University of Troms
Certificateless cryptosystem is a hybrid scheme of traditional PKI and ID-based scheme and has positive aspects of both of PKI and ID-based cryptosystem, i.e. solving key escrow problem and certificate management problem simultaneously. Cryptographic schemes constructed in such a hybrid setting, generally called certificateless setting, retain these positive aspects and have been extensively studied recently. To the best of the authors' knowledge, an Ordered Sequential Aggregate Signature (OSAS) scheme, which is a signature scheme verifying both the validity of a document and a signing order of a group of signers, has never been proposed in the certificateless setting. Therefore, they propose an OSAS scheme in a certificateless setting called CertificateLess Ordered Sequential Aggregate Signature (CLOSAS) scheme.