Program

The track provides a forum for scientists and engineers in academia and industry to present and discuss their latest research findings on selected topics in dependable, adaptive and trustworthy distributed systems and services.

The track comprises the following session:

Wed, April 11, 2018, 4:30 – 6:35pm

• Towards a Model for Comprehending and Reasoning about PoW-based Blockchain Network Sustainability
  Sotirios Liaskos and Bo Wang

  Blockchain networks have been claimed to have the potential of fundamentally changing the way humans perform economic transactions with each other. In such networks, trust-enabling agents and activities, that were traditionally arranged in a centralized fashion, are replaced by a network of nodes which collectively yet independently witness and establish the non-repudiability of transactions. Most often, a proof-of-work (PoW) requirement ensures that participants invest resources for joining the network, incentivizing conformance to the network rules, while making it highly infeasible for malicious agents to construct an alternative version of the transaction history. Nevertheless, there is limited work on how such complex networks behave under different external and internal conditions and what guarantees their sustainability, i.e., their continuous operation. Focusing on public PoW-based blockchain platforms, in this paper we sketch a model that is aimed at supporting the comprehension and reasoning about the factors that affect behavior of a blockchain network.

• Secure Publish and Subscribe Systems with Efficient Revocation
  Sana Belguith, Shujie Cui, Muhammad Rizwan Asghar and Giovanni Russello

  User revocation is one of the main security issues in publish and subscribe (pub/sub) systems. Indeed, to ensure data confidentiality, the system should be able to remove malicious subscribers without affecting the functionalities and decoupling of authorised subscribers and publishers. To revoke a user, there are solutions, but existing schemes inevitably introduce high computation and communication overheads, which can ultimately affect the system capabilities. In this paper, we propose a novel revocation technique for pub/sub systems that can efficiently remove compromised subscribers without requiring regeneration and redistribution of new keys as well as re-encryption of existing data with those keys. Our proposed solution is such that a subscriber's interest is not revealed to curious brokers and published data can only be accessed by the authorised subscribers. Finally, the proposed protocol is secure against the collusion attacks between brokers and revoked subscribers.

• Adaptive Information Distribution for Dynamic Sets
  Matthias Prellwitz, Helge Parzyjegla, Steffen Steiner and Gero Mühl

  While ubiquitous computing is becoming an integral part of our daily lives, developing applications for dynamic device ensembles is still a challenging and cumbersome task. Besides other reasons (e. g., heterogeneity), a major obstacle for application development is that the developer often does not know at design time which and how many devices will be available when the user deploys the application in his personal environment. To tackle this problem, a new programming abstraction called dynamic sets was proposed. A dynamic set allows an application to interact transparently with a set of remote objects in the same way it interacts with a single object. To achieve this, the developer programs against a proxy that replicates the calls to the objects and aggregates the return values. However, if an application is calling methods with high frequency, this can waste large amounts of network and computing resources. In this paper, we propose three adaptive heuristics tackling this problem for methods that only return information about the objects’ state. The heuristics dynamically switch between push and pull communication and use unicast as well as multicast communication to optimize resource usage. We discuss and prove algorithm details and present an evaluation based on simulations that shows that our approach can indeed reduce resource usage substantially.

• EcoVMBroker: Energy-aware Scheduling for Multi-layer Datacenters
  Rodrigo Fernandes, Jose Simao and Luís Veiga

  The cloud relies on efficient algorithms to find resources for jobs by fulfilling the job’s requirements and at the same time optimise an objective function. Utility is a measure of the client satisfaction that can be seen as an objective function maximised by schedulers based on the agreed service level agreement (SLA). We propose EcoVMBroker which can reduce energy consumption save by using dynamic voltage frequency scaling (DVFS) and applying reductions of utility, different for classes of users and across ranges of resource allocations. Using efficient data structures and a hierarchical architecture, we created a scalable solution for the fast growing heterogeneous cloud. EcoVMBroker proved that we can delegate work in a hierarchical datacenter, make decisions based on summaries of resource usage collected from several nodes and still be efficient.

• Dynamic Adaptation of Byzantine Consensus Protocols
  Carlos Carvalho, Daniel Porto, Luís Rodrigues, Manuel Bravo and Alysson Bessani

  The problem of distributed consensus in the presence of Byzantine faults has received particular attention in recent decades. Today a variety of solution to this problem exist, each optimized for particular execution conditions. Given that, in most cases, real systems operate under dynamic conditions, it is important to develop mechanisms that allow the protocols to be adapted at runtime or to switch between different protocols so that is possible to optimize the system to the current conditions. The problem of dynamic adaptation of consensus protocols is not new, but the literature is scarce for the Byzantine case and there is no comprehensive comparison of existing solutions. This work has two complementary objectives. First, it studies how the different dynamic adaptation techniques proposed for the crash failure model can be applied in the presence of Byzantine faults. Second, it presents a comparative study of the performance of these switching algorithms in practice. For that purpose, we have implemented the switching algorithms in a common software framework, based on the open source BFT-SMaRt package. Using this common framework we have performed an extensive evaluation that offers useful insights on the practical effects of different mechanisms used to support the run-time switching among Byzantine protocols.

Poster session, Wed April 11, 2018, 10:40am - 12:50pm

Track Program Co-Chairs

Important Dates