Identity-based (ID-based) cryptosystems eliminate the need for validity checking of the certificates and the need for registering
for a certificate before getting the public key. These two features are desirable especially for the efficiency and the real
spontaneity of ring signature, where a user can anonymously sign a message on behalf of a group of spontaneously conscripted
users including the actual signer.
In this paper, we propose a novel construction of ID-based ring signature which only needs two pairing computations for any
group size. The proposed scheme is proven to be existential unforgeable against adaptive chosen message-and-identity attack
under the random oracle model, using the forking lemma for generic ring signature schemes. We also consider its extension
to support the general access structure.
Keywords Identity-based signature - ring signature - bilinear pairings - efficiency - real spontaneity - general access structure - anonymity
This research is supported in part by the Areas of Excellence Scheme established under the University Grants Committee of
the Hong Kong Special Administrative Region (HKSAR), China (Project No. AoE/E-01/99), two grants from the Research Grants
Council of the HKSAR, China (Project No. HKU/7144/03E and HKU/7136/04E), and two grants from the Innovation and Technology
Commission of the HKSAR, China (Project No. ITS/170/01 and UIM/145).