Multi-identity single-key decryption without random oracles
Multi-Identity Single-Key Decryption (MISKD) is an Identity-Based Encryption (IBE) system where a private decryption key can map multiple public keys (identities). More exactly, in MISKD, a single private key can be used to decrypt multiple ciphertexts encrypted with different public keys associated to the private key. MISKD is a variant of IBE and offers convenience to users who have to manage many private keys in a standard IBE. The notion of MISKD was recently introduced by Guo, Mu and Chen in Pairing 2007. They proposed a concrete MISKD scheme and proved its security based on the Bilinear Strong Diffie-Hellman problem (q-BSDH) in random oracle model. In this paper, we present a novel MISKD scheme that is provably secure in the selective-ID model based on the Decisional Bilinear Diffie-Hellman (DBDH) assumption. Our scheme is more efficient in decryption.