Abstract:

We propose two efficient Identity-Based threshold decryption schemes They are proved secure against chosen ciphertext attacks under the standard decisional bilinear Diffie-Hellman assumption. The first one is constructed from (one of ) the Selective ID-Based Encryption (Selective-IBE) scheme proposed by Boneh and Boyen recently, yet the second one is transformed from the Full ID-Based Encryption (Full-IBE) scheme obtained by Waters. As the based IBE schemes, the attacker in the first proposal has to choose the challenge identity before the common parameter is generated, while the attacker in the second one could choose the identity adaptively. To the best of our knowledge, previous related schemes could only be proved secure in the random oracle model.

Key words: threshold decryption, chosen ciphertext security, decisional bilinear Diffie-Hellman assumption