Abstract: In the digital era, data have become a core asset for the functioning of society, and identity authentication credentials are among the most critical and sensitive data elements. Traditional password-based authentication methods require servers to store credential information such as usernames and passwords, which poses a serious risk of data leakage. Passwordless authentication technology based on public-key cryptography replaces traditional passwords with public-private key pairs. Users employ their private keys to compute signatures for authentication information, while servers only store public information like public keys, thus eliminating the issue of servers leaking private key information. However, existing passwordless authentication systems face challenges such as incompatibility across multiple platforms, high latency in online authentication, and the difficulty of recovering private keys when devices are lost. Moreover, the transparency and auditability of these systems need improvement. To address these problems, we propose an efficient, multi-platform compatible, passwordless identity authentication scheme based on blockchain technology. The scheme combines FIDO2 passwordless authentication with blockchain, allowing users to generate and upload multiple account public keys to the blockchain network for public verification by service providers. Through optimizations such as offline account pre-registration, pre-computation of signatures, and on-chain data synchronization, the scheme achieves interoperability, low overhead, and scalability for large-scale user authentication. The scheme also incorporates an encrypted backup mechanism, enabling users to recover backup data using stored encrypted keys even if their devices are lost. Furthermore, the scheme leverages the immutable data storage provided by blockchain, allowing all participants to query the status of authentication authorizations, thus enhancing system transparency. We comprehensively evaluate the security and performance of the proposed scheme. Theoretical analysis and experiments show that the proposed scheme reduces online computational overhead by 89.09% and communication overhead by 85.57% compared with similar schemes while maintaining low-latency responses under high-load conditions.