Network Working Group J. Peterson
Internet-Draft Neustar
Intended status: Informational C. Wendt
Expires: May 4, 2017 Comcast
October 31, 2016
PASSporT Extension for Caller Name
draft-peterson-stir-cnam-01.txt
Abstract
This document extends the PASSporT object, which conveys
cryptographically-signed information about the people involved in
personal communications, to include a human-readable display name
comparable to the "Caller ID" function common on the telephone
network. The element defined for this purpose is extensible to
include related information callers.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PASSporT 'cna' Claim . . . . . . . . . . . . . . . . . . . . 3
4. Using 'cna' in SIP . . . . . . . . . . . . . . . . . . . . . 4
4.1. Authentication Service Behavior . . . . . . . . . . . . . 4
4.2. Verification Service Behavior . . . . . . . . . . . . . . 4
5. Third Party Uses . . . . . . . . . . . . . . . . . . . . . . 5
6. Further Information Associated with Callers . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8.1. JSON Web Token Claims . . . . . . . . . . . . . . . . . . 6
8.2. PASSporT Types . . . . . . . . . . . . . . . . . . . . . 6
8.3. PASSporT CNA Types . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10. Informative References . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
PASSporT [I-D.ietf-stir-passport] is a token format based on JWT
[RFC7519] for conveying cryptographically-signed information about
the people involved in personal communications; it is used with STIR
[I-D.ietf-stir-rfc4474bis] to convey a signed assertion of the
identity of the participants in real-time communications established
via a protocol like SIP. This specification extends PASSporT to
carry the name of the person on one side of a communications session,
along with related display information that would typically be
rendered to the called party during alerting. This format is
designed to be extended with additional elements to convey richer
information.
In the traditional telephone network, the display name associated
with a call is typically provided in one of three ways: by the
originator of a call, by a third-party service queried by the
terminating side, or through a local address book maintained by a
device on the terminating side. The STIR architecture lends itself
especially to the first of these approaches, as it assumes that an
authority on the originating side of the call provides a
cryptographic assurance of the validity of the calling party number
in order to prevent impersonation attacks. That same authority could
sign for a display name associated with that number, which the
terminating side could render to the user when the call is alerting.
But even when the originating side cannot provide a display name for
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the caller, the cryptographic attestation of the validity of the
number provided by STIR allows the terminating side to query a local
or remote service for a name associated with that number without fear
that the number has been impersonated. This specification also
outlines various ways that a display name for a calling party could
be associated with a call on the terminating side in a secure
fashion.
The STIR problem statement [RFC7340] notes that securing the display
name of callers is outside of STIR's immediate scope, so it includes
no core feature for caller name. This specification documents an
optional extension to PASSporT and the associated STIR mechanisms to
provide this function.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in RFC 2119 [RFC2119] and RFC 6919 [RFC6919].
3. PASSporT 'cna' Claim
This specification defines a new JSON Web Token claim for "cna",
which provides a display name associated with the originator of
personal communications. This name may for example derive from the
display-name component of the From header field value of a SIP
request, or a similar field in other PASSporT using protocols.
The "cna" claim may appear in the PASSporT claim as an optional
element. The creator of a PASSporT object can however add a "ppt"
value of "cna" to the header of a PASSporT object as well, in which
case the PASSporT claims MUST contain a "cna" claim, and any entities
verifying the PASSporT object will be required to understand the
"ppt" extension in order to process the PASSporT in question. A
header wih the "ppt" included will look as follows:
{ "typ":"passport",
"ppt":"cna",
"alg":"RS256",
"x5u":"https://www.example.com/cert.cer" }
The PASSporT claims object will then contain the "cna" key with its
corresponding value. The value of "cna" is an array of JSON objects,
of which one, the "nam" object, is mandatory. The key syntax of
"nam" follows the display-name ABNF given in [RFC3261].
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{ "orig":{"tn":"12155551212"},
"dest":{"tn":"12155551213"},
"iat":1443208345,
"cna":{"nam":"Alice A"} }
After the header and claims PASSporT objects have been constructed,
their signature is generated normally per the guidance in
[I-D.ietf-stir-passport].
4. Using 'cna' in SIP
This section specifies SIP-specific usage for the "cna" claim in
PASSporT, and in the SIP Identity header field value. Other using
protocols of PASSporT may define their own usages for the "cna"
claim.
4.1. Authentication Service Behavior
A PASSporT containing a "cna" claim may contain a "ppt" for "cna" or
not. If "ppt" does contain a "cna", then any SIP authentication
services MUST add a "ppt" parameter to the Identity header containing
that PASSporT with a value of "cna". The resulting Identity header
might look as follows:
Identity: "sv5CTo05KqpSmtHt3dcEiO/1CWTSZtnG3iV+1nmurLXV/HmtyNS7Ltrg9dlxkWzo
eU7d7OV8HweTTDobV3itTmgPwCFjaEmMyEI3d7SyN21yNDo2ER/Ovgtw0Lu5csIp
pPqOg1uXndzHbG7mR6Rl9BnUhHufVRbp51Mn3w0gfUs="; \
info=<https://biloxi.example.org/biloxi.cer>;alg=RS256;ppt="cna"
Otherwise, there is no no need for the "ppt" parameter of the SIP
Identity header.
A SIP authentication service typically will derive the value of "cna"
from the display-name component of the From header field value. It
is however a matter of authentication service policy to decide how it
populates the value of "cna", which might also derive from other
fields in the request, from customer profile data or from access to
external services. If the authentication service generates a
PASSporT object containing "cna" with a value that is not equivalent
to the From header field display-name value, it MUST use the full
form of the PASSporT object.
4.2. Verification Service Behavior
[I-D.ietf-stir-rfc4474bis] Section 6.2 Step 5 requires that
specifications defining "ppt" values describe any additional verifier
behavior. The behavior specified for the "ppt" values of "cna" is as
follows. If the PASSporT is in compact form, then the verification
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service SHOULD extract the display-name from the From header field
value, if any, and use that as the value for the "cna" key when it
recomputes the header and claims of the PASSporT object. If the
signature validates over the recomputed object, then the verification
should be considered successful.
However, if the PASSport is in full form with a "ppt" value of "cna",
then the verification service MUST extract the value associated with
the "cna" "nam" key in the object. If the signature validates, then
the verification service can use the value of the "cna" "nam" key as
the display name of calling party, which would in turn be rendered to
alerted users or otherwise leveraged in accordance with local policy.
This will allow SIP networks that convey the display name through a
field other than the From header field to interoperate with this
specification.
The behavior of a SIP UAS upon receiving an INVITE containing a
PASSporT object with a "cna" claim will largely remain a matter of
implementation policy. In most cases, implementations would render
this calling party name information to the user while alerting. Any
user interface additions to express confidence in the veracity of
this information are outside the scope of this specification.
5. Third Party Uses
When calling name information cannot be provided on the originating
side, a third-party information service may be queried by the
terminating side with the calling party's number in order to learn
the name of the calling party. This query could come from an
intermediary on the terminating side, or from the terminating user
agent, such as a smart phone.
An intermediary use case might look as follows: a SIP INVITE carries
a display name in its From header field value and an initial PASSporT
object without the "cna" claim. When the terminating verification
service receives this request, and determines that the signature is
valid, it might query a third-party service that maps telephone
numbers to calling party names. Upon receiving the response, the
terminating side could add a new Identity to the request (effectively
acting as an authentication service) which contains a "cna" PASSporT
object provided by the third-party service. If the display name in
the "cna" PASSporT object matches the display name in the INVITE,
then the name would presumably be rendered to the end user by the
terminating user agent.
Alternatively, it might be the terminating user agent that queries a
third-party service. In this case, no new Identity header would be
gneerated, though the terminating user agent might receive a PASSporT
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object in return from the third-party service, and use the "cna"
field in the object as a calling name to render to users during
alerting.
Detailed behavior for third-party uses is left for future versions of
this specification.
6. Further Information Associated with Callers
Beyond naming information, there may be additional information about
the calling party that should be rendered to the end user. This may
include information related to the location of the caller, or to any
institutions that the caller is associated with, or even categories
of institutions. All of these data elements would benefit from the
secure attestations provided by the STIR and PASSporT frameworks.
The specification of the "cna" claim could entail the optional
presence of one or more such additional information fields.
A new IANA registry has been defined to hold potential values of the
"cna" array; see Section 8.3. Details of extensions to the "cna"
claim to encompass other data elements are left for future version of
this specification.
7. Acknowledgments
We would like to thank YOU for contributions to this problem
statement and framework.
8. IANA Considerations
8.1. JSON Web Token Claims
This specification requests that the IANA add a new claim to the JSON
Web Token Claims registry as defined in [RFC7519].
Claim Name: "cna"
Claim Description: Caller Name Information
Change Controller: IESG
Specification Document(s): [RFCThis]
8.2. PASSporT Types
This specification requests that the IANA add a new entry to the
PASSporT Types registry for the type "cna" which is specified in
[RFCThis].
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8.3. PASSporT CNA Types
This document requests that the IANA create a new registry for
PASSporT CNA types. Registration of new PASSporT CNA types shall be
under the Specification Required policy.
This registry is to be initially populated with a single value for
"nam" which is specified in [RFCThis].
9. Security Considerations
TBD.
10. Informative References
[I-D.ietf-stir-passport]
Wendt, C. and J. Peterson, "Personal Assertion Token
(PASSporT)", draft-ietf-stir-passport-09 (work in
progress), October 2016.
[I-D.ietf-stir-rfc4474bis]
Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-14
(work in progress), October 2016.
[RFC2119] 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>.
[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,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC6919] Barnes, R., Kent, S., and E. Rescorla, "Further Key Words
for Use in RFCs to Indicate Requirement Levels", RFC 6919,
DOI 10.17487/RFC6919, April 2013,
<http://www.rfc-editor.org/info/rfc6919>.
[RFC7340] Peterson, J., Schulzrinne, H., and H. Tschofenig, "Secure
Telephone Identity Problem Statement and Requirements",
RFC 7340, DOI 10.17487/RFC7340, September 2014,
<http://www.rfc-editor.org/info/rfc7340>.
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[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<http://www.rfc-editor.org/info/rfc7519>.
Authors' Addresses
Jon Peterson
Neustar, Inc.
1800 Sutter St Suite 570
Concord, CA 94520
US
Email: jon.peterson@neustar.biz
Chris Wendt
Comcast
One Comcast Center
Philadelphia, PA 19103
USA
Email: chris-ietf@chriswendt.net
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