  Decentralized identity mechanisms endeavor to endow users with complete
sovereignty over their digital assets within the Web3 ecosystem. Unfortunately,
this benefit frequently comes at the expense of users' credential and identity
privacy. Additionally, existing schemes fail to resist Sybil attacks that have
long plagued Web3, and lack reasonable key recovery mechanisms to regain
control of digital assets after loss. In this work, we propose LinkDID, a
privacy-preserving, Sybil-resistant, and key-recoverable decentralized identity
scheme that supports selective disclosure of credentials for arbitrary
predicates while maintaining privacy for credentials and identities. Through an
identifier association mechanism, LinkDID can privately and forcibly aggregate
users' identifiers, providing Sybil resistance without relying on any external
data or collateral from benign users. To enable key recovery, LinkDID permits
users to establish proofs of ownership for identifiers with lost keys and
request an update of corresponding keys from the decentralized ledger. We
provide a detailed theoretical analysis and security proofs of LinkDID, along
with an exhaustive performance evaluation that shows its ability to complete
interactions in less than 10 seconds on consumer-grade devices.
