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rfc:rfc7966

Internet Engineering Task Force (IETF) H. Tschofenig Request for Comments: 7966 Category: Informational J. Korhonen, Ed. ISSN: 2070-1721 Broadcom Limited

                                                               G. Zorn
                                                           Network Zen
                                                             K. Pillay
                                                    Internet Solutions
                                                        September 2016
        Security at the Attribute-Value Pair (AVP) Level for
     Non-neighboring Diameter Nodes: Scenarios and Requirements

Abstract

 This specification specifies requirements for providing Diameter
 security at the level of individual Attribute-Value Pairs (AVPs).

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7966.

Tschofenig, et al. Informational [Page 1] RFC 7966 Diameter AVP-Level Security September 2016

Copyright Notice

 Copyright (c) 2016 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
 3.  Security Threats  . . . . . . . . . . . . . . . . . . . . . .   5
 4.  Scenarios for Diameter AVP-Level Protection . . . . . . . . .   7
 5.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   8
 6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
 7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
   7.2.  Informative References  . . . . . . . . . . . . . . . . .  10
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  10
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

Tschofenig, et al. Informational [Page 2] RFC 7966 Diameter AVP-Level Security September 2016

1. Introduction

 The Diameter base protocol specification [2] defines security
 protection between neighboring Diameter peers.  Diameter mandates
 that peer connections must be protected by Transport Layer Security
 (TLS) [6] for TCP, by Datagram TLS (DTLS) [7] for the Stream Control
 Transmission Protocol (SCTP), or by security mechanisms that are
 independent of Diameter (such as IPsec [5]).  These security
 protocols offer a wide range of security properties, including entity
 authentication, data-origin authentication, integrity protection,
 confidentiality protection, and replay protection.  They also support
 a large number of cryptographic algorithms, algorithm negotiation,
 and different types of credentials.  It should be understood that
 TLS/DTLS/IPsec in the Diameter context does not provide end-to-end
 security unless the Diameter nodes are direct peers, i.e.,
 neighboring Diameter nodes.  The current Diameter security is
 realized hop by hop.
 The need to also offer additional security protection of AVPs between
 non-neighboring Diameter nodes was recognized very early in the work
 on Diameter.  This led to work on Diameter security using the
 Cryptographic Message Syntax (CMS) [3].  However, due to the lack of
 deployment interest at that time (and the complexity of the developed
 solution), the specification was never completed.
 In the meanwhile, Diameter had received a lot of deployment interest
 from the cellular operator community, and because of the
 sophistication of those deployments, the need for protecting Diameter
 AVPs between non-neighboring nodes resurfaced.  Since the early 2000s
 (when the work on [3] was discontinued), the Internet community has
 seen advances in cryptographic algorithms (for example, authenticated
 encryption algorithms), and new security building blocks have been
 developed.
 This document specifies requirements for developing a solution to
 protect Diameter AVPs between non-neighboring Diameter nodes.

Tschofenig, et al. Informational [Page 3] RFC 7966 Diameter AVP-Level Security September 2016

2. Terminology

 The key words '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].
 This document reuses terminology from the Diameter base specification
 [2].
 In the figures below, AVP refers to an unprotected AVP, and {AVP}k
 refers to an AVP that experiences security protection (using key "k")
 without further distinguishing between integrity and confidentiality
 protection.
 The following terms are also used in this document:
 AAA broker
    An entity that manages Authentication, Authorization, and
    Accounting (AAA) traffic between roaming partner networks.
 AAA broker network
    A network operated by a AAA broker, which consists of necessary
    AAA functions to provide AAA brokering services for its customer
    AAA networks.
 Diameter firewall
    A Diameter firewall is a proxy (or a relay) agent that acts
    similarly to conventional IP traffic firewalls but only at the
    Diameter AVP and command level.  A Diameter firewall may, for
    example, discard AVPs that violate security policy, thus
    preventing them from traversing the firewall.  The Diameter
    firewall may even discard entire Diameter messages based on the
    security policy.

Tschofenig, et al. Informational [Page 4] RFC 7966 Diameter AVP-Level Security September 2016

3. Security Threats

 This section describes various security threats that raise the need
 for protecting Diameter Attribute-Value Pairs (AVPs).  Figure 1
 illustrates an example of a Diameter-based roaming architecture in
 which Diameter clients within the visited networks need to interact
 with Diameter servers in the home domain.  AAA domains are
 interconnected using a Diameter-based AAA interconnection network
 labeled as "AAA broker network".
    +oooooooooooooooooo+              +====================+
    |   Example.net    |              |                    |
    |                  |              |                    |
 +--------+      +--------+        +--------+        +--------+
 |Diameter|      |Diameter+--------+Diameter|        |Diameter|
 |Client 1|      |Proxy A1|        |Proxy B |        |Proxy C |
 | (NAS)  +------+        | +------+        +--------+        |----+
 +--------+      +--------+ |      +--------+        +--------+    |
    |                  |    |         |                    |       |
    | Visited Domain 1 |    |         | AAA Broker Network |       |
    +oooooooooooooooooo+    |         +====================+       |
                            |                                      |
                            |                                      |
                            |                                      |
                            |            +\\\\\\\\\\\\\\\\\\\\+    |
                            |     +--------+  Example.com     |    |
                            |     |Diameter|                  |    |
    +oooooooooooooooooo+    |     |Server X+--+         +--------+ |
    |   Example.org    |    |     +--------+  |         |Diameter| |
    |                  |    |     +--------+  +---------+Proxy D |-+
 +--------+      +--------+ |     |Diameter|  |         +--------+
 |Diameter|      |Diameter| |     |Server Y+--+               |
 |Client 2+------+Proxy A2+-+     +--------+    Home Domain   |
 | (NAS)  |      |        |              +////////////////////+
 +--------+      +--------+
    |                  |
    | Visited Domain 2 |
    +oooooooooooooooooo+
                 Figure 1: Example Diameter Deployment
 Eavesdropping:  Some Diameter applications carry information that is
    only intended for consumption by end points, either by the
    Diameter client or by the Diameter server but not by
    intermediaries.  As an example, consider the Diameter Extensible
    Authentication Protocol (EAP) application [4] that allows the

Tschofenig, et al. Informational [Page 5] RFC 7966 Diameter AVP-Level Security September 2016

    transport of keying material between the Diameter server to the
    Diameter client (using the EAP-Master-Session-Key AVP) for the
    protection of the air interface (i.e., the wireless link) between
    the end device (such as a mobile phone; not shown in the figure)
    and the Network Access Server (NAS).  The content of the EAP-
    Master-Session-Key AVP should benefit from protection against
    eavesdropping by intermediaries.  Other AVPs (for example, those
    listed in Section 13.3 of [2]) might also carry sensitive personal
    data that, when collected by intermediaries, allow for traffic
    analysis.
    In the context of the deployment shown in Figure 1, the adversary
    could, for example, be in the AAA broker network.
 Injection and Manipulation:  The Diameter base protocol specification
    mandates security protection between neighboring nodes, but
    Diameter agents may be compromised or misconfigured and inject or
    manipulate AVPs.  To detect such actions, additional security
    protection needs to be applied at the Diameter layer.
    Nodes that could launch such an attack are any Diameter agents
    along the end-to-end communication path.
 Impersonation:  Imagine a case where a Diameter message from
    Example.net contains information claiming to be from Example.org.
    This would either require strict verification at the edge of the
    AAA broker network or cryptographic assurance at the Diameter
    layer to prevent a successful impersonation attack.
    Any Diameter realm could launch such an attack aiming for
    financial benefits or to disrupt service availability.

Tschofenig, et al. Informational [Page 6] RFC 7966 Diameter AVP-Level Security September 2016

4. Scenarios for Diameter AVP-Level Protection

 This scenario outlines a number of cases for deploying security
 protection of individual Diameter AVPs.
 In the first scenario, shown in Figure 2, end-to-end security
 protection is provided between the Diameter client and the Diameter
 server with any number of intermediate Diameter agents.  Diameter
 AVPs exchanged between these two Diameter nodes may be protected end
 to end (notation '{AVP}k') or unprotected (notation 'AVP').
 +--------+                                                +--------+
 |Diameter| AVP, {AVP}k                                    |Diameter|
 |Client  +-----------------........... -------------------+Server  |
 +--------+                                                +--------+
         Figure 2: End-to-End Diameter AVP Security Protection
 In the second scenario, shown in Figure 3, a Diameter proxy acts on
 behalf of the Diameter client with regard to security protection.  It
 applies security protection to outgoing Diameter AVPs and verifies
 incoming AVPs.  Typically, the proxy enforcing the security
 protection belongs to the same domain as the Diameter client/server
 without end-to-end security features.
 +--------+     +--------+                                 +--------+
 |Diameter| AVP |Diameter|   AVP, {AVP}k                   |Diameter|
 |Client  +-----+Proxy A +---------- .......... -----------+Server  |
 +--------+     +--------+                                 +--------+
       Figure 3: Middle-to-End Diameter AVP Security Protection
 In the third scenario, shown in Figure 4, a Diameter proxy acts on
 behalf of the Diameter server.
 +--------+                                 +--------+     +--------+
 |Diameter| AVP, {AVP}k                     |Diameter| AVP |Diameter|
 |Client  +-----------------........... ----+Proxy D +-----+Server  |
 +--------+                                 +--------+     +--------+
       Figure 4: End-to-Middle Diameter AVP Security Protection
 The fourth and the final scenario (see Figure 5) is a combination of
 the middle-to-end and the end-to-middle scenarios shown in Figures 3
 and 4.  From a deployment point of view, this scenario is easier to
 accomplish for two reasons.  First, Diameter clients and Diameter
 servers remain unmodified.  This ensures that no modifications are
 needed to the installed Diameter infrastructure, except for the

Tschofenig, et al. Informational [Page 7] RFC 7966 Diameter AVP-Level Security September 2016

 security-enabled proxies, obviously.  Second, the key management is
 also simplified since a fewer number of keys need to be negotiated
 and provisioned.  The assumption here is that the number of security-
 enabled proxies would be significantly less than unprotected Diameter
 nodes in the installed base.
 +--------+     +--------+                  +--------+     +--------+
 |Diameter| AVP |Diameter|   AVP, {AVP}k    |Diameter| AVP |Diameter|
 |Client  +-----+Proxy A +-- .......... ----+Proxy D +-----+Server  |
 +--------+     +--------+                  +--------+     +--------+
      Figure 5: Middle-to-Middle Diameter AVP Security Protection

5. Requirements

 Requirement #1:  The solution MUST support an extensible set of
    cryptographic algorithms.
       Motivation: Solutions MUST be able to evolve to adapt to
       evolving cryptographic algorithms and security requirements.
       This may include the provision of a modular mechanism to allow
       cryptographic algorithms to be updated without substantial
       disruption to deployed implementations.
 Requirement #2:  The solution MUST support confidentiality,
    integrity, and data-origin authentication.  Solutions for
    integrity protection MUST work in a backwards-compatible way with
    existing Diameter applications and therefore be able to traverse
    legacy proxy and relay agents.
 Requirement #3:  The solution MUST support replay protection.
 Requirement #4:  The solution MUST support the ability to delegate
    security functionality to another entity.
       Motivation: As described in Section 4, the ability to let a
       Diameter proxy perform security services on behalf of all
       clients within the same administrative domain is important for
       incremental deployability.  The same applies to the other
       communication side where a load balancer terminates security
       services for the servers it interfaces.
 Requirement #5:  The solution MUST be able to selectively apply its
    cryptographic protection to certain Diameter AVPs.
       Motivation: Some Diameter applications assume that certain AVPs
       are added, removed, or modified by intermediaries.  As such, it
       must be possible to apply security protection selectively.

Tschofenig, et al. Informational [Page 8] RFC 7966 Diameter AVP-Level Security September 2016

       Furthermore, there are AVPs that must not be confidentiality
       protected but may still be integrity protected, such as those
       required for Diameter message routing.
 Requirement #6:  The solution MUST define a mandatory-to-implement
    cryptographic algorithm.
       Motivation: For interoperability purposes, it is beneficial to
       have a mandatory-to-implement cryptographic algorithm specified
       (unless profiles for specific usage environments specify
       otherwise).
 Requirement #7:  The solution MUST support symmetric keys and
    asymmetric keys.
       Motivation: Symmetric and asymmetric cryptographic algorithms
       provide different security services.  Asymmetric algorithms,
       for example, allow non-repudiation services to be offered.
 Requirement #8:  A solution for dynamic key management MUST be
    included in the overall solution framework.
       However, it is assumed that no "new" key management protocol
       needs to be developed; instead, existing ones are reused, if at
       all possible.  Rekeying could be triggered by (a) management
       actions and (b) expiring keying material.

6. Security Considerations

 This entire document focuses on the discussion of new functionality
 for securing Diameter AVPs selectively between non-neighboring nodes.
 Various security threats are mitigated by selectively applying
 security protection for individual Diameter AVPs.  Without
 protection, there is the possibility for password sniffing,
 confidentiality violation, and AVP insertion, deletion, or
 modification.  Additionally, applying a digital signature offers non-
 repudiation capabilities, a feature not yet available in today's
 Diameter deployment.  Modification of certain Diameter AVPs may not
 necessarily be the act of malicious behavior but could also be the
 result of misconfiguration.  An over-aggressively configured
 firewalling Diameter proxy may also remove certain AVPs.  In most
 cases, data-origin authentication and integrity protection of AVPs
 will provide the most benefits for existing deployments with minimal
 overhead and (potentially) operate in a full-backwards compatible
 manner.

Tschofenig, et al. Informational [Page 9] RFC 7966 Diameter AVP-Level Security September 2016

7. References

7.1. Normative References

 [1]        Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [2]        Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
            Ed., "Diameter Base Protocol", RFC 6733,
            DOI 10.17487/RFC6733, October 2012,
            <http://www.rfc-editor.org/info/rfc6733>.

7.2. Informative References

 [3]        Calhoun, P., Farrell, S., and W. Bulley, "Diameter CMS
            Security Application", Work in Progress,
            draft-ietf-aaa-diameter-cms-sec-04, March 2002.
 [4]        Eronen, P., Ed., Hiller, T., and G. Zorn, "Diameter
            Extensible Authentication Protocol (EAP) Application",
            RFC 4072, DOI 10.17487/RFC4072, August 2005,
            <http://www.rfc-editor.org/info/rfc4072>.
 [5]        Kent, S. and K. Seo, "Security Architecture for the
            Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
            December 2005, <http://www.rfc-editor.org/info/rfc4301>.
 [6]        Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246,
            DOI 10.17487/RFC5246, August 2008,
            <http://www.rfc-editor.org/info/rfc5246>.
 [7]        Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
            Transport Layer Security (DTLS) for Stream Control
            Transmission Protocol (SCTP)", RFC 6083,
            DOI 10.17487/RFC6083, January 2011,
            <http://www.rfc-editor.org/info/rfc6083>.

Acknowledgments

 We would like to thank Guenther Horn, Martin Dolly, Steve Donovan,
 Lionel Morand, and Tom Taylor (rest in peace, Tom) for their review
 comments.
 The authors also thank Qin Wu, Christer Holmberg, Ben Campbell, and
 Radia Perlman, who provided additional reviews during the Last Call.

Tschofenig, et al. Informational [Page 10] RFC 7966 Diameter AVP-Level Security September 2016

Authors' Addresses

 Hannes Tschofenig
 Hall in Tirol 6060
 Austria
 Email: Hannes.tschofenig@gmx.net
 URI:   http://www.tschofenig.priv.at
 Jouni Korhonen (editor)
 Broadcom Limited
 3151 Zanker Rd.
 San Jose, CA  95134
 United States of America
 Email: jouni.nospam@gmail.com
 Glen Zorn
 Network Zen
 227/358 Thanon Sanphawut
 Bang Na, Bangkok  10260
 Thailand
 Email: glenzorn@gmail.com
 Kervin Pillay
 Internet Solutions
 South Africa
 Email: kervin.pillay@gmail.com

Tschofenig, et al. Informational [Page 11]

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