Unconditionally Anonymous Controllable ID-Based Ring Signatures

Abstract

ID-Based ring signatures are result of application of ID-Based cryptosystems to ring signature schemes. The contribution of this paper is twofold. At first the paper introduces a new variant of ID-based ring signatures named as controllable ID-Based ring signatures (CIBRS). This new primitive has additional properties like control linkability, anonymous authorship and convertibility. Formal definitions of these properties and the security model for the new primitive were presented. Secondly, the paper presents the first unconditionally anonymous CIBRS scheme from Chow et al.’s [4] scheme. The proposed scheme uses control linkability to achieve high efficiency of computation and storage. In the proposed scheme, to generate k signatures, a member of an n-member-ring needs only n+k scalar point multiplications and 2n+k-1 hash computations when compared to kn operations of Chow et al.’s scheme. Also, to verify k signatures the scheme requires only 2 pairing operations and n+k-1 hash computations compared to 2k and nk operations respectively. Link-signatures due to the proposed scheme are independent of size of the ring. Using the link-signatures our scheme achieves a significant signature size of 3(n+k)-1 compared to 2k(n+1) (in the units of size of the field element). The scheme provides unconditional anonymity and uncontrollability to the signer even in case of compromise of the key-escrow.