Proxy Signature Scheme for Warrant Partial Delegation

The idea of a proxy signature scheme was first presented by Mambo et al. [1] in 1996. Their proxy signature scheme allows an original signer to delegate his signing right to a proxy signer to sign the message on behalf of an original signer. Later, the verifier, which knows the public keys of original signer and a proxy signer can check a validity of a proxy signature issued by a proxy signer. Till now we have the following types of delegations. In general, there are three different types of delegations: full delegation, partial delegation and delegation by warrant. In a full delegation proxy signature scheme, a proxy signer uses the same private key as an original signer and creates the proxy signature as an original signer does. The drawback of a full delegation comes from a difficulty of distinctive between an original signer and a proxy signer. In a partial delegation proxy signature scheme, the original signer derives the proxy key from his private key and passes it to the proxy signer in a secure channel. In the proxy signature scheme with delegation by warrant, an original signer provides the proxy signer a special message namely warrant. The warrant certifies that a proxy signer is legal and contains signer identity, delegation period and the types of a message on which a proxy signer can sign. Also, there are two types in the second one: protected and unprotected proxy signature schemes. In unprotected proxy signature scheme, a proxy signature is generated by both the proxy signer and an original signer. In this case, the verifier cannot distinguish the identity of a signer. In the protected proxy signature scheme, a proxy signature is generated by the proxy signature key of an original signer and also with a private key of a proxy signer. PROXY SIGNATURE SCHEME FOR WARRANT PARTIAL DELEGATION