TokenWeaver: Privacy Preserving and Post-Compromise Secure Attestation

Modern attestation based on Trusted Execution Environments (TEEs) can significantly reduce the risk of secret compromise by attackers, while allowing users to authenticate across various services. However, this has also made TEEs a high-value attack target, driving an arms race between novel compromise attacks and continuous TEEs updates. Ideally, we would like to ensure that we achieve Post-Compromise Security (PCS): even after a compromise, we can update the TEE into a secure state. However, at the same time, we would like the privacy of users to be respected, preventing providers (such as Intel, Google, or Samsung) or services from tracking users. In this work, we develop TokenWeaver, the first privacy-preserving post-compromise secure attestation method with automated formal proofs for its core properties. We base our construction on weaving together two types of token chains, one of which is linkable and the other is unlinkable. We provide the full formal models, including protocol, security properties, and proofs for reproducibility, as well as a proof-of-concept implementation in python that shows the simplicity and applicability of our solution

Privacy Preserving Cryptographic Protocols for Secure Heterogeneous Networks

Disertační práce se zabývá kryptografickými protokoly poskytující ochranu soukromí, které jsou určeny pro zabezpečení komunikačních a informačních systémů tvořících heterogenní sítě. Práce se zaměřuje především na možnosti využití nekonvenčních kryptografických prostředků, které poskytují rozšířené bezpečnostní požadavky, jako je například ochrana soukromí uživatelů komunikačního systému. V práci je stanovena výpočetní náročnost kryptografických a matematických primitiv na různých zařízeních, které se podílí na zabezpečení heterogenní sítě. Hlavní cíle práce se zaměřují na návrh pokročilých kryptografických protokolů poskytujících ochranu soukromí. V práci jsou navrženy celkově tři protokoly, které využívají skupinových podpisů založených na bilineárním párování pro zajištění ochrany soukromí uživatelů. Tyto navržené protokoly zajišťují ochranu soukromí a nepopiratelnost po celou dobu datové komunikace spolu s autentizací a integritou přenášených zpráv. Pro navýšení výkonnosti navržených protokolů je využito optimalizačních technik, např. dávkového ověřování, tak aby protokoly byly praktické i pro heterogenní sítě.The dissertation thesis deals with privacy-preserving cryptographic protocols for secure communication and information systems forming heterogeneous networks. The thesis focuses on the possibilities of using non-conventional cryptographic primitives that provide enhanced security features, such as the protection of user privacy in communication systems. In the dissertation, the performance of cryptographic and mathematic primitives on various devices that participate in the security of heterogeneous networks is evaluated. The main objectives of the thesis focus on the design of advanced privacy-preserving cryptographic protocols. There are three designed protocols which use pairing-based group signatures to ensure user privacy. These proposals ensure the protection of user privacy together with the authentication, integrity and non-repudiation of transmitted messages during communication. The protocols employ the optimization techniques such as batch verification to increase their performance and become more practical in heterogeneous networks.

DP5: A Private Presence Service

Users of social applications like to be notified when their friends are online. Typically, this is done by a central server keeping track of who is online and offline, as well as of all of the users’ “buddy lists”, which contain sensitive information. We present DP5, a cryptographic service that implements online presence indication in a privacy-friendly way. DP5 allows clients to register their online presence and query the presence of their list of friends while keeping this list secret. Besides presence, high-integrity status updates are supported, to facilitate key update and rendezvous protocols. While infrastructure services are required for DP5 to operate, they are designed to not require any long-term secrets and provide perfect forward secrecy in case of compromise. We provide security arguments for the indistinguishability properties of the protocol, as well as an evaluation of its scalability and performance

Multi-Party Revocation in Sovrin: Performance through Distributed Trust

Accumulators provide compact representations of large sets and compact membership witnesses. Besides constant-size witnesses, public-key accumulators provide efficient updates of both the accumulator itself and the witness. However, bilinear group based accumulators come with drawbacks: they require a trusted setup and their performance is not practical for real-world applications with large sets. In this paper, we introduce multi-party public-key accumulators dubbed dynamic (threshold) secret-shared accumulators. We present an instantiation using bilinear groups having access to more efficient witness generation and update algorithms that utilize the shares of the secret trapdoors sampled by the parties generating the public parameters. Specifically, for the q-SDH-based accumulators, we provide a maliciously-secure variant sped up by a secure multi-party computation (MPC) protocol (IMACC\u2719) built on top of SPDZ and a maliciously secure threshold variant built with Shamir secret sharing. For these schemes, a performant proof-of-concept implementation is provided, which substantiates the practicability of public-key accumulators in this setting. We explore applications of dynamic (threshold) secret-shared accumulators to revocation schemes of group signatures and credentials system. In particular, we consider it as part of Sovrin\u27s system for anonymous credentials where credentials are issued by the foundation of trusted nodes

When Whereabouts is No Longer Thereabouts:Location Privacy in Wireless Networks

Modern mobile devices are fast, programmable and feature localization and wireless capabilities. These technological advances notably facilitate mobile access to Internet, development of mobile applications and sharing of personal information, such as location information. Cell phone users can for example share their whereabouts with friends on online social networks. Following this trend, the field of ubiquitous computing foresees communication networks composed of increasingly inter-connected wireless devices offering new ways to collect and share information in the future. It also becomes harder to control the spread of personal information. Privacy is a critical challenge of ubiquitous computing as sharing personal information exposes users' private lives. Traditional techniques to protect privacy in wired networks may be inadequate in mobile networks because users are mobile, have short-lived encounters and their communications can be easily eavesdropped upon. These characteristics introduce new privacy threats related to location information: a malicious entity can track users' whereabouts and learn aspects of users' private lives that may not be apparent at first. In this dissertation, we focus on three important aspects of location privacy: location privacy threats, location-privacy preserving mechanisms, and privacy-preservation in pervasive social networks. Considering the recent surge of mobile applications, we begin by investigating location privacy threats of location-based services. We push further the understanding of the privacy risk by identifying the type and quantity of location information that statistically reveals users' identities and points of interest to third parties. Our results indicate that users are at risk even if they access location-based services episodically. This highlights the need to design privacy into location-based services. In the second part of this thesis, we delve into the subject of privacy-preserving mechanisms for mobile ad hoc networks. First, we evaluate a privacy architecture that relies on the concept of mix zones to engineer anonymity sets. Second, we identify the need for protocols to coordinate the establishment of mix zones and design centralized and distributed approaches. Because individuals may have different privacy requirements, we craft a game-theoretic model of location privacy to analyze distributed protocols. This model predicts strategic behavior of rational devices that protects their privacy at a minimum cost. This prediction leads to the design of efficient privacy-preserving protocols. Finally, we develop a dynamic model of interactions between mobile devices in order to analytically evaluate the level of privacy provided by mix zones. Our results indicate the feasibility and limitations of privacy protection based on mix zones. In the third part, we extend the communication model of mobile ad hoc networks to explore social aspects: users form groups called "communities" based on interests, proximity, or social relations and rely on these communities to communicate and discover their context. We analyze using challenge-response methodology the privacy implications of this new communication primitive. Our results indicate that, although repeated interactions between members of the same community leak community memberships, it is possible to design efficient schemes to preserve privacy in this setting. This work is part of the recent trend of designing privacy protocols to protect individuals. In this context, the author hopes that the results obtained, with both their limitations and their promises, will inspire future work on the preservation of privacy

Internet Authentication for Remote Access

It is expected that future IP devices will employ a variety of different network access technologies to gain ubiquitous connectivity. Currently there are no authentication protocols available that are lightweight, can be carried over arbitrary access networks, and are flexible enough to be re-used in the many different contexts that are likely to arise in future Internet remote access. Furthermore, existing access procedures need to be enhanced to offer protection against Denial-of-Service (DoS) attacks, and do not provide non-repudiation. In addition to being limited to specific access media, some of these protocols are limited to specific network topologies and are not scalable. This thesis reviews the authentication infrastructure challenges for future Internet remote access supporting ubiquitous client mobility, and proposes a series of solutions obtained by adapting and reinforcing security techniques arising from a variety of different sources. The focus is on entity authentication protocols that can be carried both by the IETF PANA authentication carrier and by the EAP mechanisms, and possibly making use of an AAA infrastructure. The core idea is to adapt authentication protocols arising from the mobile telecommunications sphere to Internet remote access. A proposal is also given for Internet access using a public key based authentication protocol. The subsequent security analysis of the proposed authentication protocols covers a variety of aspects, including: key freshness, DoS-resistance, and "false-entity-in-the-middle" attacks, in addition to identity privacy of users accessing the Internet via mobile devices. This work aims primarily at contributing to ongoing research on the authentication infrastructure for the Internet remote access environment, and at reviewing and adapting authentication solutions implemented in other spheres, for instance in mobile telecommunications systems, for use in Internet remote access networks supporting ubiquitous mobilit

A Backward Unlinkable Secret Handshake Scheme with Revocation Support in the Standard Model

Secret handshake schemes have been proposed to achieve private mutual authentications, which allow the members of a certain organization to anonymously authenticate each other without exposing their affiliations. In this paper, a backward unlinkable secret handshake scheme with revocation support (BU-RSH) is constructed. For a full-fledged secret handshake scheme, it is indispensable to furnish it with practical functionality, such as unlinkability, revocation and traceability. The revocation is achieved in the BU-RSH scheme, as well as the unlinkability and the traceability. Moreover, the anonymity of revoked members is improved, so that the past transcripts of revoked members remain private, i.e., backward unlinkability. In particular, the BU-RSH scheme is provably secure in the standard model by assuming the intractability of the `-hidden strong Diffie-Hellman problem and the subgroup decision problem

A Backward Unlinkable Secret Handshake Scheme with Revocation Support in the Standard Model

Secret handshake schemes have been proposed to achieve private mutual authentications, which allow the members of a certain organization to anonymously authenticate each other without exposing their affiliations. In this paper, a backward unlinkable secret handshake scheme with revocation support (BU-RSH) is constructed. For a full-fledged secret handshake scheme, it is indispensable to furnish it with practical functionality, such as unlinkability, revocation and traceability. The revocation is achieved in the BU-RSH scheme, as well as the unlinkability and the traceability. Moreover, the anonymity of revoked members is improved, so that the past transcripts of revoked members remain private, i.e., backward unlinkability. In particular, the BU-RSH scheme is provably secure in the standard model by assuming the intractability of the `-hidden strong Diffie-Hellman problem and the subgroup decision problem

Cryptographic Approaches To Security and Privacy Issues In Pervasive Computing

Technological innovation has enabled tiny devices to participate in pervasive com- puting. Such devices are particularly vulnerable to security and privacy threats, because of their limited computing resources and relatively weak physical security. We investigate possible cryptographic solutions to security and privacy problems arising in two kinds of emerging pervasive computing networks: Personal Area Net- works (PANs) and the EPCglobal Network. A number of key management schemes have been proposed for use in PANs, but these schemes only support key management within a PAN. However, as people are increasingly equipped with multiple wireless devices, PANs are likely to be intercon- nected to share information or services. We introduce a term, iPANs, to name such interconnected PANs. We define system models and design goals for key manage- ment in iPANs, and propose a novel security initialisation scheme for use in iPANs. The proposed scheme achieves desirable security and efficiency properties by making use of the unique characteristics of PANs. The EPCglobal Network is designed to give efficiency and cost savings in and beyond the supply chain using Radio Frequency Identification (RFID) technology; however, privacy threats affecting such networks are particularly serious. We construct a formal privacy model for RFID systems accurately reflecting adversarial threats and power. We then give brief privacy analysis for the existing privacy-enhanced RFID schemes which have received wide attention in the literature. We then construct a secure refresh-based RFID system based on re-encryption techniques, and prove its privacy using the defined privacy model. Finally, we show that the proposed scheme can greatly enhance the security and privacy of EPC tags, making the maximum use of given tag functionalities as specified in the standards

Lightweight mutual authentication and privacy preservation schemes for IOT systems.

Internet of Things (IoT) presents a holistic and transformative approach for providing services in different domains. IoT creates an atmosphere of interaction between humans and the surrounding physical world through various technologies such as sensors, actuators, and the cloud. Theoretically, when everything is connected, everything is at risk. The rapid growth of IoT with the heterogeneous devices that are connected to the Internet generates new challenges in protecting and preserving user’s privacy and ensuring the security of our lives. IoT systems face considerable challenges in deploying robust authentication protocols because some of the IoT devices are resource-constrained with limited computation and storage capabilities to implement the currently available authentication mechanism that employs computationally expensive functions. The limited capabilities of IoT devices raise significant security and privacy concerns, such as ensuring personal information confidentiality and integrity and establishing end-to-end authentication and secret key generation between the communicating device to guarantee secure communication among the communicating devices. The ubiquity nature of the IoT device provides adversaries more attack surfaces which can lead to tragic consequences that can negatively impact our everyday connected lives. According to [1], authentication and privacy protection are essential security requirements. Therefore, there is a critical need to address these rising security and privacy concerns to ensure IoT systems\u27 safety. This dissertation identifies gaps in the literature and presents new mutual authentication and privacy preservation schemes that fit the needs of resource-constrained devices to improve IoT security and privacy against common attacks. This research enhances IoT security and privacy by introducing lightweight mutual authentication and privacy preservation schemes for IoT based on hardware biometrics using PUF, Chained hash PUF, dynamic identities, and user’s static and continuous biometrics. The communicating parties can anonymously communicate and mutually authenticate each other and locally establish a session key using dynamic identities to ensure the user’s unlinkability and untraceability. Furthermore, virtual domain segregation is implemented to apply security policies between nodes. The chained-hash PUF mechanism technique is implemented as a way to verify the sender’s identity. At first, this dissertation presents a framework called “A Lightweight Mutual Authentication and Privacy-Preservation framework for IoT Systems” and this framework is considered the foundation of all presented schemes. The proposed framework integrates software and hardware-based security approaches that satisfy the NIST IoT security requirements for data protection and device identification. Also, this dissertation presents an architecture called “PUF Hierarchal Distributed Architecture” (PHDA), which is used to perform the device name resolution. Based on the proposed framework and PUF architecture, three lightweight privacy-preserving and mutual authentication schemes are presented. The Three different schemes are introduced to accommodate both stationary and mobile IoT devices as well as local and distributed nodes. The first scheme is designed for the smart homes domain, where the IoT devices are stationary, and the controller node is local. In this scheme, there is direct communication between the IoT nodes and the controller node. Establishing mutual authentication does not require the cloud service\u27s involvement to reduce the system latency and offload the cloud traffic. The second scheme is designed for the industrial IoT domain and used smart poultry farms as a use case of the Industrial IoT (IIoT) domain. In the second scheme, the IoT devices are stationary, and the controller nodes are hierarchical and distributed, supported by machine-to-machine (M2M) communication. The third scheme is designed for smart cities and used IoV fleet vehicles as a use case of the smart cities domain. During the roaming service, the mutual authentication process between a vehicle and the distributed controller nodes represented by the Roadside Units (RSUs) is completed through the cloud service that stores all vehicle\u27s security credentials. After that, when a vehicle moves to the proximity of a new RSU under the same administrative authority of the most recently visited RSU, the two RSUs can cooperate to verify the vehicle\u27s legitimacy. Also, the third scheme supports driver static and continuous authentication as a driver monitoring system for the sake of both road and driver safety. The security of the proposed schemes is evaluated and simulated using two different methods: security analysis and performance analysis. The security analysis is implemented through formal security analysis and informal security analysis. The formal analysis uses the Burrows–Abadi–Needham logic (BAN) and model-checking using the automated validation of Internet security protocols and applications (AVISPA) toolkit. The informal security analysis is completed by: (1) investigating the robustness of the proposed schemes against the well-known security attacks and analyze its satisfaction with the main security properties; and (2) comparing the proposed schemes with the other existing authentication schemes considering their resistance to the well-known attacks and their satisfaction with the main security requirements. Both the formal and informal security analyses complement each other. The performance evaluation is conducted by analyzing and comparing the overhead and efficiency of the proposed schemes with other related schemes from the literature. The results showed that the proposed schemes achieve all security goals and, simultaneously, efficiently and satisfy the needs of the resource-constrained IoT devices