Sharif Digital Repository

Blockchains are not scalable by design, and it is known to be the most important barrier in the way of development of these systems. One of the main approaches to this problem is sharding, that is under development in industry and academia. Sharding scales the system up by reducing redundancy, that makes blockchains vulnerable in terms of security. In this paper, we will study the effect of sharding on availability of these systems, and will show that sharding can magnify the unavailability of the service, and introduce an adversary threat model that takes real concerns of availability in today’s Internet like DoS attacks into account. We also introduce a basic unavailability-resistant... 

By entering the concepts of transactive energy systems, microgrids and peer-to-peer networks into the local energy market, it has made it possible to implement local energy market in the microgrids more than ever. In transactive energy systems, with the elimination of the intermediate entity, exchanges take place directly between the different parts of the system, which results in increased system flexibility and reduced system costs. In this study, by applying blockchains in local energy market and in micro-grids and transactive energy systems, a framework is proposed to implement local energy market in an energy micro-grid based on blockchain. By using blockchain features and structure,... 

In today’s world, social networks have become one of the primary sources for the creation and propagation of news. Social news aggregators are one of the main actors in this area in which users create news items and use positive or negative votes to indicate their preference
toward a news item. This approach suffers from several problems raging from being prone to the dominance of a united adversary to difficulty in decerning between correct and fake new news and lack of incentive for honest behaviors. In this paper, we propose a graphbased news aggregator in which instead of voting on new items, users submit their votes on the relations between news items. This method of voting... 

A distributed ledger is a method of digital data storage and sharing in different places, and the blockchain technology is a way of implementing a distributed ledger. This technology has been employed in many of the cryptocurrencies like Ethereum to store transactions. In addition to storing transactions, Ethereum deploys scripts called smart contracts that are automatically executable. These scripts execute transparently and without preserving the privacy of participants. On the other hand, confidentiality and privacy are among the important components in data, network, and system security. Models such as Hawk and Enigma have been presented to obtain privacy-preserving in smart contracts;... 

With the recent considerable developments in the Internet of Things (IoT), billions of resource-constrained devices are interconnected through the internet. Monitoring this huge number of IoT devices that are heterogeneous in terms of underlying communication protocols and data format is challenging. The majority of existing IoT device monitoring solutions heavily rely on centralized architectures. Since using centralized architectures comes at the expense of trusting an authority, it has several inherent drawbacks, including vulnerability to security attacks, lack of data privacy, and unauthorized data manipulation. Hence, a new decentralized approach is crucial to remedy these drawbacks.... 

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... 

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... 

Voting has been considered as one of the principal of democracy which by this, people can announce their convictions and ideas officially. E-voting is a method of online voting based on cryptographic mechanisms. E-voting schemes by keeping voters' privacy safe and providing security requirement same as verifiability, fairness, coercion resistance, receipt freeness, undeniability, and eligibility has been noticed in recent years. Security of many presenting schemes is based on existence of trusted third party that plays an important role in process of getting and counting votes. Also, some of security problems which are in this scheme, originated from centralization and generic trust of third... 

The Oil and gas industry is one of the most important industries in the world. It has great role in Iran’s economy also. Regarding complexities of new companies, there is room for more cooperation and coordination within the industry and with other actors. Oil and gas niches have close interdependency with financial sector. The new encrypted currencies play great role in new financial models. Blockchain technology can help the oil and gas industry by using its appropriate features. Blockchain is a system of recording information in a way that makes it difficult or impossible to change, hack, or cheat the system. The supply chain of oil and gas industry in Iran includes upstream, midstream... 

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... 

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... 

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... 

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...