Date post: | 13-Jan-2016 |
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Emergency Alerts as RSS Feeds with Interdomain
Authorization
Filippo Gioachin1, Ravinder Shankesi1, Michael J. May1,2, Carl A. Gunter1, Wook Shin1
1 University of Illinois Urbana-Champaign2 University of Pennsylvania
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Emergency Messaging• Emergency messaging has requirements we see
in other contexts as well• Scalability• Timeliness• Targeted delivery
• Public health emergency messaging has additional requirements
• Sender integrity and authentication• Message integrity• Recipient integrity and authentication• Wide scale distribution with targeted delivery
• We need interdomain messaging with multiple levels of authentication
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Emergency Messaging
4
Emergency Messaging
auth
alerts
alerts
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Emergency Messaging
alerts
•Roles•Permission•Location•Employer•Specialty
•Policies for permissions•Access Control Lists
•Alert policies•Permissions•Scope•Location
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Emergency Messaging
alerts
auth
token
tokenAlerts summary
• Attribute based policies
• Summaries
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Our approach
• Leverage existing technologies for a scalable interdomain authentication and authorization system
• Rights as user attributes• Policies given in terms of attributes• Interdomain federation and trust between state
authorities and local organizations
• Alerts as messages with policies• Policies based on CDC standardized messaging format• Policies defined by CDC, enforced by states
• Alerts provided as summaries• Natural mechanism for regularly updating and dynamic
content
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Our approach
• Shibboleth attribute based authentication• SAML token based• Users authenticate to a local Identity Provider
(IdP) which provides a signed attribute cookie• Users use the cookie to authenticate to the
service provider• RSS based message feeds
• XML based message summary format• Widely deployed mechanism for distributing
links to dynamically updated content• SSL encryption between nodes• Result: Shibboleth RSS
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Contributions
• Architecture and implementation of Shibboleth RSS
• Application to standards based messaging formats
• Scalability and performance estimates from experiments
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Design Considerations
• What attributes to consider?• Attributes from CDC message format - Common Alerting
Protocol (CAP) and Public Health Directory Schema (PHINDir)
• What workload to put on server and client?• RSS from CAP on the server• RSS to HTML done on client• Custom user filtering done with JavaScript on client
• How to design policies?• Forcing redesign of policies are a burden on alert
authors• Generic policies will match most messages and speed
policy filtering• Custom policies can be attached if desired
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Policy Evaluation
• System architect predefines common policies• Policy names are associated with each alert
• Policies need to be evaluated only once per request• User attributes compared once against existing
policies and stored for later use
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High Level Architecture
1 Req
1: Redirect
IdentityProvider
Public HealthDirectory
2: Auth
3 4
5: Token
Alert Filter
Alert Database
Policies
Alerts to RSS6
5
7: Alerts
8: RSS
8: RSS
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Performance Evaluation• Vary the number of policies and number of alerts
• Alerts• Small = 128 Kb (54 infos in 15 alerts) • Big = 512 Kb (216 infos in 60 alerts)
• Policies• Few = 10 rules• Many = 50 rules
• Critical operations• SSL tunnel establishment• PHP web page processing• Policy evaluation• Message filtering based on policy• Summarizing messages in RSS• Transforming RSS to HTML for viewing
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Performance Evaluation
Dow
nloads per second
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Performance Evaluation
• Optimizations:• CAP to RSS feed format• Cached policies per
user• Searched for all policies
at once
• Results:• SSL the biggest
performance hit• Size of the input
matters, not number of policies
Dow
nloads per
second
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Conclusion
• Shibboleth RSS offers a scalable method for interdomain emergency alerts• Attributes let us define policies• RSS lets us summarize policies for reading
• Performance penalty reasonable after SSL• About 45% - 60% throughput
• Federated trust makes interdomain messaging practical
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References
• Illinois Security Lab• http://seclab.uiuc.edu
• Shibboleth RSS Project• http://seclab.uiuc.edu/securerss
• Demo video• http://seclab.uiuc.edu/resources/shibbol
ethRSSDemo.html
• Or Google “Shibboleth RSS”