The article provides an in-depth analysis of the challenges associated with linking identities to public keys in public key cryptography and proposes three solutions: public key directories, identity-based encryption (IBE), and registration-based encryption (RBE). It discusses the application of these solutions in blockchain technology, including their impact on anonymity, interactivity, and efficiency. The article also explores the advantages and limitations of each method, such as IBE's reliance on a strong trust foundation and RBE's optimization of on-chain storage requirements. By comparing these approaches, readers gain a better understanding of the challenges and trade-offs involved in building secure, decentralized systems.