Supporting Software-based TPM Emulator in ARM Virtualization Environment

Abstract

As mobile technology matures, mobile devices (principally smart phones and tablets) are increasingly being used in both personal and corporate environments. While mobile devices bring great convenience to us, security problems also ensue. Current mobile devices lack the hardware-based root of trust features (e.g., Trusted PlatformModule, or TPM) that are increasingly built into laptops, PCs and other types of hosts. Unfortunately, mobile devices are constrained in space, cost and power dimensions that make the use of a discrete TPM difficult. Since a software-based TPM emulator can provide the same capabilities of a hardware TPM in terms of TPM Commands, thus, if 1) the roots of trust of the TPM emulator can be securely handled, 2) an isolated secure environment can be provisioned in the mobile device, be it software environment or hardware environment, without the presence of a hardware TPM, the approximate same capabilities of a hardware TPM can be obtained by running a software-based TPM emulator in the said secure environment. In this thesis, we assume the roots of trust of a software-based TPM emulator are securely handled. However, even with the above assumption, how to provision the isolated secure environment is still a challenging task.In this thesis, three approaches are proposed in the context of ARM virtualization environment, i.e., Linux Container (LXC)-based Approach, Virtual Machine (VM)-based Approach, and Firmware TPM (which is based on TrustZone Virtualization). LXC-based approach uses a LXC to protect the software-based TPM emulator, and VM-based approach uses a VM

these two approaches were implemented and evaluated. Firmware TPM refers to the alternate software implementation of the TPM specification in the context of a Trusted Execution Environment

the proposed reference architecture for Firmware TPM is given in the thesis, but its implementation is left as future work in that this approach requires far more programming effort than a master’s thesis project.The evaluation result showed that the software-based TPM emulator can provide the same capabilities of a hardware TPM provided that 1) the roots of trust of the emulator are securely handled, 2) the proposed secure environments (Linux Container or VM) are secure enough. Though the addition of a software-based TPM Emulator on a mobile device incurs some overhead on the system, the overhead is acceptable for modern mobile devices, which typically shipped with more than 1GB memory and 1GHZ or faster CPUs.In the last, recommended optimizations for current work are provided, along with considerations on future implementation of Firmware TPM.