SIPPING H. Tschofenig, Ed.
Internet-Draft Nokia Siemens Networks
Intended status: Informational G. Dawirs
Expires: January 15, 2009 University of Namur
T. Froment
Alcatel-Lucent
D. Wing
Cisco
H. Schulzrinne
Columbia University
July 14, 2008
Requirements for Authorization Policies to tackle Spam and Unwanted
Communication for Internet Telephony
draft-froment-sipping-spit-requirements-03
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Internet-Draft SPIT Authorization Policy Requirements July 2008
Abstract
Spam over Internet Telephony (SPIT) is one of the foreseen future
forms of spamming that SIP open-wide networks may have to handle.
SPIT also has more impact on users than email spam since it is more
intrusive. Email as a store-and-forward communication mechanism
allows for several filtering mechanisms to be applied to the full
content before being presented to the user. Session Initiation
Protocol (SIP) interaction is, in contrast, real-time communication
and therefore does not provide much information prior to the
transmission of the content, making it both harder to filter and more
annoying to users. The responsibility for filtering, blocking calls,
or taking any other preventive action can belong to different
elements in the call flow and may depend on various factors. This
document discusses the requirements to define authorization policies
that should allow end users or other parties to setup anti-SPIT
policies for triggering these actions. These policies typically
match a particular SIP communication pattern based on a number of
attributes. The range of attributes includes information provided,
for example, by the SIP protocol itself, by the SIP identity
mechanism, by information carried within SAML assertions or by
reputation systems of social networks.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Conditions . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Actions . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Transformations . . . . . . . . . . . . . . . . . . . . . 8
3.4. Generic Requirements . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. References . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
Today, most of the anti-SPAM solutions are coming from email
experience, and their applicability to SIP has been discussed
in[RFC5039].
As outlined in [RFC5039], it is likely that many different techniques
will need to be combined to deal with SPIT. Users will make
different trade-offs when rejecting suspicious calls, for example,
trading a lower probability of being interrupted for occasional
erroneous call rejection. Also, different types of users, such as
businesses and private residences, have different call
characteristics. We propose to define a policy language that allows
users to easily define their call handling preferences for SPIT. The
policy would be executed by trusted SIP proxy or any other SIP
element, altering how they handle incoming requests. Policy rules
are likely to be define by different actors, including end users
themselves, parents on behalf of their children or system
administrators. This document enumerates and motivates requirements
for such a policy language. Some attributes in an incoming message
play a more important role than others. For example, applying
authorization policies based on authenticated identity [RFC4474], is
an effective way to make decisions regarding unwanted traffic in some
cases.
This document identifies requirements for authorization policies when
used to influence message handling for unwanted communication
attempts.
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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 [RFC2119],
with the important qualification that, unless otherwise stated, these
terms apply to the design of the authorization policies, not its
implementation or application.
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3. Requirements
This section lists the requirements categorized according to their
applicability for the "conditions", "actions" and "transformation"
parts typically found in authorization policies.
3.1. Conditions
The first set of requirements refer to identity related information.
Req-C 1: Policies MUST allow conditions to express single
authenticated identities.
Req-C 2: Policies MUST allow filtering based on the domain part of
the identity.
Req-C 3: Policies MUST support the differentiation between
authenticated and unauthenticated identities.
Req-C 4: Policies MUST be able to express exceptions within a group
of users or a domain.
Req-C 5: Policies SHOULD allow an anonymous identity as a condition.
Message handling may depend on the content of SIP request header
fields.
Req-C 6: Policies SHOULD allow conditions to refer to the
"destination" (which corresponds to the "Request-URI") and
"original-destination" (which corresponds to the "To" header).
Req-C 7: Policies SHOULD allow conditions to refer to the method
invoked by the caller (e.g., INVITE, REFER, MESSAGE,
SUBSCRIBE).
Motivation: Some SIP methods are more intrusive than others
(the default applicative behaviour when SIP MESSAGEs are
received is often to pop-up the message on the UAS side),
adopting a different filtering policy depending of the method
invoked will enhance the user's protection.
Req-C 8: Policies SHOULD allow the entity that writes the rules to
take actions on messages that are marked as Spam.
Note that such a condition element should be seen in
context of the authenticated domain or, otherwise, of a
protected information to avoid security
vulnerabilities.
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Req-C 9: Policies MAY allow to make decisions based on the current
state of the user. E.g., his sphere or other presence
information.
Req-C 10: Policies SHOULD support consitions based on the content
type and/or offered (or used) media of a message.
Message handling may depend on time of day or the date.
Req-C 11: Policies SHOULD allow conditions that refer to the
reception date, time, timezone or period of time of the
incoming request.
Message handling might be based on the caller's preferred languages.
Req-C 12: Policies SHOULD allow to make decisions based on the
languages in which the originator of the call wishes to
communicate.
3.2. Actions
Req-A 1: Policies SHOULD allow messages to get "blocked", i.e., to
stop forwarding the request and to return an answer with a
"403 Forbidden''.
Req-A 2: Policies SHOULD allow messages to get "politely blocked",
i.e., to stop the request with, for instance, a "486 Busy"
response.
Req-A 3: Policies SHOULD allow messages to get "marked", i.e., to
forward the request and mark it as "potential Spam" for
filtering at the end point or at subsequent entities along the
signaling path.
Req-A 4: Policies SHOULD allow messages to be "allowed", i.e., to
forward this message.
Req-A 5: Policies MUST allow messages to be "redirected" to, for
example, voicemail or to a different device in the possession
of the user.
Req-A 6: Policies MUST allow executing other SPIT prevention
procedures, such as computational puzzles
[I-D.jennings-sip-hashcash] or the consent framework
[I-D.ietf-sip-consent-framework]. A specification developing
a SPIT prevention mechanism should provide information on how
they can be incorporated into the authorization policy
framework.
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Req-A 7: Policies MAY allow an e-mail (or SMS, MMS) or other
notifications to be sent to the user about the actions taken
due to a specific call attempt.
R8: Policies MAY allow the usage of one or many feedback
mechanisms.
3.3. Transformations
Req-T 1: Policies SHOULD allow SIP messages to be marked with a
certain SPIT probability in case SPIT detection and policy
enforcement is excecuted on different entities. For example,
a network element might run a statistical SPIT detection tool
but the authorization policies are executed on a different
entity, such as the end host. Note that it needs to be
ensured that an adversary is not able to set the SPIT
probabity values since otherwise the authorization policies
that rely on such information are misguided.
3.4. Generic Requirements
Req-G 1: It SHOULD be possible to allow a hierarchy of authorization
policies to be used.
It is quite likely that a rules from different rule writing
entities are provided. For example, in a company environment
policies from the system administrator are provided in
addition to the end users policies. The former might reflect
the overall company policy. The impact for the policy is
mainly on the definition of an appropriate conflict resolution
mechanism.
Req-G 2: It MUST be possible for a client to learn the supported
authorization policy capabilities implemented by the server.
Req-G 3: Policies MUST be extensible and these extensions MUST exist
within a different namespace. Furthermore, a published schema
and the namespace for elements defined within it MUST NOT be
altered by future specifications.
Req-G 4: The policies MUST provide a mandatory-to-implement conflict
resolution mechanism.
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4. IANA Considerations
This document does not require actions by IANA.
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5. Security Considerations
This document describes the requirements for elements contained in
the authorization policies that allow communication attempts to be
treated differently based on the content of the message, time-of-day,
context of the user, reputation of the sending party, and many other
factors.
The security concerns are related to the ability of certain entities
to create, update and delete authorization policies. If an
unauthorized entity is allowed to modify policies (and to distribute
them to other domains) then a denial of service attack is the
consequence with impact for more than a single end point. These
security aspects are, however, not the subject of this document.
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6. Acknowledgements
The content of this document is inspired by the work of CPL
[RFC3880], SIEVE [RFC5228], Common Policy [RFC4745] and Presence
Authorization Policy [RFC5025]. We would like to thank the authors
of these documents for their work.
Furthermore, we would like to thank Eva Leppanen for the detailed
review provided in June 2006.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2. References
[I-D.ietf-sip-consent-framework]
Rosenberg, J., Camarillo, G., and D. Willis, "A Framework
for Consent-based Communications in the Session Initiation
Protocol (SIP)", draft-ietf-sip-consent-framework-04 (work
in progress), January 2008.
[I-D.jennings-sip-hashcash]
Jennings, C., "Computational Puzzles for SPAM Reduction in
SIP", draft-jennings-sip-hashcash-06 (work in progress),
July 2007.
[RFC3880] Lennox, J., Wu, X., and H. Schulzrinne, "Call Processing
Language (CPL): A Language for User Control of Internet
Telephony Services", RFC 3880, October 2004.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC4745] Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J.,
Polk, J., and J. Rosenberg, "Common Policy: A Document
Format for Expressing Privacy Preferences", RFC 4745,
February 2007.
[RFC5025] Rosenberg, J., "Presence Authorization Rules", RFC 5025,
December 2007.
[RFC5039] Rosenberg, J. and C. Jennings, "The Session Initiation
Protocol (SIP) and Spam", RFC 5039, January 2008.
[RFC5228] Guenther, P. and T. Showalter, "Sieve: An Email Filtering
Language", RFC 5228, January 2008.
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Authors' Addresses
Hannes Tschofenig (editor)
Nokia Siemens Networks
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Email: Hannes.Tschofenig@nsn.com
URI: http://www.tschofenig.com
Geoffrey Dawirs
University of Namur
21, rue Grandgagnage
Namur B-5000
Belgique
Email: gdawirs@gdawirs.be
Thomas Froment
Alcatel-Lucent
Route de Villejust
Nozay, Paris 91620
France
Email: Thomas.Froment@alcatel-lucent.fr
Dan Wing
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
Email: dwing@cisco.com
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Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
Email: hgs@cs.columbia.edu
URI: http://www.cs.columbia.edu
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