Biblio

Distributed storage systems and caching systems are becoming widespread, and this motivates the increasing interest on assessing their achievable performance in terms of reliability for legitimate users and security against malicious users. While the assessment of reliability takes benefit of the availability of well established metrics and tools, assessing security is more challenging. The classical cryptographic approach aims at estimating the computational effort for an attacker to break the system, and ensuring that it is far above any feasible amount. This has the limitation of depending on attack algorithms and advances in computing power. The information-theoretic approach instead exploits capacity measures to achieve unconditional security against attackers, but often does not provide practical recipes to reach such a condition. We propose a mixed cryptographic/information-theoretic approach with a twofold goal: estimating the levels of information-theoretic security and defining a practical scheme able to achieve them. In order to find optimal choices of the parameters of the proposed scheme, we exploit an effective probabilistic model checker, which allows us to overcome several limitations of more conventional methods.

In this paper we propose a protocol that allows end-users in a decentralized setup (without requiring any trusted third party) to protect data shipped to remote servers using two factors - knowledge (passwords) and possession (a time based one time password generation for authentication) that is portable. The protocol also supports revocation and recreation of a new possession factor if the older possession factor is compromised, provided the legitimate owner still has a copy of the possession factor. Furthermore, akin to some other recent works, our approach naturally protects the outsourced data from the storage servers themselves, by application of encryption and dispersal of information across multiple servers. We also extend the basic protocol to demonstrate how collaboration can be supported even while the stored content is encrypted, and where each collaborator is still restrained from accessing the data through a multi-factor access mechanism. Such techniques achieving layered security is crucial to (opportunistically) harness storage resources from untrusted entities.