Imperial College London

DrNarankerDulay

Faculty of EngineeringDepartment of Computing

Reader in Computing Science
 
 
 
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Contact

 

+44 (0)20 7594 8288n.dulay Website

 
 
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Location

 

562Huxley BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

189 results found

Khalil R, Dulay N, 2022, AC/DC: Adaptive Cutoffs and Disputable Cutoffs for robust critical transactions in smart-contracts, IEEE Transactions on Network and Service Management, ISSN: 1932-4537

To guarantee delivery of their intended functionalities in the presence of unresponsive parties, current smart-contracts cut users off from being able to commit their responses after a fixed period of time has elapsed. However, current blockchains have limited transaction processing capacities, so a fixed amount of time will not always be sufficient to receive every (C-TX). This paper presents a mechanism for adaptive cutoffs (ACs) which ensures that users retain the opportunity to commit despite blockchain congestion, and enables early cutoffs when the number of required is low. A non-interactive argument system for setting adaptive cutoffs under the current Ethereum Virtual Machine is described. Additionally, disputable cutoffs (DCs) are presented, which are a more efficient approach used in parallel to ACs based on a bisection-based dispute. Furthermore, it’s empirically demonstrated that an AC/DC-enabled smart-contract can receive a larger number of than its non-adaptive counterparts when user responsiveness is slowed due to denial of service or congestion.

Journal article

Khalil R, Dulay N, 2022, Towards Equity in Proof-of-Work Mining Rewards, The 3rd International Conference on Mathematical Research for Blockchain Economy

Conference paper

Khalil RA, Dulay N, 2022, RANC: reward-all nakamoto consensus, SAC '22: The 37th ACM/SIGAPP Symposium on Applied Computing, Publisher: ACM, Pages: 236-245

In this work we present Reward-All Nakamoto-Consensus (RANC), a Proof-of-Work cryptocurrency that resiliently rewards each miner with a number of coins that is directly proportional to its individual mining power, rather than to its relative share of the entire network's mining power as done in Bitcoin. Under this approach, the security of mining in RANC achieves near-perfect incentive compatibility, and near-zero censorship susceptibility, for adversarial mining shares up to 45%, but at the cost of regression in subversion-gain resilience. Moreover, mining rewards in RANC exhibit significantly lower variance for non-majority miners compared to NC, enabling dependable reward stability. Consequently, depending on the network transaction-fees, RANC improves miner's waiting time for rewards, and incentivizes forming mining pools smaller than required in Bitcoin for equal reward stability. A detailed specification of RANC is presented, along with an evaluation of the practicality and efficiency achieved by our prototype RANC implementation.

Conference paper

Khalil R, Dulay N, 2021, Adaptive layer-two dispute cutoffs in smart-contract blockchains, 3rd Conference on Blockchain Research and Applications for Innovative Networks and Services (BRAINS), Publisher: IEEE, Pages: 129-136

Conference paper

Khalil R, Dulay N, 2021, PoSH in Practice: Implementing Proof of Staked Hardware Consensus with Limited Storage, 3rd IEEE International Conference on Blockchain and Cryptocurrency (IEEE ICBC), Publisher: IEEE

Conference paper

Khalil R, Dulay N, 2020, Adaptive layer-two dispute periods in blockchains., Publisher: Cryptology ePrint Archive

Second-layer or off-chain protocols increase the throughput of permissionless blockchains by enabling partiesto lock funds into smart-contracts and perform payments through peer-to-peer communication, only resorting to the smart-contracts for protection against fraud. Current protocols have fixed time periods during which participants can dispute any fraud attempts. However, current blockchains have limited transaction processing capacity, so a fixed dispute period will not always be sufficient to deter all fraudulent behaviour in an off-chain protocol. In this work, we describe how to set adaptive dispute periods that accommodate the congestion and capacity of the underlying blockchain. Adaptive dispute periods ensure that users retain the opportunity to dispute fraudulent behaviours during blockchain congestion, while increasing second-layer protocol efficiency by reducing dispute period lengths when the number of disputes is low. We describe a non-interactive argument system for setting adaptive dispute periods under the current Ethereum Virtual Machine, and discuss how to efficiently integrate built-in support for adaptive dispute periods in any blockchain. We empirically demonstrate that an adaptive-dispute second-layer protocol can handle a larger number of disputes and prevent more fraud than its non-adaptive counterparts even when users are slow to issue disputes, due to denial of service or blockchain congestion.

Working paper

Khalil R, Dulay N, 2020, Short paper: PoSH proof of staked hardware consensus., Publisher: Cryptology ePrint Archive

This paper introduces the PoSH Consensus protocol, a novel work-in-progress construction for achieving Sybil-resistant Nakamoto-style probabilistic consensus on the contents of a cryptocurrency ledger in a permissionless decentralized network where parties stake their hardware’s computational power towards participation in leader election. PoSH aims to establish an openly mintable cryptocurrency that eliminates the requirement for block rewards and disincentivizes mining pools.

Working paper

Spina A, Breza M, Dulay N, McCann Jet al., 2020, XPC: fast and reliable synchronous transmission protocols for 2-phase commit and 3-phase commit, The 2020 International Conference on Embedded Wireless Systems and Networks, Publisher: ACM, Pages: 73-84

The improvement of software abstractions and frame-works for programmers is one of the major challenges forthe engineering of reliable and efficient wireless sensing sys-tems. We address this challenge with X Process Commit(XPC), an atomic commit protocol framework, andHybrid,a Synchronous Transmission (ST) communication approach.Hybridexploits the reliability of Glossy and the speed ofChaos, two Synchronous Transmission primitives, to getlower latency and higher reliability than either on their own.Hybridis a general approach that can provide reliable com-munication for any round based protocol. We use XPC andHybridto build the classical 2-phase and 3-phase commitprotocols. Through extensive experimentation, we comparethe performance of the 2-phase and 3-phase commit proto-cols when they useHybrid, Glossy, and Chaos for commu-nication. Our results show thatHybridis more robust thanChaos to radio interference, with almost 100% reliability in anetwork of nodes suffering from moderate radio interference,13% to 50% faster than Glossy, and has comparable over-heads to other state of the art ST atomic commit approachesA2/Synchrotron.

Conference paper

Leahy F, Dulay N, 2018, DejaVu: visual diffing of cyber-physical systems, International Conference on Embedded Wireless Systems and Networks 2018, Publisher: ACM, Pages: 1-2

In this paper we present DejaVu, a novel 3D virtual worldco-simulator for ‘visual diffing’ of cyber-physical systemdeployments in indoor and outdoor environments. Usingfaster-than-real-time simulation and efficient recording DejaVucan record days of simulation data, including environmental,sensor and network data for later replay and analysis.DejaVu enables developers to replay and visually comparemultiple simulations simultaneously using different visualdiffing techniques, including ghosts, paths, colour andsize, highlighting differences between runs, including energyconsumption, radio metrics, movement, etc. We demonstrateseveral of these visual diffing techniques in an CPSenhancedevacuation case study.

Conference paper

Dulay N, Micheletti M, Mostarda L, Piermarteri Aet al., 2018, PICO-MP: De-centralised macro-programming for wireless sensor and actuator networks, 32nd IEEE International Conference on Advanced Information Networking and Applications, Publisher: IEEE, ISSN: 2332-5658

Macro-programming advocates the use of high-levelabstractions to specify distributed systems as a whole. However,macro-programming implementations are often centralised. Inthis paper we present PICO-MP, the first fully decentralisedmacro-programming middleware for wireless sensor and actuatornetwork (WSAN) applications. PICO-MP incorporates a novelpublish-subscribe service that can correlate events scatteredacross a WSAN using global formulae specifications that areautomatically checked in a distributed fashion. PICO-MP hasbeen implemented for the TinyOS operating system and validatedon a case study that uses global formulae to improve energyefficiency (lifetime) of the implementation.

Conference paper

Leahy F, Dulay N, 2018, Dejavu: Visual diffing of cyber-physical systems, Pages: 157-162

In this paper we present DejaVu, a novel 3D virtual world co-simulator for ‘visual diffing’ of cyber-physical system deployments in indoor and outdoor environments. Using faster-than-real-time simulation and efficient recording DejaVu can record days of simulation data, including environmental, sensor and network data for later replay and analysis. DejaVu enables developers to replay and visually compare multiple simulations simultaneously using different visual diffing techniques, including ghosts, paths, colour and size, highlighting differences between runs, including energy consumption, radio metrics, movement, etc. We demonstrate several of these visual diffing techniques in an CPSenhanced evacuation case study.

Conference paper

Leahy F, Dulay N, 2017, Poster abstract: DejaVu - visual diffing of cyber physical systems

In this abstract we present DejaVu, a 3D virtual world co-simulator for’visual diffing’ of cyber-physical system deployments in indoor and outdoor environments. Using faster-than-real-time simulation and efficient recording DejaVu can record days of simulation data, including environmental, sensor and network data for later replay and analysis. DejaVu enables developers to replay and visually compare multiple simulations simultaneously using different visual diffing techniques, including ghosts, paths, colour and size, highlighting differences between runs, including energy consumption, radio metrics, movement, etc. We demonstrate several of these visual diffing techniques in an CPS-enhanced evacuation case study.

Conference paper

Leahy F, Dulay N, 2017, Ardan: Using 3D Game Engines in Cyber-Physical Simulations (Tool Paper), Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 61-70, ISSN: 0302-9743

Conference paper

Pediaditakis D, 2015, HomeShaper: Regulating the use of Bandwidth Resources in Home Networks

Thesis dissertation

Bucchiarone A, Dulay N, Lavygina A, Marconi A, Raik H, Russo Aet al., 2015, An approach for collective adaptation in socio-technical systems, SASOW 2015, Publisher: IEEE, Pages: 43-48

Socio-technical systems are systems where autonomous humans and computational entities collectively collaborate with each other to satisfy their goals in a dynamic environment. To be resilient, such systems need to adapt to unexpected human behaviours and exogenous changes in the environment. In this paper, we describe a framework for the development of social-technical systems where adaptation is itself a collective process driven by the awareness of capabilities, goals, constraints and preferences of humans and entities, and knowledge of the environment. The adaptation is controlled by a multi-criteria decision making function combined with an analytic hierarchic process (AHP). We present our approach, the collective adaptation algorithm, and its application to a smart mobility scenario.

Conference paper

Lavygina A, Russo A, Dulay N, 2015, Integrating Privacy and Safety Criteria into Planning Tasks, 11th International Workshop on Security and Trust Management (STM), Publisher: SPRINGER INT PUBLISHING AG, Pages: 20-36, ISSN: 0302-9743

Conference paper

Lavygina A, Dulay N, Bucchiarone A, Tariq MA, Karastoyanova Det al., 2015, Preface to the first international workshop on business processes in collective adaptive systems, ISBN: 9783319158945

Book

Marinovic S, Dulay N, Sloman MS, 2014, Rumpole - An Introspective Break-glass Access Control Language, ACM Transactions on Information and System Security

Access control policies define what resources can be accessed by which subjects and under which conditions. It is, however, often not possible to anticipate all subjects that should be permitted access and the conditions under which they should be permitted. For example, predicting and correctly encoding all emergency and exceptional situations is impractical. Traditional access control models simply deny all requests that are not permitted, and in doing so may cause unpredictable and unacceptable consequences. To overcome this issue, break-glass access control models permit a subject to override an access control denial, if he accepts a set of obligatory actions and certain override conditions are met. Existing break-glass models are limited in how the override decision is specified. They either grant overrides for a pre-defined set of exceptional situations, or they grant unlimited overrides to selected subjects, and as such they suffer from the difficulty of correctly encoding and predicting all override situations and permissions. To address this, we develop Rumpole, a novel break-glass language that explicitly represents and infers knowledge gaps and knowledge conflicts about the subject’s attributes and the contextual conditions, such as emergencies. For example, a Rumpole policy can distinguish whether or not it is known that an emergency holds. This leads to a more informed decision for an override request, whereas current break-glass languages simply assume that there is no emergency if the evidence for it is missing. To formally define Rumpole, we construct a novel many- valued logic programming language called Beagle. It has a simple syntax similar to that of Datalog, and its semantics is an extension of Fitting’s bilattice-based semantics for logic programs. Beagle is a knowledge non-monotonic langauge, and as such is strictly more expressive than current many-valued logic program- ming languages.

Journal article

Smith J, Lavygina A, Russo A, Dulay Net al., 2014, When Did Your Smartphone Bother You Last?, ACM International Joint Conference on Pervasive and Ubiquitous Computing (UbiComp), Publisher: ASSOC COMPUTING MACHINERY, Pages: 409-414

Conference paper

Smith J, Lavygina A, Ma J, Russo A, Dulay Net al., 2014, Learning to recognise disruptive smartphone notifications, 16th International Conference on Human-Computer Interaction with Mobile Devices and Services, Publisher: ACM, Pages: 121-124

Short term studies in controlled environments have shown that user behaviour is consistent enough to predict disruptive smartphone notifications. However, in practice, user behaviour changes over time (concept drift) and individual user preferences need to be considered. There is a lack of research on which methods are best suited for predicting disruptive smartphone notifications longer-term, taking into account varying error costs. In this paper we report on a 16 week field study comparing how well different learners perform at mitigating disruptive incoming phone calls.

Conference paper

Smith J, Dulay N, 2014, RingLearn: Long-term Mitigation of Disruptive Smartphone Interruptions, 12th IEEE International Conference on Pervasive Computing and Communication (PERCOM), Publisher: IEEE, Pages: 27-35, ISSN: 2474-2503

Conference paper

Smith J, Dulay N, Toth MA, Amft O, Zhang Yet al., 2013, Exploring Concept Drift using Interactive Simulations, IEEE International Conference on Pervasive Computing and Communications Workshops (PERCOM Workshops), Publisher: IEEE, Pages: 49-54, ISSN: 2474-2503

Conference paper

Pediaditakis D, Gopalan A, Dulay N, Sloman M, Lodge Tet al., 2012, Home network management policies: Putting the user in the loop, Pages: 9-16

Home networks are becoming increasingly complex but existing management solutions are not simple to use since they are not tailored to the needs of typical home-users. In this paper we present a new approach to home network management that allows users to formulate quite sophisticated "comic-strip" policies using an attractive iPad application. The policies are based on the management wishes of home users elicited in a user study. Comic-strip policies are passed to a Policy engine running on a new Home Network Router designed to facilitate a variety of management tasks. We illustrate our approach via a number end-to-end experiments in an actual home deployment, using our prototype implementation. © 2012 IEEE.

Conference paper

Asmare E, Gopalan A, Sloman M, Dulay N, Lupu ECet al., 2012, Self-Management Framework for Mobile Autonomous Systems, Journal of Network and Systems Management, Vol: 20, Pages: 244-275

The advent of mobile and ubiquitous systems has enabled the de- velopment of autonomous systems such as wireless-sensors for environmental data collection and teams of collaborating Unmanned Autonomous Vehicles (UAVs) used in missions unsuitable for humans. However, with these range of new application-domains come a new challenge – enabling self-management in mobile autonomous systems. Autonomous systems have to be able to manage themselves individually as well as to form self-managing teams which are able to recover or adapt to failures, protect themselves from attacks and optimise performance.This paper proposes a novel distributed policy-based framework that en- ables autonomous systems of varying scale to perform self-management indi- vidually and as a team. The framework allows missions to be specified in terms of roles in an adaptable and reusable way, enables dynamic and secure team formation with a utility-based approach for optimal role assignment, caters for communication link maintenance amongst team-members and recovery from failure. Adaptive management is achieved by employing a policy-based archi- tecture to enable dynamic modification of the management strategy relating to resources, role behaviour, communications and team management, without interrupting the basic software within the system.Evaluation of the framework shows that it is scalable with respect to the number of roles, and consequently the number of autonomous systems par- ticipating in the mission. It is also shown to be optimal with respect to role assignments, and robust to intermittent communication link disconnections and permanent team-member failures.

Journal article

Pediaditakis D, Gopalan A, Dulay N, Sloman Met al., 2012, A Configuration Service for Home Networks, IEEE Network Operations and Management Symposium (NOMS 2012): Mini-Conference, Pages: 1048-1053

Conference paper

Pediaditakis D, Dulay N, 2011, Verifying home network bandwidth sharing plans

Experimental evidence from recent measurement studies has shown that bandwidth bottlenecks usually reside at the edges of the Internet, which is also true for residential networks where users share network resources and there is a need to regulate the usage of bandwidth. In this paper we introduce a rule-based approach for specifying bandwidth sharing plans for home networks which are enforced in a distributed manner across the network. More specifically we focus on the problem of verifying these sharing plans detecting potential inconsistencies which may arise from the rules that are specified by users. We describe a novel tree-based structure to model and verify the network's sharing scheme and support the specification of custom conflict resolution policies. © 2011 IFIP.

Conference paper

Dong C, Dulay N, 2011, Argumentation-based fault diagnosis for home networks, Pages: 37-42

Home networks are a fast growing market but managing them is a difficult task, and diagnosing faults is even more challenging. Current fault management tools provide comprehensive information about the network and the devices but it is left to the user to interpret and reason about the data and experiment in order to find the cause of a problem. Home users may not have motivation or time to learn the required skills. Furthermore current tools adopt a closed approach which hardcodes a knowledge base, making them hard to update and extend. This paper proposes an open fault management framework for home networks, whose goal is to simplify network troubleshooting for non-expert users. The framework is based on assumption-based argumentation that is an AI technique for knowledge representation and reasoning. With the underlying argumentation theory, we can easily capture and model the diagnosis procedures of network administrators. The framework is rule-based and extensible, allowing new rules to be added into the knowledge base and diagnostic strategies to be updated on the fly.The framework can also utilise external knowledge and make distributed diagnosis. Copyright 2011 ACM.

Conference paper

Sventek J, Koliousis A, Sharma O, Dulay N, Pediaditakis D, Sloman M, Rodden T, Lodge T, Bedwell Bet al., 2011, An Information Plane Architecture Supporting Home Network Management, IEEE International Symposium on Integrated Network Management (IM 2011), Pages: 1-8

Home networks have evolved to become small-scale versions of enterprise networks. The tools for visualizing and managing such networks are primitive and continue to require networked systems expertise on the part of the home user. As a result, non-expert home users must manually manage non- obvious aspects of the network ‐ e.g., MAC address filtering, network masks, and firewall rules, using these primitive tools.The Homework information plane architecture uses stream da- tabase concepts to generate derived events from streams of raw events. This supports a variety of visualization and monitoring techniques, and also enables construction of a closed-loop, policy-based management system. This paper describes the information plane architecture and its associated policy-based management infrastructure. Exemplar visualization and closed-loop management applications enabled by the resulting system (tuned to the skills of non-expert home users) are discussed.

Conference paper

Russello G, Mostarda L, Dulay N, 2011, A policy-based publish/subscribe middleware for sense-and-react applications, JOURNAL OF SYSTEMS AND SOFTWARE, Vol: 84, Pages: 638-654, ISSN: 0164-1212

Journal article

Dong C, Dulay N, 2011, Longitude: A privacy-preserving location sharing protocol for mobile applications, Pages: 133-148, ISSN: 1868-4238

Location sharing services are becoming increasingly popular. Although many location sharing services allow users to set up privacy policies to control who can access their location, the use made by service providers remains a source of concern. Ideally, location sharing providers and middleware should not be able to access users' location data without their consent. In this paper, we propose a new location sharing protocol called Longitude that eases privacy concerns by making it possible to share a user's location data blindly and allowing the user to control who can access her location, when and to what degree of precision. The underlying cryptographic algorithms are designed for GPS-enabled mobile phones. We describe and evaluate our implementation for the Nexus One Android mobile phone. © 2011 International Federation for Information Processing.

Conference paper

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