A Novel Non-interactive Deniable Authentication Protocol with Designated Verifier on elliptic curve cryptosystem

Recently, many non-interactive deniable authentication (NIDA) protocols have been proposed. They are mainly composed of two types, signature-based and shared-secrecy based. After reviewing these schemes, we found that the signature-based approach can not deny the source of the message and thus can not achieve full deniability; and that, the shared-secrecy based approach suffers KCI attack although it can achieve full deniability. In addition, both types of schemes lack efficiency consideration for they mainly base on DLP, factoring, or bilinear pairing. Due to this observation, in this paper, we use the Fiat-Shamir heuristic method to propose a new ECC-based NIDA protocol which not only can achieve full deniability but also is more efficient than all of the proposed schemes due to the inheritent property of elliptic curve cryptosystem. Further, we prove the properties of full deniability and KCI resistance conflict for a NIDA protocol. Besides, we deduce that a NIDA protocol is deniable if and only if it is perfect zero-knowledge

ECC-Based Non-Interactive Deniable Authentication with Designated Verifier

Recently, researchers have proposed many non-interactive deniable authentication (NIDA) protocols. Most of them claim that their protocols possess full deniability. However, after reviewing, we found that they either cannot achieve full deniability, or suffer KCI or SKCI attack; moreover, lack efficiency, because they are mainly based on DLP, factoring problem, or bilinear pairings. Due to this observation, and that ECC provides the security equivalence to RSA and DSA by using much smaller key size, we used Fiat-Shamir heuristic to propose a novel ECC-based NIDA protocol for achieving full deniability as well as getting more efficient than the previous schemes. After security analyses and efficiency comparisons, we confirmed the success of the usage. Therefore, the proposed scheme was more suitable to be implemented in low power mobile devices than the others

A publicly verifiable quantum blind signature scheme without entanglement based on asymmetric cryptography

In recent years, several cryptographic scholars have proposed quantum blind signature schemes. However, their methods require the signatories and the inspectors to share common keys in advance, which makes them not only complicated in concept, but also suffering deniable problem. Moreover, due to the fact that not everyone can verify the blind signature, it needs to have a designated verifier. In view of Laurent, et al.’s argument that other than the assumption of the pre-image being collision-free, the one-way hash function is an attractive cryptographic component in the post-quantum era when designing a cryptosystem. Inspired by this, we propose a publicly verifiable quantum blind signature scheme based on the hash function. After security analyses, we confirm that our quantum blind signature not only is secure, but also have the needed properties. It includes anonymity, unforgeability, non-repudiation, blindness, public verifiability, and traceability. Hence, we conclude that this approach is better than the state-of-the-art, and is therefore more suitable for applications in real life, such as, mobile payments, quantum voting, or quantum government

Authentication schemes for Smart Mobile Devices: Threat Models, Countermeasures, and Open Research Issues

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.This paper presents a comprehensive investigation of authentication schemes for smart mobile devices. We start by providing an overview of existing survey articles published in the recent years that deal with security for mobile devices. Then, we give a classification of threat models in smart mobile devices in five categories, including, identity-based attacks, eavesdropping-based attacks, combined eavesdropping and identity-based attacks, manipulation-based attacks, and service-based attacks. This is followed by a description of multiple existing threat models. We also provide a classification of countermeasures into four types of categories, including, cryptographic functions, personal identification, classification algorithms, and channel characteristics. According to the characteristics of the countermeasure along with the authentication model iteself, we categorize the authentication schemes for smart mobile devices in four categories, namely, 1) biometric-based authentication schemes, 2) channel-based authentication schemes, 3) factors-based authentication schemes, and 4) ID-based authentication schemes. In addition, we provide a taxonomy and comparison of authentication schemes for smart mobile devices in form of tables. Finally, we identify open challenges and future research directions

A publicly verifiable quantum signature scheme based on asymmetric quantum cryptography

In 2018, Shi et al. \u27s showed that Kaushik et al.\u27s quantum signature scheme is defective. It suffers from the forgery attack. They further proposed an improvement, trying to avoid the attack. However, after examining we found their improved quantum signature is deniable, because the verifier can impersonate the signer to sign a message. After that, when a dispute occurs, he can argue that the signature was not signed by him. It was from the signer. To overcome the drawback, in this paper, we raise an improvement to make it publicly verifiable and hence more suitable to be applied in real life. After cryptanalysis, we confirm that our improvement not only resist the forgery attack but also is undeniable

Cryptography in privacy-preserving applications.

Tsang Pak Kong.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.Includes bibliographical references (leaves 95-107).Abstracts in English and Chinese.Abstract --- p.iiAcknowledgement --- p.ivChapter 1 --- Introduction --- p.1Chapter 1.1 --- Privacy --- p.1Chapter 1.2 --- Cryptography --- p.5Chapter 1.2.1 --- History of Cryptography --- p.5Chapter 1.2.2 --- Cryptography Today --- p.6Chapter 1.2.3 --- Cryptography For Privacy --- p.7Chapter 1.3 --- Thesis Organization --- p.8Chapter 2 --- Background --- p.10Chapter 2.1 --- Notations --- p.10Chapter 2.2 --- Complexity Theory --- p.11Chapter 2.2.1 --- Order Notation --- p.11Chapter 2.2.2 --- Algorithms and Protocols --- p.11Chapter 2.2.3 --- Relations and Languages --- p.13Chapter 2.3 --- Algebra and Number Theory --- p.14Chapter 2.3.1 --- Groups --- p.14Chapter 2.3.2 --- Intractable Problems --- p.16Chapter 2.4 --- Cryptographic Primitives --- p.18Chapter 2.4.1 --- Public-Key Encryption --- p.18Chapter 2.4.2 --- Identification Protocols --- p.21Chapter 2.4.3 --- Digital Signatures --- p.22Chapter 2.4.4 --- Hash Functions --- p.24Chapter 2.4.5 --- Zero-Knowledge Proof of Knowledge --- p.26Chapter 2.4.6 --- Accumulators --- p.32Chapter 2.4.7 --- Public Key Infrastructure --- p.34Chapter 2.5 --- Zero Knowledge Proof of Knowledge Protocols in Groups of Unknown Order --- p.36Chapter 2.5.1 --- The Algebraic Setting --- p.36Chapter 2.5.2 --- Proving the Knowledge of Several Discrete Logarithms . --- p.37Chapter 2.5.3 --- Proving the Knowledge of a Representation --- p.38Chapter 2.5.4 --- Proving the Knowledge of d Out of n Equalities of Discrete Logarithms --- p.39Chapter 2.6 --- Conclusion --- p.42Chapter 3 --- Related Works --- p.43Chapter 3.1 --- Introduction --- p.43Chapter 3.2 --- Group-Oriented Signatures without Spontaneity and/or Anonymity --- p.44Chapter 3.3 --- SAG Signatures --- p.46Chapter 3.4 --- Conclusion --- p.49Chapter 4 --- Linkable Ring Signatures --- p.50Chapter 4.1 --- Introduction --- p.50Chapter 4.2 --- New Notions --- p.52Chapter 4.2.1 --- Accusatory Linking --- p.52Chapter 4.2.2 --- Non-slanderability --- p.53Chapter 4.2.3 --- Linkability in Threshold Ring Signatures --- p.54Chapter 4.2.4 --- Event-Oriented Linking --- p.55Chapter 4.3 --- Security Model --- p.56Chapter 4.3.1 --- Syntax --- p.56Chapter 4.3.2 --- Notions of Security --- p.58Chapter 4.4 --- Conclusion --- p.63Chapter 5 --- Short Linkable Ring Signatures --- p.64Chapter 5.1 --- Introduction --- p.64Chapter 5.2 --- The Construction --- p.65Chapter 5.3 --- Security Analysis --- p.68Chapter 5.3.1 --- Security Theorems --- p.68Chapter 5.3.2 --- Proofs --- p.68Chapter 5.4 --- Discussion --- p.70Chapter 5.5 --- Conclusion --- p.71Chapter 6 --- Separable Linkable Threshold Ring Signatures --- p.72Chapter 6.1 --- Introduction --- p.72Chapter 6.2 --- The Construction --- p.74Chapter 6.3 --- Security Analysis --- p.76Chapter 6.3.1 --- Security Theorems --- p.76Chapter 6.3.2 --- Proofs --- p.77Chapter 6.4 --- Discussion --- p.79Chapter 6.5 --- Conclusion --- p.80Chapter 7 --- Applications --- p.82Chapter 7.1 --- Offline Anonymous Electronic Cash --- p.83Chapter 7.1.1 --- Introduction --- p.83Chapter 7.1.2 --- Construction --- p.84Chapter 7.2 --- Electronic Voting --- p.85Chapter 7.2.1 --- Introduction --- p.85Chapter 7.2.2 --- Construction . --- p.87Chapter 7.2.3 --- Discussions --- p.88Chapter 7.3 --- Anonymous Attestation --- p.89Chapter 7.3.1 --- Introduction --- p.89Chapter 7.3.2 --- Construction --- p.90Chapter 7.4 --- Conclusion --- p.91Chapter 8 --- Conclusion --- p.92A Paper Derivation --- p.94Bibliography --- p.9

Exploring the Use of Biometric Smart Cards for Voters’ Accreditation: A Case Study of Nigeria Electoral Process

Voting remains an integral component of every democratic electoral process. it is an avenue for citizens to exercise their rights in order to elect those who will lead them in various vacant political offices. However, enhancing voters’ trust and confidence in electoral processes are significant factors that could encourage the active participation of citizens in elections. Eligible voters tend to decline to participate in an election when they have a feeling that their votes may not eventually count. Furthermore, electoral processes that lead to the emergence of candidates must be adjudged to be free, fair and credible to a high degree for the result to be widely acceptable. Unacceptable election results could lead to protests and total cancelation of the election thereby resulting in loss of time and resources invested in it. To ensure that only registered voters cast their votes on election days, measures must be put in place to accredit voters on election days effectively. Therefore, this article explores the use of biometric smart cards for voters’ verification and identification. With the Nigerian electoral process in view, the existing Nigerian voting procedure was reviewed, lapses were identified and solutions based on the use of the biometric smart card were proffered. If adopted, the proposed adoption of biometric smart cards for voters’ accreditation will enhance the country’s electoral process thereby ensuring that only registered voters cast their votes. The approach presented could also reduce the number of electoral processes and personnel required during election days, thus reducing voting time and cost

On Provable Security for Complex Systems

We investigate the contribution of cryptographic proofs of security to a systematic security engineering process. To this end we study how to model and prove security for concrete applications in three practical domains: computer networks, data outsourcing, and electronic voting. We conclude that cryptographic proofs of security can benefit a security engineering process in formulating requirements, influencing design, and identifying constraints for the implementation

Security and Privacy in Unified Communication

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The use of unified communication; video conferencing, audio conferencing, and instant messaging has skyrocketed during the COVID-19 pandemic. However, security and privacy considerations have often been neglected. This paper provides a comprehensive survey of security and privacy in Unified Communication (UC). We systematically analyze security and privacy threats and mitigations in a generic UC scenario. Based on this, we analyze security and privacy features of the major UC market leaders and we draw conclusions on the overall UC landscape. While confidentiality in communication channels is generally well protected through encryption, other privacy properties are mostly lacking on UC platforms

Cryptographic Protocols for Privacy Enhancing Technologies: From Privacy Preserving Human Attestation to Internet Voting

Desire of privacy is oftentimes associated with the intention to hide certain aspects of our thoughts or actions due to some illicit activity. This is a narrow understanding of privacy, and a marginal fragment of the motivations for undertaking an action with a desired level of privacy. The right for not being subject to arbitrary interference of our privacy is part of the universal declaration of human rights (Article 12) and, above that, a requisite for our freedom. Developing as a person freely, which results in the development of society, requires actions to be done without a watchful eye. While the awareness of privacy in the context of modern technologies is not widely spread, it is clearly understood, as can be seen in the context of elections, that in order to make a free choice one needs to maintain its privacy. So why demand privacy when electing our government, but not when selecting our daily interests, books we read, sites we browse, or persons we encounter? It is popular belief that the data that we expose of ourselves would not be exploited if one is a law-abiding citizen. No further from the truth, as this data is used daily for commercial purposes: users’ data has value. To make matters worse, data has also been used for political purposes without the user’s consent or knowledge. However, the benefits that data can bring to individuals seem endless and a solution of not using this data at all seems extremist. Legislative efforts have tried, in the past years, to provide mechanisms for users to decide what is done with their data and define a framework where companies can use user data, but always under the consent of the latter. However, these attempts take time to take track, and have unfortunately not been very successful since their introduction. In this thesis we explore the possibility of constructing cryptographic protocols to provide a technical, rather than legislative, solution to the privacy problem. In particular we focus on two aspects of society: browsing and internet voting. These two events shape our lives in one way or another, and require high levels of privacy to provide a safe environment for humans to act upon them freely. However, these two problems have opposite solutions. On the one hand, elections are a well established event in society that has been around for millennia, and privacy and accountability are well rooted requirements for such events. This might be the reason why its digitalisation is something which is falling behind with respect to other acts of our society (banking, shopping, reading, etc). On the other hand, browsing is a recently introduced action, but that has quickly taken track given the amount of possibilities that it opens with such ease. We now have access to whatever we can imagine (except for voting) at the distance of a click. However, the data that we generate while browsing is extremely sensitive, and most of it is disclosed to third parties under the claims of making the user experience better (targeted recommendations, ads or bot-detection). Chapter 1 motivates why resolving such a problem is necessary for the progress of digital society. It then introduces the problem that this thesis aims to resolve, together with the methodology. In Chapter 2 we introduce some technical concepts used throughout the thesis. Similarly, we expose the state-of-the-art and its limitations. In Chapter 3 we focus on a mechanism to provide private browsing. In particular, we focus on how we can provide a safer, and more private way, for human attestation. Determining whether a user is a human or a bot is important for the survival of an online world. However, the existing mechanisms are either invasive or pose a burden to the user. We present a solution that is based on a machine learning model to distinguish between humans and bots that uses natural events of normal browsing (such as touch the screen of a phone) to make its prediction. To ensure that no private data leaves the user’s device, we evaluate such a model in the device rather than sending the data over the wire. To provide insurance that the expected model has been evaluated, the user’s device generates a cryptographic proof. However this opens an important question. Can we achieve a high level of accuracy without resulting in a noneffective battery consumption? We provide a positive answer to this question in this work, and show that a privacy-preserving solution can be achieved while maintaining the accuracy high and the user’s performance overhead low. In Chapter 4 we focus on the problem of internet voting. Internet voting means voting remotely, and therefore in an uncontrolled environment. This means that anyone can be voting under the supervision of a coercer, which makes the main goal of the protocols presented to be that of coercionresistance. We need to build a protocol that allows a voter to escape the act of coercion. We present two proposals with the main goal of providing a usable, and scalable coercion resistant protocol. They both have different trade-offs. On the one hand we provide a coercion resistance mechanism that results in linear filtering, but that provides a slightly weaker notion of coercion-resistance. Secondly, we present a mechanism with a slightly higher complexity (poly-logarithmic) but that instead provides a stronger notion of coercion resistance. Both solutions are based on a same idea: allowing the voter to cast several votes (such that only the last one is counted) in a way that cannot be determined by a coercer. Finally, in Chapter 5, we conclude the thesis, and expose how our results push one step further the state-of-the-art. We concisely expose our contributions, and describe clearly what are the next steps to follow. The results presented in this work argue against the two main claims against privacy preserving solutions: either that privacy is not practical or that higher levels of privacy result in lower levels of security.Programa de Doctorado en Ciencia y Tecnología Informática por la Universidad Carlos III de MadridPresidente: Agustín Martín Muñoz.- Secretario: José María de Fuentes García-Romero de Tejada.- Vocal: Alberto Peinado Domíngue