In recent years, the medical industry is generating a large amount of data. How to securely store and reliably share these medical data has been a hot research topic. Cloud storage technology can be applied to the medical industry to adapt to the rapid growth of medical data. However, cloud-based data storage and sharing systems face a series of security issues: whether the integrity of outsourced medical data can be guaranteed, and malicious access between different medical institutions may leak user's privacy. This article proposes a system that simultaneously solves the integrity auditing of medical data and securely data sharing between different medical institutions under the terminal-edge-cloud framework. Specifically, patients/doctors are treated as terminal users, medical institutions are viewed as edge nodes, and medical clouds form the central storage layer. In the process of data auditing, third-party auditor can achieve integrity auditing of medical cloud storage data. Moreover, different medical institutions use private-set-intersection technology to share the common user's electronic medical data, while for other users not in intersection set, their data does not need to be shared. Finally, security and performance analyses show that our proposed system is provable secure and has high computational and communication efficiency.

Vehicular ad hoc network (VANET), as an important part of intelligent transportation system, attracts more and more attention since it can provide communication about traffic and vehicle conditions, and optimize the transportation. It is noted that it also faces a series of security challenges. One of core issues is how to achieve secure data sharing and access control. Ciphertext-policy attribute-based encryption (CP-ABE) technique is often used to achieve these goals simultaneously. However, in the execution process of applying CP-ABE to VANET, there are two crucial issues that need to be resolved. One is key-escrow issue, which means that all vehicles’ secret keys will be leaked once if the central attribute authority (CAA) is compromised, and another is the revocation issue of departing vehicles from current region. In order to resolve these two issues simultaneously, in this paper, we propose an efficient data sharing protocol for VANET with the key-escrow-free and vehicle-revocable properties. More specifically, we design a sub-protocol between CAA and vehicles, which interactively issues secret keys for these vehicles. But CAA does not know any user’s true secret key, which guarantees that it is still secure even if CAA is compromised. In addition, we additionally introduce an entity named group manager, which manages and updates the unrevoked users in the current group. In order to improve the efficiency of the whole system, we adopt the online/offline encryption method for data owner and outsourced decryption technique for the resource-constraint data users. Finally, the performance analysis show that our proposed protocol is competitive in the phases of online encryption, key generation and CAA-setup, and thus is useful in the practical applications of VANET.

Recently, Rabaninejadet al.(2019) proposed an excellent auditing protocol for shared data (CoRPA, for short) [IEEE Trans. Ser. Comp., DOI 10.1109/TSC.2019.2919627], which has many better properties, like the identity-privacy, collusion resistant, efficient user revocation and supporting dynamic update etc. In addition, they also presented the detailed security analysis for CoRPA and described the reduction from the soundness of CoRPA to discrete logarithm assumption. However, in this article, we analyze their original security reduction (to discrete logarithm) and find out that it is incorrect and misleading. That is, the soundness of CoRPA cannot be obtained from the discrete logarithm assumption. Now, we give a new proof for their CoRPA based on the square-CDH assumption, which is also used by them to prove the security of homomorphic proxy re-signature scheme. We also hope the new security proof will provide theoretical guarantee when using CoRPA in practical scenes.

Homomorphic signature is an extremely important public key authentication technique for network coding to defend against pollution attacks. As a public key cryptographic primitive, it also encounters the same problem of how to confirm the relationship between some public key pk and the identity ID of its owner. In the setting of distributed network coding, the intermediate and destination nodes need to use the public key of source node S to check the validity of vector-signature pairs. Therefore, the binding of S and its corresponding public key becomes crucial. The popular and traditional solution is based on certificates which are issued by a trusted certification authority (CA) center. However, the generation and management of certificates is extremely cumbersome. Hence, in recent work, Lin et al. proposed a new notion of identity-based homomorphic signature, which intends to avoid using certificates. But the key escrow problem is inevitable for identity-based primitives. In this article, we propose another new notion (for network coding): certificateless homomorphic signature (CLHS), which is a compromise for the above two techniques. In particular, we first describe the definition and security model of certificateless homomorphic signature. Then based on bilinear map and the computational Diffie-Hellman (CDH) assumption, give a concrete implementation and detailedly analyze its security. Finally, performance analysis illustrates that our construction is practical.

In 2014, Wu et al. proposed a tag encoding scheme, named KEPTE, to protect network coding against pollution attack. They also carefully analyzed the security of KEPTE based on the transmission of a data file through their key-pre-distributed network. In this article, we point out that their security analysis only holds for single data file transmitted in this network. If multiple files are multicasted though it, then any adversary may completely recover source node's signing key. A concrete example says that, after pre-distributing 90 keys to all the nodes in the network, it only allows to securely transmit (at most) 3 data files. More importantly, this scheme is completely insecure in standard security model for network model since the adversary is allowed to make polynomial times queries on any data files of its choice before outputting its final forgery. Finally, we also propose a twisted KEPTE scheme that is secure against any eavesdropping adversary no matter how many data files it has queried.

Abstract In PKC 2000, Pointcheval presented a generic technique to make a highly secure cryptosystem from any partially trapdoor one-way function in the random oracle model. More precisely, any suitable problem providing a one-way cryptosystem can be efficiently derived into a chosen-ciphertext attack (CCA) secure public key encryption (PKE) scheme. In fact, the overhead only consists of two hashing and a XOR. In this paper, we consider the key-dependent message (KDM) security of the Pointcheval’s transformation. Unfortunately, we do not know how to directly prove its KDM-CCA security because there are some details in the proof that we can not bypass. However, a slight modification of the original transformation (we call twisted Pointcheval’s scheme) makes it possible to obtain the KDM-CCA security. As a result, we prove that the twisted Pointcheval’s scheme achieves the KDM-CCA security without introducing any new assumption. That is, we can construct a KDM-CCA secure PKE scheme from partial trapdoor one-way injective family in the random oracle model.