Remote data integrity checking (RDIC) enables a data storage server, say a cloud server, to prove to a verifier that it is actually storing a data owner's data honestly. To date, a number of RDIC protocols have been proposed in the literature, but most of the constructions suffer from the issue of a complex key management, that is, they rely on the expensive public key infrastructure (PKI), which might hinder the deployment of RDIC in practice. In this paper, we propose a new construction of identity-based (ID-based) RDIC protocol by making use of key-homomorphic cryptographic primitive to reduce the system complexity and the cost for establishing and managing the public key authentication framework in PKI-based RDIC schemes. We formalize ID-based RDIC and its security model, including security against a malicious cloud server and zero knowledge privacy against a third party verifier. The proposed ID-based RDIC protocol leaks no information of the stored data to the verifier during the RDIC process. The new construction is proven secure against the malicious server in the generic group model and achieves zero knowledge privacy against a verifier. Extensive security analysis and implementation results demonstrate that the proposed protocol is provably secure and practical in the real-world applications.

In an attribute-based signature (ABS), users sign messages with any predicate of their attributes issued from an attribute authority. Under this notion, a signature attests not to the identity of the individual who signed a message, but a claim regarding the attributes the underlying signer possesses. In ABS, users cannot forge signatures with attributes they do not possess even through colluding. On the other hand, a legitimate signer remains anonymous without the fear of revocation and is indistinguishable among all the users whose attributes satisfying the predicate specified in the signature. ABS is useful in many important applications such as anonymous authentication and attribute-based messaging systems. In this paper, we propose two efficient ABS constructions supporting flexible threshold predicate by exploring a new technique for signature signing. Compared with existed schemes, the new constructions provide better efficiency in terms of both the computational cost and signature size. The first new construction is provably secure in the random oracle model, while the second construction does not rely on the random oracle assumption. To further reduce the trust on attribute authority, we also show an ABS construction with multiple attribute authorities. It is worth noting that the security of all the proposed constructions is not relying on generic group. As an illustrative application, we construct an efficient non-transferable access control system from ABS.

Monero provides a high level of anonymity for both users and their transactions. However, many criminal activities might be committed with the protection of anonymity in cryptocurrency transactions. Thus, user accountability (or traceability) is also important in Monero transactions, which is unfortunately lacking in the current literature. In this paper, we fill this gap by introducing a new cryptocurrency named \textit{Traceable Monero} to balance the user anonymity and accountability. Our framework relies on a tracing authority, but is optimistic, in that it is only involved when investigations in certain transactions are required. We formalize the system model and security model of Traceable Monero. We present a detailed construction of Traceable Monero by overlaying Monero with two types of tracing mechanisms, tracing the one-time addresses with money flows and tracing the long-term addresses. We prove the security of Traceable Monero and implement a prototype of the system, which demonstrates that Traceable Monero incurs merely a very small overhead in generating and verifying a transaction compared to Monero transactions.