Purse: Post-Quantum Unique Ring Signature for Anonymous Transactions

Distributed public ledger (e.g., blockchain) has been proven to be a powerful technique that allows users to sign transactions in an untrusted environment, where identity-privacy disclosure is gaining attention in practice. Ring signatures can protect identities by providing anonymity property for users. However, a malicious anonymous user may generate multiple signatures on the same transaction, called double-spending attack. A unique ring signature avoids this attack by attaching a unique identifier to the transaction. In addition, future-proof cryptographic solutions are attracting attention in the quantum era. Thus, we aim to propose a post-quantum unique ring signature scheme for anonymous transactions, named Purse. We initially provide verifiable random functions over lattices (L-VRF, in short) with tight security and optimize the proof size (compared with the work of Nguyen et al., ESORICS’ 22) using compression techniques. We then obtain Purse from L-VRF inspired by the previous solution of Franklin-Zhang (FC’ 13) while Purse enables to prevent of quantum computer attacks. Finally, Purse is analyzed under the quantum random oracle model (QROM) while providing a prototype via C language. The performance evaluation shows Purse offers a smaller communication load.