Linkable, k-Times Traceable, and Revocable Ring Signature for Fine-Grained Accountability in Blockchain Transactions

—Ring signatures are a useful cryptographic technique for anonymous transactions on the blockchain, which allows a user to sign a message on behalf of a group, without revealing which specific member of the group did the signing. However, the anonymity it provides can at times be too powerful and needs to be controlled when used in practice (e.g., on a reliable blockchain anonymous transaction system). In order to address this issue, we propose a linkable, k-times traceable and revocable ring signature (Lk-TRS). Specifically, with respect to the same issue, Lk-TRS not only establishes links among fewer than k signatures of a signer but also enables tracing of the identity when the signer signs k times. Based on our Lk-TRS, we propose a blockchain anonymous transaction system that supports the identity binding of a single user to multiple accounts, as well as the dynamic joining and exiting of users. This ensures the system meets practical requirements and offers runtime flexibility. We prove that our Lk-TRS achieves anonymity, unforgeability, linkability, k-traceability, and exculpability. Compared to the state-of-the-art, our Lk-TRS is more practical for large blockchain systems, maintaining a constant signature size regardless of the ring size.