[Resource Topic] 2024/675: Olympic Privacy-Preserving Blueprints: Faster Communication, Highly Functional, Stronger Security

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Olympic Privacy-Preserving Blueprints: Faster Communication, Highly Functional, Stronger Security

Authors: Scott Griffy, Markulf Kohlweiss, Anna Lysyanskaya, Meghna Sengupta


Introduced by Kohlweiss, Lysyanskaya, and Nguyen (Eurocrypt’23), an f-privacy-preserving blueprint (PPB) system allows an auditor with secret input x to create a public encoding of the function f(x,\cdot) that verifiably corresponds to a commitment C_x to x. The auditor will then be able to derive f(x,y) from an escrow Z computed by a user on input the user’s private data y corresponding to a commitment C_y. Z verifiably corresponds to the commitment C_y and reveals no other information about y.
PPBs provide an abuse-resistant escrow mechanism: for example, if f is the watchlist function where f(x,y) outputs y only in the event that y is on the list x, then an f-PPB allows the auditor to trace watchlisted users in an otherwise anonymous system. Yet, the auditor’s x must correspond to a publicly available (and potentially authorized by a transparent, lawful process) C_x, and the auditor will learn nothing except f(x,y).
In this paper, we build on the original PPB results in three ways: (1) We define and satisfy a stronger notion of security where a malicious auditor cannot frame a user in a transaction to which this user was not a party. (2) We provide efficient schemes for a bigger class of functions f; for example, for the first time, we show how to realize f that would allow the auditor to trace e-cash transactions of a criminal suspect. (3) For the watchlist and related functions, we reduce the size of the escrow Z from linear in the size of the auditor’s input x, to logarithmic.

ePrint: https://eprint.iacr.org/2024/675

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