Privacy-preserving outsourcing of brute-force key searches

Abstract

In this work, we investigate the privacy-preserving properties of encryption algorithms in the special case where encrypted data might be brute-force decrypted in a distributed setting. For that purpose, we consider a problem where a supervisor holds a ciphertext and wants to search for the corresponding key assisted by a set of helper nodes, without the nodes learning any information about the plaintext or the decryption key. We call this a privacy-preserving cryptographic key search. We provide a model for privacy-preserving cryptographic searches and we introduce two types of privacy-preserving key search problems: plaintext-hiding and key-hiding cryptographic search. We show that a number of private-key and public-key encryption schemes enable the construction of efficient privacy-preserving solvers for plaintext hiding searches. We also discuss possible constructions of privacy-preserving solvers for key-hiding cryptographic searches. Our results highlight the need to consider the property of enabling efficient privacy-preserving solvers as an additional criterion for choosing which cryptographic algorithm to use.