Publish-Subscribe Systems and

Confidentiality/Privacy

Nabeel Mohamed

nabeel@cs.purdue.edu

4/4/08

Outline

• Different Publish-Subscribe Systems

• Security Issues and Possible Directions

(Confidentiality/Privacy)

Publish/Subscribe

Publisher

Publisher

Publisher

SubscriberNotify()

SubscriberNotify()

SubscriberNotify()

Distributed

Subscription

Mgmt and Routing

Distributed

Content Routers

Notify()

Subscribe()

Unsubscribe()

publish

publish

notify

subscribe

unsubscribe

General Properties of Pub-Sub

• Many-to-Many structured P2P system

• Loosely coupled form of interaction

– Space decoupling

– Time decoupling

– Synchronization decoupling

References: [1]

Filtering

• Topic-based

• Content-based

• Type-based

• Structure-based

Filtering: Topic-based

• Events are grouped into channels

• Each channel is identified by a keyword

• Publisher publishes each event to a specific channel

• Subscribers subscribe to channels they are interested in

• Simplest scheme of matching events to subscribers

• Example: Disseminating Trades and Quotes in two channels

Filtering: Content-based

• More expressive power to subscribers

than topic-based

• Can be used for fine-grained access

control as well

• Added complexity of matching an event to

a subscription

• Example: Notify me of all quotes for

Google with bid_price >= 400

Filtering: Type-based

• Relate event kind to event type

• Closer integration of the language and the middleware

• Allows for compile-time type safety checks

• Match events to subscriptions by their types (and further to members of these types)

• Example: StockQuote and StockTrade are sub-types of Stock. Public members of these event types can be used to do content-based filtering while ensuring encapsulation.

References: [8]

Filtering: Structure-based

• First three filtering methods

– Many documents to many subscribers

• Structure-based routing address a

different data dissemination problem

– Different parts of one document to many

subscribers

• Only for hierarchically structured data

References: [7]

Streaming Systems

• Special kind of pub-sub systems

• Usually have stringent timing, storage and

performance requirements

• Database community (DSMS) to

Distributed systems

Next

• Different Publish-Subscribe Systems

• Security Issues and Possible Directions

(Confidentiality/Privacy)

Generic Issues

• Authentication

• Integrity

– Information Integrity

– Subscription Integrity

– Service Integrity

• User Anonymity

– Onion routing

• Accountability

• Availability

Confidentiality/Privacy

• Information Confidentiality

– Can we perform content-based routing without

revealing the content to the infrastructure?

• Subscription Privacy

– Can subscribers specify filters without revealing

their interest to the infrastructure?

• Publication Confidentiality

– How can publishers be sure that only the

intended subscribers get the data?

References: [2]

Information Confidentiality

• Out-of-band key agreement issue

– Attribute-based encryption [11]

• Conflicting goals of keeping information

secret and content-based routing

– Computing with the encrypted/perturbed data

• Feigenbaum and Abadi et. al. [3]

• Agrawal et. al. [4]

Subscription Privacy

• Examples

– Trading preferences

– Resume service

• No node in the infrastructure should be able

to infer about data items retrieved by users

– Secure multiparty computations (E.g.:

Millionaires‘ problem. A. Yao [6])

– Database research in private information retrieval

(E.g.: O. Goldreich et. al. [5])

Publication Confidentiality

• Application of access control

• Information leakage issue

• Most of the research on confidentiality has

been done in this area

• Out-of-band key agreement issue

• Some solutions trust users to get over the

issue of key agreement

Issues due to Optimization

• Bandwidth minimization [9]

• Coping with limited storage

– Digests

• Regulating high input/output rates

• Continuous security enforcement as

opposed to one time [10]

• Different data representations

References

[1] The Many Faces of Publish/Subscribe, Patrick Eugster, Pascal Felber, Rachid Guerraoui, 2003

[2] Security Issues and Requirements for Internet-Scale Publish-Subscribe Systems Chenxi Wang, Antonio Carzaniga,

David Evans, Alexander Wolf, 2002

[3] On Hiding Information from an Oracle, Martin Abadi, Joan Feigenbaum, Joe Kilian, 1987

[4] Order Preserving Encryption for Numerical Data, Rakesh Agrawal, Jerry Kiernan, Ramakrishnan Srikant, Yirong

Xu, 2004

[5] Private Information Retrival, B. Chor, O. Goldreich, E. Kushilevitz, M. Sudan, 1998

[6] Protocols for Secure Compuations, Andrew C. Yao, 1982

[7] Secure Dissemination of XML Content Using Structure-based Routing, A. Kundu, E. Bertino, 2006

[8] On Objects and Events, P. Eugster, R. Guerraoui, C. Damm, 2001.

[9] Secure Delta-Publishing of XML Content , Mohamed Nabeel, Elisa Bertino, 2008

[10] Security Punctuation Framework for Enforcing Access Control on Streaming Data, Rimma V. Nehme, Elke A.

Rundensteiner and Elisa Bertino, 2008

[11] Secure Attribute-Based Systems, M. Pirretti, P. Traynor, P. McDaniel, B. Waters, 2006