Lotus: A Hybrid Cross-Chain Framework for Privacy-Preserving Digital Identity

Abstract

Integrating decentralized identity (DID) systems with state authorities introduces complex challenges related to trust, privacy, and auditability. The Lotus Bridge framework addresses these by proposing a hybrid digital identity architecture suitable for national-scale deployment. It integrates a permissioned Proof-of-Authority (PoA) blockchain for sovereign credential issuance with a cross-chain verification bridge that utilizes zero-knowledge proofs to enable privacy-preserving selective disclosure. This architecture is one of the first to combine state-backed issuance with interoperable, private cross-chain verification in a unified system. Two core protocols—state-anchored issuance and cross-chain verification—are formally defined and implemented in a working prototype. Experimental results demonstrate strong performance: cryptographic proofs remain under 600 bytes and end-to-end verification latency consistently stays below 2 seconds, enabling real-time applicability. Additionally, parallelization reduces proof generation time by over 90%, and the system achieves significant cost efficiency, with on-chain verification starting at 244 Gwei per credential and scaling to 14K Gwei for 1,000, offering up to 75% cost savings compared to existing Ethereum and Polygon solutions. These findings establish Lotus Bridge as a scalable and costeffective foundation for sovereign digital identity in cross-chain ecosystems.