Securing Software Architectures for Trusted Processor Environments

Jan-Erik Ekberg

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    Processor hardware support for security dates back to the 1970s, and such features were then primarily used for hardening operating systems. This idea has re-emerged as hardware security features in contemporary cost-efficient mobile processors. These support specific operating-system functionality such as communication stack isolation and identity binding, which are needed on mobile devices to satisfy regulatory requirements for e.g. cellular phones. This thesis builds on these hardware security features to implement a generic trusted execution environment (TEE) that can be used for a larger variety of applications. We present software building blocks and infrastructure for isolated trustworthy execution on these hardware environments. The goal is to achieve the same level of isolation as in smart cards or trusted platform modules implemented as separate integrated circuits. The thesis contributes to the state of the art in several ways: We present mechanisms for isolated piecemeal execution of code and processing of data in these very memory-constrained hardware environments. Isolation, freshness and data commit guarantees are provided by cryptographic means. We present security proofs for selected cryptographic primitives used in this hardware context. The thesis also improves on the integrity guarantees of contemporary processor support by implementing rollback protection even when the device is powered down. This is done by combining the security functionality of the processor with auxilliary hardware and firmware logic. We advance the understanding of trusted execution by describing a minimal set of hardware trust roots needed to implement an engine for isolated execution. Ideally, advancement of computer science can be translated into implementable designs with real-world impact. The mechanims presented in this thesis were implemented and deployed in the On-board Credentials (ObC) architecture, and partly standardized as features for the Mobile Trusted Module (MTM). These technologies enable implementation of isolated execution at significant cost savings compared to the deployment of discrete hardware components. The MTM specification, co-designed by the author, is the first global security standard that provides an adaptation to processor hardware mechanisms for isolated execution. The TEE part of On-board Credentials, designed and implemented by the author, is deployed in more than 100 million devices in the field, and has already been used in several public trials and demonstrations of end-user applications. Both ObC and MTM rely on the results of this thesis research.
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Aura, Tuomas, Supervisor
    • Asokan, N., Advisor
    Publisher
    Print ISBNs978-952-60-5149-9
    Electronic ISBNs978-952-60-3632-8
    Publication statusPublished - 2013
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • platform security
    • cryptography

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