Network Working Group M. Blaze
Request for Comments: 3586 AT&T Labs - Research
Category: Standards Track A. Keromytis
Columbia University
M. Richardson
Sandelman Software Works
L. Sanchez
Xapiens Corporation
August 2003
IP Security Policy (IPSP) Requirements
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes the problem space and solution requirements
for developing an IP Security Policy (IPSP) configuration and
management framework. The IPSP architecture provides a scalable,
decentralized framework for managing, discovering and negotiating the
host and network security policies that govern access, authorization,
authentication, confidentiality, data integrity, and other IP
Security properties. This document highlights such architectural
components and presents their functional requirements.
Table of Contents
1. Introduction.................................................. 2
1.1. Terminology............................................. 2
1.2. Security Policy and IPsec............................... 2
2. The IP Security Policy Problem Space.......................... 3
3. Requirements for an IP Security Policy Configuration and
Management Framework.......................................... 5
3.1. General Requirements.................................... 5
3.2. Description and Justification........................... 5
3.2.1. Policy Model.................................... 5
3.2.2. Security Gateway Discovery...................... 6
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RFC 3586 IP Security Policy (IPSP) Requirements August 2003
3.2.3. Policy Specification Language................... 6
3.2.4. Distributed policy.............................. 6
3.2.5. Policy Discovery................................ 6
3.2.6. Security Association Resolution................. 6
3.2.7. Compliance Checking............................. 7
4. Security Considerations....................................... 7
5. IANA Considerations........................................... 7
6. Intellectual Property Statement............................... 7
7. References.................................................... 8
7.1. Normative References.................................... 8
7.2. Informative References.................................. 8
8. Disclaimer.................................................... 8
9. Acknowledgements.............................................. 8
10. Authors' Addresses............................................ 9
11. Full Copyright Statement...................................... 10
1. Introduction
1.1. Terminology
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].
1.2. Security Policy and IPsec
Network-layer security now enjoys broad popularity as a tool for
protecting Internet traffic and resources. Security at the network
layer can be used as a tool for at least two kinds of security
architecture:
a) Security gateways. Security gateways (including "firewalls") at
the edges of networks use IPsec [RFC-2401] to enforce access
control, protect the confidentiality and authenticity of network
traffic entering and leaving a network, and to provide gateway
services for virtual private networks (VPNs).
b) Secure end-to-end communication. Hosts use IPsec to implement
host-level access control, to protect the confidentiality and
authenticity of network traffic exchanged with the peer hosts with
which they communicate, and to join virtual private networks.
On one hand, IPsec provides an excellent basis for a very wide range
of protection schemes; on the other hand, this wide range of
applications for IPsec creates complex management tasks that become
especially difficult as networks scale up and require different
security policies, and are controlled by different entities, for
different kinds of traffic in different parts of the network.
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As organizations deploy security gateways, the Internet divides into
heterogeneous regions that enforce different access and security
policies. Yet it is often still necessary for hosts to communicate
across the network boundaries controlled by several different
policies. The wide range of choices of cryptographic parameters (at
multiple protocol layers) complicates matters and introduces the need
for hosts and security gateways to identify and negotiate a set of
security parameters that meets each party's requirements. Even more
complexity arises as IPsec becomes the means through which firewalls
enforce access control and VPN membership; two IPsec endpoints that
want to establish a security association must identify, not only the
mutually acceptable cryptographic parameters, but also exactly what
kind of access the combined security policy provides.
While the negotiation of cryptographic and other security parameters
for IPsec security associations (SAs) is supported by key management
protocols (e.g., ISAKMP [RFC-2408]), the IPsec key management layer
does not provide a scheme for managing, negotiating, or enforcing the
security policies under which SAs operate.
IPSP provides the framework for managing IPsec security policy,
negotiating security association (SA) parameters between IPsec
endpoints, and distributing authorization and policy information
among hosts that require the ability to communicate via IPsec.
2. The IP Security Policy Problem Space
IPSP aims to provide a scalable, decentralized framework for
managing, discovering and negotiating the host and network IPsec
policies that govern access, authorization, cryptographic mechanisms,
confidentiality, data integrity, and other IPsec properties.
The central problem solved by IPSP is that of controlling security
policy in a manner that is useful for the wide range of IPsec
applications and modes of operation. In particular:
- IPSP hosts may serve as IPsec endpoints, security gateways,
network management hubs, or a combination of these functions.
IPSP will manage end-users computers (which may be fixed
workstations controlled by a single organization or mobile
laptops that require remote access to a corporate VPN),
firewalls (which provide different services and allow different
levels of access to different classes of traffic and users),
VPN routers (which support links to other VPNs that might be
controlled by a different organization's network policy), web
and other servers (which might provide different services
depending on where a client request came from), and so on.
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- IPSP administration will be inherently heterogeneous and
decentralized. A basic feature of IPsec is that two hosts can
establish a Security Association even though they might not
share a common security policy, or, indeed, trust one another
at all. This property of IPsec becomes even more pronounced at
the higher level abstraction managed by IPSP.
- The SA parameters acceptable to any pair of hosts (operating
under different policies) will often not be specified in
advance. IPSP will often have to negotiate and discover the
mutually-acceptable SA parameters on-the-fly when two hosts
attempt to create a new SA.
- Some hosts will be governed by policies that are not directly
specified in the IPSP language. For example, a host's IPsec
policy might be derived from a more comprehensive higher-layer
security policy managed by some other system. Similarly, some
vendors might develop specialized (and proprietary) tools for
managing policy in their products. In such cases, it is
necessary to derive an IPSP policy specification for only those
aspects of a host's policy that involve interoperability with
other hosts running IPSP.
- IPSP must scale to support complex policy administration
schemes. In even modest-size networks, one administrator must
often control policy remotely, and must have the ability to
change the policy on many different hosts at the same time. In
larger networks (or those belonging to large organizations), a
host's policy might be governed by several different
authorities (e.g., several different departments might have the
authority to add users to a firewall or open access to new
services). Different parts of a policy might be "owned" by
different entities in a complex hierarchy. IPSP must provide a
mechanism for delegating specific kinds of authority to
specific entities.
- The semantics of IPSP must be well defined, particularly with
respect to any security-critical aspects of the system.
- IPSP must be secure, sound, and comprehensible. It should be
possible to understand what an IPSP policy does; the difficulty
of understanding an IPSP policy should be somewhat proportional
to the complexity of the problem it solves. It should also be
possible to have confidence that an IPSP policy does what it
claims, and that IPSP implementation is correct;
architecturally, the security-critical parts of IPSP should be
small and well-specified enough to allow verification of their
correct operation. Ideally, IPSP should be compatible with
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formal methods, such as implementing security policies with
provable properties.
3. Requirements for an IP Security Policy Configuration and
Management Framework
3.1. General Requirements
An IPSP solution MUST include:
- A policy model with well-defined semantics that captures the
relationship between IPsec SAs and higher-level security
policies,
- A gateway discovery mechanism that allows hosts to discover
where to direct IPsec traffic intended for a specific endpoint,
- A well-specified language for describing host policies,
- A means for distributing responsibility for different aspects
of policy to different entities,
- A mechanism for discovering the policy of a host,
- A mechanism for resolving the specific IPsec parameters to be
used between two hosts governed by different policies (and for
determining whether any such parameters exist); and,
- A well-specified mechanism for checking for compliance with a
host's policy when SAs are created.
The mechanisms used in IPSP must not require any protocol
modifications in any of the IPsec standards (ESP [RFC-2406], AH,
[RFC-2402], IKE [RFC-2409]). The mechanisms must be independent of
the SA-negotiation protocol, but may assume certain functionality
from such a protocol (this is to ensure that future SA-negotiation
protocols are not incompatible with IPSP).
3.2. Description and Justification
3.2.1. Policy Model
A Policy Model defines the semantics of IPsec policy. Policy
specification, checking, and resolution should implement the
semantics defined in the model. However, the model should be
independent of the specific policy distribution mechanism and policy
discovery scheme, to the extent possible.
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3.2.2. Security Gateway Discovery
The gateway discovery mechanism may be invoked by any host or
gateway. Its goal is to determine what IPsec gateways exist between
the initiator and the intended communication peer. The actual
mechanism employed may be used to piggy-back information necessary by
other components of the IPSP architecture (e.g., policy discovery, as
is done in [SPP]). The discovery mechanism may have to be invoked at
any time, independently of existing security associations or other
communication, to detect topology changes.
3.2.3. Policy Specification Language
In order to allow for policy discovery, compliance checking, and
resolution across a range of hosts, a common language is necessary in
which to express the policies of hosts that need to communicate with
one another. Statements in this language are the output of policy
discovery, and provide the input to the policy resolution and
compliance checking systems. Note that a host's or network's
security policy may be expressed in a vendor-specific way, but would
be translated to the common language when it is to be managed by the
IPSP services.
3.2.4. Distributed policy
As discussed above, it must be possible for all or part of a host's
policy to be managed remotely, possibly by more than one entity.
This is a basic requirement for large-scale networks and systems.
3.2.5. Policy Discovery
A policy discovery mechanism must provide the essential information
that two IPsec endpoints can use to determine what kinds of SAs are
possible between one another. This is especially important for hosts
that are not controlled by the same entity, and that might not
initially share any common information about one another. Note that
a host need not reveal its entire security policy, only enough
information to support the SA resolution system for hosts that might
want to communicate with it.
3.2.6. Security Association Resolution
Once two hosts have learned enough about each other's policies, it
must be possible (and computationally feasible) to find an acceptable
set of SA parameters that meets both host's requirements and will
lead to the successful creation of a new SA.
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3.2.7. Compliance Checking
When a host proposes the output of the SA resolution scheme, it must
be checked for compliance with the local security policy of each
host. The security and soundness of the SAs created by IPSP-managed
communication should depend only on the correctness of the compliance
checking stage. In particular, even if the SA resolution scheme
(which is likely to be computationally and conceptually complex)
produces an incorrect result, it should still not be possible to
violate the specified policy of either host.
4. Security Considerations
This document discusses the high-level requirements for a policy
framework and architecture for IPsec. A justification for the
various components is given.
5. IANA Considerations
No action is required by IANA.
6. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11.
Copies of claims of rights made available for publication and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
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7. References
7.1. Normative References
[RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Level", BCP 14, RFC 2119, March 1997.
[RFC-2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
7.2. Informative References
[RFC-2402] Kent, S. and R. Atkinson, "IP Authentication Header", RFC
2402, November 1998.
[RFC-2406] Kent, S. and R. Atkinson, "IP Encapsulating Security
Payload (ESP)", RFC 2406, November 1998.
[RFC-2408] Maughan, D., Shertler, M., Schneider, M. and J. Turner,
"Internet Security Association and Key Management Protocol
(ISAKMP)", RFC 2408, November 1998.
[RFC-2409] Harkins, D and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[SPP] Sanchez, L. and M. Condell, "The Security Policy
Protocol", Work in Progress.
8. Disclaimer
The views and specification here are those of the authors and are not
necessarily those of their employers. The authors and their
employers specifically disclaim responsibility for any problems
arising from correct or incorrect implementation or use of this
specification.
9. Acknowledgements
The authors thank the members of the IPsec Policy working group that
contributed to this document.
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10. Authors' Addresses
Matt Blaze
AT&T Labs - Research
180 Park Avenue
Florham Park, NJ 07932 USA
EMail: mab@crypto.com
Angelos D. Keromytis
Computer Science Department
Columbia University
1214 Amsterdam Avenue, M.C. 0401
New York, NY 10027, USA
EMail: angelos@cs.columbia.edu
Michael C. Richardson
Sandelman Software Works Corp.
470 Dawson Avenue
Ottawa, ON K1Z 5V7 Canada
Phone: +1 613 276-6809
EMail: mcr@sandelman.ottawa.on.ca
Luis A. Sanchez
Xapiens Corporation
PO Box 9023694
San Juan, PR 00902 USA
Phone: +1 (787) 832-4717
EMail: lsanchez@xapiens.com
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11. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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RFC, FYI, BCP