





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]

