# Information Security and Cryptography Research Group

## Privacy-Preserving Outsourcing of Brute-Force Key Searches

### Ghassan O. Karame, Srdjan Capkun, and Ueli Maurer

Proc. 2011 ACM Cloud Computing Security Workshop (CCSW), ACM, Oct 2011.

In this work, we investigate the privacy-preserving prop- erties of encryption algorithms in the special case where encrypted data might be brute-force decrypted in a dis- tributed setting. For that purpose, we consider a prob- lem 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 intro- duce 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 encryp- tion 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.

## BibTeX Citation

@inproceedings{KaCaMa11,
author       = {Ghassan O. Karame and Srdjan Capkun and Ueli Maurer},
title        = {Privacy-Preserving Outsourcing of Brute-Force Key Searches},
editor       = {T. Ristenpart and C. Cachin},
booktitle    = {Proc. 2011 ACM Cloud Computing Security Workshop (CCSW)},
year         = 2011,
month        = 10,
publisher    = {ACM},
}