Agenda

Establishing and Maintaining Root of Trust on Commodity Computer Systems [PDF]
Suppose that a trustworthy program must be booted on a commodity system that may contain persistent malware. Establishing root of trust (RoT) assures the system has all and only the content chosen by a trusted verifier or the verifier discovers unaccounted content, with high probability. Hence, RoT establishment assures that verifiable boot takes place in a malware-free state, whp. Obtaining such an assurance is challenging because malware can survive in system states across repeated secure- and trusted-boot operations and act on behalf of a powerful remote adversary; e.g., anti-malware tools do not have malware-unmediated access to device controllers’ processors and memories nor prevent remote malware connections over the internet. I this presentation, I will illustrate both the theoretical and practical challenges of RoT establishment unconditionally; i.e., without secrets, privileged modules (e.g., TPMs, RoMs, HSMs), or adversary computation bounds. I will also illustrate the only unconditional solution to these challenges known in security or cryptography known to date.

Establishing root of trust is important because makes all persistent malware ephemeral and forces the adversary to repeat the malware-insertion attack, perhaps at some added cost. Nevertheless, some malware-controlled software can always be assumed to exist in commodity operating systems and applications. The inherent size and complexity of their components (aka the “giants”) render them vulnerable to successful attacks. In contrast, small and simple software components with rather limited function and high-assurance layered security properties (aka the “wimps”) can, in principle, be resistant to all attacks. Maintaining root of trust assures a user that a commodity computer’s wimps are isolated from, and safely co-exist with, adversary-controlled giants. However, regardless how secure program isolation may be (e.g., based on Intel’s SGX), I/O channel isolation must also be achieved despite the pitfalls of commodity architectures that encourage I/O hardware sharing, not isolation. In this presentation, I will also illustrate the challenges of I/O channel isolation and present and approach that enables the co-existence secure wimps with insecure giants, via an example of an experimental system; i.e., on-demand isolated I/O channels, which were designed and implemented at CMU’s CyLab.