draft-ietf-hip-arch-00.txt   draft-ietf-hip-arch-01.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: April 16, 2005 Corporation Expires: June 21, 2005 Corporation
P. Nikander P. Nikander
Ericsson Research Nomadic Lab Ericsson Research Nomadic Lab
October 16, 2004 December 21, 2004
Host Identity Protocol Architecture Host Identity Protocol Architecture
draft-ietf-hip-arch-00 draft-ietf-hip-arch-01
Status of this Memo Status of this Memo
This document is an Internet-Draft and is subject to all provisions This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with which he or she become aware will be disclosed, in accordance with
RFC 3668. RFC 3668.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 16, 2005. This Internet-Draft will expire on June 21, 2005.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). Copyright (C) The Internet Society (2004).
Abstract Abstract
This memo describes a snapshot of the reasoning behind a proposed new This memo describes a snapshot of the reasoning behind a proposed new
namespace, the Host Identity namespace, and a new protocol layer, the namespace, the Host Identity namespace, and a new protocol layer, the
Host Identity Protocol, between the internetworking and transport Host Identity Protocol, between the internetworking and transport
layers. Herein are presented the basics of the current namespaces, layers. Herein are presented the basics of the current namespaces,
strengths and weaknesses, and how a new namespace will add their strengths and weaknesses, and how a new namespace will add
completeness to them. The roles of this new namespace in the completeness to them. The roles of this new namespace in the
protocols are defined. The memo describes the thinking of the protocols are defined. The memo describes the thinking of the
authors as of Fall 2003. authors as of Fall 2003. The architecture may have evolved since.
This document represents one stable point in that evolution of
understanding.
Table of Contents Table of Contents
1. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1 Terms common to other documents . . . . . . . . . . . . . . 4 3.1 Terms common to other documents . . . . . . . . . . . . . . 4
3.2 Terms specific to this and other HIP documents . . . . . . . 4 3.2 Terms specific to this and other HIP documents . . . . . . . 4
4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1 A Desire for a Namespace for Computing Platforms . . . . . . 7 4.1 A desire for a namespace for computing platforms . . . . . . 7
5. Host Identity Namespace . . . . . . . . . . . . . . . . . . 8 5. Host Identity namespace . . . . . . . . . . . . . . . . . . 8
5.1 Host Identifiers . . . . . . . . . . . . . . . . . . . . . . 9 5.1 Host Identifiers . . . . . . . . . . . . . . . . . . . . . . 9
5.2 Storing Host Identifiers in DNS . . . . . . . . . . . . . . 9 5.2 Storing Host Identifiers in DNS . . . . . . . . . . . . . . 9
5.3 Host Identity Tag (HIT) . . . . . . . . . . . . . . . . . . 10 5.3 Host Identity Tag (HIT) . . . . . . . . . . . . . . . . . . 10
5.4 Local Scope Identifier (LSI) . . . . . . . . . . . . . . . . 10 5.4 Local Scope Identifier (LSI) . . . . . . . . . . . . . . . . 10
6. New Stack Architecture . . . . . . . . . . . . . . . . . . . 10 6. New stack architecture . . . . . . . . . . . . . . . . . . . 10
6.1 Transport associations and end-points . . . . . . . . . . . 11 6.1 Transport associations and end-points . . . . . . . . . . . 11
7. End-Host Mobility and Multi-Homing . . . . . . . . . . . . . 12 7. End-host mobility and multi-homing . . . . . . . . . . . . . 12
7.1 Rendezvous mechanism . . . . . . . . . . . . . . . . . . . . 12 7.1 Rendezvous mechanism . . . . . . . . . . . . . . . . . . . . 12
7.2 Protection against Flooding Attacks . . . . . . . . . . . . 13 7.2 Protection against flooding attacks . . . . . . . . . . . . 13
8. HIP and IPsec . . . . . . . . . . . . . . . . . . . . . . . 13 8. HIP and IPsec . . . . . . . . . . . . . . . . . . . . . . . 13
9. HIP and NATs . . . . . . . . . . . . . . . . . . . . . . . . 14 9. HIP and NATs . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1 HIP and TCP Checksum . . . . . . . . . . . . . . . . . . . . 15 9.1 HIP and TCP checksums . . . . . . . . . . . . . . . . . . . 15
10. Multicast . . . . . . . . . . . . . . . . . . . . . . . . . 15 10. Multicast . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. HIP Policies . . . . . . . . . . . . . . . . . . . . . . . . 15 11. HIP policies . . . . . . . . . . . . . . . . . . . . . . . . 15
12. Benefits of HIP . . . . . . . . . . . . . . . . . . . . . . 16 12. Benefits of HIP . . . . . . . . . . . . . . . . . . . . . . 16
12.1 HIP's Answers to NSRG questions . . . . . . . . . . . . . . 17 12.1 HIP's answers to NSRG questions . . . . . . . . . . . . . . 17
13. Security Considerations . . . . . . . . . . . . . . . . . . 19 13. Security considerations . . . . . . . . . . . . . . . . . . 19
13.1 HITs used in ACLs . . . . . . . . . . . . . . . . . . . . . 20 13.1 HITs used in ACLs . . . . . . . . . . . . . . . . . . . . . 20
13.2 Non-security Considerations . . . . . . . . . . . . . . . . 21 13.2 Non-security considerations . . . . . . . . . . . . . . . . 21
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 21 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 21
15. Informative References . . . . . . . . . . . . . . . . . . . 22 15. Informative references . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . 24 Intellectual Property and Copyright Statements . . . . . . . 24
1. Disclaimer 1. Disclaimer
The purpose of this memo is to provide a stable reference point in The purpose of this memo is to provide a stable reference point in
the development of the Host Identity Protocol architecture. This the development of the Host Identity Protocol architecture. This
memo describes the thinking of the authors as of Fall 2003; their memo describes the thinking of the authors as of Fall 2003; their
thinking may have evolved since then. In occasions, this memo may be thinking may have evolved since then. Occasionally, this memo may be
confusing or self-contradicting. That is (partially) intentional, confusing or self-contradicting. That is (partially) intentional,
and reflects the snapshot nature of this memo. and reflects the snapshot nature of this memo.
2. Introduction 2. Introduction
The Internet has created two important global namespaces: Internet The Internet has two important global namespaces: Internet Protocol
Protocol (IP) addresses and Domain Name Service (DNS) names. These (IP) addresses and Domain Name Service (DNS) names. These two
two namespaces have a set of features and abstractions that have namespaces have a set of features and abstractions that have powered
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 proposed Host Identity namespace fills an important gap between The proposed Host Identity namespace fills an important gap between
the IP and DNS namespaces. The Host Identity namespace consists of the IP and DNS namespaces. The Host Identity namespace consists of
Host Identifiers (HI). A Host Identifier is cryptographic in its Host Identifiers (HI). A Host Identifier is cryptographic in its
nature; it is the public key of an asymmetric key-pair. A Host nature; it is the public key of an asymmetric key-pair. Each host
Identity is assigned to each host. Each host will have at least one will have at least one Host Identity, but it will typically have more
Host Identity and a corresponding Host Identifier, which can either than one. Each Host Identity uniquely identifies a single host,
be public (e.g. published in DNS), or unpublished. Client systems i.e., no two hosts have the same Host Identity. The Host Identity,
will tend to have both public and unpublished Identities. 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.
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 the Host Identifiers could be used in many authentication Although the Host Identifiers could be used in many authentication
systems, such as IKEv2 [9], the presented architecture introduces a systems, such as IKEv2 [11], the presented architecture introduces a
new protocol, called the Host Identity Protocol (HIP), and a new protocol, called the Host Identity Protocol (HIP), and a
cryptographic exchange, called the HIP base exchange [4]. The new cryptographic exchange, called the HIP base exchange [6]; see also
protocol provides for limited forms of trust between systems. It Section 8. The new protocol provides for limited forms of trust
enhances mobility, multi-homing and dynamic IP renumbering [7], aids between systems. It enhances mobility, multi-homing and dynamic IP
in protocol translation / transition [4], and reduces certain types renumbering [9], aids in protocol translation / transition [6], and
of denial-of-service (DoS) attacks [4]. reduces certain types of denial-of-service (DoS) attacks [6].
When HIP is used, the actual payload traffic between two HIP hosts is When HIP is used, the actual payload traffic between two HIP hosts is
typically, but not necessarily, protected with IPsec. The Host typically, but not necessarily, protected with IPsec. The Host
Identities are used to create the needed IPsec Security Associations Identities are used to create the needed IPsec Security Associations
(SA) and to authenticate the hosts. When IPsec is used, the actual (SAs) and to authenticate the hosts. When IPsec is used, the actual
payload IP packets do not differ in any way from standard IPsec payload IP packets do not differ in any way from standard IPsec
protected IP packets. protected IP packets.
3. Terminology 3. Terminology
3.1 Terms common to other documents 3.1 Terms common to other documents
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
| Term | Explanation | | Term | Explanation |
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
| Public key | The public key from an asymmetric cryptographic | | Public key | The public key of an asymmetric cryptographic key |
| | key pair. Used as a publicly known identifier for | | | pair. Used as a publicly known identifier for |
| | cryptographic identity authentication. | | | cryptographic identity authentication. |
| | | | | |
| Private key | The private or secret key from an asymmetric | | Private key | The private or secret key of an asymmetric |
| | cryptographic key pair. Assumed to be known only | | | cryptographic key pair. Assumed to be known only |
| | to the party identified by the corresponding | | | to the party identified by the corresponding |
| | public key. Used by the identified party to | | | public key. Used by the identified party to |
| | authenticate its identity to other parties. | | | authenticate its identity to other parties. |
| | | | | |
| Public key | An asymmetric cryptographic key pair consisting of | | Public key | An asymmetric cryptographic key pair consisting of |
| pair | a public and private keys. For example, | | pair | public and private keys. For example, |
| | Rivest-Shamir-Adelman (RSA) and Digital Signature | | | Rivest-Shamir-Adelman (RSA) and Digital Signature |
| | Algorithm (DSA) key pairs are such key pairs. | | | Algorithm (DSA) key pairs are such key pairs. |
| | | | | |
| End-point | A communicating entity. For historical reasons, | | End-point | A communicating entity. For historical reasons, |
| | the term 'computing platform' is used in this | | | the term 'computing platform' is used in this |
| | document as a (rough) synonym for end-point. | | | document as a (rough) synonym for end-point. |
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
3.2 Terms specific to this and other HIP documents 3.2 Terms specific to this and other HIP documents
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definitions. See the text elsewhere in this document for more definitions. See the text elsewhere in this document for more
elaborate explanations. elaborate explanations.
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
| Term | Explanation | | Term | Explanation |
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
| Computing | An entity capable of communicating and computing, | | Computing | An entity capable of communicating and computing, |
| platform | for example, a computer. See the definition of | | platform | for example, a computer. See the definition of |
| | 'End-point', above. | | | 'End-point', above. |
| | | | | |
| HIP base | A cryptographic protocol defined in [4]. See also | | HIP base | A cryptographic protocol defined in [6]. See also |
| exchange | Section 8. | | exchange | Section 8. |
| | | | | |
| HIP packet | An IP packet that carries a 'Host Identity | | HIP packet | An IP packet that carries a 'Host Identity |
| | Protocol' message. | | | Protocol' message. |
| | | | | |
| Host | An abstract concept assigned to a 'computing | | Host | An abstract concept assigned to a 'computing |
| Identity | platform'. See 'Host Identifier', below. | | Identity | platform'. See 'Host Identifier', below. |
| | | | | |
| Host | A name space formed by all possible Host | | Host | A name space formed by all possible Host |
| Identity | Identifiers. | | Identity | Identifiers. |
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| Local Scope | A 32-bit datum denoting a Host Identity. | | Local Scope | A 32-bit datum denoting a Host Identity. |
| Identifier | | | Identifier | |
| | | | | |
| Public Host | A published or publicly known Host Identfier used | | Public Host | A published or publicly known Host Identfier used |
| Identifier | as a public name for a Host Identity, and the | | Identifier | as a public name for a Host Identity, and the |
| and Identity | corresponding Identity. | | and Identity | corresponding Identity. |
| | | | | |
| Unpublished | A Host Identifier that is not placed in any public | | Unpublished | A Host Identifier that is not placed in any public |
| Host | directory, and the corresponding Host Identity. | | Host | directory, and the corresponding Host Identity. |
| Identifier | Unpublished Host Identities are typically short | | Identifier | Unpublished Host Identities are typically short |
| and Identity | living in nature, being often replaced and | | and Identity | lived in nature, being often replaced and possibly |
| | possibly used just once. | | | used just once. |
| | | | | |
| Rendezvous | A mechanism used to locate mobile hosts based on | | Rendezvous | A mechanism used to locate mobile hosts based on |
| Mechanism | their HIT. | | Mechanism | their HIT. |
+--------------+----------------------------------------------------+ +--------------+----------------------------------------------------+
4. Background 4. Background
The Internet is built from three principal components: computing The Internet is built from three principal components: computing
platforms (end-points), packet transport (i.e. internetworking) platforms (end-points), packet transport (i.e., internetworking)
infrastructure, and services (applications). The Internet exists to infrastructure, and services (applications). The Internet exists to
service two principal components: people and robotic services service two principal components: people and robotic services
(silicon based people, if you will). All these components need to be (silicon based people, if you will). All these components need to be
named in order to interact in a scalable manner. Here we concentrate named in order to interact in a scalable manner. Here we concentrate
on naming computing platforms and packet transport elements. on naming computing platforms and packet transport elements.
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 extensions of Domain Names. addresses are really only extensions of Domain Names.
IP numbers are a confounding of two namespaces, the names of a host's IP numbers are a confounding of two namespaces, the names of a host's
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
interface is connected to the network. Originally IP numbers had interface is connected to the network. Originally, IP numbers had
long-term significance. Today, the vast number of interfaces use long-term significance. Today, the vast number of interfaces use
ephemeral and/or non-unique IP numbers. That is, every time an ephemeral and/or non-unique IP numbers. That is, every time an
interface is connected to the network, it is assigned an IP number. interface is connected to the network, it is assigned an IP number.
In the current Internet, the transport layers are coupled to the IP In the current Internet, the transport layers are coupled to the IP
addresses. Neither can evolve separately from the other. IPng addresses. Neither can evolve separately from the other. IPng
deliberations were strongly shaped by the decision that a deliberations were strongly shaped by the decision that a
corresponding TCPng would not be created. corresponding TCPng would not be created.
Domain Names provide hierarchically assigned names for some computing Domain Names provide hierarchically assigned names for some computing
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applications, and documents. Email, SIP and WWW addresses are applications, and documents. Email, SIP and WWW addresses are
extensions of Domain Names. extensions of Domain Names.
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 of these deficiencies arise because computing platforms are not All of these deficiencies arise because computing platforms are not
well named with the current namespaces. well named with the current namespaces.
4.1 A Desire for a Namespace for Computing Platforms 4.1 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
because of mobility, rehoming, or renumbering. because of mobility, rehoming, or renumbering.
If the namespace for computing platforms is based on public key If the namespace for computing platforms is based on public-key
cryptography, it can also provide authentication services. If this cryptography, it can also provide authentication services. If this
namespace is locally created without requiring registration, it can namespace is locally created without requiring registration, it can
provide anonymity. provide 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:
o The namespace should be applied to the IP 'kernel'. The IP kernel o The namespace should be applied to the IP 'kernel'. The IP kernel
is the 'component' between applications and the packet transport is the 'component' between applications and the packet transport
infrastructure. infrastructure.
o The namespace should fully decouple the internetworking layer from o 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
addresses within applications (like in the TCB). This may require addresses within applications (like in the Transport Control
changes to the current APIs. In the long run, it is probable that Block, TCB). This may require changes to the current APIs. In
some new APIs are needed. the long run, it is probable that some new APIs are needed.
o The introduction of the namespace should not mandate any o The introduction of the namespace should not mandate any
administrative infrastructure. Deployment must come from the administrative infrastructure. Deployment must come from the
bottom up, in a pairwise deployment. bottom up, in a pairwise deployment.
o The names should have a fixed length representation, for easy o The names should have a fixed length representation, for easy
inclusion in datagram headers and existing programming interfaces inclusion in datagram headers and existing programming interfaces
(e.g the TCB). (e.g the TCB).
o Using the namespace should be affordable when used in protocols. o Using the namespace should be affordable when used in protocols.
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inadequate to make the probability of collisions sufficiently low inadequate to make the probability of collisions sufficiently low
(1% chance of collision in a population of 640M); thus, (1% chance of collision in a population of 640M); thus,
approximately 100 or more bits should be used. approximately 100 or more bits should be used.
o The names should have a localized abstraction so that it can be o The names should have a localized abstraction so that it can be
used in existing protocols and APIs. used in existing protocols and APIs.
o It must be possible to create names locally. This can provide o It must be possible to create names locally. This can provide
anonymity at the cost of making resolvability very difficult. anonymity at the cost of making resolvability very difficult.
Sometimes the names may contain a delegation component. This * Sometimes the names may contain a delegation component. This
is the cost of resolvability. is the cost of resolvability.
o The namespace should provide authentication services. o The namespace should provide authentication services.
o The names should be long lived, but replaceable at any time. This o 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, a new namespace approaching these ideas is called In this document, a new namespace approaching these ideas is called
the Host Identity namespace. Using Host Identities requires its own the Host Identity namespace. Using Host Identities requires its own
protocol layer, the Host Identity Protocol, between the protocol layer, the Host Identity Protocol, between the
internetworking and transport layers. The names are based on public internetworking and transport layers. The names are based on
key cryptography to supply authentication services. Properly public-key cryptography to supply authentication services. Properly
designed, it can deliver all of the above stated requirements. designed, it can deliver all of the above stated requirements.
5. Host Identity Namespace 5. 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 with, but not with an IP stack. This identity is normally associated with, 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 unpublished or 'anonymous'. A system may self 'well known', some unpublished or 'anonymous'. A system may
assert its own identity, or may use a third-party authenticator like self-assert its own identity, or may use a third-party authenticator
DNSSEC, PGP, or X.509 to 'notarize' the identity assertion. It is like DNSSEC [2], PGP, or X.509 to 'notarize' the identity assertion.
expected that the Host Identifiers will initially be authenticated It is expected that the Host Identifiers will initially be
with DNSSEC and that all implementations will support DNSSEC as a authenticated with DNSSEC and that all implementations will support
minimal baseline. DNSSEC as a minimal baseline.
In theory, any name that can claim to be 'statistically globally In theory, any name that can claim to be 'statistically globally
unique' may serve as a Host Identifier. However, in the authors' unique' may serve as a Host Identifier. However, in the authors'
opinion, a public key of a 'public key pair' makes the best Host opinion, a public key of a 'public key pair' makes the best Host
Identifier. As documented in the Host Identity Protocol Identifier. As documented in the Host Identity Protocol
specification [4], a public key based HI can authenticate the HIP specification [6], a public-key-based HI can authenticate the HIP
packets and protect them for man-in-the-middle attacks. Since packets and protect them for man-in-the-middle attacks. Since
authenticated datagrams are mandatory to provide much of HIP's authenticated datagrams are mandatory to provide much of HIP's
denial-of-service protection, the Diffie-Hellman exchange in HIP has denial-of-service protection, the Diffie-Hellman exchange in HIP has
to be authenticated. Thus, only public key HI and authenticated HIP to be authenticated. Thus, only public-key HI and authenticated HIP
messages are supported in practice. In this document, the 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 they should not be implemented as they could theory of HI, but they should not be implemented as they could
produce worse denial-of-service attacks than the Internet has without produce worse denial-of-service attacks than the Internet has without
Host Identity. Host Identity.
5.1 Host Identifiers 5.1 Host Identifiers
Host Identity adds two main features to Internet protocols. The Host Identity adds two main features to Internet protocols. The
first is a decoupling of the internetworking and transport layers; first is a decoupling of the internetworking and transport layers;
see Section 6. This decoupling will allow for independent evolution see Section 6. This decoupling will allow for independent evolution
of the two layers. Additionally, it can provide end-to-end services of 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 for authentication in 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/private key pair. In this case, the Host Identity is a public/private key pair. In this case, the Host Identity is
referred to by its public component, the public key. Thus, the name referred to by its public component, the public key. Thus, the name
representing a Host Identity in the Host Identity namespace, i.e. 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 Host Identifier, is the public key. In a way, the possession of
the private key defines the Identity itself. If the private key is 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 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. However, at least for interconnected spoofing) and no use of IPsec. However, at least for interconnected
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Identity Tag (HIT) is used in other protocols to represent the Host Identity Tag (HIT) is used in other protocols to represent the Host
Identity. Another representation of the Host Identities, the Local Identity. Another representation of the Host Identities, the Local
Scope Identifier (LSI), can also be used in protocols and APIs. Scope Identifier (LSI), can also be used in protocols and APIs.
5.2 Storing Host Identifiers in DNS 5.2 Storing Host Identifiers in DNS
The public Host Identifiers should be stored in DNS; the unpublished The public Host Identifiers should be stored in DNS; the unpublished
Host Identifiers should not be stored anywhere (besides the Host Identifiers should not be stored anywhere (besides the
communicating hosts themselves). The (public) HI is stored in a new communicating hosts themselves). The (public) HI is stored in a new
RR type, to be defined. This RR type is likely to be quite similar RR type, to be defined. This RR type is likely to be quite similar
to the IPSECKEY RR [5]. to the IPSECKEY RR [7].
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.
5.3 Host Identity Tag (HIT) 5.3 Host Identity Tag (HIT)
A Host Identity Tag is an 128-bit representation for a Host Identity. A Host Identity Tag is a 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 the Host Identifier in protocols. Firstly, its fixed length makes
for easier protocol coding and also better manages the packet size for easier protocol coding and also better manages the packet size
cost of this technology. Secondly, it presents the identity in a cost of this technology. Secondly, it presents the identity in a
consistent format to the protocol independent of the cryptographic consistent format to the protocol independent of the cryptographic
algorithms used. algorithms used.
In the HIP packets, 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 as long as it is being used. In the extremely rare case universe as long as it is being used. In the extremely rare case of
that a single HIT happens to map to more than one Host Identity, the a single HIT mapping to more than one Host Identity, the Host
Host Identifiers (public keys) will make the final difference. If Identifiers (public keys) will make the final difference. If there
there is more than one public key for a given node, the HIT acts as a is more than one public key for a given node, the HIT acts as a hint
hint for the correct public key to use. for the correct public key to use.
5.4 Local Scope Identifier (LSI) 5.4 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 Identities in existing purpose of an LSI is to facilitate using Host Identities in existing
protocols and APIs. LSI's advantage over HIT is its size; its protocols and APIs. LSI's advantage over HIT is its size; its
disadvantage is its local scope. The generation of LSIs is defined disadvantage is its local scope. The generation of LSIs is defined
in the Host Identity Protocol specification [4]. in the Host Identity Protocol specification [6].
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 an 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 Identities into IPv4-based protocols and APIs. bridge for Host Identities into IPv4-based protocols and APIs.
6. New Stack Architecture 6. 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 [6] and, e.g., the unpublished Name Space Research Group Report [8] and, e.g., the unpublished
Internet-Draft Endpoints and Endpoint Names [10] by Noel Chiappa, the Internet-Draft Endpoints and Endpoint Names [12] by Noel Chiappa, the
IP addresses currently embody the dual role of locators and end-point IP addresses currently embody the dual role of locators and end-point
identifiers. That is, each IP address names a topological location identifiers. That is, each IP address names a topological location
in the Internet, thereby acting as a routing direction vector, or in the Internet, thereby acting as a routing direction vector, or
locator. At the same time, the IP address names the physical network locator. At the same time, the IP address names the physical network
interface currently located at the point-of-attachment, thereby interface currently located at the point-of-attachment, thereby
acting as a end-point name. acting as a end-point name.
In the HIP architecture, the end-point names and locators are In the HIP architecture, the end-point 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 end-point identifiers. It is The Host Identifiers take the role of end-point identifiers. It is
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\ | | \ | |
\ | | \ | |
\ | | \ | |
\ | | \ | |
Location --- IP address Location --- IP address Location --- IP address Location --- IP address
Figure 1 Figure 1
6.1 Transport associations and end-points 6.1 Transport associations and end-points
Architecturally, HIP provides for a different binding of transport Architecturally, HIP provides for a different binding of
layer protocols. That is, the transport layer associations, i.e., transport-layer protocols. That is, the transport-layer
TCP connections and UDP associations, are no longer bound to IP associations, i.e., TCP connections and UDP associations, are no
addresses but to Host Identities. longer bound to IP 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 end-points. With HIP, each of these end-points 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. move all the transport associations without breaking them.
Similarly, if it is possible to distribute the processing of a single Similarly, if it is possible to distribute the processing of a single
Host Identity over several physical computers, HIP provides for Host Identity over several physical computers, HIP provides for
cluster based services without any changes at the client end-point. cluster based services without any changes at the client end-point.
7. End-Host Mobility and Multi-Homing 7. End-host mobility and multi-homing
HIP decouples the transport from the internetworking layer, and binds HIP decouples the transport from the internetworking layer, and binds
the transport associations to the Host Identities (through actually the transport associations to the Host Identities (through actually
either the HIT or LSI). Consequently, HIP can provide for a degree either the HIT or LSI). Consequently, HIP can provide for a degree
of internetworking mobility and multi-homing at a low infrastructure of internetworking mobility and multi-homing at a low infrastructure
cost. HIP mobility includes IP address changes (via any method) to cost. HIP mobility includes IP address changes (via any method) to
either party. Thus, a system is considered mobile if its IP address either party. Thus, a system is considered mobile if its IP address
can change dynamically for any reason like PPP, DHCP, IPv6 prefix can change dynamically for any reason like PPP, DHCP, IPv6 prefix
reassignments, or a NAT device remapping its translation. Likewise, reassignments, or a NAT device remapping its translation. Likewise,
a system is considered multi-homed if it has more than one globally a system is considered multi-homed if it has more than one globally
routable IP address at the same time. HIP links IP addresses routable IP address at the same time. HIP links IP addresses
together, when multiple IP addresses correspond to the same Host together, when multiple IP addresses correspond to the same Host
Identity, and if one address becomes unusable, or a more preferred Identity, and if one address becomes unusable, or a more preferred
address becomes available, existing transport associations can easily address becomes available, existing transport associations can easily
be moved to another address. be moved to 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 integrity protected IPsec packet from any just accept a HIP or an integrity protected IPsec packet from any
address and totally ignore the source address. However, as discussed address and ignore the source address. However, as discussed in
in Section 7.2 below, a mobile node must send a HIP readdress packet Section 7.2 below, a mobile node must send a HIP readdress packet to
to inform the peer of the new address(es), and the peer must verify inform the peer of the new address(es), and the peer must verify that
that the mobile node is reachable through these addresses. This is the mobile node is reachable through these addresses. This is
especially helpful for those situations where the peer node is especially helpful for those situations where the peer node is
sending data periodically to the mobile node (that is re-starting a sending data periodically to the mobile node (that is re-starting a
connection after the initial connection). connection after the initial connection).
7.1 Rendezvous mechanism 7.1 Rendezvous mechanism
Making a contact to a mobile node is slightly more involved. In Making a contact to a mobile node is slightly more involved. In
order to start the HIP exchange, the initiator node has to know how order to start the HIP exchange, the initiator node has to know how
to reach the mobile node. Although infrequently moving HIP nodes to reach the mobile node. Although infrequently moving HIP nodes
could use Dynamic DNS to update their reachability information in the could use Dynamic DNS [1] to update their reachability information in
DNS, an alternative to using DNS in this fashion is to use a piece of the DNS, an alternative to using DNS in this fashion is to use a
new static infrastructure to facilitate rendezvous between HIP nodes. piece of new static infrastructure to facilitate rendezvous between
HIP nodes.
The mobile node keeps the rendezvous infrastructure continuously The mobile node keeps the rendezvous infrastructure continuously
updated with its current IP address(es). The mobile nodes must trust updated with its current IP address(es). The mobile nodes must trust
the rendezvous mechanism to properly maintain their HIT and IP the rendezvous mechanism to properly maintain their HIT and IP
address mappings. address mappings.
The rendezvous mechanism is also needed if both of the nodes happen The rendezvous mechanism is also needed if both of the nodes happen
to change their address at the same time, either because they are to change their address at the same time, either because they are
mobile and happen to move at the same time, because one of them is mobile and happen to move at the same time, because one of them is
off-line for a while, or because of some other reason. In such a off-line for a while, or because of some other reason. In such a
case, the HIP readdress packets will cross each other in the network case, the HIP readdress packets will cross each other in the network
and never reach the peer node. and never reach the peer node.
A separate document will specify the details of the HIP rendezvous A separate document will specify the details of the HIP rendezvous
mechanism. mechanism.
7.2 Protection against Flooding Attacks 7.2 Protection against flooding attacks
While the idea of informing about address changes by simply sending Although the idea of informing about address changes by simply
packets with a new source address appears appealing, it is not secure sending packets with a new source address appears appealing, it is
enough. That is, even if HIP does not rely on the source address for not secure enough. That is, even if HIP does not rely on the source
anything (once the base exchange has been completed), it appears to address for anything (once the base exchange has been completed), it
be necessary to check a mobile node's reachability at the new address appears to be necessary to check a mobile node's reachability at the
before actually sending any larger amounts of traffic to the new new address before actually sending any larger amounts of traffic to
address. the new address.
Blindly accepting new addresses would potentially lead to flooding Blindly accepting new addresses would potentially lead to flooding
Denial-of-Service attacks against third parties [8]. In a Denial-of-Service attacks against third parties [10]. In a
distributed flooding attack an attacker opens high volume HIP distributed flooding attack an attacker opens high volume HIP
connections with a large number of hosts (using unpublished HIs), and connections with a large number of hosts (using unpublished HIs), and
then claims to all of these hosts that it has moved to a target then claims to all of these hosts that it has moved to a target
node's IP address. If the peer hosts were to simply accept the move, node's IP address. If the peer hosts were to simply accept the move,
the result would be a packet flood to the target node's address. To the result would be a packet flood to the target node's address. To
close this attack, HIP includes an address check mechanism where the close this attack, HIP includes an address check mechanism where the
reachability of a node is separately checked at each address before reachability of a node is separately checked at each address before
using the address for larger amounts of traffic. using the address for 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,
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8. HIP and IPsec 8. HIP and IPsec
The preferred way of implementing HIP is to use IPsec to carry the The preferred way of implementing HIP is to use IPsec to carry the
actual data traffic. As of today, the only completely defined method 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 IPsec Encapsulated Security Payload (ESP) to carry the data
packets. In the future, other ways of transporting payload data may packets. In the future, other ways of transporting payload data may
be developed, including ones that do not use cryptographic be developed, including ones that do not use cryptographic
protection. protection.
In practise, the HIP base exchange uses the cryptographic Host In practice, the HIP base exchange uses the cryptographic Host
Identifiers to set up a pair of ESP Security Associations (SAs) to 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 enable ESP in an end-to-end manner. This is implemented in a way
that can span addressing realms. that can span addressing realms.
While it would be possible, at least in theory, to use some existing While it would be possible, at least in theory, to use some existing
cryptographic protocol, such as IKEv2 together with Host Identifiers, cryptographic protocol, such as IKEv2 together with Host Identifiers,
to establish the needed SAs, HIP defines a new protocol. There are a 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 number of historical reasons for this, and there are also a few
architectural reasons. First, IKE (and IKEv2) were not design with architectural reasons. First, IKE (and IKEv2) were not designed with
middle boxes in mind. As adding a new naming layer allows one to 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 potentially add a new forwarding layer (see Section 9, below), it is
very important that the HIP protocols are friendly towards any middle very important that the HIP protocols are friendly towards any middle
boxes. boxes.
Second, from a conceptual point of view, the IPsec Security Parameter Second, from a conceptual point of view, the IPsec Security Parameter
Index (SPI) in ESP provides a simple compression of the HITs. This 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 does require per-HIT-pair SAs (and SPIs), and a decrease of policy
granularity over other Key Management Protocols, such as IKE and granularity over other Key Management Protocols, such as IKE and
IKEv2. In particular, the current thinking is limited to a situation IKEv2. In particular, the current thinking is limited to a situation
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between a pair of HITs. between a pair of HITs.
Since HIP is designed for host usage, not for gateways or so called Since HIP is designed for host usage, not for gateways or so called
Bump-in-the-Wire (BITW) implementations, only ESP transport mode is 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 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 (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 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 the HITs. Thus, a host can easily change its address using Mobile
IP, DHCP, PPP, or IPv6 readdressing and still maintain the SAs. 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 Since the transports are bound to the SA (via an LSI or a HIT), any
active transport is also maintained. Thus, real world conditions active transport is also maintained. Thus, real-world conditions
like loss of a PPP connection and its re-establishment or a mobile like loss of a PPP connection and its re-establishment or a mobile
handover will not require a HIP negotiation or disruption of handover will not require a HIP negotiation or disruption of
transport services. [12] transport services [14].
Since HIP does not negotiate any SA lifetimes, all lifetimes are Since HIP does not negotiate any SA lifetimes, all lifetimes are
local policy. The only lifetimes a HIP implementation MUST support local policy. The only lifetimes a HIP implementation must support
are sequence number rollover (for replay protection), and SA are sequence number rollover (for replay protection), and SA timeout
timeout[4]. An SA times out if no packets are received using that [6]. An SA times out if no packets are received using that SA.
SA. Implementations MAY support lifetimes for the various ESP Implementations may support lifetimes for the various ESP transforms.
transforms.
9. HIP and NATs 9. 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) [2] or NAT Protocol translation (NAT-PT) [1]. Translation (NAT) [4] or NAT Protocol translation (NAT-PT) [3].
In a network environment where the identification is based on the IP In a network environment where identification is based on the IP
addresses, identifying the communicating nodes is difficult when NAT addresses, identifying the communicating nodes is difficult when NAT
is used. With HIP, the transport layer end-points are bound to the is used. With HIP, the transport-layer end-points are bound to the
Host Identities. 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; they may be changed freely during packet traversal.
packet traversal.
For a HIP based flow, a HIP-aware NAT or NAT-PT system tracks the 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 IPsec SPIs, to an IP address.
Many HITs can map to a single IP address on a NAT, simplifying The NAT system has to learn mappings both from HITs and from SPIs to
connections on address poor NAT interfaces. The NAT can gain much of IP addresses. Many HITs (and SPIs) can map to a single IP address on
its knowledge from the HIP packets themselves; however, some NAT a NAT, simplifying connections on address poor NAT interfaces. The
configuration may be necessary. NAT can gain much of its knowledge from the HIP packets themselves;
however, some NAT configuration may be necessary.
The NAT systems cannot touch the datagrams within the IPsec envelope, 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.
9.1 HIP and TCP Checksum 9.1 HIP and TCP checksums
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 an
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 actual is, it is not feasible to calculate the TCP checksum using the actual
IP 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
layer checksums in the NAT/NAT-PT system, since the traffic is IPsec upper-layer checksums in the NAT/NAT-PT system, since the traffic is
protected. Consequently, the TCP and UDP checksums are calculated IPsec protected. Consequently, the TCP and UDP checksums are
using the HITs in the place of the IP addresses in the pseudo header. calculated using the HITs in the place of the IP addresses in the
Furthermore, only the IPv6 pseudo header format is used. This pseudo header. Furthermore, only the IPv6 pseudo header format is
provides for IPv4 / IPv6 protocol translation. used. This provides for IPv4 / IPv6 protocol translation.
10. Multicast 10. Multicast
Back in fall 2003, there was little if any concrete thoughts about Back in the fall of 2003, there was little if any concrete thoughts
how HIP might affect IP or application layer multi-cast. about how HIP might affect IP-layer or application-layer multicast.
11. HIP Policies 11. 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 an unpublished one for at least 2 HIs, one to publish in DNS and an unpublished one for
anonymous usage. Although unpublished HIs will be rarely used as anonymous usage. Although unpublished HIs will be rarely used as
responder HIs, they are likely be common for initiators. Support for responder HIs, they are likely be common for initiators. Support for
multiple HIs is recommended. multiple HIs is 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 transforms and local lifetimes. preferred transforms and local lifetimes.
Responders would need a similar policy, describing the hosts allowed Responders would need a similar policy, describing the hosts allowed
to participate in HIP exchanges, and the preferred transforms and to participate in HIP exchanges, and the preferred transforms and
local lifetimes. local lifetimes.
12. Benefits of HIP 12. 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:
o Non-mutable: The address sent is the address received. o Non-mutable: The address sent is the address received.
o Non-mobile: The address doesn't change during the course of an o Non-mobile: The address doesn't change during the course of an
"association". "association".
o Reversible: A return header can always be formed by reversing the o Reversible: A return header can always be formed by reversing the
source and destination addresses. source and destination addresses.
o Omniscient: Each host knows what address a partner host can use to o 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 intentionally trying 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 [3] is an attempt to reinstate the fourth fourth. Realm Specific IP [5] 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. That
them. That is, if they have a Fully Qualified Domain Name (FQDN), is, if they have a Fully Qualified Domain Name (FQDN), that name
that typically belongs to a NAT device or a dial-up server, and does typically belongs to a NAT device or a dial-up server, and does not
not really identify the system itself but its current connectivity. really identify the system itself but its current connectivity.
FQDN names (and their extensions as email names) are Application FQDNs (and their extensions as email names) are application-layer
Layer names; more frequently naming services than a particular names; more frequently naming services than a particular system.
system. This is why many systems on the internet are not registered This is why many systems on the Internet are not registered in the
in DNS; they do not have services of interest to other Internet DNS; they do not have services of interest to other Internet hosts.
hosts.
DNS names are references to IP addresses. This only demonstrates the DNS names are references to IP addresses. This only demonstrates the
interrelationship of the networking and application layers. DNS, as interrelationship of the networking and application layers. DNS, as
the Internet's only deployed, distributed, database is also the the Internet's only deployed, distributed database is also the
repository of other namespaces, due in part to DNSSEC and application repository of other namespaces, due in part to DNSSEC and application
specific key records. Although each namespace can be stretched (IP specific key records. Although each namespace can be stretched (IP
with v6, DNS with KEY records), neither can adequately provide for with v6, DNS with KEY records), neither can adequately provide for
host authentication or act as a separation between internetworking host authentication or act as a separation between internetworking
and transport layers. 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 do not 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).
12.1 HIP's Answers to NSRG questions 12.1 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 [6]. In this section, we provide answers questions in their report [8]. 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?
HIP decouples the internetworking layer from the transport HIP decouples the internetworking layer from the transport
layer, allowing each to evolve separately. The decoupling layer, allowing each to evolve separately. The decoupling
makes end-host mobility and multi-homing easier, also across makes end-host mobility and multi-homing easier, also across
IPv4 and IPv6 networks. HIs make network renumbering easier, IPv4 and IPv6 networks. HIs make network renumbering easier,
and they also make process migration and clustered servers and they also make process migration and clustered servers
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A HI is a cryptographic public key. However, instead of using A HI is a cryptographic public key. However, instead of using
the keys directly, most protocols use a fixed size hash of the the keys directly, most protocols use a fixed 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 HIs are typically long lived, with a lifetime of years Stable HIs are typically long lived, with a lifetime of years
or more. The lifetime of temporary HIs depends on how long or more. The lifetime of temporary HIs depends on how long
the upper layer connections and applications need them, and the upper-layer connections and applications need them, and
can range from a few seconds to years. can range from a few seconds 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 HIs 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 Host Identifiers may be used directly or indirectly (in The Host Identifiers may be used directly or indirectly (in
the form of HITs or LSIs) by applications when they access the form of HITs or LSIs) by applications when they access
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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 [11] problems easier to solve. In practice, address ownership [13] problems easier to solve. In practice,
HIP provides security for end-host mobility and multi-homing. HIP 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 HIs and IP addresses is sufficient. simultaneously to HIs and IP addresses is sufficient.
However, if it becomes necessary to resolve HIs into IP However, if it becomes necessary to resolve HIs into IP
addresses or back to DNS names, a flat resolution addresses or back to DNS names, a flat resolution
infrastructure is needed. Such an infrastructure could be infrastructure is needed. Such an infrastructure could be
based on the ideas of Distributed Hash Tables, but would based on the ideas of Distributed Hash Tables, but would
require significant new development and deployment. require significant new development and deployment.
13. Security Considerations 13. 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 to provide a fast key exchange for secure authentication of hosts and to provide a fast key exchange for
IPsec. 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.
Resource exhausting Denial-of-service attacks take advantage of the Resource exhausting denial-of-service attacks take advantage of the
cost of setting up a state for a protocol on the responder compared cost of setting up a state for a protocol on the responder compared
to the 'cheapness' on the initiator. HIP allows a responder to 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 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 effort to reduce the cost to the responder. This is done by having
the responder start the authenticated Diffie-Hellman exchange instead the responder start the authenticated Diffie-Hellman exchange instead
of the initiator, making the HIP base exchange 4 packets long. There of the initiator, making the HIP base exchange 4 packets long. There
are more details on this process in the Host Identity Protocol are more details on this process in the Host Identity Protocol
specification [4]. specification [6].
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 replayed, the initiator only reacts to it packet is fixed and easily replayed, the initiator only reacts to it
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retrieved from a signed DNS zone or secured by some other means, the retrieved from a signed DNS zone or secured by some other means, the
initiator can use this to authenticate the signed HIP packets. initiator can use this to authenticate the signed HIP 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 unpublished HI, it However, since an initiator may choose to use an unpublished 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 initiator using an unknown HI. accept a HIP exchange with an initiator using an unknown HI.
In HIP, the Security Association for IPsec is indexed by the SPI; the In HIP, the Security Association for IPsec is indexed by the SPI; the
source address is always ignored, and the destination address may be 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 IPsec Encapsulated Security
Payload (ESP) is IP address independent. This might seem to make it Payload (ESP) is IP address independent. This might seem to make it
easier for an attacker, but ESP with replay protection is already as 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 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 IPsec ESP to DoS attacks.
Since not all hosts will ever support HIP, ICMPv4 'Destination Since not all hosts will ever support HIP, ICMPv4 'Destination
Unreachable, Protocol Unreachable' and ICMPv6 'Parameter Problem, Unreachable, Protocol Unreachable' and ICMPv6 'Parameter Problem,
Unrecognized Next Header' messages are to be expected and present a Unrecognized Next Header' messages are to be expected and present a
DoS attack. Against an initiator, the attack would look like the DoS attack. Against an initiator, the attack would look like the
responder does not support HIP, but shortly after receiving the ICMP responder does not support HIP, but shortly after receiving the ICMP
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valid. Since this is the only point in the HIP base exchange where 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 this ICMP message is appropriate, it can be ignored at any other
point in the exchange. point in the exchange.
13.1 HITs used in ACLs 13.1 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
level difficult to achieve today. As discussed above in Section 8, level difficult to achieve today. As discussed above in Section 8,
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 IPsec
packet may be used as an index, indicating the HITs. In practise, packet may be used as an index, indicating the HITs. In practice,
the firewalls can inspect the HIP packets to learn of the bindings firewalls can inspect HIP packets to learn of the bindings between
between HITs, SPI values, and IP addresses. They can even explicitly HITs, SPI values, and IP addresses. They can even explicitly control
control IPsec usage, dynamically opening IPsec ESP only for specific IPsec usage, dynamically opening IPsec ESP only for specific SPI
SPI values and IP addresses. The signatures in the HIP packets allow values and IP addresses. The signatures in HIP packets allow a
a capable firewall to make sure that the HIP exchange is indeed capable firewall to ensure that the HIP exchange is indeed happening
happening between two known hosts. This may increase firewall between two known hosts. This may increase firewall security.
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 a key needs to revoke it for any reason, the task of finding
finding all locations where the key is held in an ACL may be all locations where the key is held in an ACL may be impossible. If
impossible. If the reason for the revocation is due to private key the reason for the revocation is due to private key theft, this could
theft, this could be a serious issue. 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
to develop a secure method to issue the HIT revocation notice. to develop a secure method to issue the HIT revocation notice.
HIP-aware NATs, however, are transparent to the HIP aware systems by 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 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 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 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 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 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 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 notify its NAT of the change. In this manner, NATs will get updated
with the HIT change. with the HIT change.
13.2 Non-security Considerations 13.2 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 such a a FQDN. This document does not describe how to support such a
non-cryptographic HI. A non-cryptographic HI would still offer the non-cryptographic HI. A non-cryptographic HI would still offer the
services of the HIT or LSI for NAT traversal. It would be possible services of the HIT or LSI for NAT traversal. It would be possible
carry the HITs in HIP packets that had neither privacy nor to carry HITs in HIP packets that had neither privacy nor
authentication. Since such a mode would offer so little additional authentication. Since such a mode would offer so little additional
functionality for so much addition to the IP kernel, it has not been functionality for so much addition to the IP kernel, it has not been
defined. Given how little public key cryptography HIP requires, HIP defined. Given how little public key cryptography HIP requires, HIP
should only be implemented using public key Host Identities. should only be implemented using public key Host Identities.
If it is desirable to use HIP in a low security situation where If it is desirable to use HIP in a low security situation where
public key computations are considered expensive, HIP can be used public key computations are considered expensive, HIP can be used
with very short Diffie-Hellman and Host Identity keys. Such use with very short Diffie-Hellman and Host Identity keys. Such use
makes the participating hosts vulnerable to MitM and connection makes the participating hosts vulnerable to MitM and connection
hijacking attacks. However, it does not cause flooding dangers, hijacking attacks. However, it does not cause flooding dangers,
since the address check mechanism relies on the routing system and since the address check mechanism relies on the routing system and
not on cryptographic strength. not on cryptographic strength.
14. Acknowledgments 14. 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 the Host Identity Protocol the Acknowledgements section in the Host Identity Protocol
specification [4]. specification [6].
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. Finally, Shepard, Jukka Ylitalo, and Jorma Wall, were invaluable. Finally,
Spencer Dawkins and Dave Crocker provided valuable input during the Lars Eggert, Spencer Dawkins and Dave Crocker provided valuable input
final stages of publication, most of which was incorporated but some during the final stages of publication, most of which was
of which the authors decided to ignore in order to get this document incorporated but some of which the authors decided to ignore in order
published in the first place. to get this document published in the first place.
15 Informative References 15 Informative references
[1] Tsirtsis, G. and P. Srisuresh, "Network Address Translation - [1] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
Updates in the Domain Name System (DNS UPDATE)", RFC 2136,
April 1997.
[2] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[3] Tsirtsis, G. and P. Srisuresh, "Network Address Translation -
Protocol Translation (NAT-PT)", RFC 2766, February 2000. Protocol Translation (NAT-PT)", RFC 2766, February 2000.
[2] Srisuresh, P. and K. Egevang, "Traditional IP Network Address [4] Srisuresh, P. and K. Egevang, "Traditional IP Network Address
Translator (Traditional NAT)", RFC 3022, January 2001. Translator (Traditional NAT)", RFC 3022, January 2001.
[3] Borella, M., Lo, J., Grabelsky, D. and G. Montenegro, "Realm [5] Borella, M., Lo, J., Grabelsky, D. and G. Montenegro, "Realm
Specific IP: Framework", RFC 3102, October 2001. Specific IP: Framework", RFC 3102, October 2001.
[4] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-00 [6] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-00
(work in progress), June 2004. (work in progress), June 2004.
[5] Richardson, M., "A method for storing IPsec keying material in [7] Richardson, M., "A method for storing IPsec keying material in
DNS", draft-ietf-ipseckey-rr-10 (work in progress), April 2004. DNS", draft-ietf-ipseckey-rr-10 (work in progress), April 2004.
[6] Lear, E. and R. Droms, "What's In A Name:Thoughts from the [8] 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 [9] Nikander, P., "End-Host Mobility and Multi-Homing with Host
Identity Protocol", draft-ietf-hip-mm-00 (work in progress), Identity Protocol", draft-ietf-hip-mm-00 (work in progress),
October 2004. October 2004.
[8] Nikander, P., "Mobile IP version 6 Route Optimization Security [10] Nikander, P., "Mobile IP version 6 Route Optimization Security
Design Background", draft-ietf-mip6-ro-sec-00 (work in Design Background", draft-ietf-mip6-ro-sec-00 (work in
progress), April 2004. progress), April 2004.
[9] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", [11] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
draft-ietf-ipsec-ikev2-14 (work in progress), June 2004. draft-ietf-ipsec-ikev2-14 (work in progress), June 2004.
[10] Chiappa, J., "Endpoints and Endpoint Names: A Proposed [12] Chiappa, J., "Endpoints and Endpoint Names: A Proposed
Enhancement to the Internet Architecture", URL Enhancement to the Internet Architecture", URL
http://users.exis.net/~jnc/tech/endpoints.txt, 1999. http://users.exis.net/~jnc/tech/endpoints.txt, 1999.
[11] Nikander, P., "Denial-of-Service, Address Ownership, and Early [13] Nikander, P., "Denial-of-Service, Address Ownership, and Early
Authentication in the IPv6 World", in Proceesings of Security Authentication in the IPv6 World", in Proceesings of Security
Protocols, 9th International Workshop, Cambridge, UK, April Protocols, 9th International Workshop, Cambridge, UK, April
25-27 2001, LNCS 2467, pp. 12-26, Springer, 2002. 25-27 2001, LNCS 2467, pp. 12-26, Springer, 2002.
[12] Bellovin, S., "EIDs, IPsec, and HostNAT", in Proceesings of [14] Bellovin, S., "EIDs, IPsec, and HostNAT", in Proceesings of
41th IETF, Los Angeles, CA, March 1998. 41th IETF, Los Angeles, CA, March 1998.
Authors' Addresses Authors' Addresses
Robert Moskowitz Robert Moskowitz
ICSAlabs, a Division of TruSecure Corporation ICSAlabs, a Division of TruSecure Corporation
1000 Bent Creek Blvd, Suite 200 1000 Bent Creek Blvd, Suite 200
Mechanicsburg, PA Mechanicsburg, PA
USA USA
 End of changes. 

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