Ring confidential transactions (RingCT) is a classical protocol that enhances transaction privacy within blockchain technology. It is primarily utilized in anonymous cryptocurrencies such as Monero. In recent years, to counter the security threats posed by quantum computing to classical RingCT (C-RCT), several post-quantum RingCT (P-RCT) protocols were proposed. However, prior studies do not address the account transition from C-RCT to P-RCT, which is essential to ensure the quantum resistance and usability of user accounts following the upgrade from C-RCT to P-RCT. In this article, we introduce a RingCT account transition protocol (RAT), which allows users to migrate their accounts from the blockchain with C-RCT to that with P-RCT. The protocol consists of two cryptographic components: 1) a zero-knowledge proof scheme used to prove that two group generators correspond to the same witness and 2) a cross-cryptosystems commitment transition protocol. RAT is fully decentralized and does not require any trusted third parties. Additionally, the transition process does not disclose the account balance and maintains both atomicity and consistency. The security of our protocol relies on the cryptographic components within RingCT, without the need for additional security assumptions, such as a trusted setup. The experimental results demonstrate the effectiveness of our protocol in practice.

Ring Confidential Transactions (RingCT) is a classic cryptographic protocol for anonymous transactions on blockchains, currently used in the popular anonymous cryptocurrency Monero. The proof size of RingCT transactions is linearly related to the ring size, which limits the use of larger ring sizes due to the significant communication overhead it incurs. However, reducing the ring size also leads to decreased anonymity. Therefore, in recent years, many studies have focused on optimizing the proof sizes for RingCT, with the latest known solutions reducing the proof size to be logarithmic with the ring size. In this paper, we propose a new compact RingCT protocol (CRCT) for smaller proof sizes. To this end, we first design three extended schemes of the Sum Argument (CRYPTO’21), which are used to generate logarithmic-sized proofs for three distinct zero-knowledge arguments, respectively. We then introduce a new zero-knowledge proof scheme called the Difference Argument. It is used to prove that one has the knowledge of two secret values, with their difference being public. Based on these schemes, we construct our CRCT protocol, whose proof size is independent of the ring size and logarithmic with the number of source accounts. We provide concrete constructions and security proofs for the proposed cryptographic schemes. The experimental results demonstrate that CRCT exhibits significant advantages in computational efficiency and proof size over existing solutions when dealing with large ring sizes and moderate numbers of source accounts.

Data sharing among vehicles can effectively address the traffic congestion and accidents caused by the increasing number of vehicles, thereby enhancing traffic efficiency and the travel experience. However, it also introduces security and privacy challenges related to confidentiality, authentication, identity privacy, identity revocation, and tamper resistance. To address the above challenges, we propose a bilateral access control data sharing scheme by extending Matchmaking Encryption. Our proposal ensures data confidentiality and data source authentication by combining attribute-based encryption with identity-based encryption. Most importantly, we verify the bilateral policies within a single logical step. To achieve identity revocation, we propose a revocation scheme based on a pseudo-identity list, which can revoke all the pseudo-identities associated with a malicious user and ensure the privacy of legitimate real identity. Security analysis indicates that apart from ensuring confidentiality and authentication, our proposal resists attacks, such as tampering, guessing, and collusion. We conduct theoretical complexity analysis and experimental performance evaluations to demonstrate the efficiency and practicality of our proposal for Internet of Vehicles (IoV) data sharing.

Ring Confidential Transactions (RingCT) is a typical privacy-preserving protocol for blockchain, which is used for the most popular anonymous cryptocurrency Monero in recent years. RingCT provides the user's identity anonymity based on the linkable ring signature. At the cost of that, the transaction size is increased linearly to the involved users. In this article, we aim to overcome this inefficient aspect of RingCT by introducing the linkable threshold ring signature (LTRS). We first propose a construction of threshold ring signatures for homomorphic cryptosystems, and present an efficient instantiation based on the intractability assumption of the discrete logarithm problem. Based on this framework, an efficient LTRS scheme and a novel construction of the RingCT protocol are presented. Our proposed RingCT protocol enables multiple payers to co-construct an anonymous transaction without revealing their secret account keys, and it is more concise under multiple input accounts. For a transaction with a ring size of 100 and the input accounts number of 64, the communication overhead is about 4% of the original RingCT protocol.

Immutability is widely recognized as one of the blockchain’s key security attributes. However, in recent years, incidents involving the use of blockchain for disseminating illegal or malicious information have raised concerns over its strict immutability. To address these issues, redactable blockchains are proposed as a novel solution, permitting authorized content redactions without compromising the structural integrity of the blockchain. Unfortunately, current solutions are unable to restrict the abuse of redaction privilege, except for relying on a trusted authority or committee, which contradicts the trustlessness principle of blockchain. In this paper, we propose a controlled redactable blockchain protocol that allows for a limited number of redactions and supports a transparent setup. The cryptographic tools enabling this functionality are our proposed t-times chameleon hash (t-CH) and signature (t-CS) schemes, where generating more than t collisions will expose the trapdoor. We present security models, discrete logarithm-based instantiations, and formal security proofs for both t-CH and t-CS. Subsequently, we present the construction of our redaction protocol in both permissioned and permissionless settings. Finally, we experimentally demonstrate the effectiveness of the proposed protocol in practice.

BACKGROUND: As one of the fundamental problems in bioinformatics, the double digest problem (DDP) focuses on reordering genetic fragments in a proper sequence. Although many algorithms for dealing with the DDP problem were proposed during the past decades, it is believed that solving DDP is still very time-consuming work due to the strongly NP-completeness of DDP. However, none of these algorithms consider the privacy issue of the DDP data that contains critical business interests and is collected with days or even months of gel-electrophoresis experiments. Thus, the DDP data owners are reluctant to deploy the task of solving DDP over cloud. RESULTS: Our main motivation in this paper is to design a secure outsourcing computation framework for solving the DDP problem. We at first propose a privacy-preserving outsourcing framework for handling the DDP problem by using a cloud server; Then, to enable the cloud server to solve the DDP instances over ciphertexts, an order-preserving homomorphic index scheme (OPHI) is tailored from an order-preserving encryption scheme published at CCS 2012; And finally, our previous work on solving DDP problem, a quantum inspired genetic algorithm (QIGA), is merged into our outsourcing framework, with the supporting of the proposed OPHI scheme. Moreover, after the execution of QIGA at the cloud server side, the optimal solution, i.e. two mapping sequences, would be transferred publicly to the data owner. Security analysis shows that from these sequences, none can learn any information about the original DDP data. Performance analysis shows that the communication cost and the computational workload for both the client side and the server side are reasonable. In particular, our experiments show that PP-DDP can find optional solutions with a high success rate towards typical test DDP instances and random DDP instances, and PP-DDP takes less running time than DDmap, SK05 and GM12, while keeping the privacy of the original DDP data. CONCLUSION: The proposed outsourcing framework, PP-DDP, is secure and effective for solving the DDP problem.

Anonymous cryptocurrencies are distributed applications based on blockchain technology that enhance the anonymity of user transactions. However, they also provide cover for many criminal activities. Existing traceable modifications of anonymous transaction protocols do not support public verification of the traceability of transactions, meaning dishonest users can still evade tracing by forging partial proofs. In this paper, we first propose EPoK, which is a partially extractable zero-knowledge proof scheme designed to address this issue. We provide the instantiation of EPoK, as well as its formal security proofs. Combined with EPoK and the classic anonymous transaction protocol RingCT, we propose a traceable anonymous transaction protocol TRCT for tracing participants’ addresses and transaction amounts in anonymous transactions. Compared to previous works, TRCT is the first to implement public verification of the transaction’s traceability while still maintaining anonymity. This ensures that users cannot forge relevant proofs to evade tracing. We present and prove the security properties of TRCT, and experimentally compare its efficiency with the original RingCT protocol. The result shows that the extra overhead generated by TRCT is small.

Side-channel analysis (SCA) based on deep learning (DL) techniques have the benefit that they can disclose the secret key of protected block ciphers without preprocessing. But the size of convolutional neural network (CNN) architecture is so large that the training process is too time-consuming and the required number of traces for recovering secret key is too much. In this paper, we apply heatmap and SNR to reduce the number of parameters of our CNN architecture to 5,269,568 (i.e., one to tenth to the CNNbest). We also combine our CNN architecture with the multi-label classification and the transfer learning techniques to reduce the number of required traces. Consequently, two new CNN architectures are presented and validated on the public ASCAD dataset. The execution time of the training process approximates 15 minutes on average. The first CNN architecture can recover a key byte with only 30 synchronized traces. Combined with the transfer learning technique, the second CNN architecture requires 141 and 171 traces respectively in two different desynchronization cases. To our knowledge, for both synchronization and desynchronization cases, our analysis methods need the smallest amount of traces to extract a key byte.

Nowadays, remote user authentication protocol plays a great role in ensuring the security of data transmission and protecting the privacy of users for various network services. In this study, we discover two recently introduced anonymous authentication schemes are not as secure as they claimed, by demonstrating they suffer from offline password guessing attack, desynchronization attack, session key disclosure attack, failure to achieve user anonymity, or forward secrecy. Besides, we reveal two environment-specific authentication schemes have weaknesses like impersonation attack. To eliminate the security vulnerabilities of existing schemes, we propose an improved authentication scheme based on elliptic curve cryptosystem. We use BAN logic and heuristic analysis to prove our scheme provides perfect security attributes and is resistant to known attacks. In addition, the security and performance comparison show that our scheme is superior with better security and low computation and communication cost.

ABSTRACT Two novel public key encryption schemes based on the non‐Abelian factorization problems were proposed. Both of them are proved to be indistinguishable against adaptively chosen ciphertext attack (IND‐CCA2) in the random oracle models. These constructions have the potential to resist Shor's quantum algorithm attack proposed in 1994 and give affirmative answers for the open question announced by Myasnikov, Shpilrain and Ushakov in 2011. Copyright © 2013 John Wiley & Sons, Ltd.

In CT-RSA 2008, Yu et al. proposed a family of three efficient Online/Offline signature schemes, which are especially suitable for the devices with limited computing capabilities. In this paper, we propose a new security model of Online/Offline signature. We find that Yu et al.' basic scheme is insecure under our model. We repair Yu et al.'s loophole by proposing a modified scheme.