Security of generalized signature scheme based on discrete logarithms and factorization

In 2005, Pon et al. proposed a generalized signature scheme based on the intractability of solving two well-known cryptographic assumptions, the factorization (FAC) and the discrete logarithm problem (DLP). They claimed that their scheme is still secure, provided that one of these two assumptions is solved. This paper, however, will show that Pon et al.´s scheme is insecure against the universal forgery attack if the adversary can solve the DLP.