ECRIT B. Rosen Internet-Draft NeuStar, Inc. Intended status: Experimental H. Schulzrinne Expires: April 22, 2010 Columbia U. H. Tschofenig Nokia Siemens Networks October 19, 2009 Common Alerting Protocol (CAP) based Data-Only Emergency Alerts using the Session Initiation Protocol (SIP) draft-rosen-ecrit-data-only-ea-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 22, 2010. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Rosen, et al. Expires April 22, 2010 [Page 1] Internet-Draft Data-Only Emergency Alerts October 2009 Abstract The Common Alerting Protocol (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 alerts allow to utilize the same CAP document format. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Architectural Overview . . . . . . . . . . . . . . . . . . . . 3 4. Protocol Specification . . . . . . . . . . . . . . . . . . . . 5 4.1. CAP Transport . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Profiling of the CAP Document Content . . . . . . . . . . 6 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6.1. Forgery . . . . . . . . . . . . . . . . . . . . . . . . . 7 6.2. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 8 6.3. Injecting False Alerts . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7.1. Registration of the 'application/common-alerting-protocol+xml' MIME type . . . 9 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 9.1. Normative References . . . . . . . . . . . . . . . . . . . 10 9.2. Informative References . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Rosen, et al. Expires April 22, 2010 [Page 2] Internet-Draft Data-Only Emergency Alerts October 2009 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 may be similar to regular emergency calls in the sense that they have the same emergency call routing and location requirements; they do, however, not lead to the establishment of a voice channel. There are, however, data-only emergency alerts that are targeted directly to a dedicated entity responsible for evaluating the alerts and for taking the necessary steps, including triggering an emergency call towards a Public Safety Answering Point (PSAP). 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. Architectural Overview This section illustrates two envisioned usage modes; targeted and location-based emergency alert routing. Figure 1 shows a deployment variant where a device is pre-configured (using techniques outside the scope of this document) to issue an alert to an aggregator that processes these messages and performs whatever steps are necessary to appropriately react on the alert. In many cases the device has the address of the aggregator pre-configured and corresponding security mechanisms are in place to ensure that only alert from authorized devices are processed. Rosen, et al. Expires April 22, 2010 [Page 3] Internet-Draft Data-Only Emergency Alerts October 2009 +--------+ +------------+ | Device | | 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 this case the device issuing the alert may not know the message recipient (in case the LoST resolution is done at an emergency services routing proxy rather than at the end host). In any case, a trust relationship between the alert-issuing device and the PSAP cannot be assumed, i.e., the PSAP is likely to receive alerts from entities it cannot authorize. This scenario corresponds more to the classical emergency services classical and the description in [I-D.ietf-ecrit-phonebcp] is applicable. Rosen, et al. Expires April 22, 2010 [Page 4] Internet-Draft Data-Only Emergency Alerts October 2009 +-------+ +--------+ | SIP | +------+ | Device | | Proxy | | PSAP | +---+----+ +---+---+ +---+--+ | | | 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 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'. Rosen, et al. Expires April 22, 2010 [Page 5] Internet-Draft Data-Only Emergency Alerts October 2009 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 sender / expires combination. scope: The value of the element MUST be set to private as the alert is not meant for public consumption. parameter: The element MAY contain additional information specific to the sensor. area: For geodetic information the polygon and circle location shapes are available. The ability to conveying a structured format of civic location information is missing and hence civic information is encoded as a text string in the element. [Editor's Note: The usage of a number of CAP elements is unclear and/or insufficient and requires further discussion with the authors of the CAP specification. Based on the outcome of these discussions more fields might require profiling.] 5. Example Figure 3 shows a CAP document indicating a BURLARY alert issued by sensor1@example.com indicating that the alert was issued from the civic address NATURAL HISTORY MUSEUM, BURGRING 7, 1010 VIENNA, AUSTRIA. Additionally, the sensor provided some additional data long with the alert message using non-standardized information elements. Rosen, et al. Expires April 22, 2010 [Page 6] Internet-Draft Data-Only Emergency Alerts October 2009 S-1 sensor1@example.com 2008-11-19T14:57:00-07:00 Actual Alert Private abc1234 Security BURGLARY Expected Likely Moderate SENSOR 1 NATURAL HISTORY MUSEUM, BURGRING 7, 1010 VIENNA, AUSTRIA SENSOR-DATA-NAMESPACE1 123 SENSOR-DATA-NAMESPACE2 TRUE Figure 3: Example for an alert triggered by a sensor 6. Security Considerations This section discusses security considerations when using SIP to make data-only emergency alerts utilizing CAP. 6.1. Forgery Threat: An adversary could forge or alter a CAP document to report false emergency alarms. Rosen, et al. Expires April 22, 2010 [Page 7] Internet-Draft Data-Only Emergency Alerts October 2009 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: Theft of CAP documents described in this document and replay of it 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, to tie the CAP message to the SIP message. 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. Countermeasures: For some types of data-only emergency calls the entity issuing the alert and the entity consuming the alert have a relationship with each other and hence it is possible (using cryptographic authentication ) to verify whether a message was indeed issued by an authorized entity. There are, however, other types of data- only emergency calls where there is no such relationship between the sender and the consumer. In that case incoming alerts need to be treated more carefully, as the possibilities to place phrank calls are higher than with regular emergency calls that at least Rosen, et al. Expires April 22, 2010 [Page 8] Internet-Draft Data-Only Emergency Alerts October 2009 setup an audio channel. 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. 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 Rosen, et al. Expires April 22, 2010 [Page 9] Internet-Draft Data-Only Emergency Alerts October 2009 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. 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. 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. 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-13 (work in progress), July 2009. Rosen, et al. Expires April 22, 2010 [Page 10] Internet-Draft Data-Only Emergency Alerts October 2009 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 22, 2010 [Page 11]