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The paper analyzed the security threats and system flaws of present proxy authorization signatures, and a forward secure proxy authorization signature scheme with conditionally anonymity based on ECC (elliptic curves cryptosystem) was presented. The identity blinding and probabilistic encryption algorithm of the scheme enable the proxy signer to be conditionally anonymous for secrecy protection, and the anonymity can also be conveniently revoked if necessary. The scheme avoids the misuse of proxy authorization and proxy signature, prevents generalized signature forgery and coalition attack of original signer with proxy signers. If a signature is successfully attacked or the identity tracing protocol is executed, other signatures generated by the same proxy signer and signatures generated by other signers are still secure and anonymous, so the scheme proves to be forward secure. Further detailed analyses also justify its brevity, security, high efficiency, and thus considerable improvement on system overheads regarding software and hardware application.