DIME H. Tschofenig
Internet-Draft ARM Limited
Intended status: Informational J. Korhonen, Ed.
Expires: December 10, 2016 Broadcom Limited
G. Zorn
Network Zen
K. Pillay
Internet Solutions
June 8, 2016
AVP Level Security for Non-neighboring Diameter Nodes: Scenarios and
Requirements
draft-ietf-dime-e2e-sec-req-05.txt
Abstract
This specification specifies requirements for providing Diameter
security at the level of individual Attribute-Value Pairs.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Security Threats . . . . . . . . . . . . . . . . . . . . . . 3
4. Scenarios for Diameter AVP-Level Protection . . . . . . . . . 5
5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Diameter base protocol specification [2] defines security
protection between neighboring Diameter peers. The Diameter mandates
that peer connections must be protected by TLS (for TCP) [6], DTLS
(for SCTP) [7] or using 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, 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 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 Attribute
Value Pairs (AVP) 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].
Due to lack of deployment interest at that time (and the complexity
of the developed solution) the specification was, however, 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 re-surfaced. Since early 2000
(when the work on [3] was discontinued) the Internet community had
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seen advances in cryptographic algorithms (for example, authenticated
encryption algorithms) and new security building blocks were
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
documents are to be interpreted as described in RFC 2119 [1].
This document re-uses terminology from the Diameter base
specification [2].
In the figures below Attribute Value Pair (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 AAA traffic between roaming partner
networks.
AAA Broker Network
A network operated by an 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 security policy offending AVPs from traversing
through it. The Diameter firewall may even discard entire
Diameter messages based on the security policy.
3. Security Threats
The following description aims to illustrate various security threats
that raise the need for protecting Diameter Attribute-Value Pairs
(AVPs). Figure 1 illustrates an example of Diameter based roaming
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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.
+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 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
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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 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
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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 end-to-middle and the middle-to-end scenario shown in Figure 4
and in Figure 3. 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 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.
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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 to 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 their
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).
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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 re-used, if at
all possible. Rekeying could be triggered by (a) management
actions and (b) expiring keying material.
6. Security Considerations
This entire document focused 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, AVP insertion, deletion or modification. Additionally,
applying 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) operating in a full-backwards compatible manner.
7. IANA Considerations
This document does not require actions by IANA.
8. 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.
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9. References
9.1. 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>.
9.2. Informative References
[3] Calhoun, P., Farrell, S., and W. Bulley, "Diameter CMS
Security Application", draft-ietf-aaa-diameter-cms-sec-04
(work in progress), 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>.
Authors' Addresses
Hannes Tschofenig
ARM Limited
Austria
Email: Hannes.tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
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Jouni Korhonen (editor)
Broadcom Limited
3151 Zanker Rd.
San Jose, CA 95134
USA
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
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