Public key authenticated encryption with keyword search (PAEKS) is a cryptographic primitive which ensures privacy of user's sensitive data while preserving the search ability over them. Of particular interest are certificateless PAEKS (CLAEKS) schemes which can further circumvent challenges such as certificate management and key escrow problem. Our goal in this paper is advancing existing literature on certificateless PAEKS schemes in two aspects. First, we notice that published security model of CLAEKS schemes assumes the existence of a single key generation center (KGC) to manage all the keys. Considering multiple KGCs can lead to enhancements in trust-related issues and appears more in line with reality, so we formulate the security model to cover CLAEKS with multiple KGCs. Second, as far as we know, all existing secure CLAEKS schemes are based on the time-consuming bilinear pairing operation which dramatically increases the computational cost. We construct an efficient pairing-free CLAEKS scheme and prove its security in our multiple-KGC security model. Our construction achieves security against keyword guessing attacks performed by both inside and outside adversaries. A comparison between our proposed scheme and other related schemes is also provided to assert the overall superiority of the proposed scheme.

The Encrypted Image Reversible Data Hiding (EIRDH) is a hot area of research in multimedia outsourcing scenarios. In such a setting, a content owner possesses confidential images that he wants to upload to an untrusted server. The server is supposed to embed a secret message in the images before sending them to potential receivers, and the receivers expect to recover the original images without any distortion. EIRDH schemes are designed to meet reversible data hiding goals while preserving the confidentiality of the host images. Confidentiality is provided by means of encryption algorithms; however, these algorithms, in turn, introduce the challenge of dealing with ciphered images in both embedding and extraction phases. The current paper tries to propose a privacy-preserving reversible data hiding scheme for JPEG images without the need for any levels of decompression. We propose an elliptic curve-based asymmetric, commutative, and separable EIRDH method, in which no entities other than the sender and the eligible receiver of the hidden message (embedded in the encrypted image) are able to recognize its existence. In particular, even the server that performs the embedding remains completely unaware of the content of the images. An important security feature of our scheme involves the security of its multiple encryptions against Chosen-Plaintext Attack (CPA), which is an attack model that assumes the adversary can obtain the encryptions of the images on his choice to achieve possible extra information to attack. Experimental results show that our scheme achieves full reversibility and a satisfactory level of capacity, while it accurately extracts all the hidden bits.

Currently, the existing literature on multipurpose watermarking employs multiple watermarks for simultaneous achieving of multiple security objectives. This approach can be problematic since a watermark targeting tampers might fail to detect tampering of another watermark inserted for copyright violation. Moreover, most of the current schemes follow a non‐blind approach where the original watermark is needed for authentication. A question that naturally arises is whether multipurpose watermarking can be realised with the insertion of a single watermark in a blind way or not. The goal of the authors study is to provide an affirmative answer to this important question. They show how a cryptographic primitive called verifiable threshold secret sharing can be used to come up with a generic construction for blind multipurpose watermarking which inserts a single watermark into the host image for simultaneous achieving of copyright protection, authentication, and tamper localisation. The generic property of the proposed scheme provides flexibility for choosing the embedding/extraction of the watermark based on the desired level of fidelity, robustness and capacity. Experimental results are provided to confirm the superiority of their proposed technique as compared to existing approaches.

The Industrial Internet of Things (IIoT) represents a variety of IoT applications in the industrial sector of economy and is heavily underpinned by computational capabilities of cloud computing to reduce the cost of on-demand services. However, cloud computing does not protect the privacy of the outsourced data unless some form of encryption is applied. Recently, some Certificateless Authenticated Encryption with Keyword Search (CLAEKS) schemes have been proposed. However, it is known in the literature that the security of these schemes is proved based on a weak security model. In this paper, we first provide a more powerful and realistic security model for CLAEKS schemes. Then, we propose a new CLAEKS scheme and prove its security in the enhanced security model. The comparison results show that the proposed CLAEKS scheme is the only existing searchable encryption scheme in the certificateless setting that is secure in the enhanced security model.

In 2017, the notion of public key authenticated encryption with keyword search (PAEKS) and its security model was defined by Huang and Li. Their main motivation was providing security against inside keyword guessing attacks (KGA). They also proposed a concrete PAEKS scheme secure in their proposed model. In this study, the authors first show that their security model has an important drawback and therefore, cannot handle multi‐user settings. As such settings are a necessity in the public‐key environment, it is vital to improving the model to capture multiple users. This is what they do in the first part of this study. Then, they consider Huang and Li's PAEKS scheme and prove that it is not secure against inside (and even outside) KGA. Finally, they propose a modified scheme to fix the problem without any additional communication or computation costs. They further prove that the new scheme is secure in the improved model.

Abstract The concept of social secret sharing was introduced in 2010 by Nojoumian et al. In the scheme of Nojoumian et al. (called SSS), the number of shares allocated to each party depends on the player's reputation and the way he interacts with other parties. In other words, weights of the players are periodically adjusted such that cooperative participants receive more shares compared with non‐cooperative parties. As our contribution, we propose an ideal social secret sharing in which the size of each player's share is equal to the size of the secret. This property will be achieved using hierarchical threshold secret sharing. We show that the proposed scheme is secure in a passive adversary model. Compared with SSS, our proposed scheme is more efficient in terms of the share size, communication complexity, and computational complexity of the “sharing” protocol. However, the “social tuning” and “reconstruction” protocols of SSS are computationally more efficient than those of the proposed scheme. Depending on the number of execution of social tuning protocol, this might be a reasonable compromise because the reconstruction protocol is executed only once throughout the secret's lifetime. Copyright © 2016 John Wiley & Sons, Ltd.

A distributed key generation (DKG) protocol is a central component in distributed cryptosystems. It allows a group of participants to jointly generate a pair of keys (private key and public key) without assuming any trusted participant. The public key is output in clear but only authorised subgroups of participants are able to reconstruct or use the private key. Existing literature on DKG protocols assumes equal authority for participants. In this study, the authors consider the problem of DKG in groups with hierarchical structure where the authorised subsets can be defined by a hierarchical threshold access structure. They first propose a verifiable hierarchical threshold secret sharing protocol. On the basis of this construction, they then propose a new DKG protocol with hierarchical threshold access structure for discrete‐logarithm‐based cryptosystems. It is shown that the proposed protocols satisfy all the security requirements.