An Ad Hoc Group Signature Scheme for Accountable and Anonymous Access to Outsourced Data

This paper presents a group signature scheme called AdHocSign for dynamically formed groups, to support accountable and anonymous access to outsourced data. Each user is assigned a certain set of attributes and the secrets associated with these attributes when joining the system; the access to outsourced data is regulated by a logical expression of attribute which defines an ad hoc group of authorized users. The proposed AdHocSign enables a user who is allowed to access a piece of data to authenticate himself/herself to the host of the data using its preloaded secrets and some auxiliary information provided by the host; no extra secrets are needed to be distributed to the users when new access structures are constructed or existing access structures are modified. The selfless-anonymity and traceability of the AdHocSign scheme has been proved based on the hardness assumption of the q-SDH and the Decisional Linear problems.