A Multi-proxy Signature Scheme for Partial delegation with Warrant
  In some cases, the original signer may delegate its signing power to a specified proxy group while ensuring individual accountability of each participantsigner. The proxy signature scheme that achieves such purpose is called the multi-proxy signature scheme and the signature generated by the specified proxy group is called multi-proxy signature for the original signer. Recently such scheme has been discussed by Lin et al. Lins scheme is based on partial delegation by Mambo et al. In present chapter we introduce a new multi-proxy signature scheme, which requires less computational overhead in comparison to Lin et al, and also fulfill the requirement of partial delegation with warrant simultaneously. 
Amit K Awasthi and Sunder Lal