Trip Report: Meeting on Privacy-Enhancing Cryptography at NIST

Last week I participated in the Meeting on Privacy-Enhancing Cryptography at NIST. The meeting was organized by Rene Peralta, who brought together a diverse international group of cryptographers and privacy stakeholders. The agenda is online with links to the workshop presentations.

The presentations covered many applications of privacy-enhancing cryptography, including auctions with encrypted bids, database search and data stream filtering with hidden queries, smart metering, encryption-based access control to medical records, format-preserving encryption of credit card data, and of course authentication. There was a talk on U-Prove by Christian Paquin, and a talk on Idemix by Gregory Neven. There were also talks on several techniques besides anonymous credentials that could be used to implement privacy-friendly authentication: group signatures, direct anonymous attestation, and EPID (Enhanced Privacy ID). Kazue Sako’s talk described several possible applications of group signatures, including a method of paying anonymously with a credit card.

A striking demonstration of the practical benefits of privacy-enhancing cryptography was the presentation on the Danish auctions of sugar beets contracts by Thomas Toft. A contract gives a farmer the right to grow a certain quantity of beets for delivery to Danisco, the only Danish sugar producer. A yearly auction allows farmers to sell and buy contracts. Each farmer submits a binding bid, consisting of a supply curve or a demand curve. The curves are aggregated into a market supply curve and a market demand curve, whose intersection determines the market clearing price at which transactions take place. What’s remarkable is that farmers submit encrypted bids, and bids are never decrypted. The market clearing price is obtained by computations on encrypted data, using secure multiparty computation techniques. Auctions have been successfully held every year since 2008.

I was asked to participate in the panel on Privacy in the Identification Domain and to start the discussion by presenting a few slides summarizing my series of blog posts on privacy-enhancing technologies and NSTIC. In response to my slides, Gregory Neven of IBM reported that a credential presentation takes less than one second on his laptop, and Brian La Macchia of Microsoft pointed out that deployment is difficult for public key certificates as well as for privacy-friendly credentials. There were discussions with Gregory Neven on revocation and with Anna Lysyanskaya on how to avoid the sharing of anonymous credentials; these are big topics that deserve their own blog posts, which I plan to write soon, so I won’t say any more here. Jeremy Grant brought the audience up to date about NSTIC, which has received funding and is getting ready to launch pilots. Then there was a wide ranging discussion.

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