IP Security Policy (IPSP) Requirements
RFC 3586

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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             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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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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