Internet DRAFT - draft-peterson-stir-messaging
draft-peterson-stir-messaging
Network Working Group J. Peterson
Internet-Draft Neustar
Intended status: Standards Track C. Wendt
Expires: August 26, 2021 Comcast
February 22, 2021
Messaging Use Cases and Extensions for STIR
draft-peterson-stir-messaging-01
Abstract
Secure Telephone Identity Revisited (STIR) provides a means of
attesting the identity of a telephone caller via a signed token in
order to prevent impersonation of a calling party number, which is a
key enabler for illegal robocalling. Similar impersonation is
sometimes leveraged by bad actors in the text messaging space. This
document considers the applicability of STIR's Persona Assertion
Token (PASSporT) and certificate issuance framework to instant text
and multimedia messaging use cases, both for messages carried or
negotiated by SIP, and for non-SIP messaging.
Status of This Memo
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This Internet-Draft will expire on August 26, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability to Messaging Systems . . . . . . . . . . . . . 3
3.1. Message Sessions . . . . . . . . . . . . . . . . . . . . 4
3.2. PASSporTs and Messaging . . . . . . . . . . . . . . . . . 4
3.2.1. PASSporT Conveyance with Messaging . . . . . . . . . 5
4. Certificates and Messaging . . . . . . . . . . . . . . . . . 6
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6.1. JSON Web Token Claims Registration . . . . . . . . . . . 6
6.2. PASSporT Type Registration . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The STIR problem statement [RFC7340] describes widespread problems
enabled by impersonation in the telephone network, including illegal
robocalling, voicemail hacking, and swatting. As telephone services
are increasingly migrating onto the Internet and using Voice over IP
(VoIP) protocols such as SIP [RFC3261], it is necessary for these
protocols to support stronger identity mechanisms to prevent
impersonation. [RFC8224] defines a SIP Identity header field capable
of carrying PASSporT [RFC8225] objects in SIP as a means to
cryptographically attest that the originator of a telephone call is
authorized to use the calling party number (or, for native SIP cases,
SIP URI) associated with the originator of the call.
The problem of bulk, unsolicited commercial communications is not
however limited to telephone calls. Although the problem is not
currently widespread, in some environments spammers and fraudsters
are turning to messaging applications to deliver undesired content to
consumers. In some respects, mitigating these unwanted messages
resembles the email spam problem: textual analysis of the message
contents can be used to fingerprint content that is generated by
spammers, for example. However, encrypted messaging is becoming more
common, and analysis of message contents may no longer be a reliably
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way to mitigate messaging spam in the future. And as STIR sees
further deployment in the telephone network, it seems likely that the
governance structures put in place for securing telephone network
resources with STIR could be repurposed to help secure the messaging
ecosystem.
One of the more sensitive applications for message security is
emergency services. As next-generation emergency services
increasingly incorporate messaging as a mode of communication with
public safety personnel (see [RFC8876]), providing an identity
assurance could help to mitigate denial-of-service attacks, as well
as ultimately helping to identify the source of emergency
communications in general (including the swatting attacks, see
[RFC7340]).
This specification therefore explores how the PASSporT mechanism
defined for STIR could be applied to providing protection for textual
and multimedia messaging, but focuses particularly on those messages
that use telephone numbers as the identity of the sender. It
moreover considers the reuse of existing STIR certificates, which are
beginning to see widespread deployment, for signing PASSporTs that
protect messages.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Applicability to Messaging Systems
At a high level, baseline PASSporT [RFC8225] claims provide similar
value to number-based messaging as they do to traditional telephone
calls. A signature over the calling and called party numbers, along
with a timestamp, could already help to prevent impersonation in the
mobile messaging ecosystem. When it comes to protecting message
contents, broadly, there are a few ways that the PASSporT mechanism
of STIR could apply to messaging: first, a PASSporT could be used to
securely negotiate a session over which messages will be exchanged;
and second, in sessionless scenarios, a PASSporT could be generated
on a per-message basis with its own built-in message security.
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3.1. Message Sessions
For the first case, where SIP negotiates a session where the media
will be text messages, as for example with the Message Session Relay
Protocol (MSRP) [RFC4975], the usage of STIR would deviate little
from [RFC8224]. An INVITE request sent with an Identity header
containing a PASSporT with the proper calling and called party
numbers would then negotiate an MSRP session the same way that an
INVITE for a telephone call would negotiate an audio session. This
could be applicable to MSRP sessions negotiated for RCS [RCC.07].
Note that if TLS is used to secure MSRP (per RCS [RCC.15]),
fingerprints of those TLS keys could be secured via the "mkey" claim
of PASSporT using the [RFC8862] framework. Similar practices would
apply to sessions that negotiate text over RTP via [RFC4103] or
similar mechanisms. For the most basic use cases, STIR for messaging
should not require any further protocol enhancements.
[TBD: liase with GSMA on this]
However, current usage of baseline [RFC8224] Identity is largely
confined to INVITE requests. RCS-style applications would require
PASSporTs for all conversation participants. This would in turn
require the implementation of STIR connected identity
[I-D.peterson-stir-rfc4916-update].
3.2. PASSporTs and Messaging
In the second case, SIP also has a method for sending messages in the
body of a SIP request: the MESSAGE [RFC3428] method, which is used in
some North American emergency services use cases. The interaction of
STIR with MESSAGE is not as straightforward as the potential use case
with MSRP. An Identity header could be added to any SIP MESSAGE
request, but without some extension to the PASSporT claims, the
PASSporT would offer no protection to the message content. As the
bodies of SIP requests are MIME encoded, S/MIME [RFC8591] has been
proposed as a means of providing integrating for MESSAGE (and some
MSRP cases as well). The interaction of [RFC8226] STIR certificates
with S/MIME for messaging applications would require some further
explication; and potentially, PASSporT could provide its own
integrity check for message contents.
Moreover, a variety of non-SIP protocols, both those integrated into
the traditional telephone network and those based on over-the-top
applications, are responsible for most of the messaging that is sent
to and from telephone numbers. This specification proposes that the
STIR credentials assigned to service providers could be leveraged to
sign for PASSporTs for messages that originate from telephone
numbers. In order to apply PASSporT to textual or multimedia
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messaging, a new claim is here defined to provide a hash over message
contents.
In order to differentiate a PASSporT for an individual message from a
PASSporT used to secure a telephone call or message stream, this
document defines a new "msg" PASSporT Type. This helps to prevent
the replay of a PASSporT for a message to putatively secure a call,
or vice versa.
This specification defines a new optional JWT [RFC7519] claim "msgi"
which provides a digest over the contents of a message, which may be
a text message, or a more complex multimedia message. "msgi" MUST NOT
appear in PASSporTs with a type other than "msg", but they are
OPTIONAL in "msg" PASSporTs, as integrity for messages may be
provided by some other service (e.g. [RFC8591]). Implementations of
"msgi" MUST support the following hash algorithms: "SHA256",
"SHA384", or "SHA512", which are defined as part of the SHA-2 set of
cryptographic hash functions by the NIST.
[TBD: Do we need algorithmic agility here?]
In order to generate the message digest, the following steps are
taken:
[TBD: Canonicalization procedures. Maybe we need separate procedures
for plain text (like, SMPP), rich text, and then more complex
multimedia messages? Definitely a danger of scope creep. For the
emergency services case, we want OASIS CAP, right? Maybe focus on
that. Anything we could easily steal here?]
At the end result of the process, the digest becomes the value of the
JWT "msgi" claim, as per this example:
"msgi" :
"sha256-H8BRh8j48O9oYatfu5AZzq6A9RINQZngK7T62em8MUt1FLm52t+eX6xO"
3.2.1. PASSporT Conveyance with Messaging
If the message is being conveyed in SIP, via the MESSAGE method, then
the PASSporT could be conveyed in an Identity header field in that
request. The authentication and verification service procedures for
populating that PASSporT would follow [RFC8224], with the addition of
the "msgi" claim defined in Section 3.2.
In text messaging today, multimedia message system (MMS) messages are
often conveyed with SMTP. There are thus a suite of additional email
security tools available in this environment for sender
authentication, such as DMARC [RFC7489]. The interaction of these
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mechanisms with STIR certificates and/or PASSporTs would require
further study.
For other cases where messages are conveyed by some protocol other
than SIP, that protocol might itself have some way of conveying
PASSporTs. But there will surely be cases where legacy transmission
of messages will not permit an accompanying PASSporT, in which case
something like out-of-band [I-D.ietf-stir-oob] conveyance would be
the only way to deliver the PASSporT. This may be necessary to
support cases where legacy SMPP systems cannot be upgraded, for
example.
[TBD: I mean, if you can deliver a PASSporT OOB, you can deliver a
message OTT - there may be limits to how useful a mechanism like this
would be. In any event, the precise way to do OOB for messaging
would need to be sketched out here.]
4. Certificates and Messaging
The [RFC8226] STIR certificate profiles defines a way to issue
certificates that sign PASSporTs, which attest through their
TNAuthList either a Service Provider Code (SPC), or a set of one or
more telephone numbers. This specification proposes that the
semantics of this certificates should suffice for signing for
messages from a telephone number without further modification.
[TBD: Or should there be? Should for example certificates have to
have some special authority to sign for messages instead of calls?]
5. Acknowledgments
We would like to thank Brian Rosen, Ben Campbell, and Alex Bobotek
for their contributions to this specification.
6. IANA Considerations
6.1. JSON Web Token Claims Registration
This specification requests that the IANA add one new claim to the
JSON Web Token Claims registry as defined in [RFC7519].
Claim Name: "msgi"
Claim Description: Message Integrity Information
Change Controller: IESG
Specification Document(s): [RFCThis]
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6.2. PASSporT Type Registration
This specification defines one new PASSporT type for the PASSport
Extensions Registry defined in [RFC8225], which resides at
https://www.iana.org/assignments/passport/passport.xhtml#passport-
extensions. It is:
"msg" as defined in [RFCThis] Section 3.2.
7. Security Considerations
TBD.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474,
DOI 10.17487/RFC4474, August 2006,
<https://www.rfc-editor.org/info/rfc4474>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8224] Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 8224,
DOI 10.17487/RFC8224, February 2018,
<https://www.rfc-editor.org/info/rfc8224>.
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[RFC8225] Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
<https://www.rfc-editor.org/info/rfc8225>.
[RFC8226] Peterson, J. and S. Turner, "Secure Telephone Identity
Credentials: Certificates", RFC 8226,
DOI 10.17487/RFC8226, February 2018,
<https://www.rfc-editor.org/info/rfc8226>.
8.2. Informative References
[I-D.ietf-stir-oob]
Rescorla, E. and J. Peterson, "STIR Out-of-Band
Architecture and Use Cases", draft-ietf-stir-oob-07 (work
in progress), March 2020.
[I-D.ietf-stir-passport-divert]
Peterson, J., "PASSporT Extension for Diverted Calls",
draft-ietf-stir-passport-divert-09 (work in progress),
July 2020.
[I-D.peterson-stir-rfc4916-update]
Peterson, J. and C. Wendt, "Connected Identity for STIR",
draft-peterson-stir-rfc4916-update-02 (work in progress),
November 2020.
[RCC.07] GSMA RCC.07 v9.0 | 16 May 2018, "Rich Communication Suite
8.0 Advanced Communications Services and Client
Specification", 2018.
[RCC.15] GSMA PRD-RCC.15 v5.0 | 16 May 2018, "IMS Device
Configuration and Supporting Services", 2018.
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP)
UPDATE Method", RFC 3311, DOI 10.17487/RFC3311, October
2002, <https://www.rfc-editor.org/info/rfc3311>.
[RFC3428] Campbell, B., Ed., Rosenberg, J., Schulzrinne, H.,
Huitema, C., and D. Gurle, "Session Initiation Protocol
(SIP) Extension for Instant Messaging", RFC 3428,
DOI 10.17487/RFC3428, December 2002,
<https://www.rfc-editor.org/info/rfc3428>.
[RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text
Conversation", RFC 4103, DOI 10.17487/RFC4103, June 2005,
<https://www.rfc-editor.org/info/rfc4103>.
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[RFC4916] Elwell, J., "Connected Identity in the Session Initiation
Protocol (SIP)", RFC 4916, DOI 10.17487/RFC4916, June
2007, <https://www.rfc-editor.org/info/rfc4916>.
[RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed.,
"The Message Session Relay Protocol (MSRP)", RFC 4975,
DOI 10.17487/RFC4975, September 2007,
<https://www.rfc-editor.org/info/rfc4975>.
[RFC7340] Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
Telephone Identity Problem Statement and Requirements",
RFC 7340, DOI 10.17487/RFC7340, September 2014,
<https://www.rfc-editor.org/info/rfc7340>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[RFC8591] Campbell, B. and R. Housley, "SIP-Based Messaging with
S/MIME", RFC 8591, DOI 10.17487/RFC8591, April 2019,
<https://www.rfc-editor.org/info/rfc8591>.
[RFC8862] Peterson, J., Barnes, R., and R. Housley, "Best Practices
for Securing RTP Media Signaled with SIP", BCP 228,
RFC 8862, DOI 10.17487/RFC8862, January 2021,
<https://www.rfc-editor.org/info/rfc8862>.
[RFC8876] Rosen, B., Schulzrinne, H., Tschofenig, H., and R.
Gellens, "Non-interactive Emergency Calls", RFC 8876,
DOI 10.17487/RFC8876, September 2020,
<https://www.rfc-editor.org/info/rfc8876>.
Authors' Addresses
Jon Peterson
Neustar, Inc.
1800 Sutter St Suite 570
Concord, CA 94520
US
Email: jon.peterson@team.neustar
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Chris Wendt
Comcast
One Comcast Center
Philadelphia, PA 19103
USA
Email: chris-ietf@chriswendt.net
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