Anonymous Authentication of Membership in Dynamic Groups

Abstract

We present a series of protocols for authenticating an in- dividual’s membership in a group without revealing that individual’s identity and without restricting how the membership of the group may be changed. In systems using these protocols a single message to the authenticator may be used by an individual to replace her lost key or by a trusted third party to add and remove members of the group. Ap- plications in electronic commerce and communication can thus use these protocols to provide anonymous authentication while accommodating frequent changes in membership. We build these protocols on top of a new primitive: the verifiably common secret encoding. We show a con- struction for this primitive, the security of which is based on the existence of public-key cryptosystems capable of securely encoding multiple mes- sages containing the same plaintext. Because the size of our construct grows linearly with the number of members in the group, we describe techniques for partitioning groups to improve performance.