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Network Working Group J. Peterson
Internet-Draft Neustar
Intended status: Informational C. Wendt
Expires: May 6, 2021 Comcast
November 2, 2020
Messaging Use Cases for STIR
draft-peterson-stir-messaging-00
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
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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 6, 2021.
Copyright Notice
Copyright (c) 2020 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
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability to Messaging Systems . . . . . . . . . . . . . 3
4. PASSporTs and Messaging . . . . . . . . . . . . . . . . . . . 4
4.1. PASSporTs Conveyance with Messaging . . . . . . . . . . . 5
5. Certificates and Messaging . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7.1. JSON Web Token Claims Registration . . . . . . . . . . . 6
7.2. PASSporT Type Registration . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Informative References . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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. Increasingly, 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 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
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network resources with STIR could be repurposed to help secure the
messaging ecosystem.
This specification therefore explores how the PASSporT mechanism
defined for STIR could be applied to providing protection for textual
and multimedia messaging, but only for 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 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.
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. The
same would apply to sessions that negotiate text over RTP via
[RFC4103] or similar mechanisms. In these cases, STIR for messaging
should not require any further protocol enhancements.
[TBD: Also consider the applicability of "mkey" to these schemes, and
RFC8862? Also, any interest in MLS interaction?]
In the second case, SIP also has a method for sending messages a the
body of a SIP request: the MESSAGE [RFC3428] method. The interaction
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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
potentially for securing MSRP 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, the MESSAGE method is not commonly used today to carry
messages for consumer devices. A variety of non-SIP protocols, both
those integrated in to 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 messaging, a new claim is here defined to
provide a hash over message contents.
4. PASSporTs and Messaging
In order to differentiate a PASSporT for a message from a PASSporT
used to secure a telephone call, this document defines a new "msg"
PASSporT Type. This prevents 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. Anything
we could easily steal here?]
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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"
4.1. PASSporTs 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 4.
In 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.
[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.]
5. 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?]
6. Acknowledgments
We would like to thank YOU for your contributions to this
specification.
7. IANA Considerations
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7.1. 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]
7.2. 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 4.
8. Security Considerations
TBD.
9. 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.
[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>.
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[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
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[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>.
[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>.
[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>.
Authors' Addresses
Jon Peterson
Neustar, Inc.
1800 Sutter St Suite 570
Concord, CA 94520
US
Email: jon.peterson@team.neustar
Chris Wendt
Comcast
One Comcast Center
Philadelphia, PA 19103
USA
Email: chris-ietf@chriswendt.net
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