Just One Bit Vector: Complement-Free Ring Confidential Transactions with Transparent Setup

Ring Confidential Transactions (RingCTs) rely on their signature schemes to ensure transaction validity while preserving user privacy. In the discrete-logarithm setting, state-of-theart RingCT signatures leverage Bulletproof as their backbone. In this work, we conduct a thorough analysis of existing Bulletproof-based RingCT signatures and identify two pervasive sources of inefficiency: (i) redundant complement advice induced by binary constraints, and (ii) substantial overhead incurred by defenses against the Knowledge-of-Known-Discrete-Logarithm (KKDL) issue. We present new techniques that eliminate the first inefficiency and significantly reduce the second. We introduce the Weighted-Norm Inner Linear Argument (WNILA) as a new compression pivot and leverage it to design zero-knowledge proofs that capture constraints arising in RingCT without introducing complement advice. We then adopt the techniques of Omniring and Lin et al. to unify the K-Weight and K-Link techniques proposed by ZGSX23 and BulletCT. Building on this framework, we derive three RingCT signature schemes: UniBit, UniBit + , and UniBitRange. We implement all three schemes and benchmark them against BulletCT and Omniring ⋆ under practical parameter regimes. Our experimental results demonstrate 2.5-40× improvements in signing and verification speed over Omniring ⋆ , and 1.6-2.3× signing speedups together with up to 1.65× verification speedup over BulletCT, while achieving comparable signature sizes.