Digital signature has recently played an increasingly important role in cyberspace security. Most of them are based on the public key cryptogra-phy. Public key cryptography is a mainstream crypto-graphic algorithm system that has been widely used in cyberspace security in recent years. The most clas-sic public key cryptography algorithm is RSA and its difficulty is based on the large integer decompo-sition problem. In 2017, ISRSAC was proposed by M.Thangaval. ISRSAC has made security improve-ments to the RSA algorithm by increasing the com-plexity in factoring the value of modulus'n'. A dig-ital signature algorithm based on ISRSAC algorithm was completed in this paper, and furthermore, a proxy signature algorithm based on ISRSAC and two kinds of multi-signature algorithms were presented, which include sequential multi-signature and broadcasting multi-signature.