Network Working Group J. Peterson
Internet-Draft Neustar Inc.
Intended status: Informational C. Wendt
Expires: April 25, 2019 Comcast
October 22, 2018
PASSporT Extension for Rich Call Data
draft-ietf-stir-passport-rcd-01
Abstract
This document extends PASSporT, a token for conveying
cryptographically-signed information about personal communications,
to include rich data that can be rendered to users, such as 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 calls that helps
people decide whether to pick up the phone.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 25, 2019.
Copyright Notice
Copyright (c) 2018 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
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Peterson & Wendt Expires April 25, 2019 [Page 1]
Internet-Draft STIR Caller Name October 2018
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PASSporT 'rcd' Claim . . . . . . . . . . . . . . . . . . . . 3
4. Further Information Associated with Callers . . . . . . . . . 4
5. Third-Party Uses . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Signing as a Third Party . . . . . . . . . . . . . . . . 6
6. Levels of Assurance . . . . . . . . . . . . . . . . . . . . . 6
7. Using 'rcd' in SIP . . . . . . . . . . . . . . . . . . . . . 7
7.1. Authentication Service Behavior . . . . . . . . . . . . . 7
7.2. Verification Service Behavior . . . . . . . . . . . . . . 7
8. Using 'rcd' as additional claims to other PASSporT extensions 8
8.1. Procedures for applying 'rcd' as claims only . . . . . . 9
8.2. Example for applying 'rcd' as claims only . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10.1. JSON Web Token Claim . . . . . . . . . . . . . . . . . . 10
10.2. PASSporT Types . . . . . . . . . . . . . . . . . . . . . 10
10.3. PASSporT RCD Types . . . . . . . . . . . . . . . . . . . 10
11. Security Considerations . . . . . . . . . . . . . . . . . . . 10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
12.1. Normative References . . . . . . . . . . . . . . . . . . 11
12.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
PASSporT [RFC8225] is a token format based on JWT [RFC7519] for
conveying cryptographically-signed information about the people
involved in personal communications; it is used to convey a signed
assertion of the identity of the participants in real-time
communications established via a protocol like SIP [RFC8224]. 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: 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 be rendered to the called party during alerting, or potentially
Peterson & Wendt Expires April 25, 2019 [Page 2]
Internet-Draft STIR Caller Name October 2018
used by an automaton to determine whether and how to alert a called
party.
In the traditional telephone network, the display name associated
with a call is typically provided in one of three ways: by a third-
party service queried at the terminating side, by the originator of
the call, 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. 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 [RFC2119] and [RFC6919].
3. PASSporT 'rcd' Claim
This specification defines a new JSON Web Token claim for "rcd", Rich
Call Data, the value of which is an array of JSON subelements. The
initial subelement defined here is a display name, "nam", associated
with the originator of personal communications, which 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 "rcd" claim may appear in any PASSporT claims object as an
optional element. The creator of a PASSporT MAY however add a "ppt"
value of "rcd" to the header of a PASSporT as well, in which case the
PASSporT claims MUST contain a "rcd" 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:
Peterson & Wendt Expires April 25, 2019 [Page 3]
Internet-Draft STIR Caller Name October 2018
{ "typ":"passport",
"ppt":"rcd",
"alg":"ES256",
"x5u":"https://www.example.com/cert.cer" }
The PASSporT claims object will then contain the "rcd" key with its
corresponding value. The value of "rcd" 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.",
"rcd":{"nam":"Alice Atlanta"} }
After the header and claims PASSporT objects have been constructed,
their signature is generated normally per the guidance in [RFC8225].
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 is not limited to information about the
caller, but includes information about the call itself, which may
derive from analytics that determine based on call patterns or
similar data if the call is likely to be one the called party wants
to receive. Such data 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 processed 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 "rcd" array; see
Peterson & Wendt Expires April 25, 2019 [Page 4]
Internet-Draft STIR Caller Name October 2018
Section 10.3. Specific extensions to the "rcd" PASSporT claim are
left for future specification.
While in the traditional telephone network, the business relationship
between calling customers and their telephone service providers is
the ultimate root of information about a calling party's name, some
other forms of data like crowdsourced reputation scores might derive
from third parties. It is more likely that when those elements are
present, they will be in a third-party "rcd" PASSporT.
5. Third-Party Uses
While rich data about the call can be provided by an originating
authentication service, the terminating side or an intermediary in
the call path could also acquire rich call data by querying a third-
party service. In telephone operations today, a third-party
information service is commonly queried with the calling party's
number in order to learn the name of the calling party, and
potentially other helpful information could also be passed over that
interface. The value of using a PASSporT 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.ietf-stir-oob] use cases. The manner in which third-party
services are discovered is outside the scope of this document.
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 "rcd" claim. When the a terminating verification
service implemented at a SIP proxy server 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 for the "rcd" PASSporT object provided by the third-party
service. It would then forward the INVITE to the terminating user
agent. If the display name in the "rcd" 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.
A very similar flow could be followed by an intermediary closer to
the origination of the call. Presumably such a service could be
implemented at an originating network in order to decouple the
systems that sign for calling party numbers from the systems that
provide rich data about calls.
Peterson & Wendt Expires April 25, 2019 [Page 5]
Internet-Draft STIR Caller Name October 2018
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
"rcd" field in the object as a calling name to render to users while
alerting.
5.1. Signing as a Third Party
When a third party issues a PASSporT with an "rcd" claim, the
PASSporT MUST contain the "rcd" "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.
A PASSporT with a "ppt" of "rcd" 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. Levels of Assurance
As "rcd" can be provided by either first or third parties, relying
parties could benefit from an additional claim that indicates the
relationship of the attesting party to the caller. Even in first
party cases, this admits of some complexity: the Communications
Service Provider (CSP) to which a number was assigned might in turn
delegate the number to a reseller, who would then sell the number to
an enterprise, in which case the CSP might have little insight into
the caller's name. In third party cases, a caller's name could
derive from any number of data sources, on a spectrum between public
data scraped from web searches to a direct business relationship to
the caller. As multiple PASSporTs can be associated with the same
call, potentially a verification service could receive attestations
of the caller name from multiple sources, which have different levels
of granularity or accuracy.
Therefore PASSporTs that carry "rcd" data SHOULD also carry an
indication of the relationship of the generator of the PASSporT to
the caller. [TBD claim - take from SHAKEN?]
Peterson & Wendt Expires April 25, 2019 [Page 6]
Internet-Draft STIR Caller Name October 2018
7. Using 'rcd' in SIP
This section specifies SIP-specific usage for the "rcd" claim in
PASSporT, and in the SIP Identity header field value. Other using
protocols of PASSporT may define their own usages for the "rcd"
claim.
7.1. Authentication Service Behavior
An authentication service creating a PASSporT containing a "rcd"
claim MAY include a "ppt" for "rcd" or not. Third-party
authentication services following the behavior in Section 5.1 MUST
include a "ppt" of "rcd". If "ppt" does contain a "rcd", then any
SIP authentication services MUST add a "ppt" parameter to the
Identity header containing that PASSporT with a value of "rcd". 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="rcd"
This specification assumes that by default, a SIP authentication
service will derive the value of "rcd" 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 "rcd", 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 "rcd" 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.
7.2. Verification Service Behavior
[RFC8224] Section 6.2 Step 5 requires that specifications defining
"ppt" values describe any additional verifier behavior. The behavior
specified for the "ppt" values of "rcd" is as follows. If the
PASSporT is in compact form, then the verification service SHOULD
extract the display-name from the From header field value, if any,
and use that as the value for the "rcd" 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 "rcd",
then the verification service MUST extract the value associated with
the "rcd" "nam" key in the object. If the signature validates, then
Peterson & Wendt Expires April 25, 2019 [Page 7]
Internet-Draft STIR Caller Name October 2018
the verification service can use the value of the "rcd" "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 third-party "rcd" PASSporT cases presents some new challenges, as
an attacker could attempt to cut-and-paste such a third-party
PASSporT into a SIP request in an effort to get the terminating user
agent to render the display name or confidence values it contains to
a call that should have no such assurance. A third-party "rcd"
PASSporT provides no assurance that the calling party number has not
been spoofed: if it is carried in a SIP request, for example, then
some other PASSporT in another Identity header field value would have
to carry a PASSporT attesting that. A verification service MUST
determine that the calling party number shown in the "orig" of the
"rcd" PASSporT corresponds to the calling party number of the call it
has received, and that the "iat" field of the "rcd" PASSporT is
within the date interval that the verification service would
ordinarily accept for a PASSporT.
Verification services may alter their authorization policies for the
credentials accepted to sign PASSporTs when third parties generate
PASSporT objects, per Section 5.1. This may include accepting a
valid signature over a PASSporT even if it is signed with a
credential that does not attest authority over the identity in the
"orig" claim of the PASSporT, provided that the verification service
has some other reason to trust the signer. No further guidance on
verification service authorization policy is given here.
The behavior of a SIP UAS upon receiving an INVITE containing a
PASSporT object with a "rcd" 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.
8. Using 'rcd' as additional claims to other PASSporT extensions
Rich Call Data, including, for example, calling name information, is
often data that is additive data to the personal communications
information defined in the core PASSporT data required to support the
security properties defined in [RFC8225]. For cases where the entity
that is originating the personal communications and additionally is
supporting the authentication service and also is the authority of
the Rich Call Data, rather than creating multiple identity headers
with multiple PASSporT extensions or defining multiple combinations
Peterson & Wendt Expires April 25, 2019 [Page 8]
Internet-Draft STIR Caller Name October 2018
and permutations of PASSporT extension definitions, the
authentication service can alternatively directly add the 'rcd'
claims to the PASSporT it is creating, whether it is constructed with
a PASSporT extension or not.
8.1. Procedures for applying 'rcd' as claims only
For a given PASSporT using some other extension than 'rcd,' the
Authentication Service MAY additionally include the 'rcd' claim as
defined in this document. This would result in a set of claims that
correspond to the original intended extension with the addition of
the 'rcd' claim.
The Verification service that receives the PASSporT, if it supports
this specification and chooses to, should interpret the 'rcd' claim
as simply just an additional claim intended to deliver and/or
validate delivered Rich Call Data.
8.2. Example for applying 'rcd' as claims only
In the case of [I-D.ietf-stir-passport-shaken] which is the PASSporT
extension supporting the SHAKEN specification [ATIS-1000074], a
common case for an Authenication service to co-exist in a CSP network
along with the authority over the calling name used for the call.
Rather than require two identity headers, the CSP Authenticaton
Service can apply both the SHAKEN PASSporT claims and extension and
simply add the 'rcd' required claims defined in this document.
For example, the PASSporT claims for the 'shaken' PASSporT with 'rcd'
claims would be as follows:
Protected Header
{
"alg":"ES256",
"typ":"passport",
"ppt":"shaken",
"x5u":"https://cert.example.org/passport.cer"
}
Payload
{
"attest":"A"
"dest":{"uri":["sip:alice@example.com"]}
"iat":"1443208345",
"orig":{"tn":"12155551212"},
"origid":"123e4567-e89b-12d3-a456-426655440000"
"rcd":{"nam":"Alice Atlanta"} }
}
Peterson & Wendt Expires April 25, 2019 [Page 9]
Internet-Draft STIR Caller Name October 2018
A Verification Service that supports 'rcd' and 'shaken' PASSporT
extensions will be able to receive the above PASSporT and interpret
both the 'shaken' claims as well as the 'rcd' defined claim.
If the Verification Service only understands the 'shaken' extension
claims but doesn't support 'rcd', the 'rcd' can simply be ignored and
disregarded.
9. Acknowledgements
We would like to thank Robert Sparks for helpful suggestions.
10. IANA Considerations
10.1. JSON Web Token Claim
This specification requests that the IANA add a new claim to the JSON
Web Token Claims registry as defined in [RFC7519].
Claim Name: "rcd"
Claim Description: Caller Name Information
Change Controller: IESG
Specification Document(s): [RFCThis]
10.2. PASSporT Types
This specification requests that the IANA add a new entry to the
PASSporT Types registry for the type "rcd" which is specified in
[RFCThis].
10.3. PASSporT RCD Types
This document requests that the IANA create a new registry for
PASSporT RCD types. Registration of new PASSporT RCD 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].
11. 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
Peterson & Wendt Expires April 25, 2019 [Page 10]
Internet-Draft STIR Caller Name October 2018
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.
12. References
12.1. Normative References
[I-D.ietf-stir-oob]
Rescorla, E. and J. Peterson, "STIR Out-of-Band
Architecture and Use Cases", draft-ietf-stir-oob-03 (work
in progress), July 2018.
[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>.
[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,
<https://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,
<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>.
[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>.
Peterson & Wendt Expires April 25, 2019 [Page 11]
Internet-Draft STIR Caller Name October 2018
12.2. Informative References
[ATIS-1000074]
ATIS/SIP Forum NNI Task Group, "Signature-based Handling
of Asserted information using toKENs (SHAKEN)
<https://access.atis.org/apps/group_public/
download.php/32237/ATIS-1000074.pdf>", January 2017.
[I-D.ietf-stir-passport-shaken]
Wendt, C. and M. Barnes, "PASSporT SHAKEN Extension
(SHAKEN)", draft-ietf-stir-passport-shaken-04 (work in
progress), October 2018.
[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>.
Authors' Addresses
Jon Peterson
Neustar Inc.
1800 Sutter St Suite 570
Concord, CA 94520
US
Email: jon.peterson@neustar.biz
Chris Wendt
Comcast
Comcast Technology Center
Philadelphia, PA 19103
USA
Email: chris-ietf@chriswendt.net
Peterson & Wendt Expires April 25, 2019 [Page 12]
