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.

Hash Families and Cover-Free Families with Cryptographic Applications

This thesis is focused on hash families and cover-free families and their application to problems in cryptography. We present new necessary conditions for generalized separating hash families, and provide new explicit constructions. We then consider three cryptographic applications of hash families and cover-free families. We provide a stronger de nition of anonymity in the context of shared symmetric key primitives and give a new scheme with improved anonymity properties. Second, we observe that nding the invalid signatures in a set of digital signatures that fails batch veri cation is a group testing problem, then apply and compare many group testing algorithms to solve this problem e ciently. In particular, we apply group testing algorithms based on cover-free families. Finally, we construct a one-time signature scheme based on cover-free families with short signatures

Enabling Machine-aided Cryptographic Design

The design of cryptographic primitives such as digital signatures and public-key encryption is very often a manual process conducted by expert cryptographers. This persists despite the fact that many new generic or semi-generic methods have been proposed to construct new primitives by transforming existing ones in interesting ways. However, manually applying transformations to existing primitives can be error-prone, ad-hoc and tedious. A natural question is whether automating the process of applying cryptographic transformations would yield competitive or better results? In this thesis, we explore a compiler-based approach for automatically performing certain cryptographic designs. Similar approaches have been applied to various types of cryptographic protocol design with compelling results. We extend this same approach and show that it also can be effective towards automatically applying cryptographic transformations. We first present our extensible architecture that automates a class of cryptographic transformations on primitives. We then propose several techniques that address the aforementioned question including the Charm cryptographic framework, which enables rapid prototyping of cryptographic primitives from abstract descriptions. We build on this work and show the extent to which transformations can be performed automatically given these descriptions. To illustrate this automation, we present a series of cryptographic tools that demonstrate the effectiveness of our automated approach. Our contributions are listed as follows: - AutoBatch: Batch verification is a transformation that improves signature verification time by efficiently processing many signatures at once. Historically, this manual process has been prone to error and tedious for practitioners. We describe the design of an automated tool that finds efficient batch verification algorithms from abstract descriptions of signature schemes. - AutoGroup: Cryptographers often prefer to describe their pairing-based constructions using symmetric group notation for simplicity, while they prefer asymmetric groups for implementation due to the efficiency gains. The symmetric- to-asymmetric translation is usually performed through manual analysis of a scheme and finding an efficient translation that suits applications can be quite challenging. We present an automated tool that uses SMT solvers to find efficient asymmetric translations from abstract descriptions of cryptographic schemes. - AutoStrong: Strongly unforgeable signatures are desired in practice for a variety of cryptographic protocols. Several transformations exist in the literature that show how to obtain strongly unforgeable signatures from existentially unforgeable ones. We focus on a particular highly-efficient transformation due to Boneh, Shen and Waters that is applicable if the signature satisfies a notion of partitioning. Checking for this property can be challenging and has been less explored in the literature. We present an automated tool that also utilizes SMT solvers to determine when this property is applicable for constructing efficient strongly unforgeable signatures from abstract descriptions. We anticipate that these proof-of-concept tools embody the notion that certain cryptographic transformations can be safely and effectively outsourced to machines

Research Philosophy of Modern Cryptography

Proposing novel cryptography schemes (e.g., encryption, signatures, and protocols) is one of the main research goals in modern cryptography. In this paper, based on more than 800 research papers since 1976 that we have surveyed, we introduce the research philosophy of cryptography behind these papers. We use ``benefits and ``novelty as the keywords to introduce the research philosophy of proposing new schemes, assuming that there is already one scheme proposed for a cryptography notion. Next, we introduce how benefits were explored in the literature and we have categorized the methodology into 3 ways for benefits, 6 types of benefits, and 17 benefit areas. As examples, we introduce 40 research strategies within these benefit areas that were invented in the literature. The introduced research strategies have covered most cryptography schemes published in top-tier cryptography conferences

Security in Delay Tolerant Networks

Delay- and Disruption-tolerant wireless networks (DTN), or opportunistic networks, represent a class of networks where continuous end-to-end connectivity may not be possible. DTN is a well recognized area in networking research and has attracted extensive attentions from both network designers and application developers. Applications of this emergent communication paradigm are wide ranging and include sensor networks using scheduled intermittent connectivity, vehicular DTNs for dissemination of location-dependent information (e.g., local ads, traffic reports, parking information, etc.), pocket-switched networks to allow humans to communicate without network infrastructure, and underwater acoustic networks with moderate delays and frequent interruptions due to environmental factors, etc. Security is one of the main barriers to wide-scale deployment of DTNs, but has gained little attention so far. On the one hand, similar to traditional mobile ad hoc networks, the open channel and multi-hop transmission have made DTNs vulnerable to various security threats, such as message modification/injection attack or unauthorized access and utilization of DTN resources. On the other hand, the unique security characteristics of DTNs including: long round-trip delay, frequent disconnectivity, fragmentation, opportunistic routing as well as limited computational and storage capability, make the existing security protocols designed for the conventional ad hoc networks unsuitable for DTNs. Therefore, a series of new security protocols are highly desired to meet stringent security and efficiency requirements for securing DTNs. In this research, we focus on three fundamental security issues in DTNs: efficient DTN message (or bundle) authentication, which is a critical security service for DTN security; incentive issue, which targets at stimulating selfish nodes to forward data for others; and certificate revocation issue, which is an important part of public key management and serves the foundation of any DTN security protocols. We have made the following contributions: First of all, the unique ``store-carry-and-forward'' transmission characteristic of DTNs implies that bundles from distinct/common senders may opportunistically be buffered at some common intermediate nodes. Such a ``buffering'' characteristic distinguishes DTN from any other traditional wireless networks, for which intermediate cache is not supported. To exploit such buffering opportunities, we propose an Opportunistic Batch Bundle Authentication Scheme (OBBA) to dramatically reduce the bundle authentication cost by seamlessly integrating identity-based batch signatures and Merkle tree techniques. Secondly, we propose a secure multi-layer credit based incentive scheme to stimulate bundle forwarding cooperation among DTNs nodes. The proposed scheme can be implemented in a fully distributed manner to thwart various attacks without relying on any tamper-proof hardware. In addition, we introduce several efficiency-optimization techniques to improve the overall efficiency by exploiting the unique characteristics of DTNs. Lastly, we propose a storage-efficient public key certificate validation method. Our proposed scheme exploits the opportunistic propagation to transmit Certificate Revocation List (CRL) list while taking advantage of bloom filter technique to reduce the required buffer size. We also discuss how to take advantage of cooperative checking to minimize false positive rate and storage consumption. For each research issue, detailed simulation results in terms of computational time, transmission overhead and power consumption, are given to validate the efficiency and effectiveness of the proposed security solutions

Holistic security 4.0

The future computer climate will represent an ever more aligned world of integrating technologies, affecting consumer, business and industry sectors. The vision was first outlined in the Industry 4.0 conception. The elements which comprise smart systems or embedded devices have been investigated to determine the technological climate. The emerging technologies revolve around core concepts, and specifically in this project, the uses of Internet of Things (IoT), Industrial Internet of Things (IIoT) and Internet of Everything (IoE). The application of bare metal and logical technology qualities are put under the microscope to provide an effective blue print of the technological field. The systems and governance surrounding smart systems are also examined. Such an approach helps to explain the beneficial or negative elements of smart devices. Consequently, this ensures a comprehensive review of standards, laws, policy and guidance to enable security and cybersecurity of the 4.0 systems

Divisible E-Cash from Constrained Pseudo-Random Functions

International audienceElectronic cash (e-cash) is the digital analogue of regular cash which aims at preservingusers’ privacy. Following Chaum’s seminal work, several new features were proposed for e-cash toaddress the practical issues of the original primitive. Among them,divisibilityhas proved very usefulto enable efficient storage and spendings. Unfortunately, it is also very difficult to achieve and, todate, quite a few constructions exist, all of them relying on complex mechanisms that can only beinstantiated in one specific setting. In addition security models are incomplete and proofs sometimeshand-wavy.In this work, we first provide a complete security model for divisible e-cash, and we study the linkswith constrained pseudo-random functions (PRFs), a primitive recently formalized by Boneh andWaters. We exhibit two frameworks of divisible e-cash systems from constrained PRFs achievingsome specific properties: either key homomorphism or delegability. We then formally prove theseframeworks, and address two main issues in previous constructions: two essential security notionswere either not considered at all or not fully proven. Indeed, we introduce the notion ofclearing,which should guarantee that only the recipient of a transaction should be able to do the deposit,and we show theexculpability, that should prevent an honest user to be falsely accused, was wrongin most proofs of the previous constructions. Some can easily be repaired, but this is not the casefor most complex settings such as constructions in the standard model. Consequently, we providethe first construction secure in the standard model, as a direct instantiation of our framework