Provably Secure Timed-Release Public Key Encryption

A timed-release cryptosystem allows a sender to encrypt a message so that only the intended recipient can read it only after a specified time. The authors formalize the concept of a secure timed-release public-key cryptosystem and show that, if a third party is relied upon to guarantee decryption after the specified date, this concept is equivalent to identity-based encryption; this explains the observation that all known constructions use identity-based encryption to achieve timed-release security. They then give several provably-secure constructions of timed-release encryption: a generic scheme based on any identity-based encryption scheme, and two more efficient schemes based on the existence of cryptographically admissible bilinear mappings.