Insecurity of a Certificate-free Ad Hoc Anonymous Authentication

The ring signature scheme is a simplified group signature scheme for no manager while preserving unconditionally anonymous of the signer. Certificateless cryptography is introduced for eliminating the use of certificates in Public Key Infrastructure and solving the key-escrow problem in ID-based cryptogratography. Recently, Qin et al. proposed the first RSA-based certificateless ring signature scheme which was proved unforgeable in random oracle model. In this paper, we demonstrated that this scheme was not secure against the Type I adversary.