The paper introduces a new cryptosystem called Key-Policy Attribute-Based Encryption (KP-ABE) for fine-grained access control of encrypted data. KP-ABE allows users to selectively share encrypted data with others based on specific attributes, addressing the limitations of traditional encryption methods that only allow coarse-grained sharing. The system associates private keys with access structures that control which ciphertexts a user can decrypt. The authors demonstrate the applicability of KP-ABE in sharing audit log information and broadcast encryption. They also provide a delegation mechanism that allows users to derive new private keys for more restrictive access structures, subsuming Hierarchical Identity-Based Encryption (HIBE). The paper includes a detailed construction, security proofs, and applications to audit logs and broadcast encryption, showing how KP-ABE can enhance security and flexibility in data sharing.The paper introduces a new cryptosystem called Key-Policy Attribute-Based Encryption (KP-ABE) for fine-grained access control of encrypted data. KP-ABE allows users to selectively share encrypted data with others based on specific attributes, addressing the limitations of traditional encryption methods that only allow coarse-grained sharing. The system associates private keys with access structures that control which ciphertexts a user can decrypt. The authors demonstrate the applicability of KP-ABE in sharing audit log information and broadcast encryption. They also provide a delegation mechanism that allows users to derive new private keys for more restrictive access structures, subsuming Hierarchical Identity-Based Encryption (HIBE). The paper includes a detailed construction, security proofs, and applications to audit logs and broadcast encryption, showing how KP-ABE can enhance security and flexibility in data sharing.