Zero-Knowledge Proof (ZKP) is a useful tools for proving that a prover possesses a secret without revealing it to the verifier. Designated Verifier Proof (DVP) is a special type of ZKP that adds the ability to restrict the identity of verifiers so that only pre-determined authorized verifiers can verify. However, DVP and other similar schemes do not work if the verifier provides some additional information to indicate the provenance of the proof. Since this information may be stored on the blockchain, the proof can be accepted by third parties even if the verifier is willing to protect the privacy of the prover. In this paper, we propose the concept of Blockchain Designated Verifier Proof (BDVP), and design a BDVP scheme suitable for blockchain applications. The key technique behind our BDVP scheme is that the verifier can forge a fake secret to simulate the proof. Therefore, a third party cannot determine whether the prover possesses the secret. This enables the verifier to protect the privacy of the prover, which is required by law or regulation. We also address the quantum attack problem and propose a post-quantum solution. We evaluate and compare the performances of the proposed protocol with other related protocols.

Attribute-based encryption (ABE) is a useful tool for sharing an encrypted data to a target group. In a ciphertext-policy ABE (CP-ABE) scheme, a ciphertext includes a policy to indicate its receivers and only those receivers can correctly decrypt the ciphertext. Since this design leaks the receiver identity, it may raise a new security issue about user privacy. Some hidden-policy ABE schemes, where the policy is secretly protected, are proposed to keep user privacy. However, these hidden-policy ABE schemes rely on the user trying all possibilities to decide if it belongs to the wanted receiver group. The decryption costs too much and every potential receiver will run the decryption process in vain since it does not know the policy. In this work, we apply the deniability concept to solve this problem. The encryption scheme allows the sender to claim the ciphertext is for some receiver group while actually it is for another receiver group. Both receiver groups can correctly decrypt the ciphertext except that the real group can get the real message and the cover group will get the cover message. While coercion, the sender can definitely claim the ciphertext is for the cover group and the real group is kept confidential.

Currently, online social networks are essential platforms for political organizations to monitor public opinion, disseminate information, argue with the opposition, and even achieve spin control. However, once such purposeful/aggressive articles flood social sites, it would be more difficult for users to distinguish which messages to read or to trust. In this paper, we aim to address this issue by identifying potential “cyber-armies/professional users” during election campaigns on social platforms. We focus on human-operated accounts who try to influence public discussions, for instance, by publishing hundreds/thousands of comments to show their support or rejection of particular candidates. To achieve our objectives, we collected activity data over six months from a prominent Taiwan-based social forum before the 2018 national election and applied a series of statistical analyses to screen out potential targets. From the results, we successfully identified several accounts according to distinctive characteristics that corresponded to professional users. According to the findings, users and platforms could realize potential information manipulation and increase the transparency of the online society.

Cloud-assisted cyber–physical systems (CCPSs) integrate the physical space with cloud computing. To do so, sensors on the field collect real-life data and forward it to clouds for further data analysis and decision-making. Since multiple services may be accessed at the same time, sensor data should be forwarded to different cloud service providers (CSPs). In this scenario, attribute-based encryption (ABE) is an appropriate technique for securing data communication between sensors and clouds. Each cloud has its own attributes and a broker can determine which cloud is authorized to access data by the requirements set at the time of encryption. In this paper, we propose a privacy-preserving broker-ABE scheme for multiple CCPSs (MCCPS). The ABE separates the policy embedding job from the ABE task. To ease the computational burden of the sensors, this scheme leaves the policy embedding task to the broker, which is generally more powerful than the sensors. Moreover, the proposed scheme provides a way for CSPs to protect data privacy from outside coercion.

Blockchain-based bidding systems are becoming increasingly popular nowadays. Due to the properties of blockchain, bidding records are unchangeable. With existing encryption techniques, these bidding records can only be shared by the bidder and the seller. Although this scenario sounds secure, it does not consider a coercion case. A powerful coercer may force the bidding system to open the records stored on the blockchain, and the system loses privacy. To solve this problem, in this paper, we introduce a new encryption scheme called deniable matchmaking encryption (DME). This new encryption scheme provides deniability not only for the message, but also for the identities.We use the chameleon hash function to make fake message and fake identities indistinguishable from the real message and the real identities. Therefore, the bidding system can use fake information to answer the coercer, and user privacy is kept by the blockchain-based bidding system.