Trading of data is increasingly prevalent as data gain significant economic value, but existing data exchange schemes often suffer from third-party dependency, high verification costs, or inadequate protection of fairness and confidentiality. An efficient decentralized fair exchange scheme for data trading which uses cryptographic commitment scheme and smart contract was proposed in this paper. Our solution guarantees exchange fairness, which requires payments and data to be exchanged correctly between the data buyer and the data seller. First, we design a data verification method with constant verification cost by using polynomial commitments, ensuring that the buyer receives the data matching an agreed-upon commitment. Second, we employ smart contracts to complete the atomic exchange of data and funds, and design a key transmission method by using the properties of bilinear pairings to ensure the confidentiality of trading data. Moreover, our scheme was proved to satisfy the desired security properties: seller fairness, buyer fairness and confidentiality. Simulation results demonstrate the efficiency and practicality of the proposed scheme.

Considering the immutability of traditional blockchain restricts the governance and regulation of sensitive data on chain, this paper proposes a redactable blockchain scheme with k-time controllable cheating editing (CCE-RB for short). In the CCE-RB scheme, the regulator requires editors to generate vector commitments, so as to set the number of times each editor’s editing permissions can be used. The editor needs to open each component of the vector commitment successively before each editor prove that he/she has enough number of times of editing. The regulator has the right to revoke the editor’s editing permission when the editor’s editing times are exhausted or cheating editing behavior occurs, thus realizing the revocability of the editor’s editing permission. In a word, CCE-RB achieves regulation of whole editing process by block editability, controllability of editing times and revocability of editing permissions. By comparing and analyzing related schemes, the experiment results show that CCE-RB scheme has good efficiency.

In this paper, we analyze on the use of token-controlled public key encryption (TCE)schemes. We argue that for many of the applications in some possibilities of application in financial or legal scenarios, for example, the millionaire's will problem, the `private-opening' commitment, the scheduled payment problem, and the sealed-bid auctions and electronic lotteries problem, in the literature, the use of token-controlled public key encryption on its own, leads to inadequate solutions. We suggest that when considering applications of TCE, it is advisable to pay close attention to the lack of authentication and incorporate defences against the problems highlighted in this paper.

Jakobsson et al. first proposed the notions of designated verifier signature (DVS) and an enhanced version, strong designated verifier signature (SDVS) that only the designated verifier can verify the signature's validity. Since then, many improved schemes and variants have been proposed. In 2005, Lipmaa et al. introduced a delegation-attack and proposed a corresponding security concept, namely non-delegatability, which means that both the signer and the designated verifier can not delegate signing right to a third party to generate a valid signature. In this paper, we present a stronger security notion for the SDVS schemes, full non-delegatability, which not only needs the non-delegatability of signing, but also requires that non-delegatability of verifying. And we also analyze some previous SDVS schemes and find that all of them are not secure under the new security notion. At last, we propose an improved SDVS scheme based on identity (ID-SDVS). The proposed scheme is provably secure under the new security notion in the random oracle model.