Universal forgery of the identity-based sequential aggregate signature scheme

At CCS'07, a novel identity-based sequential aggregate signature scheme was proposed and the security of the scheme was proven under the hardness assumption of a new computational problem called modified LRSW problem. In the paper, unfortunately, we show that the scheme is universally forgeable, i.e., anyone can generate forged signatures on any messages of its choice. In addition, we show that the computational assumption is not correct by concretely presenting a constant-time algorithm solving the problem. The contribution of the new scheme and assumption is a natural step in cryptologic research that calls for further investigation, which is a step we perform in the current work.