Leakage-resilient Cryptography with key derived from sensitive data

TL;DR

This paper introduces a method to derive cryptographic keys from private data on-the-fly, reducing storage needs and maintaining security in leakage-resilient protocols within the Random Oracle model.

Contribution

It presents a novel approach to generate keys from weakly random data, preserving security and privacy without additional storage in leakage-resilient cryptography.

Findings

Keys derived from private data retain security levels of original protocols.

The method guarantees privacy of the underlying private data.

Applicable in the Random Oracle model for broad classes of protocols.

Abstract

In this paper we address the problem of large space consumption for protocols in the Bounded Retrieval Model (BRM), which require users to store large secret keys subject to adversarial leakage. We propose a method to derive keys for such protocols on-the-fly from weakly random private data (like text documents or photos, users keep on their disks anyway for non-cryptographic purposes) in such a way that no extra storage is needed. We prove that any leakage-resilient protocol (belonging to a certain, arguably quite broad class) when run with a key obtained this way retains a similar level of security as the original protocol had. Additionally, we guarantee privacy of the data the actual keys are derived from. That is, an adversary can hardly gain any knowledge about the private data except that he could otherwise obtain via leakage. Our reduction works in the Random Oracle model.