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CSE Colloquium Series: Ninghui Li

CSE Colloquium Series

How to make Discretionary Access Control Resistant to Trojan Horses?

Dr. Ninghui Li

Purdue University

Friday, April 4, 2008
Talk: 11:00 am - 12:00 pm
3105 Engineering

Host: Alex Liu


Modern operating systems primarily use Discretionary Access Control (DAC) to protect files and other operating system resources. DAC mechanisms are more user-friendly than Mandatory Access Control (MAC) systems, but are vulnerable to Trojan horse attacks and attacks exploiting buggy software.

We show that it is possible to have the best of both worlds: DAC's easy-to-use discretionary policy specification and MAC's defense against Trojan horses and buggy programs. This is made possible by a key new insight that DAC has this weakness not because it uses the discretionary principle, but because existing DAC enforcement mechanisms assume that a single principal is responsible for any request, whereas in reality a request may be influenced by multiple principals; thus these mechanisms cannot correctly identify the true origin(s) of a request and fall prey to Trojan horses.

We propose to solve this problem by combining DAC's policy specification with new enforcement techniques that use ideas from MAC's information flow tracking. Our model, called Information Flow Enhanced Discretionary Access Control (IFEDAC), is the first DAC model that can defend against Trojan horses and attacks exploiting buggy software. IFEDAC significantly strengthens end host security, while preserving to a large degree DAC's ease of use. In this talk, we present the IFEDAC model, analyze its security properties, and discuss our design and implementation for Linux.


Ninghui Li is an Assistant Professor of Computer Science at Purdue University, where he joined in 2003. He received a Bachelor’s degree from the University of Science and Technology of China in 1993 and a Ph.D. in Computer Science from New York University in 2000.Before joining Purdue, he was a Research Associate at Stanford University Computer Science Department for 3 years.Prof. Li's research interests include access control, data privacy, and applied cryptography.He has published over 60 refereed papers in conference proceedings and journals, and has served on the Program Committees of more than three dozen international conferences and workshops.In 2005, he was awarded the NSF CAREER award for proposed work on "Access Control Policy Verification Through Security Analysis And Insider Threat Assessment".