Abstract
Bitcoin is a digital currency based on a peer-to-peer network to propagate and verify transactions. Bitcoin is gaining wider adoption than any previous crypto-currency and many well-known businesses have begun accepting bitcoins as means of financial payments. However, the mechanism of peers randomly choosing logical neighbors without any knowledge about the underlying physical topology can cause a delay overhead in information propagation which makes the system vulnerable to double spend attacks due to inconsistencies in the blockchain. Aiming at alleviating the propagation delay problem, this thesis evaluates the concept of network clustering in tackling the propagation delay problem in the Bitcoin network throughout introducing a proximity-aware extensions to the current Bitcoin protocol, named Locality Based Clustering (LBC), Ping Time Based Clustering (BCBPT), Super Node Based Clustering (BCBSN), and Master Node Based Clustering (MNBC). The ultimate purpose of the proposed protocols, that are based on how clusters are formulated and nodes define their membership, is to improve the information propagation delay in the Bitcoin network. The proximity of connectivity in the Bitcoin network is increased in the LBC and BCBPT protocol by grouping Bitcoin nodes based on different criteria, physical location in LBC protocol and link latencies between nodes in the BCBPT. In the BCBSN protocol, geographical connectivity increases as well as the number of hops between nodes decreases through assigning one node to be a cluster head that is responsible for maintaining the cluster. Whereas, MNBC incorporates master node technology and proximity-awareness into the existing Bitcoin protocol with the aim of creating fully connected clusters based on physical Internet proximity. We show, through simulations, that the proposed approaches define better clustering structures that optimize the transaction propagation delay over the Bitcoin protocol. However, MNBC is more effective at reducing the transaction propagation delay compared to the BCBPT, LBC, and BCBSN.On the other hand, this thesis evaluates the resistance of the Bitcoin network and the proposed approaches against the partitioning attack. Even though the Bitcoin network is more resistant against partition attacks than the proposed approaches, more resources need to be spent to split the network in the proposed approaches especially with a higher number of nodes.
Finally, this thesis introduces a novel methodology to measure the transaction propagation delay in the real Bitcoin network with the aim of validating any model of the Bitcoin network. Transaction propagation measurements show that the transaction propagation time is significantly affected by the number of connected nodes and the network topology which is not proximity defined. In addition, large-scale measurements of the real Bitcoin network are performed in thesis with the aim of providing an opportunity to parameterise any model of the Bitcoin network accurately. Furthermore, this thesis presents a simulation model of the Bitcoin peer-to-peer network which is an event based simulation.
| Date of Award | Dec 2018 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Gareth Owenson (Supervisor) & Athanasios Paraskelidis (Supervisor) |