Paper 2022/1463 Original: eprint.iacr.org/2022/1463 ↗

How to Obfuscate MPC Inputs

Abstract

We introduce the idea of input obfuscation for secure two-party computation ($\textsf{io2PC}$). Suppose Alice holds a private value $x$ and wants to allow clients to learn $f(x,y_i)$, for their choice of $y_i$, via a secure computation protocol. The goal of $\textsf{io2PC}$ is for Alice to encode $x$ so that an adversary who compromises her storage gets only oracle access to the function $f(x,\cdot)$. At the same time, there must be a 2PC protocol for computing $f(x,y)$ that takes only this encoding (and not the plaintext $x$) as input. We show how to achieve $\textsf{io2PC}$ for functions that have virtual black-box (VBB) obfuscation in either the random oracle model or generic group model. For functions that can be VBB-obfuscated in the random oracle model, we provide an $\textsf{io2PC}$ protocol by replacing the random oracle with an oblivious PRF. For functions that can be VBB-obfuscated in the generic group model, we show how Alice can instantiate a "personalized" generic group. A personalized generic group is one where only Alice can perform the algebraic operations of the group, but where she can let others perform operations in that group via an oblivious interactive protocol.