Multi-user protocols with access control for computational privacy in public clouds

TL;DR

This paper introduces a novel technique to extend Fully Homomorphic Encryption schemes for multi-user cloud applications, enabling attribute-based access control without revealing user trust levels or requiring assumptions on the underlying FHE scheme.

Contribution

The paper proposes a Complementary Key Pairs technique and protocols that adapt FHE for multi-user scenarios with access control, without relying on specific FHE scheme details.

Findings

Protocols are secure under analysis.

Enables multi-user attribute-based access control.

Does not assume specifics of FHE schemes.

Abstract

Computational privacy is a property of cryptographic system that ensures the privacy of data being processed at an untrusted server. Fully Homomorphic Encryption Schemes (FHE) promise to provide such property. Contemporary FHE schemes are suited for applications that have single user and server. In reality many of the cloud applications involve multiple users with various degrees of trust and the server need not necessarily be aware of it too. We present a Complementary Key Pairs technique and protocols based on that to scale any generic FHE schemes to multi user scenarios. We also use such technique along with FHE to show how attribute based access control can be achieved while server being oblivious of the same. We analyze the protocols and their security. Our protocols don't make any assumptions on how FHE scheme itself works.