Hardware assisted control flow obfuscation for embedded processors

Abstract

With more applications being deployed on embedded platforms, software protection becomes increasingly important. This problem is crucial on embedded systems like financial transaction terminals, pay-TV access-control decoders, where adversaries may easily gain full physical accesses to the systems and critical algorithms must be protected from being cracked. However, as this paper points out that protecting software with either encryption or obfuscation cannot completely preclude the control flow information from being leaked. Encryption has been widely studied and employed as a traditional approach for software protection, however, the control flow information is not 100% hidden with solely encrypting the code. On the other hand, pure software-based obfuscation has been proved inefficient to protect software due to its lack of theoretical foundation and considerable performance overhead introduced by complicated transformations. Moreover, even though obfuscation can prevent static reverse engineering, attacker can still successfully bypass the obfuscation by monitoring the dynamic program execution.To address all of these shortcomings, this paper presents a hardware assisted obfuscation technique that is capable of obfuscating the control flow information dynamically. Dynamic obfuscation changes memory access sequence on-the-fly and conceals recurrent instruction access sequences from being identified. Our scheme makes it provably difficult for the attacker to extract any useful information. Our results show that a high-level security protection is possible with only minor performance penalty. Finally, we show that our scheme can be implemented on embedded systems with very little hardware overhead.