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Certificateless public key cryptosystem combines the advantages of identity-based cryptosystem and traditional PKI public key cryptosystem,overcomes the key escrow problem of identity-based public key cryptosystem and the certificate management problem of PKI system,and has obvious advantages.By analysing the security of a strongly secure certificateless signature scheme proposed by Hassouna,et al,it shows that the scheme cannot resist the attack of falsifying messages and do not use private key generated by system master key to sign.So it is not a certificateless signature scheme.On this basis,an improved certificateless signature scheme is proposed and it proves the scheme can resist the attack of the first class of strong adversaries and the second class of adversaries.In the random oracle model and under the assumption of the Diffie-Hellman problem of the elliptic curve,the improved scheme satisfies the existential forgery.