Sharif Digital Repository

Fair exchange of digital items through computer network is an important research topic of modern cryptography. Generallty, a fair exchange protocol is a way which helps two parties to exchange their digital items fairly, so that at the end of the protocol execution, both parties recieve their desirable items or none of them recieves anything. In a practical applications, fair exchange protocol is widely used in different but related fields like contract signing protocols,non-repudiation protocols,e-ayment system and certified e-mails. In a fair exchange protocol, a trusted third party (TTP) acts as an arbitrator between two parties. To reduce the traffic load of the arbitrator, the concept... 

Cake Cutting is an old problem that studies how to allocate a resource among a number of agents to achieve fairness or maximize the revenue by selling the chunks fairly. The primary assumption in the conventional methods of studying Cake Cutting was that the allocator knows everything about the agents and their valuation functions for the different cuts of the cake, which could be impossible in real life. Here we addressed a new setting for an online Cake Cutting problem with unconnected pieces and studied four different objectives upon the setting. There we studied fair and efficient Online Cake Cutting by means of linear fairness and envy freeness. We also added a payment rule to study the... 

Solid State Drives (SSDs) have an electronic architecture based on non-volatile memories. The unique merit of a SSD is its internal parallelism. Thus, adopting SSDs as the storage media in the storage systems in various devices, such as smart phones, personal computers, large workstations, and etc., improves the performance of the device, substantially. However, the conventional host interface protocols in SSDs, i.e. SATA and SAS, have critical limitations, like low bus bandwidth (maximum 12Gbps), and a single shared request queue. With such limitations, the host interface turns into a performance bottleneck in conventional SSDs. Therefore, the high performance provided by such SSDs cannot... 

Increasing use of World Wide Web and users tend to accompany in the electronic transaction has caused a fair exchange becomes very important and pervasive electronic transaction. These transactions have a lot of usage and benefits. In this study, the optimistic fair exchange has been studied. It is a special case of the fair exchange while having more advantages than the fair exchange. A situation considered that a signer could not sign a message by himself so he delegates his right in signing to a person as a proxy signer. In this study, a protocol of optimistic fair exchange for proxy signature is presented. So, the proxy signer can accompany in the optimistic fair exchange instead of the... 

One of the advantage of the mutual funds is their liquidity. They should pay back investor’s money based on Net Asset Value (NAV) anytime they request. Sometimes, NAV computed by fund is different from the real value of it. This error in pricing could be more intense in Iran because Iran stock market liquidity is low, ticker become closed frequently, and stocks can’t be traded and the change of price in one day has the limitation. All of these reasons make the price of stock in Iran stale which doesn’t contain the latest market information. The staleness of stock price makes the return of funds predictable and provide the opportunity of arbitrage which causes the transfer of the wealth among... 

Validation is an important enterprise especially when the test to be validated is a high-stakes one the results of which bring about life-changing implications for the candidates (Roever, 2001). Messick’s (1988) notion of construct irrelevant factors is pertinent in test validation. Demographic variables like gender, field of study and age can affect test results and interpretations. A fair test needs to be neutral when it comes to construct irrelevant factors such as gender. Differential Item Functioning is a way of making sure that the test does not favor one group of test takers over the others. The current study investigated differential item functioning (DIF) in terms of gender in the... 

In this study, we consider the fair division problem. In this problem, a heterogeneous resource must be fairly divided among a set of agents with different preferences.The resource can be either a divisible good (i.e., time, land), or a set of indivisible goods. When the resource is a single divisible good, the problem is commonly known as cake cutting. To measure fairness, several notions are defined, i.e., envy-freeness, proportionality, equability, maximin-share. In this thesis, we first give a formal definition of these notions. Next, we present our results for envy-freeness and maximin-share.First, we prove the existence of an allocation that guarantees each agent a factor 3/4 of his... 

In recent years, introduction of new technologies has highlighted the need to more data rate in mobile networks. Classical methods of resource allocation in mobile networks cannot respond to this huge demand for data rate because of their limitations. Resource allocation, as one of the operators’ tasks, plays a key role in the network efficiency and users’ data rate. Opportunistic resource allocation and scheduling have gained attention in recent years. On the other, using single-channel (frequency reuse-1) networks is also one of the methods to improve data rate in mobile networks. It is expected that the use of opportunistic scheduling in single-channel networks can repond to the huge... 

In wireless powered communication networks (WPCNs), wireless nodes are charged via an access point. In these networks, an access point transfers power to the nodes, and then, the nodes use the received power to transmit their information to the access point. Due to the wireless transmission of the information, eavesdropping of it is an important vulnerability in these networks. The conventional method to resolve this security problem is using cryptography algorithms. However, this method needs key management and complex encryption algorithms to be used by the nodes, which may not be applicable. Physical layer security (PLS), which uses the channel characteristics, is a more suitable way to... 

Queuing algorithms are used in packet forwarding elements such as routers or switches and the goal is to minimize transmission delays as well as to help manage network congestions. On the other hand, over 90 to 95% of the packets in the Internet use TCP and correspond to the transfer of digital documents of one form or another (Web pages, data files, MP3 tracks etc.) ; this kind of traffic is called elastic. In this thesis, we present a new Start-time Fair Queuing (SFQ) algorithm called Weighted Start-time Fair Queuing (WSFQ) which is more efficient and achieves better fairness than SFQ in the presence of small and huge elastic traffic flows. WSFQ scheduler, like SFQ uses a start time...