Sharif Digital Repository

According to increasing energy demand in Iran and the world, the role of natural gas as a relatively clean and cost-effective source has received more attention. Given the high share of the residential sector in the country's natural gas consumption, providing a model for forecasting the demand of this sector is of great importance for policy makers and decision makers in this field. In the present study, we employ three popular methods of machine learning, support vector regression, artificial neural network and decision tree to predict the consumption of natural gas in the residential sector in Tehran according to meteorological parameters (including temperature, precipitation and wind... 

In many sciences, including computer science, generating random numbers have always been an interesting problem.Pseudo-random generators are one of the most important solutions to this problem and one of the primitives, used especially in cryptography and computer science, which have made it easier for us to generate random numbers.The main purpose of these generators is to increase the length of an n-bit string to an l-bit string where l>n.We need an initial value called Seed in this definition. We will present a new and stronger definition in this essay, called the Hinting Pseudorandom Generator, which has different outputs as well. Thus, our input is n bits and our output is n.l bits. We... 

Voting is a detachable part of the democratic governments. In the era of modern computer systems, the need for electronic voting systems in no longer avoidable.Designing a secure electronic voting system is a difficult problem since both privacy and integrity must be achieved at the same time. This difficulty has cast the problem to the center of attention of many researchers.In this thesis we will consider the new generation of voting systems known as end-to-end that were designed to solve the problems in the previous generations of voting systems and to uphold the security of the system. Many of end-toend voting systems use concepts of cryptography in addition to machine tools.A central... 

The Gaussian mixture (cardinalized) probability hypothesis density (GM-(C)PHD) filter is a closed form approximation of multi-target Bayes filter which can overcome most of multi-target tracking problems. Limited field of view, decreasing cost of cameras and its advances induce us to use large-scale camera networks. Increasing the size of camera networks make centralized networks practically inefficient. On the other hand, scalability, simplicity and low data transmission cost has made distributed networks a good replacement for centralized networks. However, data fusion in distributed network is sub-optimal due to unavailable cross-correlation.Among data fusion algorithms which deal with... 

In this thesis we will focus on Functional Encryption. At first a wide range of different types of requirements and applications which are not fulfilled by Public-Key Encryption are considered. These types of requirements finally led us to Functional Encryption. Then a breaf explanation of differrent types of Functional Encryption is presented. In the sequel we will exlain Functional Encryption more formally. Finally we will consider the latest achievemnets and open problems in this area  

Using “Searchable Encryption” enables us to encrypt the data, while preserving the possibility of running search queries. One of the most important applications of the mentioned is in Cloud Storage. As users do not trust the Cloud space, they are not inclined to store their data on the Could. The solution to this problem is of course, Cryptography. However, ordinary Cryptography methods, eliminate the data’s searchability. Hence, we need encryption schemes that code the data while retaining their searchability. So far, various schemes has been proposed that differ in their performance, security level, and usage. In this thesis, we aim to discuss and analyze these methods  

One of the main requirements in today’s computer networks such as the Internet is protecting the privacy of users. Hence, anonymity is a useful tool for privacy and provides user’s anonymity. So far, several protocols have been designed to provide anonymity but most of the times, attackers found a way to take advantage of weaknesses in the design and implementation of these protocols. There is a class of attacks,where attacker tries to relate clients of anonymity system to each other, regardless of the communication protocols they use, just by observing networks traffic.The MIX technique forms the basis of many popular ervices that offer anonymity of communication in open and shared networks... 

In recent years, different cryptographic tools have been introduced for a wide range of cloud computing applications that can be classified based on a trade-off between performance and security. In this thesis, we introduced the private set operation schemes, and at their heart, private set intersection schemes, in the cloud computing platform. These schemes are of particular importance because they can be used as basic cryptographic schemes for a wide range of functionalities in the cloud platform. Using these schemes, the user can securely store datasets on the cloud, run set queries remotely and receive the desired results. To this end, we first modeled the syntax and the security notions... 

In this thesis, in addition to reviewing the previous work done in the study of ideal access structures, we present the author's recent results in this field. As a first result, we introduce a new technique for reducing the size of the secret space in ideal homomorphic secret sharing schemes. The concept of decomposition of secret sharing schemes is formally introduced for the first time. In this regard, we show that ideal homomorphic and abelian secret sharing schemes are decomposable. We also examine the inherent group-characterizability of secret sharing schemes and show that an ideal secret sharing scheme is not necessarily inherently group-characterizable. Some weaker definitions of the... 

Side channel attacks, where an attacker learns some physical information about the state of a device, are one of the ways in which cryptographic schemes are broken in practice. leakage resilient ryptography addressed this issue at a higher abstraction level, proposing models capturing such attacks. Auxiliary Input is one of these models. In this thesis, we study public-key encryption schemes in this model of leakage. we also propose a method to consider this leakage continuously (i.e., not just one observation of the adversary). at the end, we consider the leakage from both the secret key owner and the encryptor. This odel captures a wider class of side-channel attacks  

Designing efficient and secure electronic voting protocols without the presence of trusted authorities, which are known as decentralized voting protocols, is one of the most interesting and challenging problems in cryptography. In these protocols the outcome of the protocol is determined by voters collaborating with each other. Since voting is a significant concept in every society, the correctness and security of voting protocols are important. For security analysis of electronic voting protocols, an intuitive proof is not enough and we require a comprehensive approach that provides provable security. In this thesis, we use universal composition framework to analyze a decentralized e-voting... 

A secret sharing scheme involves a dealer who has a secret and distribute that among a set of participants, in such a way that only authorized subsets can recover the secret value. The collection of authorized subsets called the access structure and a secret sharing scheme in which unauthorized subset cannot reveal any partial information about the secret is called a perfect secret sharing scheme. One of the problems in secret sharing schemes is finding the appropriate lower bound for a parameter called the information ratio and optimizing it. A perfect secret sharing scheme is ideal when it has an optimal information ratio. In other words, if all shares have the same length as the secret,...