Network Working Group J. Peterson
Internet-Draft Neustar
Intended status: Informational C. Wendt
Expires: December 14, 2017 Comcast
June 12, 2017
PASSporT Extension for Caller Name
draft-peterson-stir-cnam-02.txt
Abstract
This document extends PASSporT, a token for conveying
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 about callers that helps people decide
whether to pick up the phone.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PASSporT 'cna' Claim . . . . . . . . . . . . . . . . . . . . 3
4. Further Information Associated with Callers . . . . . . . . . 4
5. Third Party Uses . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Signing as a Third Party . . . . . . . . . . . . . . . . 5
6. Using 'cna' in SIP . . . . . . . . . . . . . . . . . . . . . 6
6.1. Authentication Service Behavior . . . . . . . . . . . . . 6
6.2. Verification Service Behavior . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8.1. JSON Web Token Claims . . . . . . . . . . . . . . . . . . 7
8.2. PASSporT Types . . . . . . . . . . . . . . . . . . . . . 8
8.3. PASSporT CNA Types . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. Informative References . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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. The STIR problem statement [RFC7340]
declared securing the display name of callers outside of STIR's
initial scope, so baseline STIR provides no features for caller name.
This specification documents an optional mechanism for PASSporT and
the associated STIR mechanisms which extends PASSporT to carry
additional elements conveying richer information, provided it is
information that is intended to be rendered to an end user to assist
a called party in determining whether to accept or trust incoming
communications. This includes the name of the person on one side of
a communications session, the traditional "Caller ID" of the
telephone network, along with related display information that would
typically be rendered to the called party during alerting.
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 at the
terminating side, or through a local address book maintained by a
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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.
Even when the originating side does not provide a display name for
the caller, the cryptographic attestation of the validity of the
calling number provided by STIR still 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 by the
caller; STIR thus makes "Caller ID" more secure even when there is no
first-party attestation of a display name. For these cases, this
specification outlines various ways that a display name for a calling
party could be determined at the terminating side in a secure
fashion.
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", the
value of which is an array of JSON elements which always includes 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 any PASSporT claims object as an
optional element. The creator of a PASSporT MAY 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
PASSporT header wih the "ppt" included will look as follows:
{ "typ":"passport",
"ppt":"cna",
"alg":"RS256",
"x5u":"https://www.example.com/cert.cer" }
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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].
{ "orig":{"tn":"12155551212"},
"dest":{"tn":"12155551213"},
"iat":1443208345,
"iss":"Example, Inc.",
"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. Further Information Associated with Callers
Beyond naming information, there may be additional human-readable
information about the calling party that should be rendered to the
end user in order to help the called party decide whether or not to
pick up the phone. This could include:
information related to the location of the caller, or
any organizations or institutions that the caller is associated
with, or even categories of institutions (is this a government
agency, or a bank, or what have you), or
hyperlinks to images, such as logos or pictures of faces, or to
similar external profile information, or
information that will be process by an application before
rendering it to a user, like social networking data that shows
that an unknown caller is a friend-of-a-friend, or reputation
scores derived from crowdsourcing, or confidence scores based on
broader analytics about the caller and callee.
All of these data elements would benefit from the secure attestations
provided by the STIR and PASSporT frameworks. A new IANA registry
has been defined to hold potential values of the "cna" array; see
Section 8.3. Specific extensions to the "cna" PASSporT claim are
left for future specification.
While in the telephone network, information about the name of the
calling party traditionally derives from the originating service
provider, some other forms of data like crowdsourced reputation
scores might derive from third parties. It is more likely that when
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those elements are present, they will be in a third-party "cna"
object, which requires special signing rules.
5. Third Party Uses
When secure calling name information is not provided by an
originating authentication service, the terminating side may use
other means to determine the caller's name. For example, a third-
party information service might be queried with the calling party's
number in order to learn the name of the calling party and other
helpful information. This query could come from an intermediary, or
from an end user device, such as a smart phone. The value of using
the PASSporT object to convey this information from third parties
lies largely in the preservation of the original authority's
signature over the data, and the potential for the PASSporT to be
conveyed from intermediaries to endpoint devices. Effectively, these
use cases form of subcase of out-of-band [I-D.rescorla-stir-fallback]
use cases.
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 PASSport in a
response from that third-party service, the terminating side could
add a new Identity header field 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.
In an alternative use case, the terminating user agent might query a
third-party service. In this case, no new Identity header field
would be generated, though the terminating user agent might receive a
PASSporT object in return from the third-party service, and use the
"cna" field in the object as a calling name to render to users while
alerting.
5.1. Signing as a Third Party
A third-party PASSporT MUST contain the "cna" "ppt" type in its
header object. It moreover MUST include an "iss" claim as defined in
[RFC7519] to indicate the source of this PASSporT; that field SHOULD
be populated with the subject of the credential used to sign the
PASSporT.
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A PASSporT with a "ppt" and "cna" MAY be signed with credentials that
do not have authority over the identity that appears in the "orig"
element of the PASSporT claims. Relying parties in STIR have always
been left to make their own authorization decisions about whether or
not the trust the signers of PASSporTs, and in the third-party case,
where an entity has explicitly queried a service to acquire the
PASSporT object, it may be some external trust or business
relationship that induces the relying party to trust a PASSporT.
6. 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.
6.1. Authentication Service Behavior
An authentication service creating a PASSporT containing a "cna"
claim MAY include a "ppt" for "cna" or not. Third party
authentication services as described in Section 5.1 MUST include a
"ppt" of "cna". 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=ES256;ppt="cna"
This specification assumes that by default, a SIP authentication
service will derive the value of "cna" from the display-name
component of the From header field value of the request. It is
however a matter of authentication service policy to decide how it
populates the value of "cna", which MAY 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 in SIP.
6.2. 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.
Verification services may alter their authorization policies for the
credentials accepted to sign PASSporTs when third parties generate
PASSporT objects, per Section 5.1. No guidance on verification
service policy is given here.
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.
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]
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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].
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
Revealing information such as the name, location, and affiliation of
a person necessarily entails certain privacy risks. Baseline
PASSporT has no particular confidentiality requirement, as the
information it signs over in a using protocol like SIP is all
information that SIP carries in the clear anyway. Transport-level
security can hide those SIP fields from eavesdroppers, and the same
confidentiality mechanisms would protect any PASSporT(s) carried in
SIP.
More TBD.
10. Informative References
[I-D.ietf-stir-passport]
Wendt, C. and J. Peterson, "Personal Assertion Token
(PASSporT)", draft-ietf-stir-passport-11 (work in
progress), February 2017.
[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-16
(work in progress), February 2017.
[I-D.rescorla-stir-fallback]
Rescorla, E. and J. Peterson, "STIR Out of Band
Architecture and Use Cases", draft-rescorla-stir-
fallback-01 (work in progress), October 2016.
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[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>.
[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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