# simTPM: User-centric TPM for Mobile Devices (Technical Report)

## TL;DR

simTPM introduces a novel, user-centric Trusted Platform Module implementation leveraging SIM cards in mobile devices, addressing resource constraints and integration challenges, and demonstrating competitive performance with existing TPM solutions.

## Contribution

This work presents the first implementation of a mobile TPM based on SIM cards, integrating it into the secure boot process and addressing binding to the device's root of trust.

## Key findings

- simTPM is feasible within resource-constrained SIM environments
- It can be integrated into the secure boot chain of mobile devices
- Performance benchmarks show simTPM is competitive with existing TPM solutions

## Abstract

Trusted Platform Modules are valuable building blocks for security solutions and have also been recognized as beneficial for security on mobile platforms, like smartphones and tablets. However, strict space, cost, and power constraints of mobile devices prohibit an implementation as dedicated on-board chip and the incumbent implementations are software TPMs protected by Trusted Execution Environments. In this paper, we present simTPM, an alternative implementation of a mobile TPM based on the SIM card available in mobile platforms. We solve the technical challenge of implementing a TPM2.0 in the resource-constrained SIM card environment and integrate our simTPM into the secure boot chain of the ARM Trusted Firmware on a HiKey960 reference board. Most notably, we address the challenge of how a removable TPM can be bound to the host device's root of trust for measurement. As such, our solution not only provides a mobile TPM that avoids additional hardware while using a dedicated, strongly protected environment, but also offers promising synergies with co-existing TEE-based TPMs. In particular, simTPM offers a user-centric trusted module. Using performance benchmarks, we show that our simTPM has competitive speed with a reported TEE-based TPM and a hardware-based TPM.