Trustful Cumulus Clouds

Cloud computing offers an appealing business model and it is tempting for companies to delegate their IT services to the cloud. Yet, a company might find it risky to do so for sensible services and to depend entirely on a single provider, which can be vulnerable and constitute a clearly identified target for attackers. We explore in this paper a replication approach where copies of the same IT service are placed on several (cumulus) clouds that are not only independent but actually unaware of each other. Replica consistency is ensured using CBFT, a new BFT protocol designed for wide area networks. CBFT uses a primary to handle contention among multiple client requests but shares the load of multi- casting and encrypting them among the clients. We evaluate CBFT on an Emulab cluster with a wide area topology and convey its scalability with respect to state of the art BFT protocols.