## Cryptology ePrint Archive: Report 2006/344

A Subject-Delegated Decryption Scheme with Tightly" Limited Authority

Lihua Wang and Takeshi Okamoto and Masahiro Mambo and Eiji Okamoto

Abstract: In this paper, we present a new proxy cryptosystem named subject-delegated decryption scheme, in which the original decryptor delegates decryption authority to multiple proxies according to different subjects. The advantage of our scheme is that the proxy authorities are tightly limited (Tightly" Limited Authority). This means that the proxy authority can be temporarily aborted even if the validity period of the proxy key does not expire. Consequently, our protocol is more practical than the existential protocols because the secrecy of the original decryptor can be protected efficiently from his proxy, especially when the proxy becomes corrupted. Our scheme is efficient because the encryption method in our scheme is based on a hybrid of symmetric key and public key cryptographic techniques. We give the provable security using a variant decisional Bilinear Diffie-Hellman (BDH) assumption.

Category / Keywords: cryptographic protocols /