< draft-moskowitz-hip-arch-04.txt   draft-moskowitz-hip-arch-05.txt >
Network Working Group R. Moskowitz Network Working Group R. Moskowitz
Internet-Draft ICSAlabs, a Division of TruSecure Internet-Draft ICSAlabs, a Division of TruSecure
Expires: March 1, 2004 Corporation Expires: March 1, 2004 Corporation
P. Nikander P. Nikander
Ericsson Research Nomadic Lab Ericsson Research Nomadic Lab
Sep 2003 Sep 2003
Host Identity Protocol Architecture Host Identity Protocol Architecture
draft-moskowitz-hip-arch-04 draft-moskowitz-hip-arch-05
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts. groups may also distribute working documents as Internet-Drafts.
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http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on March 1, 2004. This Internet-Draft will expire on March 1, 2004.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract Abstract
This memo describes the reasoning behind proposing a new namespace, This memo describes the reasoning behind a proposed new namespace,
the Host Identity namespace, and a new layer, Host Identity Layer, the Host Identity namespace, and a new protocol layer, the Host
between the internetworking and transport layers. Herein are Identity Protocol, between the internetworking and transport layers.
presented the basics of the current namespaces, strengths and Herein are presented the basics of the current namespaces, strengths
weaknesses, and how a new namespace will add completeness to them. and weaknesses, and how a new namespace will add completeness to
The roles of this new namespace in the protocols are defined. them. The roles of this new namespace in the protocols are defined.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 A Desire for Namespace for Computing Platforms . . . . . . . . 5 2.1 A Desire for a Namespace for Computing Platforms . . . . . . 5
3. Host Identity Namespace . . . . . . . . . . . . . . . . . . . 7 3. Host Identity Namespace . . . . . . . . . . . . . . . . . . 7
3.1 Host Identifiers . . . . . . . . . . . . . . . . . . . . . . . 7 3.1 Host Identifiers . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Storing Host Identifiers in DNS . . . . . . . . . . . . . . . 8 3.2 Storing Host Identifiers in DNS . . . . . . . . . . . . . . 8
3.3 Host Identity Tag (HIT) . . . . . . . . . . . . . . . . . . . 8 3.3 Host Identity Tag (HIT) . . . . . . . . . . . . . . . . . . 8
3.4 Local Scope Identity (LSI) . . . . . . . . . . . . . . . . . . 9 3.4 Local Scope Identifier (LSI) . . . . . . . . . . . . . . . . 9
4. The New Architecture . . . . . . . . . . . . . . . . . . . . . 10 4. New Stack Architecture . . . . . . . . . . . . . . . . . . . 10
4.1 Transport associations and endpoints . . . . . . . . . . . . . 10 4.1 Transport associations and endpoints . . . . . . . . . . . . 10
5. End-Host Mobility and Multi-Homing via HIP . . . . . . . . . . 12 5. End-Host Mobility and Multi-Homing . . . . . . . . . . . . . 12
5.1 Rendezvous server . . . . . . . . . . . . . . . . . . . . . . 12 5.1 Rendezvous server . . . . . . . . . . . . . . . . . . . . . 12
5.2 Protection against Flooding Attacks . . . . . . . . . . . . . 13 5.2 Protection against Flooding Attacks . . . . . . . . . . . . 13
6. HIP and NATs . . . . . . . . . . . . . . . . . . . . . . . . . 14 6. HIP and IPsec . . . . . . . . . . . . . . . . . . . . . . . 14
6.1 HIP and TCP Checksum . . . . . . . . . . . . . . . . . . . . . 14 7. HIP and NATs . . . . . . . . . . . . . . . . . . . . . . . . 15
7. HIP Policies . . . . . . . . . . . . . . . . . . . . . . . . . 15 7.1 HIP and TCP Checksum . . . . . . . . . . . . . . . . . . . . 15
8. Benefits of HIP . . . . . . . . . . . . . . . . . . . . . . . 16 8. HIP Policies . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1 HIP's Answers to NSRG questions . . . . . . . . . . . . . . . 17 9. Benefits of HIP . . . . . . . . . . . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19 9.1 HIP's Answers to NSRG questions . . . . . . . . . . . . . . 18
9.1 HITs used in ACLs . . . . . . . . . . . . . . . . . . . . . . 20 10. Security Considerations . . . . . . . . . . . . . . . . . . 20
9.2 Non-security Considerations . . . . . . . . . . . . . . . . . 21 10.1 HITs used in ACLs . . . . . . . . . . . . . . . . . . . . . 21
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 10.2 Non-security Considerations . . . . . . . . . . . . . . . . 22
References (informative) . . . . . . . . . . . . . . . . . . . 23 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 23 References (informative) . . . . . . . . . . . . . . . . . . 24
Intellectual Property and Copyright Statements . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 24
Intellectual Property and Copyright Statements . . . . . . . 26
1. Introduction 1. Introduction
The Internet has created two global namespaces: Internet Protocol The Internet has created two global namespaces: Internet Protocol
(IP) addresses, and Domain Name Service (DNS) names. These two (IP) addresses and Domain Name Service (DNS) names. These two
namespaces have a set of features and abstractions that have powered namespaces have a set of features and abstractions that have powered
the Internet to what it is today. They also have a number of 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 weaknesses. Basically, since they are all we have, we try and do too
much with them. Semantic overloading and functionality extensions much with them. Semantic overloading and functionality extensions
have greatly complicated these namespaces. have greatly complicated these namespaces.
The Host Identity namespace fills an important gap between the IP and The Host Identity namespace fills an important gap between the IP and
DNS namespaces. The Host Identity namespace consist of Host DNS namespaces. The Host Identity namespace consist of Host
Identifiers (HI). A Host Identifier is cryptographic in its nature; Identifiers (HI). A Host Identifier is cryptographic in its nature;
it is the public key of an asymmetric key-pair. A HI is assigned to it is the public key of an asymmetric key-pair. A Host Identity is
each host, or technically its networking kernel or stack. Each host assigned to each host, or technically its networking kernel or stack.
will have at least one Host Identifier, which can either be public Each host will have at least one Host Identity and a corresponding
(e.g. published in DNS), or anonymous. Client systems will tend to Host Identifier, which can either be public (e.g. published in DNS),
have both public and anonymous HIs. or anonymous. Client systems will tend to have both public and
anonymous Identities.
Although the Host Identity can be used in many authentication Although the Host Identities could be used in many authentication
systems, its design principle calls out for a new protocol and systems, the presented architecture introduces a new protocol, called
exchange [5] that will support limited forms of trust between the Host Identity Protocol (HIP), and a cryptographic exchange,
systems, enhance mobility, multi-homing and dynamic IP renumbering, called the HIP base exchange [4]. The new protocol provides for
aid in protocol translation / transition, and greatly reduce denial limited forms of trust between systems. It enhances mobility,
of service (DoS) attacks. multi-homing and dynamic IP renumbering [7], aids in protocol
translation / transition [4], and reduces certain types of
denial-of-service (DoS) attacks [4].
When HIP is used, the actual payload traffic between two HIP hosts is
typically protected with IPsec. The Host Identities are used to
create the needed IPsec Security Associations (SA) and to
authenticate the hosts. The actual payload IP packets do not differ
in any way from standard IPsec protected IP packets.
2. Background 2. Background
The Internet is built from three principle components: computing The Internet is built from three principle components: computing
platforms, packet transport (i.e. internetworking) infrastructure, platforms, packet transport (i.e. internetworking) infrastructure,
and services (applications). The Internet exists to service two and services (applications). The Internet exists to service two
principal components: people and robotic processes (silicon based principal components: people and robotic processes (silicon based
people, if you will). All these components need to be named in order people, if you will). All these components need to be named in order
to interact in a scalable manner. to interact in a scalable manner.
There are two principal namespaces in use in the Internet for these There are two principal namespaces in use in the Internet for these
components: IP numbers, and Domain Names. Email, HTTP and SIP components: IP numbers, and Domain Names. Email, HTTP and SIP
addresses are really only an extension of Domain Names. addresses are really only extensions of Domain Names.
IP numbers are a confounding of two namespaces, the names of the IP numbers are a confounding of two namespaces, the names of the
networking interfaces and the names of the locations ('confounding' networking interfaces and the names of the locations ('confounding'
is a term used in statistics to discuss metrics that are merged into 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 one with a gain in indexing, but a loss in informational value). The
names of locations should be understood as denoting routing direction names of locations should be understood as denoting routing direction
vectors, i.e., information that is used to deliver packets to their vectors, i.e., information that is used to deliver packets to their
destinations. destinations.
IP numbers name networking interfaces, and typically only when the IP numbers name networking interfaces, and typically only when the
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in so far as a named service is responsible for managing a person's in so far as a named service is responsible for managing a person's
mail. There is some anonymity in Email addresses. mail. There is some anonymity in Email addresses.
There are three critical deficiencies with the current namespaces. There are three critical deficiencies with the current namespaces.
Firstly, dynamic readdressing cannot be directly managed. Secondly, Firstly, dynamic readdressing cannot be directly managed. Secondly,
anonymity is not provided in a consistent, trustable manner. anonymity is not provided in a consistent, trustable manner.
Finally, authentication for systems and datagrams is not provided. Finally, authentication for systems and datagrams is not provided.
All because computing platforms are not well named with the current All because computing platforms are not well named with the current
namespaces. namespaces.
2.1 A Desire for Namespace for Computing Platforms 2.1 A Desire for a Namespace for Computing Platforms
An independent namespace for computing platforms could be used in An independent namespace for computing platforms could be used in
end-to-end operations independent of the evolution of the end-to-end operations independent of the evolution of the
internetworking layer and across the many internetworking layers. internetworking layer and across the many internetworking layers.
This could support rapid readdressing of the internetworking layer This could support rapid readdressing of the internetworking layer
either from mobility or renumbering. either from mobility or renumbering.
If the namespace for computing platforms is cryptographically based, If the namespace for computing platforms is cryptographically based,
it can also provide authentication services for IPsec. If this it can also provide authentication services. If this namespace is
namespace is locally created without requiring registration, it can locally created without requiring registration, it can provide
provide anonymity. anonymity.
Such a namespace (for computing platforms) and the names in it should Such a namespace (for computing platforms) and the names in it should
have the following characteristics: have the following characteristics:
The namespace should be applied to the IP 'kernel'. The IP kernel The namespace should be applied to the IP 'kernel'. The IP kernel
is the 'component' between services and the packet transport is the 'component' between services and the packet transport
infrastructure. infrastructure.
The namespace should fully decouple the internetworking layer from The namespace should fully decouple the internetworking layer from
the higher layers. The names should replace all occurrences of IP the higher layers. The names should replace all occurrences of IP
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The namespace should provide authentication services. This is a The namespace should provide authentication services. This is a
preferred function. preferred function.
The names should be long lived, but replaceable at any time. This The names should be long lived, but replaceable at any time. This
impacts access control lists; short lifetimes will tend to result impacts access control lists; short lifetimes will tend to result
in tedious list maintenance or require a namespace infrastructure in tedious list maintenance or require a namespace infrastructure
for central control of access lists. for central control of access lists.
In this document, such a new namespace is called the Host Identity In this document, such a new namespace is called the Host Identity
namespace. Using Host Identities requires its own protocol layer namespace. Using Host Identities requires its own protocol layer,
(the Host Identity Protocol), between the internetworking and the Host Identity Protocol, between the internetworking and transport
transport layers. The names are based on public key cryptography to layers. The names are based on public key cryptography to supply
supply authentication services. Properly designed, it can deliver all authentication services. Properly designed, it can deliver all of the
of the above stated requirements. above stated requirements.
3. Host Identity Namespace 3. Host Identity Namespace
A name in the Host Identity namespace, a Host Identifier (HI), A name in the Host Identity namespace, a Host Identifier (HI),
represents a statistically globally unique name for naming any system represents a statistically globally unique name for naming any system
with an IP stack. This identity is normally associated, but not with an IP stack. This identity is normally associated, but not
limited to, an IP stack. A system can have multiple identities, some limited to, an IP stack. A system can have multiple identities, some
'well known', some anonymous. A system may self assert its identity, '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 or may use a third-party authenticator like DNSSEC, PGP, or X.509 to
'notarize' the identity assertion. DNSSEC is a "SHOULD" implement 'notarize' the identity assertion. It is expected that the Host
authenticator for the Host Identity namespace. Identifiers will initially be authenticated with DNSSEC and that all
implementations will support DNSSEC as a minimal baseline.
There is a subtle but important difference between Host Identities There is a subtle but important difference between Host Identities
and Host Identifiers. An Identity refers to the abstract entity that and Host Identifiers. An Identity refers to the abstract entity that
is identified. An Identifier, on the other hand, refers to the is identified. An Identifier, on the other hand, refers to the
concrete bit pattern that is used in the identification process. concrete bit pattern that is used in the identification process.
Although a Host Identifier could be any name that can claim In theory, any name that can claim to be 'statistically globally
'statistically globally unique', a public key of a 'public key' pair unique' may serve as a Host Identifier. However, in the authors'
makes the best Host Identifiers. As documented in the Host Identity opinion, a public key of a 'public key pair' makes the best Host
Protocol (HIP) specification [5], a public key based HI can Identifiers. As documented in the Host Identity Protocol
authenticate the HIP packets and protect them for man-in-the-middle specification [4], a public key based HI can authenticate the HIP
attacks. And since authenticated datagrams are mandatory to provide packets and protect them for man-in-the-middle attacks. Since
much of HIP's DoS protection, the Diffie-Hellman exchange in HIP has authenticated datagrams are mandatory to provide much of HIP's
to be authenticated. Thus, only public key HI and authenticated denial-of-service protection, the Diffie-Hellman exchange in HIP has
datagrams are supported in practice. In this document, the to be authenticated. Thus, only public key HI and authenticated HIP
messages are supported in practice. In this document, the
non-cryptographic forms of HI and HIP are presented to complete 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 theory of HI, but they should not be implemented as they could
worse DoS attacks than the Internet has without HI. produce worse denial-of-service attacks than the Internet has without
Host Identity.
3.1 Host Identifiers 3.1 Host Identifiers
Host Identity adds two main features to Internet protocols. The first Host Identity adds two main features to Internet protocols. The first
is a decoupling of the internetworking and transport layers, see is a decoupling of the internetworking and transport layers; see
Section 4. This decoupling will allow for independent evolution of Section 4. This decoupling will allow for independent evolution of
the two layers. Additionally, it can provide end-to-end services the two layers. Additionally, it can provide end-to-end services
over multiple internetworking realms. The second feature is host over multiple internetworking realms. The second feature is host
authentication. Because the Host Identifier is a public key, this authentication. Because the Host Identifier is a public key, this
key can be used to authenticate security protocols like IPsec. key can be used to authenticate security protocols like IPsec.
The only completely defined structure of the Host Identity is that of The only completely defined structure of the Host Identity is that of
a public key pair. In this case, the Host Identity is referred to by a public key pair. In this case, the Host Identity is referred to by
its public component, the public key. Thus, the name representing a its public component, the public key. Thus, the name representing a
Host Identity in the Host Identity namespace, i.e. the Host Host Identity in the Host Identity namespace, i.e. the Host
Identifier, is the public key. In a way, the possession of the Identifier, is the public key. In a way, the possession of the
private key defines the Identity itself. It the private key is private key defines the Identity itself. If the private key is
possessed by more than one node, the Identity can be considered to be possessed by more than one node, the Identity can be considered to be
a distributed one. a distributed one.
Architecturally, any other Internet naming convention might form a Architecturally, any other Internet naming convention might form a
usable base for Host Identifiers. However, non-cryptographic names usable base for Host Identifiers. However, non-cryptographic names
should only be used in situations of high trust - low risk. That is 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 any place where host authentication is not needed (no risk of host
spoofing) and no use of IPsec. The current HIP documents do not spoofing) and no use of IPsec. The current HIP documents do not
specify how to use any other types of Host Identifiers but public specify how to use any other types of Host Identifiers but public
keys. keys.
The actual Host Identities are never directly used in any Internet The actual Host Identities are never directly used in any Internet
protocols. The corresponding Host Identifiers (public keys) may be protocols. The corresponding Host Identifiers (public keys) may be
stored in various DNS or LDAP directories as identified elsewhere in stored in various DNS or LDAP directories as identified elsewhere in
this document, and they are passed in the HIP protocol. A Host 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 Tag (HIT) is used in other protocols to represent the Host
Identities. Another representation of the Host Identities, the Local Identities. Another representation of the Host Identities, the Local
Scope Identity (LSI), can also be used in protocols and APIs. LSI's Scope Identifier (LSI), can also be used in protocols and APIs.
advantage over HIT is its size; its disadvantage is its local scope.
3.2 Storing Host Identifiers in DNS 3.2 Storing Host Identifiers in DNS
The Host Identifiers should be stored in DNS. The exception to this The Host Identifiers should be stored in DNS. The exception to this
is anonymous identities. The HI is stored in a new RR type, to be is anonymous identities. The HI is stored in a new RR type, to be
defined. This RR type is likely to be very similar to the IPSECKEY defined. This RR type is likely to be quite similar to the IPSECKEY
RR [6]. RR [5].
Alternatively, or in addition to storing Host Identifiers in the DNS, Alternatively, or in addition to storing Host Identifiers in the DNS,
they may be stored in various kinds of Public Key Infrastructure they may be stored in various kinds of Public Key Infrastructure
(PKI). Such a practice may allow them to be used for purposes other (PKI). Such a practice may allow them to be used for purposes other
than pure host identification. than pure host identification.
3.3 Host Identity Tag (HIT) 3.3 Host Identity Tag (HIT)
A Host Identity Tag is an 128 bit representation for a Host Identity. A Host Identity Tag is an 128-bit representation for a Host Identity.
It is created by taking a cryptographic hash over the corresponding It is created by taking a cryptographic hash over the corresponding
Host Identifier. There are two advantages of using a hash over using Host Identifier. There are two advantages of using a hash over using
the Host Identifier in protocols. Firstly, its fixed length makes for the Host Identifier in protocols. Firstly, its fixed length makes for
easier protocol coding and also better manages the packet size cost easier protocol coding and also better manages the packet size cost
of this technology. Secondly, it presents a consistent format to the of this technology. Secondly, it presents the identity in a
protocol independent of the whatever underlying identity technology consistent format to the protocol independent of the whatever
is used. underlying technology is used.
In the HIP protocol, the HITs identify the sender and recipient of a In the HIP packets, the HITs identify the sender and recipient of a
packet. Consequently, a HIT should be unique in the whole IP packet. Consequently, a HIT should be unique in the whole IP
universe. In the extremely rare case that a single HIT happens to universe. In the extremely rare case that a single HIT happens to
map to more than one Host Identities, the Host Identifiers (public map to more than one Host Identities, the Host Identifiers (public
keys) will make the final difference. If there is more than one 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 for a given node, the HIT acts as a hint for the correct
public key to use. public key to use.
3.4 Local Scope Identity (LSI) 3.4 Local Scope Identifier (LSI)
An LSI is a 32 bit localized representation for a Host Identity. The An LSI is a 32-bit localized representation for a Host Identity. The
purpose of an LSI is to facilitate using Host Identity in existing purpose of an LSI is to facilitate using Host Identities in existing
protocols and APIs. The generation of LSIs is defined in [5]. protocols and APIs. LSI's advantage over HIT is its size; its
disadvantage is its local scope. The generation of LSIs is defined in
the Host Identity Protocol specification [4].
Examples of how LSIs can be used include: as the address in a FTP 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 command and as the address in a socket call. Thus, LSIs act as a
bridge for Host Identifier into old protocols and APIs. bridge for Host Identities into old protocols and APIs.
4. The New Architecture 4. New Stack Architecture
One way to characterize Host Identity is to compare the proposed new One way to characterize Host Identity is to compare the proposed new
architecture with the current one. As discussed above, the IP architecture with the current one. As discussed above, the IP
addresses can be seen to be a confounding of routing direction addresses can be seen to be a confounding of routing direction
vectors and interface names. Using the terminology from the IRTF vectors and interface names. Using the terminology from the IRTF
Name Space Research Group Report [7] and, e.g., the unpublished Name Space Research Group Report [6] and, e.g., the unpublished
Internet-Draft Endpoints and Endpoint Names [9], currently the IP Internet-Draft Endpoints and Endpoint Names [9] by Noel Chiappa, the
addresses embody the dual role of locators and endpoint identifiers. IP addresses currently embody the dual role of locators and endpoint
That is, each IP address names a topological location in the identifiers. That is, each IP address names a topological location
Internet, thereby acting as a routing direction vector or locator. in the Internet, thereby acting as a routing direction vector, or
At the same time, the IP address names the physical network interface locator. At the same time, the IP address names the physical network
currently located at the point-of-attachment, thereby acting as a interface currently located at the point-of-attachment, thereby
endpoint name. acting as a endpoint name.
In the HIP Architecture, the endpoint names and locators are In the HIP architecture, the endpoint names and locators are
separated from each other. IP addresses continue to act as locators. separated from each other. IP addresses continue to act as locators.
The Host Identifiers take the role of endpoint identifiers. It is The Host Identifiers take the role of endpoint identifiers. It is
important to understand that the endpoint names based on Host important to understand that the endpoint names based on Host
Identities are slightly different from interface names; a Host Identities are slightly different from interface names; a Host
Identity can be simultaneously reachable through several interfaces. Identity can be simultaneously reachable through several interfaces.
The difference between the bindings of the logical entities are The difference between the bindings of the logical entities are
illustrated in Figure 1. illustrated in Figure 1.
Process ------ Socket Process ------ Socket Process ------ Socket Process ------ Socket
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Figure 1 Figure 1
4.1 Transport associations and endpoints 4.1 Transport associations and endpoints
Architecturally, HIP provides for a different binding of transport Architecturally, HIP provides for a different binding of transport
layer protocols. That is, the transport layer associations, i.e., layer protocols. That is, the transport layer associations, i.e.,
TCP connections and UDP associations, are no more bound to IP TCP connections and UDP associations, are no more bound to IP
addresses but to Host Identities. addresses but to Host Identities.
It is possible that a single physical computer hosts several logical It is possible that a single physical computer hosts several logical
end-points. With HIP, each of these end-points would have a distinct endpoints. With HIP, each of these endpoints would have a distinct
Host Identity. Furthermore, since the transport associations are Host Identity. Furthermore, since the transport associations are
bound to Host Identities, HIP provides for process migration and bound to Host Identities, HIP provides for process migration and
clustered servers. That is, if a Host Identity is moved from one clustered servers. That is, if a Host Identity is moved from one
physical computer to another, it is also possible to simultaneously physical computer to another, it is also possible to simultaneously
move all the transport associations without breaking them. Similarly, move all the transport associations without breaking them. Similarly,
if it is possible to distribute the processing of a single Host if it is possible to distribute the processing of a single Host
Identity over several physical computers, HIP provides for cluster Identity over several physical computers, HIP provides for cluster
based services without any changes at the client end-point. based services without any changes at the client endpoint.
5. End-Host Mobility and Multi-Homing via HIP 5. End-Host Mobility and Multi-Homing
As HIP decouples the transport from the internetworking layer, and HIP decouples the transport from the internetworking layer, and binds
binds the transport associations to the Host Identifiers (through the transport associations to the Host Identities (through actually
actually either the HIT or LSI), HIP can provide for a degree of either the HIT or LSI). Consequently, HIP can provide for a degree
internetworking mobility and multi-homing at a very low of internetworking mobility and multi-homing at a very low
infrastructure cost. HIP mobility includes IP address changes (via infrastructure cost. HIP mobility includes IP address changes (via
any method) to either the initiator or responder. Thus, a system is any method) to either party. Thus, a system is considered mobile if
considered mobile if its IP address can change dynamically for any its IP address can change dynamically for any reason like PPP, DHCP,
reason like PPP, DHCP, IPv6 TLA reassignments, or a NAT device IPv6 prefix reassignments, or a NAT device remapping its translation.
remapping its translation. Likewise, a system is considered Likewise, a system is considered multi-homed if it has more than one
multi-homed if it has more than one globally routable IP address at globally routable IP address at the same time. HIP allows these IP
the same time. HIP allows these IP addresses to be linked with each addresses to be linked with each other, and if one address becomes
other, and if one address becomes unusable (e.g. due a network unusable (e.g. due to a network failure), existing transport
failure), existing transport associations can be easily moved to associations can be easily moved to another address.
another address.
When a node moves while communication is already on-going, address When a node moves while communication is already on-going, address
changes are rather straightforward. The peer of the mobile node can changes are rather straightforward. The peer of the mobile node can
just accept a HIP or an ESP packet from any address and totally just accept a HIP or an integrity protected IPsec packet from any
ignore the source address. As discussed in Section 5.2 below, a address and totally ignore the source address. However, as discussed
mobile node must send a HIP readdress packet to inform the peer of in Section 5.2 below, a mobile node must send a HIP readdress packet
the new address(es), and the peer must verify that the new mobile to inform the peer of the new address(es), and the peer must verify
node is reachable through these addresses. This is especially that the mobile node is reachable through these addresses. This is
helpful for those situations where the peer node is sending data especially helpful for those situations where the peer node is
periodically to the mobile node (that is re-starting a connection sending data periodically to the mobile node (that is re-starting a
after the initial connection). connection after the initial connection).
5.1 Rendezvous server 5.1 Rendezvous server
Making a contact to a mobile node is slightly more involved. The Making a contact to a mobile node is slightly more involved. In
initiator node has to know where the mobile node is to start the HIP order to start the HIP exchange, the initiator node has to know how
exchange. HIP need not rely on Dynamic DNS for this function, but to reach the mobile node. Although Dynamic DNS could be used for
uses a rendezvous server. Instead of registering its current dynamic this function for infrequently moving nodes, an alternative to using
address to the DNS server, the mobile node registers the address of DNS in this fashion is to use a piece of new static infrastructure
the rendezvous server. The mobile node keeps the rendezvous server called a HIP rendezvous server. Instead of registering its current
continuously updated with its current IP address(es). The rendezvous dynamic address to the DNS server, the mobile node registers the
server simply forwards the initial HIP packet from an initiator to address(es) of its rendezvous server(s). The mobile node keeps the
the mobile node at its current location. All further packets flow rendezvous server(s) continuously updated with its current IP
between the initiator and the mobile node. There is typically very address(es). A rendezvous server simply forwards the initial HIP
little activity on the rendezvous server, address updates and initial packet from an initiator to the mobile node at its current location.
HIP packet forwarding, thus one server can support a large number of All further packets flow between the initiator and the mobile node.
potential mobile nodes. The mobile nodes must trust the rendezvous There is typically very little activity on a rendezvous server,
server to properly maintain its HIT and IP address mapping. address updates and initial HIP packet forwarding. Thus, one server
can support a large number of potential mobile nodes. The mobile
nodes must trust the rendezvous server to properly maintain their HIT
and IP address mappings.
The rendezvous server is also needed if both of the nodes are mobile The rendezvous server is also needed if both of the nodes are mobile
and happen to move at the same time. In that case the HIP readdress and happen to move at the same time. In that case, the HIP readdress
packets will cross each other in the network and never reach the peer packets will cross each other in the network and never reach the peer
node. To solve this situation, the nodes should remember the node. To solve this situation, the nodes should remember the
rendezvous server address, and re-send the HIP readdress packet to rendezvous server address, and re-send the HIP readdress packet to
the rendezvous server if no reply is received. the rendezvous server if no reply is received.
The mobile node keeps its address current on the rendezvous server by The mobile node keeps its address current on the rendezvous server by
setting up a HIP based SA with the rendezvous server and sending it setting up a HIP association with the rendezvous server and sending
HIP readdress packets. A rendezvous server will permit two mobile HIP readdress packets to it. A rendezvous server will permit two
systems to use HIP without any extraneous infrastructure (in addition mobile systems to use HIP without any extraneous infrastructure (in
to the rendezvous server itself), including DNSSEC if they have a addition to the rendezvous server itself), including DNS if they have
method other than a DNS query to get each other's HI and HIT. a method other than a DNS query to get each other's HI and HIT.
5.2 Protection against Flooding Attacks 5.2 Protection against Flooding Attacks
While the idea of informing about address changes by simply sending While the idea of informing about address changes by simply sending
packets with a new source address appears appealing, it is not secure packets with a new source address appears appealing, it is not secure
enough. That is, while receiving packets in HIP does not rely on the enough. That is, even if HIP does not rely on the source address for
source address for anything, it appears to be necessary to check the anything (once the base exchange has been completed), it appears to
mobile node's reachability at the new address(es) before actually be necessary to check a mobile node's reachability at the new address
sending any larger amounts of traffic to the address. before actually sending any larger amounts of traffic to the new
address.
Blindly accepting new addresses would potentially lead to a flooding Blindly accepting new addresses would potentially lead to flooding
Denial-of-Service attack against third parties [8]. In a distributed Denial-of-Service attacks against third parties [8]. In a
flooding attack an attacker opens (anonymous) high volume HIP distributed flooding attack an attacker opens (anonymous) high volume
connections with a large number of hosts, and then claims to all of HIP connections with a large number of hosts, and then claims to all
these hosts that it has moved to a target node's IP address. If the of these hosts that it has moved to a target node's IP address. If
peer hosts were to simply accept the move, the result would be a the peer hosts were to simply accept the move, the result would be a
packet flood to the target node's address. To close this attack, HIP packet flood to the target node's address. To close this attack, HIP
includes an address check mechanism where the reachability of the includes an address check mechanism where the reachability of a node
node is separately checked at each address before actually using the is separately checked at each address before using the address for
address for larger amounts of traffic. larger amounts of traffic.
Whenever HIP is used between two hosts that fully trust each other, Whenever HIP is used between two hosts that fully trust each other,
the hosts may optionally decide to skip the address tests. However, the hosts may optionally decide to skip the address tests. However,
such performance optimization must be restricted to be performed only such performance optimization must be restricted to peers that are
with peers that are known to be trustworthy and capable of protecting known to be trustworthy and capable of protecting themselves from
themselves from malicious software. malicious software.
6. HIP and NATs 6. HIP and IPsec
The preferred way of implementing HIP is to use IPsec 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
packets. In the future, other ways of transporting payload data may
be developed, including ones that do not use cryptographic
protection.
In practise, 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.
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. Future HIP extensions may provide for more granularity and
creation of several ESP SAs between a pair of HITs
Since HIP is designed for host usage, not for gateways, 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.
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.
7. HIP and NATs
Passing packets between different IP addressing realms requires Passing packets between different IP addressing realms requires
changing IP addresses in the packet header. This may happen, for changing IP addresses in the packet header. This may happen, for
example, when a packet is passed between the public Internet and a example, when a packet is passed between the public Internet and a
private address space, or between IPv4 and IPv6 networks. The private address space, or between IPv4 and IPv6 networks. The
address translation is usually implemented as Network Address address translation is usually implemented as Network Address
Translation (NAT) [3] or NAT Protocol translation (NAT-PT) [2]. Translation (NAT) [2] or NAT Protocol translation (NAT-PT) [1].
In a network environment where the identification is based on the IP In a network environment where the identification is based on the IP
address, identifying the communicating nodes is difficult when the addresses, identifying the communicating nodes is difficult when NAT
NAT is used. With HIP, the transport layer end-points are bound to is used. With HIP, the transport layer endpoints are bound to the
the HIT or LSI. Thus, a connection between two hosts can traverse Host Identities. Thus, a connection between two hosts can traverse
many addressing realm boundaries. The IP addresses are used only for many addressing realm boundaries. The IP addresses are used only for
routing purposes; the IP addresses may be changed freely during routing purposes; the IP addresses may be changed freely during
packet traversal. packet traversal.
For a HIP based flow, a NAT or NAT-PT system needs only track the For a HIP based flow, a NAT or NAT-PT system tracks the mapping of
mapping of the HIT or SPI to an IP address. Many HITs can map to a HITs and the corresponding IPsec SPIs to an IP address. Many HITs
single IP address on a NAT, simplifying connections on address poor can map to a single IP address on a NAT, simplifying connections on
NAT interfaces. The NAT can gain much of its knowledge from the HIP address poor NAT interfaces. The NAT can gain much of its knowledge
packets themselves; however some NAT configuration may be necessary. from the HIP packets themselves; however, some NAT configuration may
be necessary.
The NAT systems cannot touch the datagrams within the ESP envelope, The NAT systems cannot touch the datagrams within the IPsec envelope,
thus application specific address translation must be done in the end thus application specific address translation must be done in the end
systems. HIP provides for 'Distributed NAT', and uses the HIT or the systems. HIP provides for 'Distributed NAT', and uses the HIT or the
LSI as a place holder for embedded IP addresses. LSI as a place holder for embedded IP addresses.
6.1 HIP and TCP Checksum 7.1 HIP and TCP Checksum
There is no way for a host to know if any of the IP addresses in the 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. That IP header are the addresses used to calculate the TCP checksum. That
is, it is not feasible to calculate the TCP checksum using the IP is, it is not feasible to calculate the TCP checksum using the actual
addresses in the pseudo header; the addresses received in the IP addresses in the pseudo header; the addresses received in the
incoming packet are not necessarily the same as they were on the incoming packet are not necessarily the same as they were on the
sending host. Furthermore, it is not possible to recompute the upper sending host. Furthermore, it is not possible to recompute the upper
layer checksums in the NAT/NAT-PT system, since the traffic is IPsec layer checksums in the NAT/NAT-PT system, since the traffic is IPsec
protected. Consequently, the TCP and UDP checksums are calculated protected. Consequently, the TCP and UDP checksums are calculated
using the HIT in the place of the IP addresses in the pseudo header. 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.
7. HIP Policies 8. HIP Policies
There are a number of variables that will influence the HIP exchanges There are a number of variables that will influence the HIP exchanges
that each host must support. All HIP implementations should support that each host must support. All HIP implementations should support
at least 2 HIs, one to publish in DNS and one for anonymous usage. 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 are Although anonymous HIs will be rarely used as responder HIs, they are
likely be common for initiators. Support for multiple HIs is likely be common for initiators. Support for multiple HIs is
recommended. recommended.
Many initiators would want to use a different HI for different Many initiators would want to use a different HI for different
responders. The implementations should provide for a policy of responders. The implementations should provide for a policy of
initiator HIT to responder HIT. This policy should also include initiator HIT to responder HIT. This policy should also include
preferred transform and local lifetimes. preferred transforms and local lifetimes.
Responders would need a similar policy, representing which hosts they Responders would need a similar policy, representing which hosts they
accept HIP exchanges, and the preferred transform and local accept HIP exchanges, and the preferred transforms and local
lifetimes. lifetimes.
8. Benefits of HIP 9. Benefits of HIP
In the beginning, the network layer protocol (i.e. IP) had the In the beginning, the network layer protocol (i.e. IP) had the
following four "classic" invariants: following four "classic" invariants:
Non-mutable: The address sent is the address received. Non-mutable: The address sent is the address received.
Non-mobile: The address doesn't change during the course of an Non-mobile: The address doesn't change during the course of an
"association". "association".
Reversible: A return header can always be formed by reversing the Reversible: A return header can always be formed by reversing the
skipping to change at page 16, line 27 skipping to change at page 17, line 27
Omniscient: Each host knows what address a partner host can use to Omniscient: Each host knows what address a partner host can use to
send packets to it. send packets to it.
Actually, the fourth can be inferred from 1 and 3, but it is worth 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. mentioning for reasons that will be obvious soon if not already.
In the current "post-classic" world, we are trying intentionally to In the current "post-classic" world, we are trying intentionally to
get rid of the second invariant (both for mobility and for get rid of the second invariant (both for mobility and for
multi-homing), and we have been forced to give up the first and the multi-homing), and we have been forced to give up the first and the
fourth. Realm Specific IP [4] is an attempt to reinstate the fourth fourth. Realm Specific IP [3] is an attempt to reinstate the fourth
invariant without the first invariant. IPv6 is an attempt to invariant without the first invariant. IPv6 is an attempt to
reinstate the first invariant. reinstate the first invariant.
Few systems on the Internet have DNS names that are meaningful to Few systems on the Internet have DNS names that are meaningful to
them. That is, if they have a Fully Qualified Domain Name (FQDN), them. That is, if they have a Fully Qualified Domain Name (FQDN),
that typically belongs to a NAT device or a dial-up server, and does that typically belongs to a NAT device or a dial-up server, and does
not really identify the system itself but its current connectivity. not really identify the system itself but its current connectivity.
FQDN names (and their extensions as email names) are Application FQDN names (and their extensions as email names) are Application
Layer names; more frequently naming processes than a particular Layer names; more frequently naming processes than a particular
system. This is why many systems on the internet are not registered system. This is why many systems on the internet are not registered
in DNS; they do not have processes of interest to other Internet in DNS; they do not have processes of interest to other Internet
hosts. hosts.
DNS names are indirect references to IP addresses. This only DNS names are indirect references to IP addresses. This only
demonstrates the interrelationship of the networking and application demonstrates the interrelationship of the networking and application
layers. DNS, as the Internet's only deployed, distributed, database layers. DNS, as the Internet's only deployed, distributed, database
is also the repository of other namespaces, due in part to DNSSEC and is also the repository of other namespaces, due in part to DNSSEC and
KEY records. Although each namespace can be stretched (IP with v6, application specific key records. Although each namespace can be
DNS with KEY records), neither can adequately provide for host stretched (IP with v6, DNS with KEY records), neither can adequately
authentication or act as a separation between internetworking and provide for host authentication or act as a separation between
transport layers. internetworking and transport layers.
The Host Identity (HI) namespace fills an important gap between the The Host Identity (HI) namespace fills an important gap between the
IP and DNS namespaces. An interesting thing about the HI is that it 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 actually allows one to give-up all but the 3rd Network Layer
invariant. That is to say, as long as the source and destination invariant. That is to say, as long as the source and destination
addresses in the network layer protocol are reversible, then things addresses in the network layer protocol are reversible, then things
work ok because HIP takes care of host identification, and work ok because HIP takes care of host identification, and
reversibility allows one to get a packet back to one's partner host. reversibility allows one to get a packet back to one's partner host.
You don't care if the network layer address changes in transit You don't care if the network layer address changes in transit
(mutable) and you don't care what network layer address the partner (mutable) and you don't care what network layer address the partner
is using (non-omniscient). is using (non-omniscient).
Since all systems can have a Host Identity, every system can have an 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 entry in the DNS. The mobility features in HIP make it attractive to
trusted 3rd parties to offer rendezvous servers. trusted 3rd parties to offer rendezvous servers.
8.1 HIP's Answers to NSRG questions 9.1 HIP's Answers to NSRG questions
The IRTF Name Space Research Group has posed a number of evaluating The IRTF Name Space Research Group has posed a number of evaluating
questions in their report [7]. In this section, we provide answers questions in their report [6]. In this section, we provide answers
to these questions. to these questions.
1. How would a stack name improve the overall functionality of the 1. How would a stack name improve the overall functionality of the
Internet? Internet?
The HIP Host Identifiers make end-host mobility and At the fundamental level, HI decouples the internetworking
multi-homing easier by separating the transport layer and layer from the transport layer, allowing each to evolve
internetworking layer from each other. Among other things, separately. At the same time, the decoupling makes end-host
this allows mobility and multi-homing across the IPv4 and IPv6 mobility and multi-homing easier. It also allows mobility and
internets. Host Identifiers also make network re-numbering multi-homing across the IPv4 and IPv6 networks. HIs make
easier. At the conceptual level, they also make process network renumbering easier. At the conceptual level, they
migration and clustered servers easier to implement. also make process migration and clustered servers easier to
Furthermore, being cryptographic in nature, they also provide implement. Furthermore, being cryptographic in nature, they
the basis for solving the security problems related to provide the basis for solving the security problems related to
end-host mobility and multi-homing. end-host mobility and multi-homing.
2. What does a stack name look like? 2. What does a stack name look like?
A HIP Host Identifier is a cryptographic public key. However, A HI is a cryptographic public key. However, instead of using
instead of using the keys directly, most protocols use a fixed the keys directly, most protocols use a fixed size hash of the
size hash of the public key. public key.
3. What is its lifetime? 3. What is its lifetime?
HIP provides both stable and temporary Host Identifiers. HIP provides both stable and temporary Host Identifiers.
Stable Host Identifiers are typically long lived, with a Stable HIs are typically long lived, with a lifetime of years
lifetime of years or more. The lifetime of temporary Host or more. The lifetime of temporary HIs depends on how long
Identifiers depends on how long the upper layer connections the upper layer connections and applications need them, and
and applications need them, and can range from a few seconds can range from a few seconds to years.
to years.
4. Where does it live in the stack? 4. Where does it live in the stack?
The HIs live between the transport and internetworking layers.
The HIP Host Identifiers live between the transport and
internetworking layers.
5. How is it used on the end points 5. How is it used on the end points
The HIP Host Identifiers, in the form of HITs or LSIs, are The Host Identifiers, in the form of HITs or LSIs, are used by
used by legacy applications as if they were IP addresses. legacy applications as if they were IP addresses.
Additionally, the Host Identifiers, as public keys, are used Additionally, the Host Identifiers, as public keys, are used
in a built in key agreement protocol to authenticate the in the built in key agreement protocol, called the HIP base
Diffie-Hellman key exchange. exchange, to authenticate the hosts to each other.
6. What administrative infrastructure is needed to support it? 6. What administrative infrastructure is needed to support it?
It is possible to use HIP opportunistically, without any It is possible to use HIP opportunistically, without any
infrastructure. However, to gain full benefit from HIP, the infrastructure. However, to gain full benefit from HIP, the
Host Identifiers must be stored in the DNS, and a new HIs must be stored in the DNS or a PKI, and a new
infrastructure of Rendezvous servers is needed. infrastructure of rendezvous servers is needed.
7. If we add an additional layer would it make the address list in 7. If we add an additional layer would it make the address list in
SCTP unnecessary? SCTP unnecessary?
Yes Yes
8. What additional security benefits would a new naming scheme 8. What additional security benefits would a new naming scheme
offer? offer?
HIP reduces dependency on IP addresses, making the so called HIP reduces dependency on IP addresses, making the so called
address ownership problems easier to solve. In practice, HIP address ownership problems easier to solve. In practice, HIP
provides security for end-host mobility and multi-homing. provides security for end-host mobility and multi-homing.
Furthermore, since HIP Host Identifiers are public keys, Furthermore, since HIP Host Identifiers are public keys,
standard public key certificate infrastructures can be applied standard public key certificate infrastructures can be applied
on the top of HIP. on the top of HIP.
9. What would the resolution mechanisms be, or what characteristics 9. What would the resolution mechanisms be, or what characteristics
of a resolution mechanisms would be required? of a resolution mechanisms would be required?
For most purposes, an approach where DNS names are resolved For most purposes, an approach where DNS names are resolved
simultaneously to Host Identifiers and IP addresses is simultaneously to HIs and IP addresses is sufficient.
sufficient. However, if it becomes necessary to resolve Host However, if it becomes necessary to resolve HIs into IP
Identifiers into IP addresses or back to DNS names, a flat, addresses or back to DNS names, a flat, hash based resolution
hash based resolution infrastructure is needed. Such an infrastructure is needed. Such an infrastructure could be
infrastructure could be based on the ideas of Distributed Hash based on the ideas of Distributed Hash Tables, but would
Tables, but would require significant new development and require significant new development and deployment.
deployment.
9. Security Considerations 10. Security Considerations
HIP takes advantage of the new Host Identity paradigm to provide HIP takes advantage of the new Host Identity paradigm to provide
secure authentication of hosts and provide a fast key exchange for secure authentication of hosts and to provide a fast key exchange for
IPsec ESP. HIP also attempts to limit the exposure of the host to IPsec. HIP also attempts to limit the exposure of the host to
various denial-of-service (DoS) and man-in-the-middle (MitM) attacks. 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 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 that potentially could be more damaging to a host's ability to
conduct business as usual. conduct business as usual.
The Security Association for ESP is indexed by the SPI; the source Resource exhausting Denial-of-service attacks take advantage of the
address is always ignored, and the destination address may be ignored cost of setting up a state for a protocol on the responder compared
as well. Therefore, HIP enabled ESP is IP address independent. This to the 'cheapness' on the initiator. HIP allows a responder to
might seem to make it easier for an attacker, but ESP with replay increase the cost of the start of state on the initiator and makes an
protection is already as well protected as possible, and the removal effort to reduce the cost to the responder. This is done by having
of the IP address as a check should not increase the exposure of ESP the responder start the authenticated Diffie-Hellman exchange instead
to DoS attacks. of the initiator, making the HIP base exchange 4 packets long. There
are more details on this process in the Host Identity Protocol
Denial-of-service attacks take advantage of the cost of setting up a specification [4].
state for a protocol on the responder compared to the 'cheapness' on
the initiator. HIP both allows 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 protocol instead of the initiator,
making the HIP protocol 4 packets long. There are more details on
this process in the HIP protocol specification [5].
HIP optionally supports opportunistic negotiation. That is, if a HIP optionally supports opportunistic negotiation. That is, if a
host receives a start of transport without a HIP negotiation, it can host receives a start of transport without a HIP negotiation, it can
attempt to force a HIP exchange before accepting the connection. attempt to force a HIP exchange before accepting the connection.
This has the potential for DoS attacks against both hosts. If the 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 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 attacker need only spoof a TCP SYN. This would put both systems into
the expensive operations. HIP avoids this attack by having the the expensive operations. HIP avoids this attack by having the
responder send a simple HIP packet that it can pre-build. Since this responder send a simple HIP packet that it can pre-build. Since this
packet is fixed and easily spoofed, the initiator only reacts to it packet is fixed and easily replayed, the initiator only reacts to it
if it has just started a connection to the responder. if it has just started a connection to the responder.
Man-in-the-middle attacks are difficult to defend against, without Man-in-the-middle attacks are difficult to defend against, without
third-party authentication. A skillful MitM could easily handle all third-party authentication. A skillful MitM could easily handle all
parts of the HIP protocol, but HIP indirectly provides the following parts of the HIP base exchange, but HIP indirectly provides the
protection from a MitM attack. If the responder's HI is retrieved following protection from a MitM attack. If the responder's HI is
from a signed DNS zone or secured by some other means by the retrieved from a signed DNS zone or secured by some other means, the
initiator, the initiator can use this to validate the signed HIP initiator can use this to authenticate the signed HIP packets.
packets.
Likewise, if the initiator's HI is in a secure DNS zone, the Likewise, if the initiator's HI is in a secure DNS zone, the
responder can retrieve it and validate the signed HIP packets. responder can retrieve it and validate the signed HIP packets.
However, since an initiator may choose to use an anonymous HI, it However, since an initiator may choose to use an anonymous HI, it
knowingly risks a MitM attack. The responder may choose not to knowingly risks a MitM attack. The responder may choose not to
accept a HIP exchange with an anonymous initiator. accept a HIP exchange with an anonymous initiator.
Since not all hosts will ever support HIP, ICMP 'Destination Protocol In HIP, the Security Association for IPsec is indexed by the SPI; the
Unreachable' are to be expected and present a DoS attack. Against an source address is always ignored, and the destination address may be
initiator, the attack would look like the responder does not support ignored as well. Therefore, HIP enabled IPsec Encapsulated Security
HIP, but shortly after receiving the ICMP message, the initiator Payload (ESP) is IP address independent. This might seem to make it
would receive a valid HIP packet. Thus, to protect against this easier for an attacker, but ESP with replay protection is already as
attack, an initiator should not react to an ICMP message until a well protected as possible, and the removal of the IP address as a
reasonable delta time to get the real responder's HIP packet. A check should not increase the exposure of IPsec ESP to DoS attacks.
similar attack against the responder is more involved.
Another MitM attack is simulating a responder's rejection of a HIP Since not all hosts will ever support HIP, ICMPv4 'Destination
initiation. This is a simple ICMP Protocol Unreachable, Unreachable, Protocol Unreachable' and ICMPv6 'Parameter Problem,
Administratively Prohibited message. A HIP packet is not used Unrecognized Next Header' messages are to be expected and present a
because it would either have to have unique content, and thus DoS attack. Against an initiator, the attack would look like the
difficult to generate, resulting in yet another DoS attack, or just responder does not support HIP, but shortly after receiving the ICMP
as spoofable as the ICMP message. The defense against this MitM message, the initiator would receive a valid HIP packet. Thus, to
attack is for the responder to wait a reasonable time period to get a protect against this attack, an initiator should not react to an ICMP
valid HIP packet. If one does not come, then the Initiator has to message until a reasonable time has passed, allowing it to get the
assume that the ICMP message is valid. Since this is the only point real responder's HIP packet. A similar attack against the responder
in the HIP exchange where this ICMP message is appropriate, it can be is more involved.
ignored at any other point in the exchange.
9.1 HITs used in ACLs Another MitM attack is simulating a responder's administrative
rejection of a HIP initiation. This is a simple ICMP 'Destination
Unreachable, Administratively Prohibited' message. A HIP packet is
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. Like in the previous case,
the defense against this attack is for the initiator 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 base exchange where
this ICMP message is appropriate, it can be ignored at any other
point in the exchange.
10.1 HITs used in ACLs
It is expected that HITs will be used in ACLs. Future firewalls can 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 use HITs to control egress and ingress to networks, with an assurance
difficult to achieve today. level difficult to achieve today. As discussed above in Section 6,
once a HIP session has been established, the SPI value in an IPsec
packet may be used as an index, indicating the HITs. In practise,
the firewalls can inspect the 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 the HIP packets allow
a capable firewall to make sure that the HIP exchange is indeed
happening between two known hosts. This may increase firewall
security.
There has been considerable bad experience with distributed ACLs that There has been considerable bad experience with distributed ACLs that
contain public key related material, for example, with SSH. If the 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 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 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 impossible. If the reason for the revocation is due to private key
theft, this could be a serious issue. theft, this could be a serious issue.
A host can keep track of all of its partners that might use its HIT 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 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 log responder hosts. With this information, the host can notify the
various hosts about the change to the HIT. There has been no attempt 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 to develop a secure method (like in CMP and CMC) to issue the HIT
HIT revocation notice. revocation notice.
NATs, however, are transparent to the HIP aware systems by design. 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 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 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 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 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 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 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 NAT of the change. In this manner, NATs will get updated with the
HIT change. HIT change.
9.2 Non-security Considerations 10.2 Non-security Considerations
The definition of the Host Identifier states that the HI need not be 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 public key. It implies that the HI could be any value; for example
an FQDN. This document does not describe how to support a an FQDN. This document does not describe how to support such a
non-cryptographic HI. Such a HI would still offer the services of non-cryptographic HI. A non-cryptographic HI would still offer the
the HIT or LSI for NAT traversal. It would carry the HITs or LSIs in services of the HIT or LSI for NAT traversal. It would be possible
a HIP packets that had neither privacy nor authentication. Since carry the HITs in HIP packets that had neither privacy nor
such a mode would offer so little additional functionality for so authentication. Since such a mode would offer so little additional
much addition to the IP kernel, it has not been defined. Given how functionality for so much addition to the IP kernel, it has not been
little public key cryptography HIP requires, HIP should only be defined. Given how little public key cryptography HIP requires, HIP
implemented using public key Host Identities. should only be implemented using public key Host Identities.
10. Acknowledgments If it is desirable to use HIP in a low security situation where
public key computations are considered expensive, HIP can be used
with very short Diffie-Hellman and Host Identity keys. Such use
makes the participating hosts vulnerable to MitM and connection
hijacking attacks. However, it does not cause flooding dangers,
since the address check mechanism relies on the routing system and
not on cryptographic strength.
11. Acknowledgments
For the people historically involved in the early stages of HIP, see For the people historically involved in the early stages of HIP, see
the Acknowledgements section in [5]. the Acknowledgements section in the Host Identity Protocol
specification [4].
During the later stages of this document, when the editing baton was During the later stages of this document, when the editing baton was
transfered to Pekka Nikander, the comments from the early transfered to Pekka Nikander, the comments from the early
implementors and others, including Jari Arkko, Tom Henderson, Petri implementors and others, including Jari Arkko, Tom Henderson, Petri
Jokela, Miika Komu, Mika Kousa, Andrew McGregor, Jan Melen, Tim Jokela, Miika Komu, Mika Kousa, Andrew McGregor, Jan Melen, Tim
Shepard, Jukka Ylitalo, and Jorma Wall, were invaluable. Shepard, Jukka Ylitalo, and Jorma Wall, were invaluable.
References (informative) References (informative)
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Tsirtsis, G. and P. Srisuresh, "Network Address Translation -
Levels", BCP 14, RFC 2119, March 1997.
[2] Tsirtsis, G. and P. Srisuresh, "Network Address Translation -
Protocol Translation (NAT-PT)", RFC 2766, February 2000. Protocol Translation (NAT-PT)", RFC 2766, February 2000.
[3] Srisuresh, P. and K. Egevang, "Traditional IP Network Address [2] Srisuresh, P. and K. Egevang, "Traditional IP Network Address
Translator (Traditional NAT)", RFC 3022, January 2001. Translator (Traditional NAT)", RFC 3022, January 2001.
[4] Borella, M., Lo, J., Grabelsky, D. and G. Montenegro, "Realm [3] Borella, M., Lo, J., Grabelsky, D. and G. Montenegro, "Realm
Specific IP: Framework", RFC 3102, October 2001. Specific IP: Framework", RFC 3102, October 2001.
[5] Moskowitz, R., Nikander, P. and P. Jokela, "Host Identity [4] Moskowitz, R., Nikander, P. and P. Jokela, "Host Identity
Protocol", draft-moskowitz-hip-07 (work in progress), June 2003. Protocol", draft-moskowitz-hip-07 (work in progress), June 2003.
[6] Richardson, M., "A method for storing IPsec keying material in [5] Richardson, M., "A method for storing IPsec keying material in
DNS", draft-ietf-ipseckey-rr-07 (work in progress), September DNS", draft-ietf-ipseckey-rr-07 (work in progress), September
2003. 2003.
[7] Lear, E. and R. Droms, "What's In A Name:Thoughts from the [6] Lear, E. and R. Droms, "What's In A Name:Thoughts from the
NSRG", draft-irtf-nsrg-report-10 (work in progress), September NSRG", draft-irtf-nsrg-report-10 (work in progress), September
2003. 2003.
[7] Nikander, P., "End-Host Mobility and Multi-Homing with Host
Identity Protocol", draft-nikander-hip-mm-00 (work in progress),
June 2003.
[8] Nikander, P., "Mobile IP version 6 Route Optimization Security [8] Nikander, P., "Mobile IP version 6 Route Optimization Security
Design Background", draft-nikander-mobileip-v6-ro-sec-01 (work Design Background", draft-nikander-mobileip-v6-ro-sec-01 (work
in progress), July 2003. in progress), July 2003.
[9] Chiappa, J., "Endpoints and Endpoint Names: A Proposed [9] Chiappa, J., "Endpoints and Endpoint Names: A Proposed
Enhancement to the Internet Architecture", URL http:// Enhancement to the Internet Architecture", URL http://
users.exis.net/~jnc/tech/endpoints.txt, 1999. users.exis.net/~jnc/tech/endpoints.txt, 1999.
Authors' Addresses Authors' Addresses
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