Abstract
Independence of failures is a basic assumption for the correctness of BFT protocols. In literature, this subject was addressed by providing N-version like abstractions. Though this can provide a good level of obfuscation against semantic-based attacks, if the replicas know each others identities then non-semantic attacks like DoS can still compromise all replicas together. In this paper, we address the obfuscation problem in a different way by keeping replicas unaware of each other. This makes it harder for attackers to sneak from one replica to another and reduces the impact of simultaneous attacks on all replicas. For this sake, we present a new obfuscated BFT protocol, called OBFT, where the replicas remain unaware of each other by exchanging their messages through the clients. Thus, OBFT assumes honest, but possibly crash-prone clients. We show that obfuscation in our context could not be achieved without this assumption, and we give possible applications where this assumption can be accepted. We evaluated our protocol on an Emulab cluster with a wide area topology. Our experiments show that the scalability and throughput of OBFT remain comparable to existing BFT protocols despite the obfuscation overhead. © 2013 IEEE.

Abstract
Fault tolerance is essential for building reliable services; however, it comes at the price of redundancy, mainly the 'replication factor' and 'diversity'. With the increasing reliance on Internet-based services, more machines (mainly servers) are needed to scale out, multiplied with the extra expense of replication. This paper revisits the very fundamentals of fault tolerance and presents 'artificial redundancy': a formal generalization of 'exact copy' redundancy in which new sources of redundancy are exploited to build fault tolerant systems. On this concept, we show how to build 'artificial replication' and design 'artificial fault tolerance' (AFT). We discuss the properties of these new techniques showing that AFT extends current fault tolerant approaches to use other forms of redundancy aiming at reduced cost and high diversity. © 2016 IEEE.

Abstract
Enabling anonymous communication over the Internet is crucial. The first protocols that have been devised for anonymous communication are subject to freeriding. Recent protocols have thus been proposed to deal with this issue. However, these protocols do not scale to large systems, and some of them further assume the existence of trusted servers. In this paper, we present RAC, the first anonymous communication protocol that tolerates freeriders and that scales to large systems. Scalability comes from the fact that the complexity of RAC in terms of the number of message exchanges is independent from the number of nodes in the system. Another important aspect of RAC is that it does not rely on any trusted third party. We theoretically prove, using game theory, that our protocol is a Nash equilibrium, i.e, that freeriders have no interest in deviating from the protocol. Further, we experimentally evaluate RAC using simulations. Our evaluation shows that, whatever the size of the system (up to 100.000 nodes), the nodes participating in the system observe the same throughput. © 2013 IEEE.

Abstract
This paper presents the first BFT selection model and algorithm that can be used to choose the most convenient protocol according to the BFT user (i.e., an enterprise) preferences. The selection algorithm applies some mathematical formulas to make the selection process easy and automatic. The algorithm operates in three modes: Static, Dynamic, and Heuristic. The Static mode addresses the cases where a single protocol is needed; the Dynamic mode assumes that the system conditions are quite fluctuating and thus requires runtime decisions, and the Heuristic mode uses additional heuristics to improve user choices. To the best of our knowledge, this is the first work that addresses selection in BFT. © 2013 Springer-Verlag.

Abstract
Conflict-free Replicated Data Types (CRDTs) are distributed data types that make eventual consistency of a distributed object possible and non ad-hoc. Specifically, state-based CRDTs ensure convergence through disseminating the entire state, that may be large, and merging it to other replicas. We introduce Delta State Conflict-Free Replicated Data Types (delta-CRDT) that can achieve the best of both operation-based and state-based CRDTs: small messages with an incremental nature, as in operation-based CRDTs, disseminated over unreliable communication channels, as in traditional state-based CRDTs. This is achieved by defining delta-mutators to return a delta-state, typically with a much smaller size than the full state, that to be joined with both local and remote states. We introduce the delta-CRDT framework, and we explain it through establishing a correspondence to current state-based CRDTs. In addition, we present an anti-entropy algorithm for eventual convergence, and another one that ensures causal consistency. Finally, we introduce several delta-CRDT specifications of both well-known replicated datatypes and novel datatypes, including a generic map composition.

Abstract
Cryptocurrency and blockchain technologies are recently gaining wide adoption since the introduction of Bitcoin, being distributed, authority-free, and secure. Proof of Work (PoW) is at the heart of blockchain's security, asset generation, and maintenance. Although simple and secure, a hash-based PoW like Bitcoin's puzzle is often referred to as "useless", and the used intensive computations are considered "waste" of energy. A myriad of Proof of "something" alternatives have been proposed to mitigate energy consumption; however, they either introduced new security threats and limitations, or the "work" remained far from being really "useful". In this work, we introduce Proof of eXercise (PoX): a sustainable alternative to PoW where an eXercise is a real world matrix-based scientific computation problem. We provide a novel study of the properties of Bitcoin's PoW, the challenges of a more "rational" solution as PoX, and we suggest a comprehensive approach for PoX.