STIR M. Dolly
Internet-Draft AT&T
Intended status: Standards Track C. Wendt
Expires: January 14, 2021 Comcast
July 13, 2020
Assertion Values for a Resource Priority Header Claim and a SIP Priority
Header Claim in Support of Emergency Services Networks
draft-ietf-stir-rph-emergency-services-02
Abstract
This document adds new assertion values for a Resource Priority
Header ("rph") claim and a new SIP Priority Header claim ("sph") for
protection of the "psap-callback" value as part of the "rph" PASSporT
extension, in support of the security of Emergency Services Networks
for emergency call origination and callback.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. New Assertion Values for "rph" claim . . . . . . . . . . . . 3
3.1. ESorig . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. EScallback . . . . . . . . . . . . . . . . . . . . . . . 4
4. The SIP Priority header "sph" claim . . . . . . . . . . . . . 4
5. Order of Claim Keys . . . . . . . . . . . . . . . . . . . . . 5
6. Compact Form of PASSporT . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7.1. PASSporT Resource Priority Header (rph) Types . . . . . . 5
7.2. JSON Web Token claims . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Personal Assertion Token (PASSporT) Extension for Resource Priority
Authorization [RFC8443] extended the Personal Assertion Token
(PASSporT) specification defined in [RFC8225] to allow the inclusion
of cryptographically signed assertions of authorization for the
values populated in the Session Initiation Protocol (SIP) "Resource-
Priority" header field [RFC4412], which is used for communications
resource prioritization and the SIP "Priority" header field, used for
categorizing the priority use of the call.
Compromise of the SIP "Resource-Priority" header field could lead to
misuse of network resources (i.e., during congestion scenarios),
impacting the application services supported using the SIP "Resource-
Priority" header field.
[RFC8225] allows extensions by which an authority on the originating
side verifying the authorization of a particular communication for
the SIP "Resource-Priority" header field or the SIP "Priority" header
field can use PASSPorT claims to cryptographically sign the
information associated with either the SIP "Resource-Priority" or
"Priority" header fields and convey assertion of those values by the
signing party authorization. A signed SIP "Resource-Priority" or
"Priority" header fields will allow a receiving entity (including
entities located in different network domains/boundaries) to verify
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the validity of assertions to act on the information with confidence
that the information has not been spoofed or compromised.
This document adds new assertion values for a Resource Priority
Header ("rph") claim defined in [RFC8443], in support of Emergency
Services Networks for emergency call origination and callback. This
document also defines a new claim, "sph", including protection of the
SIP Priority header for the indication of an emergency service call-
back assigned the value "psap-callback" as defined in [RFC7090]. The
use of these new assertion values for real-time communications
supported using the SIP 'Resource-Priority' and 'Priority' header
fields for emergency services is introduced in
[I-D.rosen-stir-emergency-calls] but otherwise out-of-scope of this
document. In addition, the PASSPorT claims and values defined in
this document are intended for use in environments where there are
means to verify that the signer of the SIP 'Resource-Priority' and
'Priority' header fields is authoritative.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. New Assertion Values for "rph" claim
This specification defines new assertions values for:
* "ESorig": Emergency Services call origination
* "EScallback": Emergency Services callback.
3.1. ESorig
When using "ESorig" as the "rph" assertion value, the "orig" claim of
the PASSporT MUST represent the calling party number that initiates
the call to emergency services. The "dest" claim MUST either be a
country or region specific dial string (e.g., "911" for North America
or "112" GSM defined string used in Europe and other countries) or
"urn:service:sos" as defined in TBD, representing the emergency
services destination of the call.
The following is an example of an "rph" claim for SIP 'Resource-
Priority' header field with a "ESorig" assertion:
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{
"orig":{"tn":"12155551212"},
"dest":{["uri":"urn:service:sos"]},
"iat":1443208345,
"rph":{"ESorig":["esnet,x"]}
}
3.2. EScallback
When using "EScallback" as the "rph" assertion value, the "orig"
claim of the PASSporT MUST represent the emergency network telephone
number. The "dest" claim MUST be the telephone number representing
the original calling party of the emergency service call that is
being called back.
The following is an example of an "rph" claim for SIP 'Resource-
Priority' header field with a "EScallback" assertion:
{
"orig":{"tn":"12155551213"},
"dest":{["tn":"12155551212"]},
"iat":1443208345,
"rph":{"EScallback":["esnet,x"]}
}
After the header and claims PASSporT objects have been constructed,
their signature is generated normally per the guidance in [RFC8225]
using the full form of PASSPorT. The credentials (i.e., Certificate)
used to create the signature must have authority over the namespace
of the "rph" claim, and there is only one authority per claim. The
authority MUST use its credentials associated with the specific
service supported by the resource priority namespace in the claim.
If r-values are added or dropped by the intermediaries along the
path, the intermediaries must generate a new "rph" header and sign
the claim with their own authority.
4. The SIP Priority header "sph" claim
As discussed in [I-D.rosen-stir-emergency-calls], and as defined in
[RFC7090] the SIP Priority header may be set to the value "psap-
callback" for emergency services callback calls. Because some SIP
networks may act on this value and provide priority or other special
routing based on this value, it is important to protect and validate
the authoritative use associated with it.
Therefore, we define a new claim key as part of the "rph" PASSporT,
"sph", which MUST be used only for authorized emergency callbacks and
correspond to a SIP Priority header with the value "psap-callback".
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The value of the "sph" claim key should only be "psap-callback" to
match the SIP Priority header field value for authorized emergency
services callbacks.
The following is an example of an "sph" claim for SIP 'Priority'
header field with the value "psap-callback":
{
"orig":{"tn":"12155551213"},
"dest":{["tn":"12155551212"]},
"iat":1443208345,
"rph":{"EScallback":["esnet,x"]},
"sph":"psap-callback"
}
5. Order of Claim Keys
The order of the claim keys MUST follow the rules of [RFC8225]
Section 9; the claim keys MUST appear in lexicographic order.
Therefore, the claim keys discussed in this document appear in the
PASSporT Payload in the following order,
o dest
o iat
o orig
o rph
o sph
6. Compact Form of PASSporT
The use of the compact form of PASSporT is not specified in this
document or recommended for 'rph' PASSporTs.
7. IANA Considerations
7.1. PASSporT Resource Priority Header (rph) Types
This specification requests that the IANA add two new assertion
values to the "PASSporT Resource Priority Header (rph) Types"
Registry as defined in [RFC8443].
The following assertion values will be added to the registry:
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* "ESorig": Emergency Services call origination
* "EScallback": Emergency Services callback
+--------------+------------+
| rph Type | Reference |
+--------------+------------+
| ESorig | [this RFC] |
+--------------+------------+
| EScallback | [this RFC] |
+--------------+------------+
7.2. JSON Web Token claims
This specification requests that the IANA add two new claims to the
JSON Web Token Claims registry as defined in [RFC7519].
Claim Name: "sph"
Claim Description: SIP Priority header field
Change Controller: IESG
Specification Document(s): [RFCThis]
8. Security Considerations
The security considerations discussed in [RFC8224], Section 12, are
applicable here.
9. References
9.1. Normative References
[I-D.rosen-stir-emergency-calls]
Rosen, B., "Non-Interactive Emergency Calls", draft-rosen-
stir-emergency-calls-00 (work in progress), March 2020.
[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>.
[RFC4412] Schulzrinne, H. and J. Polk, "Communications Resource
Priority for the Session Initiation Protocol (SIP)",
RFC 4412, DOI 10.17487/RFC4412, February 2006,
<https://www.rfc-editor.org/info/rfc4412>.
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[RFC7090] Schulzrinne, H., Tschofenig, H., Holmberg, C., and M.
Patel, "Public Safety Answering Point (PSAP) Callback",
RFC 7090, DOI 10.17487/RFC7090, April 2014,
<https://www.rfc-editor.org/info/rfc7090>.
[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>.
[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>.
[RFC8443] Singh, R., Dolly, M., Das, S., and A. Nguyen, "Personal
Assertion Token (PASSporT) Extension for Resource Priority
Authorization", RFC 8443, DOI 10.17487/RFC8443, August
2018, <https://www.rfc-editor.org/info/rfc8443>.
9.2. Informative References
[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>.
[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>.
[RFC7375] Peterson, J., "Secure Telephone Identity Threat Model",
RFC 7375, DOI 10.17487/RFC7375, October 2014,
<https://www.rfc-editor.org/info/rfc7375>.
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[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Authors' Addresses
Martin Dolly
AT&T
Email: md3135@att.com
Chris Wendt
Comcast
Comcast Technology Center
Philadelphia, PA 19103
USA
Email: chris-ietf@chriswendt.net
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