Present a security analysis of the Qian-cao-xues new threshold proxy signature scheme from bilinear pairings

which does not posses the strong unforgeability property

anyone including original signer can forge a valid threshold proxy signature for any message

at the same time

this scheme can't resist original signer changing attack.An improved threshold proxy signature scheme (denoted as scheme one) is proposed

which can resolve the security problem existing in the Qian-cao-xues new threshold proxy signature scheme.Based on scheme one

by combining vector space secret sharing with multi-proxy signature

a new and wider multi-proxy signature (denoted as scheme two) is constructed.Then scheme one becomes the typical representative of scheme two.In scheme two

the multi-proxy signature can be easily produced if an authorized subset of participants pool their secret shares

and it is impossible for them to generate a multi-proxy signature if an unauthorized subset of participants pool their secret shares.The validity of the partial signature and the multi-proxy signature can be verified by means of verification equations.Moreover the suspected forgery can be traced and the malicious participants can be caught.None of the possible attacks can successfully break this scheme.