PASSporT Extension for Rich Call Data
draft-ietf-stir-passport-rcd-06
Network Working Group J. Peterson
Internet-Draft Neustar Inc.
Intended status: Standards Track C. Wendt
Expires: September 10, 2020 Comcast
March 09, 2020
PASSporT Extension for Rich Call Data
draft-ietf-stir-passport-rcd-06
Abstract
This document extends PASSporT, a token for conveying
cryptographically-signed call information about personal
communications, to include rich data that can be transmitted and
subsequently rendered to users, extending identifying information
beyond human-readable display name comparable to the "Caller ID"
function common on the telephone network. The element defined for
this purpose, Rich Call Data (RCD), is an extensible object defined
to either be used as part of STIR or with SIP Call-Info to include
related information about calls that helps people decide whether to
pick up the phone. This signing of the RCD information is also
enhanced with an integrity mechanism to optionally protect the
handling of this information between authoritative and non-
authoritative parties authoring and signing the Rich Call Data for
support of different usage and content policies.
Status of This Memo
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This Internet-Draft will expire on September 10, 2020.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of the use of the Rich Call Data PASSporT extension 4
4. Overview of Rich Call Data integrity . . . . . . . . . . . . 5
5. PASSporT Claims . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. PASSporT "rcd" Claim . . . . . . . . . . . . . . . . . . 5
5.1.1. "nam" key . . . . . . . . . . . . . . . . . . . . . . 6
5.1.2. "jcd" key . . . . . . . . . . . . . . . . . . . . . . 6
5.1.3. "jcl" key . . . . . . . . . . . . . . . . . . . . . . 6
5.1.4. "rcdi" RCD integrity Claim . . . . . . . . . . . . . 6
5.1.5. Creation of the "rcd" digest . . . . . . . . . . . . 7
5.1.6. JWT Constraint for "rcdi" claim . . . . . . . . . . . 8
5.2. PASSporT "crn" claim - Call Reason . . . . . . . . . . . 9
6. "rcd" and "crn" Claims Usage . . . . . . . . . . . . . . . . 9
6.1. Example "rcd" PASSporTs . . . . . . . . . . . . . . . . . 9
7. Compact form of "rcd" PASSporT . . . . . . . . . . . . . . . 11
7.1. Compact form of the "rcd" PASSporT claim . . . . . . . . 11
7.2. Compact form of the "rcdi" PASSporT claim . . . . . . . . 12
7.3. Compact form of the "crn" PASSporT claim . . . . . . . . 12
8. Further Information Associated with Callers . . . . . . . . . 12
9. Third-Party Uses . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Signing as a Third Party . . . . . . . . . . . . . . . . 14
10. Levels of Assurance . . . . . . . . . . . . . . . . . . . . . 15
11. Using "rcd" in SIP . . . . . . . . . . . . . . . . . . . . . 15
11.1. Authentication Service Behavior . . . . . . . . . . . . 15
11.2. Verification Service Behavior . . . . . . . . . . . . . 16
12. Using "rcd" as additional claims to other PASSporT extensions 17
12.1. Procedures for applying "rcd" as claims only . . . . . . 17
12.2. Example for applying "rcd" as claims only . . . . . . . 17
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
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14.1. JSON Web Token Claim . . . . . . . . . . . . . . . . . . 18
14.2. PASSporT Types . . . . . . . . . . . . . . . . . . . . . 19
14.3. PASSporT RCD Types . . . . . . . . . . . . . . . . . . . 19
15. Security Considerations . . . . . . . . . . . . . . . . . . . 19
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
16.1. Normative References . . . . . . . . . . . . . . . . . . 20
16.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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
used by an automaton to determine whether and how to alert a called
party.
Traditional telephone network signaling protocols have long supported
delivering a 'calling name' from the originating side, though in
practice, the terminating side is often left to derive a name from
the calling party number by consulting a local address book or an
external database. SIP similarly can carry a 'display-name' in the
From header field value from the originating to terminating side,
though it is an unsecured field that is not commonly trusted. The
same is true of information in the Call-Info header field.
The baseline use case for this document will be extending PASSporT to
provide cryptographic protection for the "display-name" field of SIP
requests as well as further "rich call data" (RCD) about the caller,
which includes the contents of the Call-Info header field or other
data structures that can be added to the PASSporT. This document
furthermore specifies a third-party profile that would allow external
authorities to convey rich information associated with a calling
number via a new type of PASSporT. Finally, this document describes
how to preserve the integrity of the RCD in scenarios where there may
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be non-authoritative users that may be initiating and signing RCD and
therefore a constraint on the RCD data that a PASSporT can attest via
certificate-level controls.
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. Overview of the use of the Rich Call Data PASSporT extension
The main intended use of the signing of Rich Call Data (RCD) using
STIR [RFC8224] and as a PASSporT extension [RFC8225] is from an
entity that is associated with the originated with the call. Either
the caller themselves if they are authoritative, or a service
provider, or a third-party service may be authoritative over the rich
call data on behalf of the caller or service provider representing
the caller.
The RCD described in this document is of two main categories. The
first data is a more traditional set of info about a caller
associated with "display-name" in SIP [RFC3261] and typically is the
calling name that is a textual description of the caller. The second
data is a set of RCD that is defined as part of the jCard definitions
or extensions to that data. [I-D.wendt-sipcore-callinfo-rcd]
describes the use of jCard as RCD with the "jcard" Call-Info purpose
token. Either or both of these two types of data can be incorporated
into a "rcd" claim defined in this document.
Additionally, [I-D.wendt-sipcore-callinfo-rcd] also describes a
"reason" parameter intended for description of the intent or reason
for a particular call. A new claim "crn" for call reason can contain
the string or object that describes the intent of the call. This
claim is intentionally kept separate from the "rcd" claim because it
is envisioned that reason will often change on a more frequent, per
call, type of basis and would not fit the "rcdi" claim and other
integrity methods tied to the certificate and identity of the caller.
In addition to the type of RCD that can be signed, there are three
normative modes of use of the signing of Rich Call Data (RCD). The
first and simplest mode is exclusively for when RCD content is
directly included as part of the claims (i.e. no URIs are included in
the content). In this mode the set of claims is signed via standard
PASSporT [RFC8225] and SIP identity header [RFC8224] procedures. The
second mode is an extension of the first where a "rcd" claim is
included and the content MAY or MAY NOT include a URI identifying
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external resources. In this mode, a "rcdi" integrity claim MUST be
included. This integrity claim is defined in this document and
provides a digest of the content so that, particularly for the case
where there is URI references in the RCD, the content of that RCD can
be comprehensively validated that it was received as intended by the
signer of the PASSporT. The third mode is an extension to both the
first and second modes and incorporates the ability to include the
digest of the integrity claim as a required value in the certificate
used to create the PASSporT digital signature. This mode allows for
cases where there is a different authoritative entity responsible for
the content of the RCD, separate from the signer of the PASSporT
itself allowing the ability to have policy around the content and
potential review or pre-determination of allowed RCD content.
4. Overview of Rich Call Data integrity
When incorporating call data that represents a user, even in
traditional calling name services today, often there is policy and
restrictions around what data is allowed to be used. Whether
preventing offensive language or icons or enforcing uniqueness or
whatever potential policy either via regulatory rules, a customer
service agreements, or an enterprise brand consistency there may be
the desire to pre-certify the specific use of rich data. This
document defines a mechanism that allows for an indirect party that
controls the policy to approve or certify the content, create a
cryptographic digest that can be used to validate that data and
applies a constraint in the certificate to allow the recipient and
verifier to validate that the specific content of the RCD is as
intended at its creation and approval or certification.
The integrity mechanism is a process of generating a sufficiently
strong cryptographic digest for both the "rcd" claim contents (e.g.
"nam" and "jcd") defined below and the resources defined by one or
more globally unique HTTPS URLs referenced by the contents (e.g. an
image file referenced by "jcd"). This mechanism is inspired and
based on the W3C Subresource Integrity specification
(http://www.w3.org/TR/SRI/). This mechanism additionally defines the
ability to constrain the digest and RCD integrity mechanism to be
mandatory without modification using JWT Constraints defined in
[RFC8226].
5. PASSporT Claims
5.1. PASSporT "rcd" Claim
This specification defines a new JSON Web Token claim for "rcd", Rich
Call Data, the value of which is a JSON object that can contain one
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or more key value pairs. This document defines a default set of key
values.
5.1.1. "nam" key
The "nam" key value is a display name, 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. This
key MUST be included once and MUST be included as part of the "rcd"
claim value JSON object. If there is no string associated with a
display name, the claim value SHOULD then be an empty string.
5.1.2. "jcd" key
The "jcd" key value is defined to contain a value of a jCard
[RFC7095] JSON object. This jCard object is intended to represent
and derives from the Call-Info header field value defined in
[I-D.wendt-sipcore-callinfo-rcd] with a type of "jcard". As also
defined in [I-D.wendt-sipcore-callinfo-rcd], format of the jCard and
properties used should follow the normative usage and formatting
rules and procedures. It is an extensible object where the calling
party can provide both the standard types of information defined in
jCard or can use the built-in extensibility of the jCard
specification to add additional information. The "jcd" is optional.
If included, this key MUST only be included once in the "rcd" JSON
object and SHOULD NOT be included if there is a "jcl" key included.
The "jcd" and "jcl" keys should be mutually exclusive.
5.1.3. "jcl" key
The "jcl" key value is defined to contain a HTTPS URL that refers the
recipient to a jCard [RFC7095] JSON object hosted on a HTTPS enabled
web server. This link may derive from the Call-Info header field
value defined in [I-D.wendt-sipcore-callinfo-rcd] with a type of
"jcard". As also defined in [I-D.wendt-sipcore-callinfo-rcd], format
of the jCard and properties used should follow the normative usage
and formatting rules and procedures. The "jcl" key is optional. If
included, this key MUST only be included once in the "rcd" JSON
object and SHOULD NOT be included if there is a "jcd" key included.
The "jcd" and "jcl" keys should be mutually exclusive.
5.1.4. "rcdi" RCD integrity Claim
The "rcdi" claim is an optional claim that SHOULD be included if the
application requires integrity to be applied to the content of the
"rcd" claim and if included MUST be included only once with a
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corresponding "rcd" claim. The value of the "rcdi" key pair should
contain a string that is defined as follows.
The first part of the string should define the crypto algorithm used
to generate the digest. For RCD, implementations MUST support the
following hash algorithms, "SHA256", "SHA384", or "SHA512". The SHA-
256, SHA-384, and SHA-512 are part of the SHA-2 set of cryptographic
hash functions defined by the NIST. Implementations MAY support
additional algorithms, but MUST NOT support known weak algorithms
such as MD5 or SHA-1. In the future, the list of algorithms may re-
evaluated based on security best practices. The algorithms MUST be
represented in the text by "sha256", "sha384", or "sha512". The
character following the algorithm string MUST be a minus character,
"-". The subsequent characters MUST be the base64 encoded digest of
a canonicalized and concatenated string based on the "rcd" claim and
the URLs contained in the claim. The details of the creation of this
string are defined in the next section.
Example:
"rcdi" : "sha256-H8BRh8j48O9oYatfu5AZzq6A9RINQZngK7T62em8MUt1FLm52t+eX6xO"
5.1.5. Creation of the "rcd" digest
In order to facilitate proper verification of the digest and whether
the "rcd" content was modified, the input to the digest must be
completely deterministic at three points in the process. First, at
the certification point where the content is evaluated to conform to
the application policy and the JWT Claim Constraints is applied to
the certificate containing the digest. Second, when the call is
signed at the Authentication Service, there may be a local policy to
verify that the provided "rcd" claim corresponds to the digest.
Third, when the "rcd" data is verified at the Verification Service,
it MUST verify the digest by constructing the "rcd" input digest
string.
The procedures for the creation of the "rcd" input digest string is
as follows.
1. Arrange the keys in the "rcd" claim value to be in lexicographic
order.
2. Serialize the resulting "rcd" claim value JSON object to remove
all white space and line breaks. The procedures of this
deterministic JSON serialization is defined in [RFC8225],
Section 9.
3. Identify, in order of where they appear in the serialized string,
all of the URLs referencing external resource files.
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4. Construct the "rcd" input string by first inserting the
serialized "rcd" claim value.
5. If there is at least one URL identified, insert a semicolon
character at the end of the "rcd" serialized string.
6. Follow the semicolon with the Base64 encoded contents of resource
file referenced by the first URL.
7. Repeat steps 5 and 6 for any additionally identified
corresponding URLs including URLs contained in resources
referenced by other URLs. When or if these nested URLs occur in
the contents referred to by a parent URL, the insertion of the
Base64 encoded contents should be included for all child URLs
before moving to any subsequent parent URL.
Once the input serialized string has been created, use this string to
create the base64 encoded digest output that can be inserted into the
"rcdi" claim as discussed in the last section.
Example "rcd" claim with URL:
"rcd": { "nam" : "James Bond",
"jcl" : "https://example.org/james_bond.json"
}
Example "rcd" input digest string (with line breaks for readability):
{"nam":"James Bond","jcl":"https://example.org/james_bond.json"};
ONG##*NCCCDJK123...KLJASlkJlkjsadlf2e3
Example "rcdi" claim:
"rcdi":"sha256-u5AZzq6A9RINQZngK7T62em8M"
5.1.6. JWT Constraint for "rcdi" claim
Once both the contents of the "rcd" claim is certified and the
construction of the "rcdi" claim is complete, the "rcdi" digest is
linked to the STIR certificate associated with the signature in the
PASSporT via JWT Claim Constraints as defined in [RFC8226] Section 8.
The certificate JWT Claims Constraint MUST include both of the
following:
o a "mustInclude" for the "rcd" claim
o a "mustInclude" for the "rcdi" claim and a "permittedValues" equal
to the created "rcdi" claim value string.
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The "permitedValues" for the "rcdi" claim may contain multiple
entries, to support the case where the certificate holder is
authorized to use different sets of rich call data.
5.2. PASSporT "crn" claim - Call Reason
This specification defines a new JSON Web Token claim for "crn", Call
Reason, the value of which is a single string or object that can
contains information as defined in [I-D.wendt-sipcore-callinfo-rcd]
corresponding to the "reason" parameter for the Call-Info header.
This claim is optional.
Example "crn" claim with "rcd":
"rcd": { "nam" : "James Bond",
"jcl" : "https://example.org/james_bond.json"
},
"crn" : "For your ears only"
6. "rcd" and "crn" Claims Usage
Either the "rcd" or "crn" claim may appear in any PASSporT claims
object as an optional element. The creator of a PASSporT MAY also
add a "ppt" value of "rcd" to the header of a PASSporT as well, in
which case the PASSporT claims MUST contain either a "rcd" or "crn"
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 with the "ppt" included will
look as follows:
{ "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].
After the header and claims PASSporT objects have been constructed,
their signature is generated normally per the guidance in [RFC8225].
6.1. Example "rcd" PASSporTs
An example of a "nam" only PASSporT claims obejct is shown next (with
line breaks for readability only).
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{ "orig":{"tn":"12025551000"},
"dest":{"tn":"12025551001"},
"iat":1443208345,
"rcd":{"nam":"James Bond"} }
An example of a "nam" only PASSporT claims object with an "rcdi"
claim is shown next (with line breaks for readability only).
{ "orig":{"tn":"12025551000"},
"dest":{"tn":"12025551001"},
"iat":1443208345,
"rcd":{"nam":"James Bond"}
"rcdi":"sha256-H8BRh8j48O9oYatfu5AZzq6A9R6dQZngK7T62em8MUt1FLm52t+eX6xO"
}
An example of a PASSporT claims object that includes the "jcd" which
is optional, but will also include the mandatory "nam" object is
shown next (with line breaks for readability only).
{ "orig":{"tn":"12025551000"},
"dest":{"tn":"12155551001"},
"iat":1443208345,
"rcd":{"nam":"James Bond","jcd":["vcard",[["version",{},"text","4.0"],
["fn",{},"text", "James Bond"],
["n",{},"text",["Bond","James","","","Mr."]],
["adr",{"type":"work"},"text",
["","","3100 Massachusetts Avenue NW","Washington","DC","20008","USA"]
],
["email",{},"text","007@mi6-hq.com"],
["tel",{"type":["voice","text","cell"],"pref":"1"},"uri",
"tel:+1-202-555-1000"],
["tel",{"type":["fax"]},"uri","tel:+1-202-555-1001"],
["bday",{},"date","19241116"],
["logo",{},"uri",
"https://upload.wikimedia.org/wikipedia/en/c/c5/Fleming007impression.jpg"
]]]}}
In an example PASSporT where a jCard is linked via HTTPS URL and
"jcl" a jCard file served at a particular URL will be created.
An example jCard JSON file is shown as follows:
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["vcard",
[
["version", {}, "text", "4.0"],
["fn", {}, "text", "James Bond"],
["n", {}, "text", ["Bond", "James", "", "", "Mr."]],
["adr", {"type":"work"}, "text",
["", "", "3100 Massachusetts Avenue NW", "Washington", "DC", "20008",
"USA"]
],
["email", {}, "text", "007@mi6-hq.com"],
["tel", { "type": ["voice", "text", "cell"], "pref": "1" }, "uri",
"tel:+1-202-555-1000"],
["tel", { "type": ["fax"] }, "uri", "tel:+1-202-555-1001"],
["bday", {}, "date", "19241116"]
["logo", {}, "uri",
"https://upload.wikimedia.org/wikipedia/en/c/c5/Fleming007impression.jpg"]
]
]
If that jCard is hosted at the example address of
"https://example.org/james_bond.json", the corresponding PASSporT
claims object would be as follows (with line breaks for readability
only):
{ "orig":{"tn":"12025551000"},
"dest":{"tn":"12155551001"},
"iat":1443208345,
"rcd":{"nam":"James Bond","jcl":"https://example.org/james_bond.json"}
}
If we were to add a "rcdi" integrity claim to the last example, the
corresponding PASSporT claims object would be as follows (with line
breaks for readability only):
{ "orig":{"tn":"12025551000"},
"dest":{"tn":"12155551001"},
"iat":1443208345,
"rcd":{"nam":"James Bond","jcl":"https://example.org/james_bond.json"}
"rcdi":"sha256-H8BRh8j48O9oYatfu5AZzq6A9R6dQZngK7T62em8MUt1FLm52t+eX6xO"
}
7. Compact form of "rcd" PASSporT
7.1. Compact form of the "rcd" PASSporT claim
Compact form of an "rcd" PASSporT claim has some restrictions but
mainly follows standard PASSporT compact form procedures. For re-
construction of the "nam" claim the string for the display-name in
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the From header field. For re-construction of the "jcl", the Call-
Info header as with purpose "jcard" defined in
[I-D.wendt-sipcore-callinfo-rcd] MUST be used. "jcd" claim MAY NOT be
used as part of compact form.
7.2. Compact form of the "rcdi" PASSporT claim
Compact form of an "rcdi" PASSPorT claim shall be re-constructed
following the same "rcdi" defined digest procedures in this document
of all of the content and referenced URI content once downloaded.
7.3. Compact form of the "crn" PASSporT claim
Compact form of a "crn" PASSporT claim shall be re-constructed using
the "reason" parameter of a Call-Info header as defined by
[I-D.wendt-sipcore-callinfo-rcd].
8. Further Information Associated with Callers
Beyond naming information and the information that can be contained
in a jCard [RFC7095] object, 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:
o information related to the location of the caller, or
o 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
o hyperlinks to images, such as logos or pictures of faces, or to
similar external profile information, or
o 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
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Section 14.3. 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.
9. 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. Such a service effectively acts as a STIR
Authentication Service, generating its own PASSporT, and that
PASSporT could be attached to a SIP call by either the originating or
terminating side. This third-party PASSporT attests information
about the calling number, rather than the call or caller itself, and
as such its RCD MUST NOT be used when a call lacks a first-party
PASSporT that assures verification services that the calling party
number is not spoofed. It is intended to be used in cases when the
originating side does not supply a display-name for the caller, so
instead some entity in the call path invokes a third-party service to
provide rich caller data for a call.
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 a sub-case 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
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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.
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.
9.1. Signing as a Third Party
A third-party PASSporT, which contains such an "iss" element, will
necessarily be signed with credentials that do not have authority
over the identity that appears in the "orig" element of the PASSporT
claims. The presence of "iss" signifies that a different category of
credential is being used to sign a PASSporT than the [RFC8226]
certificates used to sign STIR calls; it is instead a certificate
that identifies the source of the "rcd" data. How those credentials
are issued and managed is outside the scope of this specification;
the value of "iss" however MUST reflect the Organization (O) field of
the certificate used to sign a third-party PASSporT. 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.
An example of a Third Party issued PASSporT claims object is as
follows.
{ "orig":{"tn":"12025551000"},
"dest":{"tn":"12025551001"},
"iat":1443208345,
"iss":"Example, Inc.",
"rcd":{"nam":"James Bond"} }
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10. 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?]
11. 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.
11.1. 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 9.1 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", specifically only for the
"nam" key value, from the display-name component of the From header
field value of the request, alternatively for some calls this may
come from the P-Asserted-ID header. It is however a matter of
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authentication service policy to decide how it populates the value of
"rcd" and "nam" key, 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.
11.2. 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
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 9.1. This may include accepting a
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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.
12. 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
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.
12.1. 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.
12.2. Example for applying "rcd" as claims only
In the case of [RFC8588] which is the PASSporT extension supporting
the SHAKEN specification [ATIS-1000074], a common case for an
Authentication 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 Authentication Service can
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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":{"tn":["12025551001"]},
"iat":1443208345,
"orig":{"tn":"12025551000"},
"origid":"123e4567-e89b-12d3-a456-426655440000",
"rcd":{"nam":"James Bond"}
}
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.
13. Acknowledgements
We would like to thank David Hancock, Robert Sparks, Russ Housley,
and Eric Burger for helpful suggestions and comments.
14. IANA Considerations
14.1. JSON Web Token Claim
This specification requests that the IANA add three new claims to the
JSON Web Token Claims registry as defined in [RFC7519].
Claim Name: "rcd"
Claim Description: Rich Call Data Information
Change Controller: IESG
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Specification Document(s): [RFCThis]
Claim Name: "rcdi"
Claim Description: Rich Call Data Integrity Information
Change Controller: IESG
Specification Document(s): [RFCThis]
Claim Name: "crn"
Claim Description: Call Reason
Change Controller: IESG
Specification Document(s): [RFCThis]
14.2. 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].
14.3. 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 three values, "nam",
"jcd", and "jcl", which are specified in [RFCThis].
15. 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.
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16. References
16.1. Normative References
[I-D.ietf-stir-oob]
Rescorla, E. and J. Peterson, "STIR Out-of-Band
Architecture and Use Cases", draft-ietf-stir-oob-07 (work
in progress), March 2020.
[I-D.wendt-sipcore-callinfo-rcd]
Wendt, C. and J. Peterson, "SIP Call-Info Parameters for
Rich Call Data", draft-wendt-sipcore-callinfo-rcd-00 (work
in progress), November 2019.
[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>.
[RFC7095] Kewisch, P., "jCard: The JSON Format for vCard", RFC 7095,
DOI 10.17487/RFC7095, January 2014,
<https://www.rfc-editor.org/info/rfc7095>.
[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>.
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[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>.
[RFC8588] Wendt, C. and M. Barnes, "Personal Assertion Token
(PaSSporT) Extension for Signature-based Handling of
Asserted information using toKENs (SHAKEN)", RFC 8588,
DOI 10.17487/RFC8588, May 2019,
<https://www.rfc-editor.org/info/rfc8588>.
16.2. 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.
[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
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