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Collecting accurate profile information and protecting an individual's privacy are ordinarily viewed as being at odds. This paper presents mechanisms that protect individual privacy while presenting accurate|indeed authenticated-profile information to servers and merchants. In particular, we give a pseudonym registration scheme and system that enforces unique user registration while separating trust required of registrars, issuers, and validators. This scheme enables the issuance of global unique pseudonyms (GUPs) and attributes enabling practical applications such as authentication of accurate attributes and enforcement of "one-to-a- customer" properties. We also present a scheme resilient to even pseudonymous profiling yet preserving the ability of merchants to authenticate the accuracy of information. It is the first mechanism of which the authors are aware to guarantee recent validity for group signatures, and more generally multi- group signatures, thus effectively enabling revocation of all or some of the multi-group certificates held by a principal.

Traditional face-to-face (English) auctions rely on the auctioneer to fairly interact with bidders to accept the highest bid on behalf of the seller. On-line auctions also require fair negotiation. However, unlike face-to-face auctions, on-line auctions are inherently subject to attacks because the bidders and auctioneer are not co-present. These attacks include selectively blocking bids based on the bidder and amount and selectively closing the auction after a particular bid is received. In this paper, the authors present an on-line English auction in which bids are processed fairly and the auction closes fairly without specialized trusted parties (i.e., there is no need to trust the auctioneer to obtain a fair outcome to the auction)., Pub. in Financial Cryptography, Feb 1999, p230-240. Prepared in cooperation with CertCo, New York, NY.

We present a protocol for unlinkable serial transactions suitable for a variety of network-based subscription services. It is the first protocol to use cryptographic blinding to enable subscription services. The protocol prevents the service from tracking the behavior of its customers, while protecting the service vendor from abuse due to simultaneous or cloned use by a single subscriber. Our basic protocol structure and recovery protocol are robust against failure in protocol termination. We evaluate the security of the basic protocol and extend the basic protocol to include auditing, which further deters subscription sharing. We describe other applications of unlinkable serial transactions for pay-per-use transactions within a subscription, third-party subscription management, multivendor coupons, proof of group membership, and voting., Published in the Journal of ACM (Association for Computing Machinery) Transactions on Information and System Security, v2, n4, p354-389, Nov 1999.

We introduce the concept of a group principal and present a number of different classes of group principals, including threshold-group-principals. These appear to be naturally useful concepts for looking at security. We provide an associated epistemic language and logic and use it to reason about anonymity protocols and anonymity services, where protection properties are formulated from the intruder's knowledge of group principals. Using our language, we give an epistemic characterization of anonymity properties. We also present a specification of a simple anonymizing system using our theory., Published in Group Principals and the Formalization of Anonymity, in FM'99 - Formal Methods, v1 p814-833, Sep 1999. Prepared in collaboration with CertCo, New York, NY.

We present a protocol for unlinkable serial transactions suitable for a variety of network-based subscription services. The protocol prevents the service from tracking the behavior of its customers while protecting the service vendor from abuse due to simultaneous or "cloned" usage from a single subscription. We present variants of the protocol supporting pay-per-use transactions within a subscription. We describe other applications including third-party subscription management, multivendor package sales, proof of group membership, and voter registration., Presented at Financial Cryptography held in Anguilla, British West Indies on 24-28 Feb 1997. Published in the Proceedings of Financial Cryptography, Lecture Notes in Computer Science, v1318, 1997.

Video teleconferencing is a successful tool in the education and business industry because of its ability to reach a large audience at numerous remote locations. New computer and communications technology allows for advances in teleconferencing capabilities. In this thesis, an analysis of educational teleconferencing requirements is performed to develop viable educational teleconferencing design approaches. These design approaches must consider various transmission means and typical methods of instruction. One design approach is selected and a functional design is performed. The design is evaluated using performance models and the Simscript II.5 simulation language. Curve fitting techniques are applied to observed data to create probability distribution functions used in creating an accurate model. The performance evaluation is used to optimize the transmission protocol and validate the design. The simulation results show that with a 9600 baud transmission rate, the effects of degraded transmission lines, short display times or abnormally large file sizes, have no significant effects on the proper performance of the system.