Tactile sensors play a key role in human-machine interaction (HMI), providing essential tactile measurement capabilities for this field, where their performance directly determines the operational safety and haptic quality of HMI machines. When tactile sensors are applied to human or machine surfaces, their ability to fit comfortably and conform to the curves of the body is a significant challenge to address. Existing stretchable and flexible sensors show excellent adaptive conformability and accuracy. Yet, their fabrication methods usually rely on expensive and specialised equipment and are not accessible to many researchers from the interdisciplinary field of human-computer interaction to implement, customize and deploy. To address this problem, this paper proposes a stretchable pressure sensor of low-cost and fabrication complexity, drawing inspiration from the ancient paper-cutting art of Kirigami. The developed prototype is experimentally tested for its ability to conform to the human body, while being characterized by a high force-detection accuracy, with an average error of 4% in the range of 0 – 1000 g per cell), and the sampling electronics of it has demonstrated effective crosstalk elimination function. The proposed approach also serves as a methodology for rapid fabrication of flexible electronic devices, enabling high-precision continuous force monitoring across both preloaded (e.g., sitting/lying postures) and non-preloaded scenarios (e.g. contact detection).

In this work, we present polar code designs that offer a provably optimal solution for biometric identification and authentication systems under noisy enrollment for certain sources and observation channels. We consider a discrete memoryless biometric source and discrete symmetric memoryless observation channels. It is shown that the proposed polar code designs achieve the fundamental limits with privacy and secrecy constraints. Depending on how the secret keys are extracted and whether the privacy leakage rate should be close to zero, we consider four related setups, which are (i) the generated secret key system, (ii) the chosen secret key system, (iii) the generated secret key system with zero leakage, and (iv) the chosen secret key system with zero leakage. For the first two setups, (i) and (ii), the privacy level is characterized by the privacy leakage rate. For the last two setups (iii) and (iv), private keys are additionally employed to achieve close to zero privacy leakage rate. In setups (i) and (iii), it is assumed that the secret keys are generated, i.e., extracted from biometric information. While in setups (ii) and (iv), secret keys provided to the system are chosen uniformly at random from some trustful source. This work provides the first examples of fundamental limits-achieving code designs for identification and authentication. Moreover, since the code designs are based on polar codes and many existing works study low-complexity and short block-length polar coding, the proposed code designs in this work provide the code design structure and a framework for the application of biometric identification and authentication.

Nowadays, biometrics are more and more deployed to reinforce traditional authentication or identification that uses keys, passwords, etc. Biometric identification and authentication have been studied from various information-theoretic perspectives, where privacy and secrecy are two important aspects. Due to the uniqueness of biometrics, the abuse of biometric information can invoke privacy issues. Moreover, for authentication based on secret keys, compromised secret keys can lead to compromised access to the system.  In this thesis, we deepen the study of the privacy and secrecy perspectives, characterize fundamental limits, and propose fundamental limits-achieving polar code designs.

Based on the basic biometric identification and authentication system, we study five extensions: (i) noisy enrollment and privacy-preservation, where inevitable noise when enrolling in biometrics is incorporated; (ii) two-stage setting with privacy preservation, where both the enrollment phase and the identification phase are operated in two steps; (iii) multiple systems setting, where the biometric information of users is used in multiple systems; (iv) uncertainty setting, where two uncertainty aspects are considered, i.e., the probability mass function of users’ biometric information and the observation channel; (v) polar code designs, where fundamental limits-achieving polar code designs are derived. To preserve privacy, we propose to include additional private keys. The results reveal how the private keys can be efficiently utilized. For the two-stage setting, two layers of help data are produced in the enrollment phase. Then in the identification and authentication phase, the observed user is first processed with the first layer helper data and the system outputs a list. Then the system only processes the observation with part of the users in the system, thus the exhaustive search can be avoided. In the multiple systems setting, it is allowed to reuse the public data and thus achieves a more efficient design. Moreover, depending on whether the systems are built together at once or new systems are built based on the legacy system, we study both the joint design and the incremental design. For the polar code designs, we consider a setting where the privacy preservation level can be adapted by adapting the size of the private key. For both the uncertainty setting and the polar code designs, strong secrecy is achieved, which is more stringent than the weak secrecy requirement considered in the other settings. 

These five studied settings generalize the known setting studied in the literature. As corollaries or remarks, we provide the characterizations for related problems. The extensions reduce the gap between the models and real biometric systems. The obtained results provide a guideline for the design of biometric identification and authentication systems. 

Nuförtiden används biometri mer och mer för att förstärka traditionell autentisering eller identifiering som använder nycklar, lösenord etc. Biometrisk identifiering och autentisering har studerats ur olika informationsteoretiska perspektiv, där integritet och sekretess är två viktiga aspekter. På grund av den unika med biometriska data kan missbruk av biometrisk information åberopa integritetsproblem. Vid användning av nycklar i autentisering kan komprometterade nycklar leda till obehörig åtkomst till systemet. I denna avhandling fördjupar vi studiet av integritets- och sekretessperspektivet, karakteriserar grundläggande gränser och föreslå polarkoddesigner som uppnår fundamentala gränser.

Baserad på det grundläggande biometriska identifierings- och autentiseringssystemet studerar vi fem tillägg: (i) brusiga registrering och bevarande av integritet, där oundvikligt brus vid inskrivning i biometri inkorporerats; (ii) två-stegsinställning med bevarande av integritet, där både registreringsfasen och identifieringsfasen drivs i två steg; (iii) inställning av flera system med användarnas biometriska information i flera system; (iv) osäkerhetsinställning, där två osäkerhetsaspekter beaktas, dvs. sannolikhetsmassfunktionen för användarnas biometriska information och observationskanalen; (v) polarkoddesigner, där polära koddesigner som uppnår grundläggande gränsvärden härleds. För att bevara integriteten föreslår vi inkludering av ytterligare privata nycklar. Resultaten visar hur de privata nycklarna kan användas effektivt. För två-stegsinställning produceras två lager av hjälpdata under registreringsfasen. I identifierings- och autentiseringsfasen bearbetas sedan den observerade användaren först med det första lagrets hjälpdata och systemet matar ut en lista. Därefter bearbetar systemet endast observationen med en del av användarna i systemet. Detta så att den uttömmande sökningen undvikas. I inställningen av flera system, är det tillåtet att återanvända den offentliga informationen och uppnår därmed en mer effektiv design. Dessutom, beroende på om systemen byggs ihop på en gång eller om nya system byggs utifrån det äldre systemet, studerar vi både den gemensamma designen och den inkrementella designen. För våra polarkoddesignerna överväger vi en inställning där integritetsskyddsnivån kan anpassas genom att anpassa storleken på den privata nyckeln. Både osäkerhetsinställningen och polarkoddesignerna uppnår stark sekretess som är strängare än det svaga sekreteskravet som beaktas i de andra inställningarna.

Dessa fem studerade inställningar generaliserar den kända inställning som studerats i litteraturen. Som följder eller anmärkningar, tillhandahåller vi karaktäriseringar för relaterade problem. Förlängningarna minskar gapet mellan modellerna och riktiga biometriska system. De erhållna resultaten ger en vägledning för utformningen av biometriska identifierings- och autentiseringssystem.

In this work, a complete biometrics identification and authentication system considered in [1] is implemented. In the considered system, polar codes are applied and binary symmetric memoryless channels are used for noisy enrollment and observation. The fundamental limits can be achieved with sufficiently long block length for iid binary source sequence. Fingerprints are used as the biometric source and an autoencoder is designed for pre-processing so that images are compressed to nearly uniformly distributed binary sequences with similar correlation and entropy properties to iid binary sequence. The identification and authentication system with generated secret key in [1] is implemented and simulated using pre-processed fingerprints as biometric source and polar code-based design. The proposed system design approach is systematic and flexible in choosing the optimal trade-off. The results show that identification error rates become smaller with longer code length and when the successive cancellation list algorithm is applied. Thus, it is shown by these first promising experiments that polar codes can be used in real identification and authentication systems.

In this work, we study the uncertainty aspects in bio-metric identification and authentication systems. The uncertainty lies in two aspects, i.e., the probability mass function (p.m.f.) of users' biometric information and the observation channel. For the p.m.f. of users' biometrics, it is assumed that the users are from different groups and the distribution of each group is determined by the state. For the observation channel, it is assumed that there is a set of channels and the actual observation channel is from this set. 

In this work, we study incrementally designed secure biometric identification and authentication systems, in which a new system is designed based on an existing legacy system. By taking privacy and secrecy into consideration, we characterize the fundamental trade-offs among the identification rate, secret key rates, and privacy leakage rate. 

In this work, we present a polar code design that offers a provably optimal solution for biometric identification systems allowing authentication under noisy enrollment with secrecy and privacy constraints. Binary symmetric memoryless source and channels are considered. It is shown that the proposed polar code design achieves the fundamental limits and satisfies more stringent secrecy constraints than previously in the literature. The proposed polar code design provides the first example of a code design that achieves the fundamental limits involving both identification and authentication.

In this paper, we study fundamental trade-offs in privacy-preserving biometric identification systems with noisy enrollment. The proposed identification systems include helper data, secret keys, and private keys. Helper data are stored in a public database and used for identification. Secret keys are either stored in a secure database or provided to the user, and can be used in a next step, e.g. for authentication. Private keys are provided by users, and are also used for identification. In this paper, we impose a noisy enrollment channel and an arbitrarily small privacy and secrecy leakage rate. We characterize the optimal trade-off among the identification, secret key, private key, and helper data rates. Depending on how secret keys are produced, we study two cases of the proposed privacy-preserving identification systems, where the secret keys are generated and chosen respectively. By introducing private keys, it is shown that the identification system achieves close to zero privacy leakage rate in both generated and chosen secret key settings. The results also show that the identification rate and the secret key rate can be enlarged by increasing the private key rate. This work provides a framework for analyzing privacy-preserving identification systems and an insight on the design of optimal systems.

We study two-stage biometric identification systems that allow authentication without privacy leakage. In the enrollment phase, secret keys and two layers of the helper data for each user are generated. Additional to the helper data and secret keys, we also introduce private keys in the systems. In the identification phase, an unknown but previously enrolled user is observed, and the user's private key is also presented to the system. The system firstly compares the user with the first layer helper database, outputs a list, and obtains a set of user indices. Then the system compares the observed user with the users in the set. Therefore, the identification procedure avoids an exhaustive search and only has to do a comparison with some part of the users in the system, which leads to a systematic reduction of the search complexity. Fundamental trade-offs among the identification rate, the secret key rate, the private key rate, the helper data rate, and the list size rate are derived in the imposed two-stage biometric identification systems without privacy leakage. Moreover, the obtained results show that a private key can boost the identification rate and the secret key rate, as well as preserve privacy.

Wewithout privacy leakage. Privacy-preserving biometric identifi- cation systems that involve helper data, secret keys and private keys are considered. The helper data are stored in a public database and can be used to support the user identification. The secret key is either stored in an encrypted database or handed to the user, which can be used for authentication. Since the helper data are public and releasing the biometric information invokes privacy issues, the public helper data can only leak a negligible amount of biometric information. To achieve this, we use private keys to mask the helper data such that the public helper data contain as little as possible information about the biometrics. Moreover, a two-stage extension is also studied, where the clustering method is used such that the search complexity in the identification phase can be reduced. identification