RFC 7966
Security at the Attribute-Value Pair (AVP) Level for Non-neighboring Diameter Nodes: Scenarios and Requirements
Pages: 11
Informational
Informational
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 RequirementsAbstract
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.
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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
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.
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.
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
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.
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
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 Protection5. 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.
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.
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.
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