Sharif Digital Repository

Due to the increase of computer networks and their application, the need for secure communication has become a very important concern. We introduce Cmail, a secure messaging system that works without any central party and in addition protects privacy of users. This system is on top of a cryptocurrency system such as Bitcoin. Bitcoin is cryptocurrency that works on the Internet. The suply of bitcoins and verification of transactions is done by Bitcoin miners, which are some typical client of Bitcoin system, in a decentralizd maner. In Cmail the miners have additional task, they should transfer messages of users and if needed, they hold it for a limited time. In order to increase incentive of... 

Information and communications technologies have affected the human world rapidly, which challenges the facing today’s information society. Extensive use and impact of these technologies in different aspects of human life have led to an information revolution. This revolution, changes in our understanding of the human nature and physical world. The human is an information organism among the other agents which is living in the informational environment, that is called the infosphere. Moreover, the information revolution has caused to emerge of “Bitcoin”; a phenomenon that is changing economic relations. Bitcoin is a “crypto-currency” and “encrypted payment system” that relying on a... 

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... 

Behavioral economics demonstrates that the sentiment can affect the behaviors and financial decisions of people. Can this be generalized to societies? For instance, is it possible for societies to experience emotions that will change their ways of decision making? This thesis attempts to perform an experiment addressing these questions. Bitcoin has been facing a transient phase of price volatilities. Many articles believe that bitcoin does not have an inherent value and is only derived by factors like the perception and acceptance of it and the sentiments among the investors. Digital currencies provide the unique possibility of measuring socioeconomic signals using digital traces.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 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... 

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... 

Lightweight clients are a type of blockchain users who do not store all the blocks in the blockchain due to limited resources. These users store only a small part of each block and when needed, request transactions from full nodes that store the entire blockchain. These users have no role in block validation and only want to receive transactions related to their addresses with proof of the inclusion in the block from full nodes.Since light clients rely on full nodes for receiving transactions, their privacy against full nodes is important. The current implementation of Bitcoin uses Bloom filters for privacy, but this offers very little privacy to the users.In this thesis, we study 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... 

Classical financial literature believes that people's decisions in financial markets are rational and that asset prices remain at their intrinsic value. On the other hand, behavioral finance literature believes that there are limitations in investors' decision-making and the impact of decisions on emotions, and states that investors' emotions directly affect asset prices. The aim of this research is to investigate which of the famous indicators introduced in the literature as a representative of the emotional behavior of investors has a better performance in predicting the returns of cryptocurrencies. For this purpose, in the first step, the information related to the calculation of three... 

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... 

Price movement prediction has always been one of the traders’ concerns in the field of financial market prediction. In order to increase the profit of the trades, the traders can process the historical data and predict the movement. The large size of the data and complex relations between them lead us to use algorithmic trading and artificial intelligence.The stock and Cryptocurrency markets are two common markets attracting traders. This thesis aims to offer an approach using Twin-Delayed DDPG (TD3) and daily close price in order to achieve a trading strategy. Unlike the previous studies using a discrete action space reinforcement learning algorithm, TD3 is a continuous one offering both... 

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... 

With the huge growth of cryptocurrencies in recent years, the attention of investors has been drawn to predict and invest in it. Because of the high volatility of this market, which includes a large share of Bitcoin, there is a need for good forecasting in it. Although past studies have been able to accurately predict the price of Bitcoin using fundamental variables and variables related to the blockchain network, less attention has been paid to the use of variables related to investor sentiments in this market. In this research, variables widely used in the literature that show the emotions and attention of investors, such as sentiment analysis of Twitter texts, Google search index,... 

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... 

Today, financial exchanges have taken on a new form and cryptocurrencies were able to have a special place in these exchanges. Cryptocurrencies have attracted a lot of attention due to their decentralized nature. One of these cryptocurrencies is called Bitcoin and has the largest share of cryptocurrency exchanges. Due to the high volume of Bitcoin exchanges, a lot of energy is needed to supply this decentralized network to confirm transactions and extract it. In order for people in this industry to continue mining Bitcoin, they need to maintain their profitability. Therefore, choosing low consumption and profitable miners is one of the requirements of this industry. The aim of the thesis is... 

Currently, cryptocurrencies have attained a significant role in the financial transactions of the world, especially due to their peer-to-peer and decentralized characteristics, resulting in the elimination of intermediary oversight entities. In the cryptocurrency network, transaction security is ensured through devices known as cryptocurrency miners. People place their cryptocurrency mining devices at the disposal of the cryptocurrency network and, depending on their device’s processing power and capacity, receive rewards in the form of cryptocurrencies. Given the complexity of cryptocurrency networks, regular devices lack the ability to mine cryptocurrencies, necessitating high processing... 

Cryptocurrencies are not only regarded as a trustworthy method of financial transaction validated by a decentralized cryptographic system as opposed to a centralized authority, but also as one of the most popular and lucrative forms of trade and investing. Predicting the price of a cryptocurrency is a challenging topic in time-series research. Its intricacy is due to the volatility and large swings of cryptocurrencies' price. The emergence of brand-new cryptocurrencies, which might present a profitable trading opportunity but lack sufficient historical data for technical analysis, prompted us to develop a trading strategy that could be applied universally. The forecast of the next timestep's...