ECRIT B. Rosen Internet-Draft NeuStar, Inc. Intended status: Experimental H. Schulzrinne Expires: April 28, 2011 Columbia U. H. Tschofenig Nokia Siemens Networks October 25, 2010 Common Alerting Protocol (CAP) based Data-Only Emergency Alerts using the Session Initiation Protocol (SIP) draft-ietf-ecrit-data-only-ea-01.txt Abstract The Common Alerting Protocol (CAP) is a document format for exchanging emergency alerts and public warnings. CAP is mainly used for conveying alerts and warnings between authorities and from authorities to citizen/individuals. This document describes how data-only emergency alerts allow devices to issue alerts using the CAP document format. 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 http://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 28, 2011. Copyright Notice Copyright (c) 2010 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Rosen, et al. Expires April 28, 2011 [Page 1] Internet-Draft Data-Only Emergency Alerts October 2010 carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Architectural Overview . . . . . . . . . . . . . . . . . . . . 5 4. Protocol Specification . . . . . . . . . . . . . . . . . . . . 7 4.1. CAP Transport . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Profiling of the CAP Document Content . . . . . . . . . . 7 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6.1. Forgery . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.2. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 10 6.3. Injecting False Alerts . . . . . . . . . . . . . . . . . . 11 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 7.1. Registration of the 'application/common-alerting-protocol+xml' MIME type . . . 12 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.1. Normative References . . . . . . . . . . . . . . . . . . . 15 9.2. Informative References . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Rosen, et al. Expires April 28, 2011 [Page 2] Internet-Draft Data-Only Emergency Alerts October 2010 1. Introduction The Common Alerting Protocol (CAP) [cap] is an XML document format for exchanging emergency alerts and public warnings. CAP is mainly used for conveying alerts and warnings between authorities and from authorities to citizen/individuals. This document describes how data-only emergency calls are able to utilize the same CAP document format. Data-only emergency alerts are similar to regular emergency calls in the sense that they require emergency call routing functionality and may even have the same location requirements. On the other hand, the initial communication interaction will not lead to the establishment of a voice or video channel. Based on the deployment experience with non-IP based systems we distinguish between two types of environments, namely (1) data-only emergency alerts that are targeted directly to a recipient responsible for evaluating the alerts and for taking the necessary steps, including triggering an emergency call towards a Public Safety Answering Point (PSAP) and (2) alerts that are targeted to a Service URN as used for regular IP-based emergency calls where the recipient is not known to the originator. We describe these two cases in more detail in Section 3. Rosen, et al. Expires April 28, 2011 [Page 3] Internet-Draft Data-Only Emergency Alerts October 2010 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]. This document utilizes terminology introduced in [I-D.ietf-atoca-requirements]. Rosen, et al. Expires April 28, 2011 [Page 4] Internet-Draft Data-Only Emergency Alerts October 2010 3. Architectural Overview This section illustrates two envisioned usage modes; targeted and location-based emergency alert routing. Figure 1 shows a deployment variant where a sensor, as the author and originator of the alert, is pre-configured (using techniques outside the scope of this document) to issue an alert to a receiver or an aggregator, a special form of mediator, that processes these messages and performs whatever steps are necessary to appropriately react on the alert. For example, a security firm may use different sensor inputs to dispatch their security staff to a building they protect. +------------+ +------------+ | Sensor | | Aggregator | | | | | +---+--------+ +------+-----+ | | Sensors | trigger | emergency | alert | | MESSAGE with CAP | |----------------------------->| | | | Aggregator | processes | emergency | alert | 200 (OK) | |<-----------------------------| | | | | Figure 1: Targeted Emergency Alert Routing In Figure 2 a scenario is shown whereby the alert is routed using location information and the Service URN. In case the LoST resolution is done at an emergency services routing proxy rather than at the entity issuing the alert since it may not know the address of the receiver. A possible receiver is a PSAP and the recipient of the alert may be call taker. In the generic case, there is very likely no prior relationship between the originator and the receiver, e.g. PSAP. A PSAP, for example, is likely to receive and accept alerts from entities it cannot authorize. This scenario corresponds more to the classical emergency services use case and the description in [I-D.ietf-ecrit-phonebcp] is applicable. Rosen, et al. Expires April 28, 2011 [Page 5] Internet-Draft Data-Only Emergency Alerts October 2010 +-----------+ +----------+ +--------+ | SIP Proxy | | PSAP as | | Sensor | | as Relay | | Receiver | +---+----+ +---+-------+ +---+------+ | | | Sensors | | trigger | | emergency | | alert | | | | | | | | | MESSAGE with CAP | | | (including Service URN, | | such as urn:service:sos) | |------------------->| | | | | | SIP Proxy performs | | emergency alert | | routing | | | MESSAGE with CAP | | | (including identity info) | | |----------------------------->| | | | | | PSAP | | processes | | emergency | | alert | | 200 (OK) | | |<-----------------------------| | | | | 200 (OK) | | |<-------------------| | | | | | | | Figure 2: Location-Based Emergency Alert Routing Rosen, et al. Expires April 28, 2011 [Page 6] Internet-Draft Data-Only Emergency Alerts October 2010 4. Protocol Specification 4.1. CAP Transport Since alerts structured via CAP require a "push" medium, they SHOULD be sent via the SIP MESSAGE. The MIME type is set to 'application/ common-alerting-protocol+xml'. Alternatively, the SIP PUBLISH mechanism or other SIP messages could be used. However, the usage of SIP MESSAGE is a simple enough approach from an implementation point of view. 4.2. Profiling of the CAP Document Content The usage of CAP MUST conform to the specification provided with [cap]. For the usage with SIP the following additional requirements are imposed: sender: When the CAP was created by a SIP-based entity then the element MUST be populated with the SIP URI of that entity. incidents: The element MUST be present whenever there is a possibility that alert information needs to be updated. The initial message will then contain an incident identifier carried in the element. This incident identifier MUST be chosen in such a way that it is unique for a given combination. Note that the element is optional and may not be present. scope: The value of the element MUST be set to "private" as the alert is not meant for public consumption. The element is, however, not used by this specification since the message routing is performed by SIP and the respective address information is already available in the geolocation header. Populating location information twice into different parts of the message can quickly lead to inconsistency. parameter: The element MAY contain additional information specific to the sensor. area: It is RECOMMENDED to omit this element when constructing a message. In case that the CAP message already contained an element then the specified location information MUST be copied into the PIDF-LO structure of the geolocation header element. Rosen, et al. Expires April 28, 2011 [Page 7] Internet-Draft Data-Only Emergency Alerts October 2010 5. Example Figure 3 shows a CAP document indicating a BURLARY alert issued by a sensor with the identity 'sensor1@domain.com'. The location of the sensor can be obtained from the attached geolocation information provided via the geolocation header contained in the SIP MESSAGE structure. Additionally, the sensor provided some data long with the alert message using proprietary information elements only to be processed by the receiver, a SIP entity acting as an aggregator. This example reflects the description in Figure 1. MESSAGE sip:aggregator@domain.com SIP/2.0 Via: SIP/2.0/TCP sensor1.domain.com;branch=z9hG4bK776sgdkse Max-Forwards: 70 From: sip:sensor1@domain.com;tag=49583 To: sip:aggregator@domain.com Call-ID: asd88asd77a@1.2.3.4 Geolocation: ;routing-allowed=yes Supported: geolocation Accept: application/pidf+xml, application/common-alerting-protocol+xml CSeq: 1 MESSAGE Content-Type: multipart/mixed; boundary=boundary1 Content-Length: ... --boundary1 Content-Type: common-alerting-protocol+xml Content-ID: S-1 sip:sensor1@domain.com 2008-11-19T14:57:00-07:00 Actual Alert Private abc1234 Security BURGLARY Expected Likely Moderate SENSOR 1 Rosen, et al. Expires April 28, 2011 [Page 8] Internet-Draft Data-Only Emergency Alerts October 2010 SENSOR-DATA-NAMESPACE1 123 SENSOR-DATA-NAMESPACE2 TRUE --boundary1 Content-Type: application/pidf+xml Content-ID: 32.86726 -97.16054 yes 2010-07-30T20:00:00Z 802.11 mac:1234567890ab 2010-07-28T20:57:29Z --boundary1-- Figure 3: Example Message conveying an Alert Rosen, et al. Expires April 28, 2011 [Page 9] Internet-Draft Data-Only Emergency Alerts October 2010 6. Security Considerations This section discusses security considerations when using SIP to make data-only emergency alerts utilizing CAP. Location specific threats are not unique to this document and the discussion in [I-D.ietf-ecrit-trustworthy-location]. 6.1. Forgery Threat: An adversary could forge or alter a CAP document to report false emergency alarms. Countermeasures: To avoid this kind of attack, the entities must assure that proper mechanisms for protecting the CAP documents are employed, e.g., signing the CAP document itself. Section 3.3.2.1 of [cap] specifies the signing of CAP documents. This does not protect against a legitimate sensor sending phrank alerts after being compromised. 6.2. Replay Attack Threat: An adversary could eavesdrop alerts and reply them at a later time. Countermeasures: A CAP document contains the mandatory , , elements and an optional element. These attributes make the CAP document unique for a specific sender and provide time restrictions. An entity that has received a CAP message already within the indicated timeframe is able to detect a replayed message and, if the content of that message is unchanged, then no additional security vulnerability is created. Additionally, it is RECOMMENDED to make use of SIP security mechanisms, such as SIP Identity [RFC4474], to tie the CAP message to the SIP message. Rosen, et al. Expires April 28, 2011 [Page 10] Internet-Draft Data-Only Emergency Alerts October 2010 6.3. Injecting False Alerts Threat: When an entity receives a CAP message it has to determine whether the entity distributing the CAP messages is genuine to avoid accepting messages that are injected by adversaries. In scenario Countermeasures: For some types of data-only emergency calls author/originator and the receiver/recipient have a relationship with each other and hence it is possible (using cryptographic techniques) to verify whether a message was indeed issued by an authorized entity. Figure 1 is such an environment. Standard SIP security mechanisms can be re-used for this purpose. For example, identity based access control is a viable approach utilizing the asserted identity of the alert originator using P-Asserted-Identity [RFC3325] or SIP Identity [RFC4474]. There are, however, other types of data-only emergency calls where there is no such relationship between the author/originator and the receiver/recipient. Incoming alerts need to be treated more carefully than multi-media emergency calls that contain additional information, such as audio, to allow a call taker to sort out phrank calls. Rosen, et al. Expires April 28, 2011 [Page 11] Internet-Draft Data-Only Emergency Alerts October 2010 7. IANA Considerations 7.1. Registration of the 'application/common-alerting-protocol+xml' MIME type To: ietf-types@iana.org Subject: Registration of MIME media type application/ common- alerting-protocol+xml MIME media type name: application MIME subtype name: common-alerting-protocol+xml Required parameters: (none) Optional parameters: charset; Indicates the character encoding of enclosed XML. Default is UTF-8 [RFC3629]. Encoding considerations: Uses XML, which can employ 8-bit characters, depending on the character encoding used. See RFC 3023 [RFC3023], Section 3.2. Security considerations: This content type is designed to carry payloads of the Common Alerting Protocol (CAP). Interoperability considerations: This content type provides a way to convey CAP payloads. Published specification: RFC XXX [Replace by the RFC number of this specification]. Applications which use this media type: Applications that convey alerts and warnings according to the CAP standard. Rosen, et al. Expires April 28, 2011 [Page 12] Internet-Draft Data-Only Emergency Alerts October 2010 Additional information: OASIS has published the Common Alerting Protocol at http://www.oasis-open.org/committees/ documents.php&wg_abbrev=emergency Person & email address to contact for further information: Hannes Tschofenig, Hannes.Tschofenig@nsn.com Intended usage: Limited use Author/Change controller: IETF SIPPING working group Other information: This media type is a specialization of application/xml RFC 3023 [RFC3023], and many of the considerations described there also apply to application/ common-alerting-protocol+xml. Rosen, et al. Expires April 28, 2011 [Page 13] Internet-Draft Data-Only Emergency Alerts October 2010 8. Acknowledgments The authors would like to thank the participants of the Early Warning adhoc meeting at IETF#69 for their feedback. Additionally, we would like to thank the members of the NENA Long Term Direction Working Group for their feedback. Rosen, et al. Expires April 28, 2011 [Page 14] Internet-Draft Data-Only Emergency Alerts October 2010 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997. [cap] Jones, E. and A. Botterell, "Common Alerting Protocol v. 1.1", October 2005. [RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [RFC3903] Niemi, A., "Session Initiation Protocol (SIP) Extension for Event State Publication", RFC 3903, October 2004. [RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC 3023, January 2001. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [I-D.ietf-ecrit-trustworthy-location] Tschofenig, H., Schulzrinne, H., and B. Aboba, "Trustworthy Location Information", draft-ietf-ecrit-trustworthy-location-01 (work in progress), October 2010. 9.2. Informative References [I-D.ietf-ecrit-phonebcp] Rosen, B. and J. Polk, "Best Current Practice for Communications Services in support of Emergency Calling", draft-ietf-ecrit-phonebcp-15 (work in progress), July 2010. [I-D.ietf-atoca-requirements] Schulzrinne, H., Norreys, S., Rosen, B., and H. Tschofenig, "Requirements, Terminology and Framework for Exigent Communications", draft-ietf-atoca-requirements-00 (work in progress), September 2010. [RFC4474] Peterson, J. and C. Jennings, "Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)", RFC 4474, August 2006. [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private Extensions to the Session Initiation Protocol (SIP) for Rosen, et al. Expires April 28, 2011 [Page 15] Internet-Draft Data-Only Emergency Alerts October 2010 Asserted Identity within Trusted Networks", RFC 3325, November 2002. Rosen, et al. Expires April 28, 2011 [Page 16] Internet-Draft Data-Only Emergency Alerts October 2010 Authors' Addresses Brian Rosen NeuStar, Inc. 470 Conrad Dr Mars, PA 16046 US Phone: Email: br@brianrosen.net Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027 US Phone: +1 212 939 7004 Email: hgs+ecrit@cs.columbia.edu URI: http://www.cs.columbia.edu Hannes Tschofenig Nokia Siemens Networks Linnoitustie 6 Espoo 02600 Finland Phone: +358 (50) 4871445 Email: Hannes.Tschofenig@gmx.net URI: http://www.tschofenig.priv.at Rosen, et al. Expires April 28, 2011 [Page 17]