STIR R. Singh
Internet-Draft Vencore Labs
Intended status: Standards Track M. Dolly
Expires: July 8, 2018 AT&T
S. Das
Vencore Labs
A. Nguyen
Office of Emergency Communication/DHS
January 04, 2018
PASSporT Extension for Resource-Priority Authorization
draft-ietf-stir-rph-02
Abstract
This document extends the STIR PASSporT specification to allow the
inclusion of cryptographically-signed assertions of authorization for
the values populated in the SIP 'Resource-Priority' header field,
which is used for communications resource prioritization.
Status of This Memo
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PASSporT 'rph' Claim . . . . . . . . . . . . . . . . . . . . 3
4. 'rph' in SIP . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Authentication Service Behavior . . . . . . . . . . . . . 4
4.2. Verification Service Behavior . . . . . . . . . . . . . . 5
5. Further Information Associated with Resource-Priority . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6.1. JSON Web Token Claims Registration . . . . . . . . . . . 6
6.2. PASSporT 'rph' Types . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7.1. Avoidance of replay and cut and paste attacks . . . . . . 7
7.2. Solution Considerations . . . . . . . . . . . . . . . . . 7
7.3. Acknowledgements . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
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 identities 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
allow cryptographic-signing of the SIP 'Resource-Priority' header
field defined in [RFC4412].
[RFC4412] defines the SIP 'Resource-Priority' header field for
communications Resource Priority. As specified in [RFC4412], the
'Resource-Priority' header field may be used by SIP user agents
[RFC3261], including, Public Switched Telephone Network (PSTN)
gateways and terminals, and SIP proxy servers to influence
prioritization afforded to communication sessions,including PSTN
calls. However, the SIP 'Resource-Priority' header field could be
spoofed and abused by unauthorized entities.
The STIR architecture [RFC7340]assumes that an authority on the
originating side of a call provides a cryptographic assurance of the
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validity of the calling party number in order to prevent
impersonation attacks. The STIR architecture allows extension that
can be utilized by authorities supporting real-time communication
services using the 'Resource-Priority' header field to
cryptographically sign the SIP 'Resource-Priority' header field and
convey assertion of the authorization for 'Resource-Priority'. For
example, the authority on the originating side verifying the
authorization of a particular communication for Resource-Priority can
use a PASSPorT claim to cryptographically-sign the SIP 'Resource-
Priority' header field and convey an assertion of the authorization
for 'Resource-Priority'. This will allow a receiving entity
(including entities located in different network domains/boundaries)
to verify the validity of assertions authorizing Resource-Priority.
Cryptographically-signed SIP 'Resource-Priority' headers will allow a
receiving entity to verify and act on the information with confidence
that the information have not been spoofed or compromised.
This specification documents an optional extension to PASSporT and
the associated STIR mechanisms to provide a function to sign the SIP
'Resource-Priority' header field. This PASSporT object is used to
provide attestation of a calling user authorization for priority
communications. This is necessary in addition to the PASSporT object
that is used for calling user telephone number attestation. How the
optional extension to PASSporT is used for real-time communications
supported using SIP 'Resource-Priority' header field is defined in
other documents and is outside the scope of this document.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. PASSporT 'rph' Claim
This specification defines a new JSON Web Token claim for "rph",
which provides an assertion for information in SIP 'Resource-
Priority'header.
The creator of a PASSporT object adds a "ppt" value of "rph" to the
header of a PASSporT object, in which case the PASSporT claims MUST
contain a "rph" 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:
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{ "typ":"passport",
"ppt":"rph",
"alg":"ES256",
"x5u":"https://www.example.org/cert.cer"}
The "rph" claim will provide an assertion of authorization,"auth",
for information in the SIP "Resource-Priority" header field (i.e.,
Resource-Priority: namespace "." r-priority) based on [RFC4412].
Specifically, the "rph" claim includes assertion of the priority-
level of the user to be used for a given communication session. The
value of the "rph" claim is an array containing one or more of JSON
objects for the content of the SIP 'Resource-Priority' header that is
being asserted of which one of the "rph" object, is mandatory.
The following is an example "rph" claim for a SIP "Resource-Priority"
header field with a "namespace "." r-priority" value of "ets.0" and
with a "namespace "." r-priority" value of "wps.0".
{ "orig":{"tn":"12155551212"}
"dest":{["tn":"12125551213"]},
"iat":1443208345,
"rph":{"auth":["ets.0","wps.0"]}
After the header and claims PASSporT objects have been constructed,
their signature is generated normally per the guidance in
[I-D.ietf-stir-passport] using the full form of PASSPorT. The
credentials (e.g., authority responsible for authorizing Resource-
Priority) used to create the signature must have authority over the
"rph" claim and there is only one authority per claim. The authority
MUST use its credentials (i.e., CERT) associated with the specific
service supported by the SIP namespace in the claim.
4. 'rph' in SIP
This section specifies SIP-specific usage for the "rph" claim in
PASSporT.
4.1. Authentication Service Behavior
The Authentication Service will create the "rph" claim using the
values discussed in section 3 based on [RFC4412]. The construction
of "rph" claim follows the steps described in Section 4 of
[I-D.ietf-stir-rfc4474bis].
The resulting Identity header for "rph" might look as follows:
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"eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJleUowZVhBaU9pSnd
ZWE56Y0c5eWRDSXNEUW9pY0hCMElqb2ljbkJvSWl3TkNpSmhiR2NpT2lKRlV6STFO
aUlzRFFvaWVEVjFJanBvZEhSd2N6b3ZMM2QzZHk1bGVHRnRjR3hsTG1OdmJTOWpaW
EowTG1ObGNuME5DZzBLIHx84oCZLuKAmXx8IGV5QWliM0pwWnlJNmV5SjBiaUk2SW
pFeU1UVTFOVFV4TWpFeUluME5DaUprWlhOMElqcDdXeUowYmlJNklqRXlNVEkxTlR
VeE1qRXpJbDE5TEEwS0ltbGhkQ0k2TVRRME16SXdPRE0wTlN3TkNpSnljR2dpT25z
aVlYVjBhQ0k2V3lKbGRITXVNQ0lzSW5kd2N5NHdJbDE5RFFvPSJ9.s37S6VC8HM6D
l6YzJeQDsrZcwJ0lizxhUrA7f_98oWBHvo-cl-n8MIhoCr18vYYFy3blXvs3fslM_
oos2P2Dyw"; info= "https://www.example.org/cert.cer";alg=ES256;
ppt="rph"
A SIP authentication service typically will derive the value of "rph"
from the 'Resource-Priority' header field based on policy associated
with service specific use of the "namespace "." r-priority" values
based on [RFC4412]. The authentication service derives the value of
the PASSPorT claim by verifying the authorization for Resource-
Priority (i.e., verifying a calling user privilege for Resource-
Priority based on its identity) which might be derived from customer
profile data or from access to external services.
[RFC4412] allows multiple "namespace "." r-priority" pairs, either in
a single SIP Resource-Priority header or across multiple SIP
Resource-Priority headers. However, it is not necessary to sign all
content of a SIP Resource-Priority header or all SIP Resource-
Priority headers in a given SIP message. An authority is only
responsible for signing the content of a SIP Resource-Priority header
for which it has authority (e.g., a specific "namespace "."
r-priority").
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 "rph" is as
follows:
The verification service MUST extract the value associated with the
"auth" key in a full form PASSPorT with a "ppt" value of "rph". If
the signature validates, then the verification service can use the
value of the "rph" claim as validation that the calling party is
authorized for Resource-Priority, which would in turn be used for
priority treatment in accordance with local policy for the associated
communication service.
In addition, [I-D.ietf-stir-rfc4474bis] Section 6.2 Step 4 requires
"iat" value in "rph" claim to be verified.
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The behavior of a SIP UAs upon receiving an INVITE containing a
PASSporT object with a "rph" claim will largely remain a matter of
implementation policy for the specific communication service. In
most cases,implementations would act based on confidence in the
veracity of this information. The use of the compact form of
PASSporT is not specified in this document.
5. Further Information Associated with Resource-Priority
There may be additional information about the calling party or the
call that could be relevant to authorization for Resource-Priority.
This may include information related to the device subscription of
the caller, or to any institutions that the caller or device 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 "rph"
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
"rph" array; see Section 6.2. The definition of the "rph" claim may
have one or more such additional information field(s). Details of
such "rph" claim to encompass other data elements are left for future
version of this specification.
6. IANA Considerations
6.1. JSON Web Token Claims Registration
o Claim Name: "rph"
o Claim Description: Resource Priority Header Authorization
o Change Controller: IESG
o Specification Document(s): Section 3 of [RFCThis]
6.2. PASSporT 'rph' Types
This document requests that the IANA add a new entry to the PASSporT
Types registry for the type "rph" which is specified in [RFCThis].
This specification also requests that the IANA create a new registry
for PASSporT "rph" types. Registration of new PASSporT "rph" types
shall be under the specification required policy. This registry is
to be initially populated with a single value for "auth" which is
specified in [RFCThis].
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7. Security Considerations
The security considerations discussed in [I-D.ietf-stir-rfc4474bis]
in Section 10 are applicable here.
7.1. Avoidance of replay and cut and paste attacks
The PASSporT extension with a "ppt" value of "rph" MUST only be sent
with SIP INVITE when 'Resource-Priority' header is used to convey the
priority of the communication as defined in [RFC4412]. To avoid the
replay, and cut and paste attacks, the procedures described in
Section 10.1 of [I-D.ietf-stir-rfc4474bis] MUST be followed.
7.2. Solution Considerations
The use of extension to PASSporT tokens with "ppt" value "rph" based
on the validation of the digital signature and the associated
certificate requires consideration of the authentication and
authority or reputation of the signer to attest to the identity being
asserted. The following considerations should be recognized when
using PASSporT extension with "ppt" value of "rph":
o An authority (signer) is only allowed to sign the content of a SIP
'Resource-Priority' header for which it has the right authority.
The authority that signs the token MUST have a secure method for
authentication of the end user or the device.
o The verification of the signature MUST include means of verifying
that the signer is authoritative for the signed content of the SIP
'Resource-Priority' header.
7.3. Acknowledgements
We would like to thank STIR members, ATIS/SIP Forum Task Force on
IPNNI members, and the NS/EP Priority Services community for
contributions to this problem statement and specification. We would
also like to thank David Hancock for his valuable inputs.
8. References
8.1. Normative References
[I-D.ietf-stir-passport]
Wendt, C. and J. Peterson, "Personal Assertion Token
(PASSporT)", February 2017.
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[I-D.ietf-stir-rfc4474bis]
Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
"Authenticated Identity Management in the Session
Initiation Protocol (SIP)", February 2017.
[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>.
[RFC4412] Schulzrinne, H. and J. Polk, "Communications Resource
Priority for the Session Initiation Protocol (SIP)",
RFC 4412, DOI 10.17487/RFC4412, February 2006,
<http://www.rfc-editor.org/info/rfc4412>.
[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>.
8.2. Informative References
[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>.
[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>.
Authors' Addresses
Ray P. Singh
Vencore Labs
150 Mount Airy Road
New Jersey, NJ 07920
USA
Email: rsingh@vencorelabs.com
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Martin Dolly
AT&T
200 Laurel Avenue
Middletown, NJ 07748
USA
Email: md3135@att.com
Subir Das
Vencore Labs
150 Mount Airy Road
New Jersey, NJ 07920
USA
Email: sdas@vencorelabs.com
An Nguyen
Office of Emergency Communication/DHS
245 Murray Lane, Building 410
Washington, DC 20528
USA
Email: an.p.nguyen@HQ.DHS.GOV
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