A Partially Decentralised Protocol for a Distributed Encrypted Storage System

Decentralization is an important feature both for security and for reliability as it reduces the risks of collusion and impact of the single-point-of-failure vulnerability in a system. After having recalled the re-encryption procedure -- mainly to establish notations -- we will describe a modification of the distributed encrypted storage protocol by Ateniese-Fu-Green-Hohenberger. Such a protocol is a strongly centralized one since it assigns to the manager the possibility of storing all the symmetric keys involved in enciphering the resources required by the users of the system. Our goal here is to show how to reduce the role of the manager as being just a certifier of the access requests to the shared resources. We will achieve this by using standard public-key cryptography tools like the digital signature with message integrity.