Internet DRAFT - draft-ietf-stir-rph-emergency-services
draft-ietf-stir-rph-emergency-services
STIR M. Dolly
Internet-Draft AT&T
Intended status: Standards Track C. Wendt
Expires: September 12, 2021 Comcast
March 11, 2021
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-07
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.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. New Assertion Values for "rph" claim . . . . . . . . . . . . 3
4. The SIP Priority header "sph" claim . . . . . . . . . . . . . 4
5. Order of Claim Keys . . . . . . . . . . . . . . . . . . . . . 5
6. Compact Form of PASSporT . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8.1. JSON Web Token claims . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. 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]. [I-D.rosen-stir-emergency-calls]
introduces the need and justification for the protection of both the
SIP "Resource-Priority" and "Priority" header fields, used for
categorizing the priority use of the call in the telephone network,
specifically for emergency calls.
Compromise of the SIP "Resource-Priority" or "Priority" header fields
could lead to misuse of network resources (i.e., during congestion
scenarios), impacting the application services supported using the
SIP "Resource-Priority" header field and the handling of Public
Saftey Answering Point (PSAP) callbacks.
[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 field and convey assertion of those values by the
signing party authorization. A signed SIP "Resource-Priority" or
"Priority" header field 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 "auth" array key 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 additionally defines a new PASSporT claim,
"sph", including protection of the SIP Priority header field for the
indication of an emergency service call-back assigned the value
"psap-callback" as defined in [RFC7090]. The use of the newly
defined claim and key values corresponding to 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 the ability to sign the SIP Resource-
Priority Header field namespace for local emergency communications
defined in [RFC7135] and represented by the string "esnet.x" where x
is the priority-level allowed in the esnet namespace. As of the
writing of this specification the priority-level is between 0 and 4,
inclusive, but may be extended by future specifications.
Similar to the values defined by [RFC8443] for the "auth" JSON object
key inside the "rph" claim, the string "esnet.x" with the appropriate
value should be used when resource priority is required for local
emergency communications corresponding and exactly matching the SIP
Resource-Priority header field representing the namespace invoked in
the call.
When using "esnet.x" as the "auth" assertion value in emergency
service destined calls, 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
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"urn:service:sos" as defined in [RFC5031], representing the emergency
services destination of the call.
The following is an example of an "rph" claim for SIP 'Resource-
Priority' header field with an "esnet.1" assertion:
{
"dest":{"uri":["urn:service:sos"]},
"iat":1615471428,
"orig":{"tn":"12155551212"},
"rph":{"auth":["esnet.1"]}
}
For emergency services callbacks, the "orig" claim of the "rph"
PASSporT MUST represent the Public Saftey Answering Point (PSAP)
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 "esnet.0" assertion:
{
"dest":{"tn":["12155551212"]},
"iat":1615471428,
"orig":{"tn":"12155551213"},
"rph":{"auth":["esnet.0"]}
}
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" identity header
and sign the claim with their own authority.
4. The SIP Priority header "sph" claim
As defined in [RFC7090] the SIP Priority header field 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.
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Therefore, we define a new claim key as part of the "rph" PASSporT,
"sph". This is an optional claim that MUST only be used only with an
"auth" claim with an "esnet.x" value indicating an authorized
emergency callback call and corresponding to a SIP Priority header
field with the value "psap-callback".
The value of the "sph" claim key should only be "psap-callback" which
MUST match the SIP Priority header field value for authorized
emergency services callbacks. If the value is anything other than
"psap-callback", the PASSporT validation MUST be considered a failure
case.
Note: Because the intended use of this specification is only for
emergency services, there is also an explicit assumption that the
signer of the "rph" PASSporT can authoritatively represent both the
content of the Resource Priority Header field and Priority Header
field information associated specifically with a emergency services
callback case where both could exist. This document is not intended
to be a general mechanism for protecting SIP Priority Header fields,
this could be accomplished as part of future work with a new PASSporT
extension or new claim added to either an existing PASSporT or
PASSporT extension usage.
The following is an example of an "sph" claim for SIP 'Priority'
header field with the value "psap-callback":
{
"dest":{"tn":["12155551212"]},
"iat":1615471428,
"orig":{"tn":"12155551213"},
"rph":{"auth":["esnet.0"]},
"sph":"psap-callback"
}
5. Order of Claim Keys
The order of the claim keys MUST follow the rules of [RFC8225]
Section 9 which defines the deterministic JSON serialization used for
signature generation (and validation); 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
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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. Acknowledgements
The authors would like to thank Brian Rosen, Terry Reese, and Jon
Peterson for helpful suggestions, comments, and corrections.
8. IANA Considerations
8.1. JSON Web Token claims
This specification requests that the IANA add one new claim 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]
9. Security Considerations
The security considerations discussed in [RFC8224], [RFC8225], and
[RFC8443] are applicable here.
10. References
10.1. Normative References
[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>.
[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
Emergency and Other Well-Known Services", RFC 5031,
DOI 10.17487/RFC5031, January 2008,
<https://www.rfc-editor.org/info/rfc5031>.
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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>.
[RFC7135] Polk, J., "Registering a SIP Resource Priority Header
Field Namespace for Local Emergency Communications",
RFC 7135, DOI 10.17487/RFC7135, May 2014,
<https://www.rfc-editor.org/info/rfc7135>.
[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>.
[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>.
10.2. Informative References
[I-D.rosen-stir-emergency-calls]
Rosen, B., "Non-Interactive Emergency Calls", draft-rosen-
stir-emergency-calls-00 (work in progress), March 2020.
[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>.
[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>.
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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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