Lee and Hwang proposed group-oriented undeniable signature schemes with a trusted center to guard against Langford's attack. Unfortunately, there are some security weaknesses in Lee-Hwang's schemes. Their schemes assume that the signers and verifier should honestly perform steps; otherwise their schemes will fail. To remove this impractical assumption and the corresponding problems, our improvement is proposed.
淡江理工學刊=Tamkang journal of Science and Engineering 9(1)，頁45-54