Abstract: Multi-proxy signature is an extension of the basic proxy signature primitive. In a multi-proxy signature scheme, an original signer can 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 i- dentity-based cryptography, some identity-based multi proxy signature schemes have been proposed. But to date, no for- malized security model has been provided for identity-based multi-proxy signature schemes. This paper gave the formal definition of identity-based multi proxy signature schemes and formalize a notion of security for them.

Key words: Multi-proxy signature, Iidentity-based signature, Identity-based multi-proxy signature, Security model