Tracing and revoking leaked credentials: accountability in leaking sensitive outsourced data

Most existing proposals for access control over outsourced data mainly aim at guaranteeing that the data are only accessible to authorized requestors who have the access credentials. This paper proposes TRLAC, an a posteriori approach for tracing and revoking leaked credentials, to complement existing a priori solutions. The tracing procedure of TRLAC can trace, in a black-box manner, at least one traitor who illegally distributed a credential, without any help from the cloud service provider. Once the dishonest users have been found, a revocation mechanism can be called to deprive them of access rights. We formally prove the security of TRLAC, and empirically shows that the introduction of the tracing feature incurs little costs to outsourcing.