Trojan Horse Resistant Discretionary Access Control

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. The authors 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.