Blacklistable Anonymous Credentials: Blocking Misbehaving Users without TTPs (Extended Version) pdfauthor

Several credential systems have been proposed in which users can authenticate to services anonymously. Since anonymity can give users the license to misbehave, some variants allow the selective deanonymization (or linking) of misbehaving users upon a complaint to a trusted third party (TTP). The ability of the TTP to revoke a user’s privacy at any time, however, is too strong a punishment for misbehavior. To limit the scope of deanonymization, systems such as “e-cash” have been proposed in which users are deanonymized under only certain types of well-defined misbehavior such as “double spending.” While useful in some applications, it is not possible to generalize such techniques to more subjective definitions of misbehavior. We present the first anonymous credential system in which services can “blacklist” misbehaving users without contacting a TTP. Since blacklisted users remain anonymous, misbehaviors can be judged subjectively without users fearing arbitrary deanonymization by a TTP. ∗This paper is the extended version of the paper to appear in CCS ’07 under the same title [TAKS07]. †This work was supported in part by the Institute for Security Technology Studies, under Grant number 2005DD-BX-1091 awarded by the Bureau of Justice Assistance, and the National Science Foundation, under grant CNS0524695. The views and conclusions do not necessarily represent those of the sponsors. ‡Department of Computer Science, Dartmouth College, Hanover, NH, USA §Centre for Computer and Information Security Research, School of Computer Science and Software Engineering, University of Wollongong, Australia ¶Institute for Security Technology Studies, Dartmouth College, Hanover, NH, USA