A-MAKE: an efficient, anonymous and accountable authentication framework for WMNs

In this paper, we propose a framework, named as A-MAKE, which efficiently provides security, privacy, and accountability for communications in wireless mesh networks. More specifically, the framework provides an anonymous mutual authentication protocol whereby legitimate users can connect to network from anywhere without being identified or tracked. No single party (e.g., network operator) can violate the privacy of a user, which is provided in our framework in the strongest sense. Our framework utilizes group signatures, where the private key and the credentials of the users are generated through a secure three-party protocol. User accountability is implemented via user revocation protocol that can be executed by two semitrusted authorities, one of which is the network operator. The assumptions about the trust level of the network operator are relaxed. Our framework makes use of much more efficient signature generation and verification algorithms in terms of computation complexity than their counterparts in literature, where signature size is comparable to the shortest signatures proposed for similar purposes so far

KCRS: A Blockchain-Based Key Compromise Resilient Signature System

Digital signatures are widely used to assure authenticity and integrity of messages (including blockchain transactions). This assurance is based on assumption that the private signing key is kept secret, which may be exposed or compromised without being detected in the real world. Many schemes have been proposed to mitigate this problem, but most schemes are not compatible with widely used digital signature standards and do not help detect private key exposures. In this paper, we propose a Key Compromise Resilient Signature (KCRS) system, which leverages blockchain to detect key compromises and mitigate the consequences. Our solution keeps a log of valid certificates and digital signatures that have been issued on the blockchain, which can deter the abuse of compromised private keys. Since the blockchain is an open system, KCRS also provides a privacy protection mechanism to prevent the public from learning the relationship between signatures. We present a theoretical framework for the security of the system and a provably-secure construction. We also implement a prototype of KCRS and conduct experiments to demonstrate its practicability

A Practical Approach for Implementation of Public Key Infrastructure for Digital Signatures

In an organization with its own Private Network , it is not just enough to transfer the documents from one person to another, but also it needs to ensure that the document retains its integrity, confirms the authenticity of the sender, provides privacy, if required and it is safe against repudiations. To address these, it is proposed to establish a public key infrastructure (PKI) for digital signatures with in the organizations. Public key infrastructure provides robust and rigorous security measures to protect user data and credentials. In this paper, it is proposed that documents are digitally signed on before being sent as an authentication measure. The trust between two parties and digital signatures are reinforced by components of public key infrastructure (PKI) namely Public Key Cryptography, Certificate Authority (CA), Certificates, Certificate Repository (CR), and also a simple application to demonstrate the same would also be attempted. Keywords: Open SSL, Public Key Infrastructure, Digital signatures, Certificate Authority, Certificate Repository

Extending and Applying a Framework for the Cryptographic Verification of Java Programs

Abstract. In our previous work, we have proposed a framework which allows tools that can check standard noninterference properties but a priori cannot deal with cryptography to establish cryptographic indistinguishability properties, such as privacy properties, for Java programs. We refer to this framework as the CVJ framework (Cryptographic Verification of Java Programs) in this paper. While so far the CVJ framework directly supports public-key encryption (without corruption and without a public-key infrastructure) only, in this work we further instantiate the framework to support, among others, public-key encryption and digital signatures, both with corruption and a public-key infrastructure, as well as (private) symmetric encryption. Since these cryptographic primitives are very common in security-critical applications, our extensions make the framework much more widely applicable. To illustrate the usefulness and applicability of the extensions proposed in this paper, we apply the framework along with the tool Joana, which allows for the fully automatic verification of noninterference properties of Java programs, to establish cryptographic privacy properties of a (non-trivial) cloud storage application, where clients can store private information on a remote server.

One-Time Universal Hashing Quantum Digital Signatures without Perfect Keys

Quantum digital signatures (QDS), generating correlated bit strings among three remote parties for signatures through quantum law, can guarantee non-repudiation, authenticity, and integrity of messages. Recently, one-time universal hashing QDS framework, exploiting the quantum asymmetric encryption and universal hash functions, has been proposed to significantly improve the signature rate and ensure unconditional security by directly signing the hash value of long messages. However, similar to quantum key distribution, this framework utilizes keys with perfect secrecy by performing privacy amplification that introduces cumbersome matrix operations, thereby consuming large computational resources, causing delays and increasing failure probability. Here, we prove that, different from private communication, imperfect quantum keys with limited information leakage can be used for digital signatures and authentication without compromising the security while having eight orders of magnitude improvement on signature rate for signing a megabit message compared with conventional single-bit schemes. This study significantly reduces the delay for data postprocessing and is compatible with any quantum key generation protocols. In our simulation, taking two-photon twin-field key generation protocol as an example, QDS can be practically implemented over a fiber distance of 650 km between the signer and receiver. For the first time, this study offers a cryptographic application of quantum keys with imperfect secrecy and paves a way for the practical and agile implementation of digital signatures in a future quantum network.Comment: Comments are welcome

Security Analysis of Signature Schemes with Key Blinding

Digital signatures are fundamental components of public key cryptography. They allow a signer to generate verifiable and unforgeable proofs---signatures---over arbitrary messages with a private key, and allow recipients to verify the proofs against the corresponding and expected public key. These properties are used in practice for a variety of use cases, ranging from identity or data authenticity to non-repudiation. Unsurprisingly, signature schemes are widely used in security protocols deployed on the Internet today. In recent years, some protocols have extended the basic syntax of signature schemes to support key blinding, a.k.a., key randomization. Roughly speaking, key blinding is the process by which a private signing key or public verification key is blinded (randomized) to hide information about the key pair. This is generally done for privacy reasons and has found applications in Tor and Privacy Pass. Recently, Denis, Eaton, Lepoint, and Wood proposed a technical specification for signature schemes with key blinding in an IETF draft. In this work, we analyze the constructions in this emerging specification. We demonstrate that the constructions provided satisfy the desired security properties for signature schemes with key blinding. We experimentally evaluate the constructions and find that they introduce a very reasonable 2-3x performance overhead compared to the base signature scheme. Our results complement the ongoing standardization efforts for this primitive

Membership Privacy for Fully Dynamic Group Signatures

Group signatures present a compromise between the traditional goals of digital signatures and the need for signer privacy, allowing for the creation of unforgeable signatures in the name of a group which reveal nothing about the actual signer's identity beyond their group membership. An important consideration that is absent in prevalent models is that group membership itself may be sensitive information, especially if group membership is dynamic, i.e. membership status may change over time. We address this issue by introducing formal notions of membership privacy for fully dynamic group signature schemes, which can be easily integrated into the most expressive models of group signature security to date. We then propose a generic construction for a fully dynamic group signature scheme with membership privacy that is based on signatures with flexible public key (SFPK) and signatures on equivalence classes (SPSEQ). Finally, we devise novel techniques for SFPK to construct a highly efficient standard model scheme (i.e. without random oracles) that provides shorter signatures than even the non-private state-of-the-art from standard assumptions. This shows that, although the strictly stronger security notions we introduce have been completely unexplored in the study of fully dynamic group signatures so far, they do not come at an additional cost in practice

Public cloud data auditing with practical key update and zero knowledge privacy

Data integrity is extremely important for cloud based storage services, where cloud users no longer have physical possession of their outsourced files. A number of data auditing mechanisms have been proposed to solve this problem. However, how to update a cloud user\u27s private auditing key (as well as the authenticators those keys are associated with) without the user\u27s re-possession of the data remains an open problem. In this paper, we propose a key-updating and authenticator-evolving mechanism with zero-knowledge privacy of the stored files for secure cloud data auditing, which incorporates zero knowledge proof systems, proxy re-signatures and homomorphic linear authenticators. We instantiate our proposal with the state-of-the-art Shacham-Waters auditing scheme. When the cloud user needs to update his key, instead of downloading the entire file and re-generating all the authenticators, the user can just download and update the authenticators. This approach dramatically reduces the communication and computation cost while maintaining the desirable security. We formalize the security model of zero knowledge data privacy for auditing schemes in the key-updating context and prove the soundness and zero-knowledge privacy of the proposed construction. Finally, we analyze the complexity of communication, computation and storage costs of the improved protocol which demonstrates the practicality of the proposal

Design and Analysis of Opaque Signatures

Digital signatures were introduced to guarantee the authenticity and integrity of the underlying messages. A digital signature scheme comprises the key generation, the signature, and the verification algorithms. The key generation algorithm creates the signing and the verifying keys, called also the signer’s private and public keys respectively. The signature algorithm, which is run by the signer, produces a signature on the input message. Finally, the verification algorithm, run by anyone who knows the signer’s public key, checks whether a purported signature on some message is valid or not. The last property, namely the universal verification of digital signatures is undesirable in situations where the signed data is commercially or personally sensitive. Therefore, mechanisms which share most properties with digital signatures except for the universal verification were invented to respond to the aforementioned need; we call such mechanisms “opaque signatures”. In this thesis, we study the signatures where the verification cannot be achieved without the cooperation of a specific entity, namely the signer in case of undeniable signatures, or the confirmer in case of confirmer signatures; we make three main contributions. We first study the relationship between two security properties important for public key encryption, namely data privacy and key privacy. Our study is motivated by the fact that opaque signatures involve always an encryption layer that ensures their opacity. The properties required for this encryption vary according to whether we want to protect the identity (i.e. the key) of the signer or hide the validity of the signature. Therefore, it would be convenient to use existing work about the encryption scheme in order to derive one notion from the other. Next, we delve into the generic constructions of confirmer signatures from basic cryptographic primitives, e.g. digital signatures, encryption, or commitment schemes. In fact, generic constructions give easy-to-understand and easy-to-prove schemes, however, this convenience is often achieved at the expense of efficiency. In this contribution, which constitutes the core of this thesis, we first analyze the already existing constructions; our study concludes that the popular generic constructions of confirmer signatures necessitate strong security assumptions on the building blocks, which impacts negatively the efficiency of the resulting signatures. Next, we show that a small change in these constructionsmakes these assumptions drop drastically, allowing as a result constructions with instantiations that compete with the dedicated realizations of these signatures. Finally, we revisit two early undeniable signatures which were proposed with a conjectural security. We disprove the claimed security of the first scheme, and we provide a fix to it in order to achieve strong security properties. Next, we upgrade the second scheme so that it supports a iii desirable feature, and we provide a formal security treatment of the new scheme: we prove that it is secure assuming new reasonable assumptions on the underlying constituents