Redactable blockchain is an emerging topic in recent blockchain research. Its purpose is to delete or correct errors and harmful content on the chain without using hard forks. In other words, while preserving the public immutability of the blockchain, to allow some administrators or trusted centers with higher authority to modify the content on the blockchain without violating the integrity of the entire blockchain. In this paper, we proposed a redactable blockchain scheme based on unforgeable signatures. Compared with the existing blockchain editing solutions, this paper's solution can be efficiently and conveniently integrated into the current blockchain technology. This scheme's security is based on the collision-resistant hash function used by the original immutable blockchain and the unforgeability of the signature scheme. Besides, our solution can quickly confirm whether a chain has correctly implemented modifications issued by the central authority through the merge verification of signatures.

Privacy of RFID systems is receiving increasing attention in the RFID community. Basically, there are two kinds of RFID privacy notions in the literature: one based on the indistinguishability of two tags, denoted as ind-privacy, and the other based on the unpredictability of the output of an RFID protocol, denoted as unp-privacy. In this article, we first revisit the existing unpredictability-based RFID privacy models and point out their limitations. We then propose a new RFID privacy model, denoted as unp * -privacy, based on the indistinguishability of a real tag and a virtual tag. We formally clarify its relationship with the ind-privacy model. It is proven that ind-privacy is weaker than unp * -privacy. Moreover, the minimal (necessary and sufficient) condition on RFID tags to achieve unp * -privacy is determined. It is shown that if an RFID system is unp * -private, then the computational power of an RFID tag can be used to construct a pseudorandom function family provided that the RFID system is complete and sound. On the other hand, if each tag is able to compute a pseudorandom function, then the tags can be used to construct an RFID system with unp * -privacy. In this sense, a pseudorandom function family is the minimal requirement on an RFID tag's computational power for enforcing RFID system privacy. Finally, a new RFID mutual authentication protocol is proposed to satisfy the minimal requirement.

Privacy of RFID systems is receiving increasing attention in the RFID community. Basically, there are two kinds of RFID privacy notions: one based on the indistinguishability of two tags, denoted as ind-privacy, and the other based on the unpredictability of the output of a protocol, denoted as unp-privacy. In this paper, the definition of unp-privacy is refined and the relation between the two notions is clarified: it is proven that ind-privacy is weaker than unp-privacy. Moreover, the minimal (necessary and sufficient)condition on RFID tags to achieve unp-privacy is determined. It is shown that if an RFID system has strong (or weak) unp-privacy then the computational power of an RFID tag can be used to construct a pseudorandom function family provided that the RFID system is complete and sound. On the other hand, if each tag is able to compute a pseudorandom function, then the tags can be used to construct an RFID system with strong (or weak) unp-privacy. In this sense, a pseudorandom function family is the minimal requirement on an RFID tag's computational power for enforcing strong RFID system privacy. Finally, a new RFID protocol is proposed to satisfy the minimal requirement, which also outperforms the state-of-the-art RFID protocols in terms of computational cost and communication overhead.