An Improved Forward-Secure Multi-Proxy Signature Scheme

In 2006, Xu proposed a forward multi-proxy signature scheme, but there are some insecurities in Xu's scheme: (1) If the attacker knows a valid signature, anyone can forge some certain messages and cannot detect by the signature verifier. (2) If the attacker is one of the signers, who can forges his public key, and then sign all the unauthorized message. After that, the paper proposed a new forward-secure multi-proxy signature schemes based on quadratic residues. The improved schemes can resist lots of outsider attack and insider attack as above mentioned. The validity of the new scheme can be verified, and it is a secure multi-signature scheme.