Sharif Digital Repository

Designing a scalable protocol for the blockchain will reduce transaction fees and increase the use of cryptocurrencies for financial transactions. Increasing scalability means that if the investment of nodes increases or the number of network nodes increases, the security of the protocol and the decentralization of the network will be maintained and its throughput will increase. In this thesis, with the aim of increasing scalability, the scaling methods of layer one and layer two are examined and compared, and it is shown that sharding is a better method to achieve scalability. In sharding, nodes are divided into several shards (clusters) and each shard manages its own blockchain. The... 

In 2008, a decentralized and distributed payment solution called Bitcoin was born. Since then, it has made the payment industry think about banks and companies on the one hand and government authorities on the other. By using mathematics and cryptography, Bitcoin was able to eliminate the need for trust and in this way it was able to eliminate intermediaries such as banks. In traditional financial affairs such as banks, the user must trust the bank and everything relies on the bank’s servers. While Bitcoin stores the history of transactions in a public and distributed ledger. This ledger is encrypted so that the state of the blockchain is always reliable. In Bitcoin’s decentralized and... 

Cryptocurrency miners by solving complex mathematical calculations are responsible for verifying the transactions made in the blockchain network as well as maintaining its security, and as a reward for these activities, they receive bitcoins from the network. The devices used to mine cryptocurrency in order to perform the aforementioned calculations need high electricity consumption, so that the main cost of mining is related to its electricity consumption. For this reason, the ever-increasing development of the blockchain network, as well as the significant growth of the value of Bitcoin, has increased the number of cryptocurrency miners, especially in countries with low electricity costs.... 

A multi-agent system is a system consisting of several intelligent agents. In fact, a multi-agent system is a system that includes a large number of agents that communicate with each other through message transmission in a network structure. Multi-agent systems can solve problems that are difficult or impossible for a single agent or an integrated system to solve. Blockchain is an example of these multi-agent systems that has many use cases in different fields for example cryptocurrencies . A blockchain is a growing ledger consisting of records called blocks. In this thesis, we want to provide tools for the simulation of this multi-agent system so that we can model the issues surrounding... 

Blockchain systems are considered a subclass of distributed systems and have drawn a lot of attention from academia in recent years. The deployment of these systems in various contexts has been the focus of extensive studies. Because of their design, which places a strong focus on security and decentralization, blockchain systems have some challenges. The most prominent challenge is the one that involves scalability. A blockchain's scalability refers to its capacity to achieve a target throughput and solid performance in confirming transactions with an ever-increasing workload or number of nodes in the network. A solid performance suggests that the blockchain system can sustain its... 

With the growing product diversification and customization of demands, employing the concept of shared economy and resource sharing is more than ever needed. In this regard, with the advent of the Industry 4.0, IoT , cloud computing, and systems such as cloud manufacturing, impediments have been eliminated to form a network of businesses. Therefore, the problem of service composition, which seeks to allocate the best combination of services to a specific demand, is considered. Due to many services and various quality parameters, these problems fall into the category of mega-size problems. Moreover, in terms of computational complexity, they are from the NP-hard class. Given the... 

Cryptocurrencies (cryptos), as a new type of money, are considered a medium of exchange, an investment asset, and a hedging tool in today's world. In 2008, bitcoin as the first cryptocurrency was introduced, which has survived through recent years and has gained more and more popularity every day. Cryptos are one of the first applications of blockchain, the technology that many expect to revolutionize the future world in different ways. We aim to investigate what affects the bitcoin price, based on artificial intelligence and, in particular, machine learning. First, we find features impacting bitcoin price via a thorough investigation of the literature. Then, applying machine learning and... 

This research investigates the impact of Bitcoin and cryptocurrency news along with macroeconomic and financial indicators, on Bitcoin price fluctuations for two years (May 2016-2018). The reason for this examination is due to high variations of Bitcoin price in the late 2017 and beginning of 2018, while academic research focusing on Bitcoin price are mostly conducted before 2017. Findings show that the number of news with positive and negative contexts, and news related to cryptocurrency technology have a direct relationship with Bitcoin price change. The other result shows that among news concentrated on Bitcoin, the most effective is regarding adverse incidents, famous people concerns and... 

The purpose of this thesis is to improve the protocols for recording and transmitting medical data in terms of security and performance using blockchain technology. The approach we take in this Thesis differs in three respects from most articles written in this field. The first is that unlike those who look at the blockchain as a black box and take advantage of only its positive features, we consider the details and challenges it creates for us and solve them in order to use it. The second important point is to justify the use of blockchain in this design. It can be seen in many designs that the use of this technology is useless according to their model and goals. Finally, one of the most... 

Hyperledger Fabric is an open-source modular platform to launch permissioned-blockchains for use cases like banking and supply chains. This system uses the elliptic curve digital signature algorithm to authenticate transactions. The advent and progress of quantum computers have threatened the security of classical cryptographic schemes; therefore, the process of re- placing these schemes with post-quantum alternatives has gained considerable importance.This research intends to replace the elliptic curve digital signature algorithm with post-quantum digital signatures by using the algorithms passed to the third round of the National Institute of Science and Technologies (NIST) post- quantum... 

Managing health data and providing remote treatment services to patients has always faced security and privacy challenges. Because of the importance and sensitivity of this data, the use of centralized networks such as cloud space and trustin a cloud server can be dangerous, due to the lack of complete trust in the cloud server. To prevent the threats of centralized systems, we provide a decentralized blockchain-based system in which miners, in addition to authenticating physicians and patients, are also responsible for searching encrypted data and all user activities can be tracked in the distributed ledger. The proposed scheme preserves data privacy, and there is no need to trust a server.... 

Vaccinating the global population against Covid-19 is one of the biggest supply chain management challenges humanity has ever faced. Rapid supply of Covid-19 vaccines is essential for successful global immunization, but its effectiveness depends on a transparent supply chain that can be monitored. In this research, we have proposed an approach based on blockchain technology, which is used to ensure seamless distribution of the Covid-19 vaccine with transparency, data integrity, and full traceability of the supply chain to reduce risk, ensure safety, and immutability. Without a proper mechanism to track and guarantee the authenticity of vaccines, all involved members, including governments,... 

The ability of blockchain to record transactions and automatic execution feature in smart contracts, increase the speed of the supply chain and reduce unnecessary delays. A blockchain-enabled supply chain is more dynamic and responds to changes faster. This makes many processes more efficient in the supply chain. Supplier performance evaluation is an essential field in Supply chain management. At any time, by recording real-time data through smart contracts in the blockchain, it is possible to see the supplier’s performance in different aspects according to all the information recorded up to that moment. This research investigates the use of smart contracts and blockchain in solving supply... 

This thesis aims to create an electronic health system for transferring, verifying, and monitoring patient data. Blockchain technology is used in this system. In this system, the patient can communicate with the relevant hospital via an authentication protocol and transmit his data to the hospital. The hospital levels the patient's data creates the patient's treatment prescription and shares it with the pharmacy and insurance company to facilitate the patient's effective treatment. Blockchain technology has been used in a variety of electronic health systems. There are several problems with these systems, including the incorrect use of blockchain, a lack of comprehensiveness, a lack of... 

With the advent of the Internet of Things (IoT), e-health has become one of the main topics of research. Due to the sensitivity of patient information, patient privacy seems challenging. Nowadays, patient data is usually stored in the cloud in healthcare programs, making it difficult for users to have enough control over their data. The recent increment in announced cases of security and surveillance breaches compromising patients' privacy call into question the conventional model, in which third-parties gather and control immense amounts of patients' Healthcare data. In this work, we try to resolve the issues mentioned above by using blockchain technology. We propose a blockchain-based... 

To update Blockchains, a consensus protocol must be used to verify the integrity of registered transactions by users. Bitcoin, as the largest Blockchain network, uses a Proof-of-work mechanism to reach consensus and rewards users for doing so. This will lead to the use of costly hardware to execute heavy processing commands with a lot of energy loss. Different groups have since proposed different mechanisms for reaching consensus without costly processing. The idea we present here is that we first define a general chance variable for each miner, and the miner has to wait a certain amount of time accordingly and then be able to generate the block. Chance variables are public, so other members... 

Population and urbanization increase, intra-city travel and the use of private cars have created problems such as traffic, higher fuel consumption and air pollution. One of the approaches to deal with this phenomenon, which has been in center of attention in recent years due to the growth of technology and development of ride-hailing platforms on mobile phones, is using shared vehicles and travel sharing.The assignment problem in ride-sharing is a group of VRP problems and is classified as an NP-hard problem. Due to the high volume of demand from passengers and supply from drivers, as well as the need for fast response to reduce waiting time for passengers and drivers, there is a need to... 

This research deals with one of the current issues in the world and in Iran which is called the field of cryptocurrencies. This research has tried to map the situation of cryptocurrencies in the world and then the situation of Iran in this field.In order to understand the situation of Iran in the field of cryptocurrencies, three main questions have been defined. The Questions that first express the nature of Iran's policies and then determine the position of these policies in relation to the conceptual framework, and then it will discover the reason of the adoption of these policies in Iran.Therefore, this research has an exploratory approach and its research method is qualitative. In order... 

This research deals with one of the current issues in the world and in Iran, which is named the field of cryptocurrencies. Domain that is managed decentrally due to the use of blockchain platform. This decentralization has caused different challenges (security problems, disruption of economic governance, etc.) for governments and has created different advantages and disadvantages for each country. This study seeks to investigate how Iran is facing the challenges in the field of cryptocurrencies. In this research, three main questions have been asked to determine the situation of Iran in the field of cryptocurrencies. In the first question, what are the policies of Iran is questioned and then... 

In the light of rapid advancement in renewable energy technologies, they become an appropriate way to supply energy demands with lower costs. It also gives them the chance to earn money by selling surplus energy to other energy consumers. The coordination of different energy types and the ability of energy conversion, facilitates the rising of new energy prosumers called “Smart Energy Hub(SEH)”. This thesis proposes a model of energy trading among SEHs. The model consists of SEHs, energy utility grids, energy consumers and aggregator. In this model, aggregator aggregates between SEHs, energy consumers and utility grids in order to maximize its profit. Bilevel optimization problem has been...