Biblio

With the development of various technologies, the modern industry has been promoted to a new era known as Industry 4.0. Within such paradigm, smart factories are becoming widely recognized as the fundamental concept. These systems generate and exchange vast amounts of privacy-sensitive data, which makes them attractive targets of attacks and unauthorized access. To improve privacy and security within such environments, a more decentralized approach is seen as the solution to allow their longterm growth. Currently, the blockchain technology represents one of the most suitable candidate technologies able to support distributed and secure ecosystem for Industry 4.0 while ensuring reliability, information integrity and access authorization. Blockchain based access control frameworks address encountered challenges regarding the confidentiality, traceability and notarization of access demands and procedures. However significant additional fears are raised about entities' privacy regarding access history and shared policies. In this paper, our main focus is to ensure strong privacy guarantees over the access control related procedures regarding access requester sensitive attributes and shared access control policies. The proposed scheme called PDAMF based on ring signatures adds a privacy layer for hiding sensitive attributes while keeping the verification process transparent and public. Results from a real implementation plus performance evaluation prove the proposed concept and demonstrate its feasibility.

Wearable smart sensing devices presently become more and more popular in people's daily life, which also brings serious problems related to personal data privacy. In order to provide users better experiences, wearable smart sensing devices are collecting users' personal data all the time and uploading the data to service provider to get computing services, which objectively let service provider master each user's condition and cause a lot of problems such as spam, harassing call, etc. This paper designs a blockchain based scheme to solve such problems by cutting off the association between user identifier and its sensing data from perspective of shielding service providers and adversaries. Firstly, privacy requirements and situations in smart sensing area are reviewed. Then, three key technologies are introduced in the scheme including its theories, purposes and usage. Next, the designed protocol is shown and analyzed in detail. Finally, security analysis and engineering feasibility of the scheme are given. This scheme will give user better experience from privacy protection perspective in smart sensing area.

This paper proposes an efficient auditing scheme for checking the integrity of dynamic data shared among a static group of users outsourced at untrusted cloud storage. The scheme is designed based on CDH-based ring signature scheme. The scheme enables a third party auditor to audit the client's data without knowing the content while also preserving the identity privacy of the group member who is signing the data from the auditor as well as from the cloud server. The identity of the group member who is signing the data block can be revealed only by the authorized opener, if needed. The paper presents a comparative performance study and security analysis of the proposed scheme.

Bitcoin is a decentralized digital currency, widely used for its perceived anonymity property, and has surged in popularity in recent years. Bitcoin publishes the complete transaction history in a public ledger, under pseudonyms of users. This is an alternative way to prevent double-spending attack instead of central authority. Therefore, if pseudonyms of users are attached to their identities in real world, the anonymity of Bitcoin will be a serious vulnerability. It is necessary to enhance anonymity of Bitcoin by a coin mixing service or other modifications in Bitcoin protocol. But in a coin mixing service, the relationship among input and output addresses is not hidden from the mixing service provider. So the mixing server still has the ability to track the transaction records of Bitcoin users. To solve this problem, We present a new coin mixing scheme to ensure that the relationship between input and output addresses of any users is invisible for the mixing server. We make use of a ring signature algorithm to ensure that the mixing server can't distinguish specific transaction from all these addresses. The ring signature ensures that a signature is signed by one of its users in the ring and doesn't leak any information about who signed it. Furthermore, the scheme is fully compatible with existing Bitcoin protocol and easily to scale for large amount of users.

Though anonymity of ring signature schemes has been studied in many literatures for a long time, these papers showed different definitions and there is no consensus. Recently, Bender et al. proposed two new anonymity definitions of ring signature which is stronger than the traditional definition, that are called anonymity against attribution attacks/full key exposure. Also, ring signature schemes have two levels of unforgeability definitions, i.e., existential un-forgeability (eUF) and strong existential unforgeability (sUF). In this paper, we will redefine anonymity and unforgeability definitions from the standpoint of universally composable (UC) security framework. First, we will formulate new ideal functionalities of ring signature schemes for each security levels separately. Next, we will show relations between cryptographic security definitions and our UC definitions. Finally, we will give another proof of the Bender et al.'s ring signature scheme following the UC secure definition by constructing a simulator to an adversary of sUF, which can be adaptable to the case of sUF under the assumption of a standard single sUF signature scheme.