One of the main reasons why Byzantine fault-tolerant (BFT) systems are not widely used lies in their high resource consumption: 3f + 1 replicas are necessary to tolerate only f faults. Recent works have been able to reduce the minimum number of replicas to 2f + 1 by relying on a trusted subsystem that prevents a replica from making conflicting statements to other replicas without being detected. Nevertheless, having been designed with the focus on fault handling, these systems still employ a majority of replicas during normalcase operation for seemingly redundant work. Furthermore, the trusted subsystems available trade off performance for security; that is, they either achieve high throughput or they come with a small trusted computing base. This paper presents CheapBFT, a BFT system that, for the first time, tolerates that all but one of the replicas active in normal-case operation become faulty. CheapBFT runs a composite agreement protocol and exploits passive replication to save resources; in the absence of faults, it requires that only f + 1 replicas actively agree on client requests and execute them. In case of suspected faulty behavior, CheapBFT triggers a transition protocol that activates f extra passive replicas and brings all non-faulty replicas into a consistent state again. This approach, for example, allows the system to safely switch to another, more resilient agreement protocol. CheapBFT relies on an FPGA-based trusted subsystem for the authentication of protocol messages that provides high performance and comprises a small trusted computing base.

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Cloud computing offers a pay-per-use model and elasticity for hosted applications. The latter demands for decomposing an application into services, where each of them is executed by dedicated virtual machines. Typically, off-the-self operating systems (e.g., Linux) and managed runtime support (e.g., Java) are utilized thereby causing an unnecessary huge code base, resulting in a rather large attack surface.To address these problems, we present EsseOS, a platform for tailoring services as well as their associated runtime environment. EsseOS aims at reducing the attack surface by adapting the entire software stack that runs in a virtual machine to capture only the functionally essentially needed. This is achieved by following a clean-slate approach leveraging the advantages of Haskell, a functional programming language. We structure our software to be reconfigurable to remove unnecessary parts while still ensuring correct interaction between features by relying on Haskell's advanced type system. Initial results indicate an order of magnitude smaller code base for a tailored version of both Memcached and its execution environment compared to the original Cbased version running on top of Linux.