to learn mappings both from HITs and from SPIs to IP addresses. Many HITs (and SPIs) 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. - NAT systems cannot touch the datagrams within the IPsec envelope, - thus application-specific address translation must be done in the end + 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 HIT or the LSI as a placeholder for embedded IP addresses. - HIP and NAT interaction is defined in [RFC5770]. + An experimental HIP and NAT traversal is defined in [RFC5770]. 9.1. HIP and Upper-layer checksums There is no way for a host to know if any of the IP addresses in an IP header are the addresses used to calculate the TCP checksum. That is, it is not feasible to calculate the TCP checksum using the actual IP addresses in the pseudo header; the addresses received in the incoming packet are not necessarily the same as they were on the sending host. Furthermore, it is not possible to recompute the upper-layer checksums in the NAT/NAT-PT system, since the traffic is - IPsec protected. Consequently, the TCP and UDP checksums are + ESP protected. Consequently, the TCP and UDP checksums are calculated using the HITs in the place of the IP addresses in the pseudo header. Furthermore, only the IPv6 pseudo header format is used. This provides for IPv4 / IPv6 protocol translation. 10. Multicast - Few concrete thoughts exist about how HIP might affect IP-layer or - application-layer multicast. + Since its inception, a few studies have looked at how HIP might + affect IP-layer or application-layer multicast. 11. HIP policies There are a number of variables that will influence the HIP exchanges that each host must support. All HIP implementations should support - at least 2 HIs, one to publish in DNS and an unpublished one for - anonymous usage. Although unpublished HIs will be rarely used as - responder HIs, they are likely be common for initiators. Support for - multiple HIs is recommended. + at least 2 HIs, one to publish in DNS or similar directory service + and an unpublished one for anonymous usage. Although unpublished HIs + will be rarely used as responder HIs, they are likely be common for + initiators. Support for multiple HIs is recommended. This provides + new challenges for systems or users to decide which type of HI to + expose when they start a new session. + + Opportunistic mode (where the initator starts a HIP exchange without + prior knowledge of the responder's HI) presents a policy tradeoff. + It provides some security benefits but may be subject to MITM. Many initiators would want to use a different HI for different responders. The implementations should provide for a policy of initiator HIT to responder HIT. This policy should also include preferred transforms and local lifetimes. Responders would need a similar policy, describing the hosts allowed to participate in HIP exchanges, and the preferred transforms and local lifetimes. @@ -904,25 +913,25 @@ require significant new development and deployment. 13. Changes from RFC 4423 This section summarizes the changes made from [RFC4423]. 14. Security considerations HIP takes advantage of the new Host Identity paradigm to provide secure authentication of hosts and to provide a fast key exchange for - IPsec. HIP also attempts to limit the exposure of the host to - various denial-of-service (DoS) and man-in-the-middle (MitM) 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. + ESP. HIP also attempts to limit the exposure of the host to various + denial-of-service (DoS) and man-in-the-middle (MitM) 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. Resource exhausting denial-of-service attacks take advantage of the cost of setting up a state for a protocol on the responder compared to the 'cheapness' on the initiator. HIP allows a responder to increase the cost of the start of state on the initiator and makes an effort to reduce the cost to the responder. This is done by having the responder start the authenticated Diffie-Hellman exchange instead of the initiator, making the HIP base exchange 4 packets long. There are more details on this process in the Host Identity Protocol under development. @@ -960,27 +968,27 @@ aborted after some retries). As a drawback, this leads to an 6-way base exchange which may seem bad at first. However, since this only happens in an attack scenario and since the attack can be handled (so it is not interesting to mount anymore), we assume the additional messages are not a problem at all. Since the MitM cannot be successful with a downgrade attack, these sorts of attacks will only occur as 'nuisance' attacks. So, the base exchange would still be usually just four packets even though implementations must be prepared to protect themselves against the downgrade attack. - In HIP, the Security Association for IPsec is indexed by the SPI; the + In HIP, the Security Association for ESP is indexed by the SPI; the source address is always ignored, and the destination address may be - ignored as well. Therefore, HIP-enabled IPsec Encapsulated Security + ignored as well. Therefore, HIP-enabled Encapsulated Security Payload (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 IPsec ESP to DoS attacks. + check should not increase the exposure of ESP to DoS attacks. Since not all hosts will ever support HIP, ICMPv4 'Destination Unreachable, Protocol Unreachable' and ICMPv6 'Parameter Problem, Unrecognized Next Header' messages 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 time has passed, allowing it to get the real responder's HIP packet. A similar attack against the responder @@ -997,28 +1005,31 @@ come, then the initiator has to assume that the ICMP message is valid. Since this is the only point in the HIP base exchange where this ICMP message is appropriate, it can be ignored at any other point in the exchange. 14.1. HITs used in ACLs It is expected that HITs will be used in ACLs. Future firewalls can use HITs to control egress and ingress to networks, with an assurance level difficult to achieve today. As discussed above in Section 7, - once a HIP session has been established, the SPI value in an IPsec + once a HIP session has been established, the SPI value in an ESP packet may be used as an index, indicating the HITs. In practice, firewalls can inspect HIP packets to learn of the bindings between HITs, SPI values, and IP addresses. They can even explicitly control - IPsec usage, dynamically opening IPsec ESP only for specific SPI - values and IP addresses. The signatures in HIP packets allow a - capable firewall to ensure that the HIP exchange is indeed happening - between two known hosts. This may increase firewall security. + ESP usage, dynamically opening ESP only for specific SPI values and + IP addresses. The signatures in HIP packets allow a capable firewall + to ensure that the HIP exchange is indeed happening between two known + hosts. This may increase firewall security. + + A potential of HITs in ACLs is their 'flatness' means they cannot be + aggregated and this could result in large table searches There has been considerable bad experience with distributed ACLs that contain public key related material, for example, with SSH. If the owner of a 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 @@ -1029,21 +1040,21 @@ HIP-aware NATs, however, are transparent to the HIP aware systems by design. Thus, the host may 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 mandatory 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. -14.2. Non-security considerations +14.2. Alternative HI considerations The definition of the Host Identifier states that the HI need not be a public key. It implies that the HI could be any value; for example a FQDN. This document does not describe how to support such a non- cryptographic HI. A non-cryptographic HI would still offer the services of the HIT or LSI for NAT traversal. It would be possible to carry HITs in HIP packets that had neither privacy nor authentication. Since such a mode would offer so little additional functionality for so much addition to the IP kernel, it has not been defined. Given how little public key cryptography HIP requires, HIP @@ -1087,46 +1098,47 @@ process owes its impetuous to the three HIP development teams: Boeing, HIIT (Helsinki Institute for Information Technology), and NomadicLab of Ericsson. Without their collective efforts HIP would have withered as on the IETF vine as a nice concept. 17. References 17.1. Normative References [RFC5201-bis] - Moskowitz, R., Jokela, P., Henderson, T., and T. Heer, - "Host Identity Protocol", draft-ietf-hip-rfc5201-bis-04 - (work in progress), January 2011. + Moskowitz, R., Heer, T., Jokela, P., and T. Henderson, + "Host Identity Protocol Version 2 (HIPv2)", + draft-ietf-hip-rfc5201-bis-05 (work in progress), + March 2011. [I-D.ietf-hip-rfc5202-bis] Jokela, P., Moskowitz, R., Nikander, P., and J. Melen, "Using the Encapsulating Security Payload (ESP) Transport Format with the Host Identity Protocol (HIP)", draft-ietf-hip-rfc5202-bis-00 (work in progress), September 2010. [I-D.ietf-hip-rfc5204-bis] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP) - Rendezvous Extension", draft-ietf-hip-rfc5204-bis-00 (work - in progress), August 2010. + Rendezvous Extension", draft-ietf-hip-rfc5204-bis-01 (work + in progress), March 2011. [I-D.ietf-hip-rfc5205-bis] Laganier, J., "Host Identity Protocol (HIP) Domain Name - System (DNS) Extension", draft-ietf-hip-rfc5205-bis-00 - (work in progress), August 2010. + System (DNS) Extension", draft-ietf-hip-rfc5205-bis-01 + (work in progress), March 2011. [I-D.ietf-hip-rfc5206-bis] Nikander, P., Henderson, T., Vogt, C., and J. Arkko, "Host Mobility with the Host Identity Protocol", - draft-ietf-hip-rfc5206-bis-01 (work in progress), - October 2010. + draft-ietf-hip-rfc5206-bis-02 (work in progress), + March 2011. 17.2. Informative references [RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. [RFC2535] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999. @@ -1190,16 +1202,16 @@ Springer, 2002. [Bel1998] Bellovin, S., "EIDs, IPsec, and HostNAT", in Proceedings of 41th IETF, Los Angeles, CA, URL http://www1.cs.columbia.edu/~smb/talks/hostnat.pdf, March 1998. Author's Address Robert Moskowitz - Verizon Telcom and Business + Verizon 1000 Bent Creek Blvd, Suite 200 Mechanicsburg, PA USA - Email: robert.moskowitz@verizonbusiness.com + Email: robert.moskowitz@verizon.com