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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

5

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”