Trusted and Privacy-preserving Embedded Systems: Advances in Design, Analysis and Application of Lightweight Privacy-preserving Authentication and Physical Security Primitives

Radio Frequency Identification (RFID) enables RFID readers to perform fully automatic wireless identification of objects labeled with RFID tags and is widely deployed to many applications, such as access control, electronic tickets and payment as well as electronic passports. This prevalence of RFID technology introduces various risks, in particular concerning the privacy of its users and holders. Despite the privacy risk, classical threats to authentication and identification systems must be considered to prevent the adversary from impersonating or copying (cloning) a tag. This thesis summarizes the state of the art in secure and privacy-preserving authentication for RFID tags with a particular focus on solutions based on Physically Unclonable Functions (PUFs). It presents advancements in the design, analysis and evaluation of secure and privacy-preserving authentication protocols for RFID systems and PUFs. Formalizing the security and privacy requirements on RFID systems is essential for the design of provably secure and privacy-preserving RFID protocols. However, existing RFID security and privacy models in the literature are often incomparable and in part do not reflect the capabilities of real-world adversaries. We investigate subtle issues such as tag corruption aspects that lead to the impossibility of achieving both mutual authentication and any reasonable notion of privacy in one of the most comprehensive security and privacy models, which is the basis of many subsequent works. Our results led to the refinement of this privacy model and were considered in subsequent works on privacy-preserving RFID systems. A promising approach to enhance the privacy in RFID systems without lifting the computational requirements on the tags are anonymizers. These are special devices that take off the computational workload from the tags. While existing anonymizer-based protocols are subject to impersonation and denial-of-service attacks, existing RFID security and privacy models do not include anonymizers. We present the first security and privacy framework for anonymizer-enabled RFID systems and two privacy-preserving RFID authentication schemes using anonymizers. Both schemes achieve several appealing features that were not simultaneously achieved by any previous proposal. The first protocol is very efficient for all involved entities, achieves privacy under tag corruption. It is secure against impersonation attacks and forgeries even if the adversary can corrupt the anonymizers. The second scheme provides for the first time anonymity and untraceability of tags against readers as well as secure tag authentication against collisions of malicious readers and anonymizers using tags that cannot perform public-key cryptography (i.e., modular exponentiations). The RFID tags commonly used in practice are cost-efficient tokens without expensive hardware protection mechanisms. Physically Unclonable Functions (PUFs) promise to provide an effective security mechanism for RFID tags to protect against basic hardware attacks. However, existing PUF-based RFID authentication schemes are not scalable, allow only for a limited number of authentications and are subject to replay, denial-of-service and emulation attacks. We present two scalable PUF-based authentication schemes that overcome these problems. The first protocol supports tag and reader authentication, is resistant to emulation attacks and highly scalable. The second protocol uses a PUF-based key storage and addresses an open question on the feasibility of destructive privacy, i.e., the privacy of tags that are destroyed during tag corruption. The security of PUFs relies on assumptions on physical properties and is still under investigation. PUF evaluation results in the literature are difficult to compare due to varying test conditions and different analysis methods. We present the first large-scale security analysis of ASIC implementations of the five most popular electronic PUF types, including Arbiter, Ring Oscillator, SRAM, Flip-Flop and Latch PUFs. We present a new PUF evaluation methodology that allows a more precise assessment of the unpredictability properties than previous approaches and we quantify the most important properties of PUFs for their use in cryptographic schemes. PUFs have been proposed for various applications, including anti-counterfeiting and authentication schemes. However, only rudimentary PUF security models exist, limiting the confidence in the security claims of PUF-based security mechanisms. We present a formal security framework for PUF-based primitives, which has been used in subsequent works to capture the properties of image-based PUFs and in the design of anti-counterfeiting mechanisms and physical hash functions

SmartTokens: Delegable Access Control with NFC-enabled Smartphones (Full Version)

Today\u27s smartphones and tablets offer compelling computing and storage capabilities enabling a variety of mobile applications with rich functionality. The integration of new interfaces, in particular near field communication~(NFC) opens new opportunities for new applications and business models, as the most recent trend in industry for payment and ticketing shows. These applications require storing and processing security-critical data on smartphones, making them attractive targets for a variety of attacks. The state of the art to enhance platform security concerns outsourcing security-critical computations to hardware-isolated Trusted Execution Environments~(TrEE). However, since these TrEEs are used by software running in commodity operating systems, malware could impersonate the software and use the TrEE in an unintended way. Further, existing NFC-based access control solutions for smartphones are either not public or based on strong assumptions that are hard to achieve in practice. We present the design and implementation of a generic access control system for NFC-enabled smartphones based on a multi-level security architecture for smartphones. Our solution allows users to delegate their access rights and addresses the bandwidth constraints of NFC. Our prototype captures electronic access to facilities, such as entrances and offices, and binds NFC operations to a software-isolated TrEE established on the widely used Android smartphone operating system. We provide a formal security analysis of our protocols and evaluated the performance of our solution

PUFs: Myth, Fact or Busted? A Security Evaluation of Physically Unclonable Functions (PUFs) Cast in Silicon (Extended Version)

Physically Unclonable Functions~(PUFs) are an emerging technology and have been proposed as central building blocks in a variety of cryptographic protocols and security architectures. However, the security features of PUFs are still under investigation: Evaluation results in the literature are difficult to compare due to varying test conditions, different analysis methods and the fact that representative data sets are publicly unavailable. In this paper, we present the first large-scale security analysis of ASIC implementations of the five most popular intrinsic electronic PUF types, including arbiter, ring oscillator, SRAM, flip-flop and latch PUFs. Our analysis is based on PUF data obtained at different operating conditions from $96$ ASICs housing multiple PUF instances, which have been manufactured in TSMC 65nm CMOS technology. In this context, we present an evaluation methodology and quantify the robustness and unpredictability properties of PUFs. Since all PUFs have been implemented in the same ASIC and analyzed with the same evaluation methodology, our results allow for the first time a fair comparison of their properties

Influence of patient and tumor characteristics on therapy persistence with letrozole in postmenopausal women with advanced breast cancer: results of the prospective observational EvAluate-TM study

Background: Treatment of postmenopausal, hormone receptor-positive metastatic breast cancer (MBC) patients varies despite clear therapy guidelines, favoring endocrine treatment (ET). Aim of this study was to analyze persistence of palliative aromatase inhibitor (AI) monotherapy in MBC patients. Methods: EvAluate-TM is a prospective, multicenter, noninterventional study to evaluate treatment with letrozole in postmenopausal women with hormone receptor–positive breast cancer. To assess therapy persistence, defined as the time from therapy start to the end of the therapy (TTEOT), two pre-specified study visits took place after 6 and 12 months. Competing risk survival analyses were performed to identify patient and tumor characteristics that predict TTEOT. Results: Out of 200 patients, 66 patients terminated treatment prematurely, 26 (13%) of them due to causes other than disease progression. Persistence rate for reasons other than progression at 12 months was 77.7%. Persistence was lower in patients who reported any adverse event (AE) in the first 30 days of ET (89.5% with no AE and 56% with AE). Furthermore, patients had a lower persistence if they reported compliance problems in the past before letrozole treatment. Conclusions: Despite suffering from a life-threatening disease, AEs of an AI will result in a relevant number of treatment terminations that are not related to progression. Some subgroups of patients have very low persistence rates. Especially with regard to novel endocrine combination therapies, these data imply that some groups of patients will need special attention to guide them through the therapy process. Trial registration Clinical Trials Number: CFEM345DDE1