Sharif Digital Repository

Regarding to the emergence of quantum computers and advances in the large scale implementation of them, exploiting hard problems of coding theory is of great importance.This family of problems, like those of lattices, has an acceptable resistance against classic and quantum attacks. Thus, they can be replaced with hard problems in number theory and algebra. Increasing dominance of cyberspace made us highly dependent to it. Consequently, preparing tools and methods to mitigate future threats is necessary. Digital signatures constitute an important family of cryptographic primitives. Code-based digital signatures are mostly suffering from two main drawbacks: large public key and long time of... 

Reliable and secure communication requires low error probability and low information leakage, respectively. But there are different metrics for error probability and information leakage. Two important reliability metrics are ϵ or zero probability of error. An ϵ-error criterion requires the (average or maximal) error probability to vanish as the blocklength increases, while a zero-error criterion, demands the error to be exactly zero for every given bloklength. Three important security metrics are weak, strong, or perfect secrecy. A weak notion of secrecy requires the percentage of the message that is leaked to vanish as the code blocklength increases, while a strong notion of secrecy... 

The rapid evolution of artificial intelligence (AI) technologies has led to the widespread adoption of AI systems in diverse research and industrial fields. Deep neural networks, at the forefront of AI's power, demonstrate high performance by leveraging large volumes of training data. However, acquiring such vast amounts of data requires collaboration among individual data owners, who may have concerns about privacy. To address these concerns, various privacy-preserving methodologies have been proposed. These methodologies share a common goal of striking a balance between preserving privacy and maintaining data utility. This study aims to explore and analyze these privacy protection... 

User cooperation is an important concept in wireless networks to achieve best performance subject to low cost. Dynamic and broadcast natures of wireless networks are two indispensable characteristics of these networks. Therefore, when a user transmits his signal to the receiver, other users in his neighborhood may receive the signal as well. Hence, these neighbors can decide to cooperate with each other in transmitting their messages to the receiver. On the other hand, due to the dynamic nature of the wireless networks, one can assume that each user has some knowledge about the interference signals or the fading coefficient that are not known to the other users. Therefore by utilizing user... 

Energy Harvesting has been appeared as an approach in order to make the green communications possible. In Energy Harvesting systems, nodes extract energy from the nature to extend their lifetimes. The harvested energy can also be used for the purpose of communication and specially for the transmission process. Compared to the conventional batterypowered systems, the Energy Harvesting systems have access to an unbounded source of energy (like vibration absorption devices, water mills, wind turbines, microbial fuel cells, solar cells, thermo-electric generators, piezoelectric cells, etc). However, the diffused nature of this energy makes it difficult to be used for communication. In this work,... 

Security for wireless communication networks has become a crucial issue because of the broadcast nature of wireless channels. On every cellular network Since it is possible for passive nodes to easily overhear the confidential information transmitted between transmitter and receiver, it is necessary to provide secure communication.When a cellular user wants to communicate with a node or base station on the cellular network, it expects that information will be transmitted and received without interference, with enough quality and without eavesdropping. On the other hand In practical scenarios, we know that cellular network nodes are not equipped with ideal equipment and some percent... 

In the research area of network information theory, except in some cases, finding the exact capacity of different communication channels has always been a challenge. In the high-signal to noise ratios, the capacity of all Gaussian channels can be calculated within a low difference. Therefore, a parameter called the degree of freedom is introduced that describes the behaviour of the capacity of different networks at high signal-to-noise ratios. In other words, the DoF region is used as a tool to determine the capacity of interference channels at high $ \mathrm{SNR}$ values. In almost all interference networks, the idea of interference alignment can be used to achieve the... 

Block ciphers are one of the most necessary primitives for security protocols, and so, cryptanalysis of them is also essential as well. On the other hand, the security assessment of block ciphers is usually manual work with various specific-idea according to the target block cipher type and algorithm. Some basic known methods for cryptanalysis of block ciphers include linear, differential, meet in the middle, and integral attacks. However, cryptanalysis methods are not limited to them, and many new hybrid or innovative methods are employed to provide better results. Recently, automated cryptanalysis of block ciphers and proposing new methods for analyzes of these ciphers are in the... 

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... 

In modern wireless communication networks,that we have heterogeneous, asynchronous and ultra low latency networks and Due to the high processing power required by conventional cryptographic systems based on computational security, information theoritc security can play important role in the future development of these systems. Security in this case does not depend on the eavesdropper's computing power, but on the statistical independence between the main message and the received message of the eavesdropper. In recent years, polar codes have created new arenas, as they were the provable channel codes that could achieve capacity and reliability simultaneously. In addition, the clear structure,... 

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... 

The electronic health system plays a crucial role in modern healthcare, facilitating efficient data management, secure information exchange, and improved patient care. However, existing systems often face challenges related to security, privacy, scalability, and interoperability. The primary objectives of this study are proposing a system that ensures data security, patient and peer privacy, scalability, data integrity, deniability, traceability, secure data sharing, access control, transparency, real-time monitoring, and security in the drug supply chain. To achieve these objectives, we have proposed a system that encompasses a wide range of requirements of healthcare system. To enhance... 

The applications of Internet of Things technology are increasing day by day. In the Internet of Things, various devices are connected to each other with the help of the Internet and perform various operations automatically. Today, this technology has various applications in smart city, smart home, smart car, as well as military industries and industrial factories. One of the newest applications is its use in the field of health and hygiene, which is known as the Internet of Medical Things or Smart Health. With the emergence of new epidemic diseases, the importance of this application becomes more clear. Smart health helps the patient. without going to the hospital and doctor in person, to... 

The subject of Secret Sharing refers to the methods that a secret information is shared (by a dealer) among a number of parties, so called participants, each having one or more shares, such that the predefined subsets of the participants, called authorized subsets, are able to regenerate the secret using their shares. A more general scheme which is called Multi Stage Secret Sharing (MSSS) is to share multiple secrets among the participants such that the authorized subsets can reconstruct the secrets in the consecutive stages; in these schemes, in addition to the individual shares, the dealer should provide the participants with a number of public values regarding the secrets. A Multi-Secret... 

“Decode and Forward” is one of coding strategies used in relay channel and networks in which each relay in the network decodes the transmitted message by the sender and other relays in the network and then re-encode and transmit it to the other relays and the receiver in the network. This process results in the cooperation between the relays and the sender to remove the uncertainty of the receiver about the transmitted message. “irregular encoding-successive decoding”, “regular encoding-backward decoding” and “regular encoding-sliding window decoding” are different methods usually used in “Decode and Forward” strategy. “partial decode and forward” is a generalized form of “decode and... 

In this thesis the problem of simultaneously generating multiple keys among multiple terminals is investigated. After providing a survey on the related works and exploiting the problem of sharing a common secret key and a private key among three terminals, we introduce a new source model which we call it the Four-Terminal model. We consider the problem of generating three kinds of keys among legitimate terminals and investigate the problem under two different scenarios, Backward and Forward scenarios, which depend on the kind of restrictions imposed on the usage of the public channel. We derive an achievable region for the backward scenario, using the combination of superposition coding and... 

In order to utilize cooperative resources of a network, we have to investigate cooperative networks and strategies. Information theory, by introducing different concepts such as coordination and common information, gives us a suitable tool to study cooperative networks and using their resources. In this thesis, we investigate coordination and secret key agreement in cooperative networks. Our study consists of two parts. In the first part, we consider coordination and its applications in cooperative networks. For this purpose, we introduce the triangular multiterminal network as a proper model for studying empirical coordination in multiterminal networks and establish an inner and outer... 

In this thesis, the problem of secret key agreement in the channel model with side information is studiedx. In order to investigate the problem, we consider three models according to the different ways of side information availability which are the state-dependent broadcast channel; the state-dependent broadcast channel in presence of public channel and the state-dependent wiretap channel with degraded versions of the channel state information.For the problem of secret key agreement in broadcast channels, two models, the state-dependent wiretap channel and state-dependent three receivers broadcast channel, are considered. We obtain inner and outer bounds of the secret key capacity region for... 

Interference management is one of the key issues in wireless networks wherein multiple source-destination pairs share the same medium and frequency band and interfere with each other. The exponentially growth in the number of wireless systems and services results in the spectrum shortage which has emerged the technologies that increase the spectral efficiency. Providing the users with cognition equipments in these networks enables them to sense the medium and use the obtained data to adapt their transmissions to cooperate with other users and improve their own rates as well as the others which results in the cognitive radio technology. In order to access the full potential of this technology,...