Formalized security model of identity-based multi-proxy signature

Multi-proxy signature is an extension of the basic proxy signature primitive. In a multi-proxy signature scheme, an original signer could delegate his signing rights to a group of proxy signers. And only the cooperation of all the proxy signers can generate the proxy signature on behalf of the original signer. Combining multi-proxy signature with identity-based cryptography, some identity-based multi-proxy signature schemes have been proposed. But to date, no formalized security model has been provided for identity-based multi-proxy signature schemes. In this paper, the authors give the formal definition of identity-based multi-proxy signature schemes and formalize a notion of security for them.