Sharif Digital Repository

Today many communications take place over asynchronous insecure networks which do not provide any guarantee of security (as Internet); hence there is a must in authenticating party or parties with which we are going to interact. In many cases, more than two parties (entities) are going to interact, resulting in need of group authentication. Since authentication is inseparable from key exchange, we are going to introduce a new authenticated group key exchange protocol in this thesis which benefits from all known features for such a protocol in the literature such as contributiveness and deniability. To overcome the problem of concurrency, we use a framework dedicated to security in concurrent... 

Nowadays with development of applications that stream video over internet, compression efficiency of video has become very important. On the other hand, Watermarking and video coding are two conflicting technologies. One adds redundancy and other tries to remove it. We have proposed a H.264 watermarking method that does not increases the bit rate. Unlike most of watermarking schemes, this methods embeds the watermark in inter coded frames. Abundance of these frames in video is impressively more than intra frames, so a lot of capacityis eventuated. But these frames are highly compressed using motion compensation, and are very sparse. To avoid from bit rate increment, this method only embeds... 

Since the number of Internet users for the services such as e-applications is increasing rapidly, authentication constrains more latency as well as load to the system. It is due to large number of users whose identity needs to be checked and compared individually, and the number of simultaneous authentication requests in a specific time. To solve the stated issues, this thesis proposes a new definition of group authentication and describes group authentication protocols. Group authentication is the verification of identity of multiple requests of users at the same time. In this protocol, the authentication server inputs the multiple authentication requests in a function, and then applies... 

In today's world in which a major part of information is digitalized and a large portion of the communication is done via computer networks, entities authentication while maintaining privacy is a concern with the growing importance and value. To meet this goal, during the past two decades, anonymous authentication protocols with different approaches for use in various applications has presented and developed. These protocols enable users to authenticate based on some of their properties, without revealing their own identities. Secret handshake protocols are considered as type of anonymous authentication protocols. This protocol has the unique feature of hiding users' affiliation to the... 

Nowadays, user accounts on websites such as Google, Facebook, and Yahoo are their key to login into other websites and on the Internet. Thus, there is no need for authentication in each website and each user can access his/her other accounts just by logging in Google or Facebook. In background, single sign-on protocols such as OpenID and OAuth are being used. Since single sign-on accounts are very critical and sensitive, they are always under attack of cyber intruders. One of the most important threats is phishing in which one of the seeming trustful components could be attacker.This thesis demonstrates that OpenID providers may not be worthwhile and trustful as they are able to have... 

Zero-knowledge proofs are one of the most useful constructions of modern cryptography. Their invention has greatly affected both cryptography and complexity theories. The seemingly paradoxical characteristic of zero-knowledge proofs is that they convince the verifier of the validity of the proposition being proved, yet they yield to further knowledge to him. Two primary applications of zero-knowledge proofs are authentication protocols, as well as sub-protocols which prove that parties involved in some main protocol have acted honestly. In this research, we will survey the models and definitions of zero-knowledge, and analyze their relationship. We then pertain to the interplay between... 

With the increase in the usage of wireless networks and smart grid networks and their applications, need for broadcast transmission has been increased dramatically. In order to use these communication, first we need to secure them by cryptographic methods. As authentication is one of the most important aspect of security, introducing secure broadcast authentication schemes are critical. Because of the resources constrainted nodes of these network, it is important to use light cryptographic methods with high security in these schemes. In this work, after analyzing related works, we introduce a new symmetric broadcast authentication scheme which is more efficient in term of memory consumption... 

Nowadays, Internet of Things is considered as a global infrastructure to establish communication between physical world and virtual world by using existing technologies. Its purpose is enabling things to establish communication with anything and any person in any time and any place by using existing networks and services. This technology makes different aspects of people's life smarter, facilitates doing works, and increases the quality of people's life. But, the development of Internet of Things faces to fundamental challenges that one of the most important of them is security and privacy preserving of users. According to the projects of European Research Cluster on the Internet of Things... 

Internet of Things means making the all of things smart to access them anytime, anywhere through the Internet. Existing of IoT as a novel way of networking, opens up new issues round the communication and network world. One of them is how to establish the security in such a diffuse network. Because the members of this network are not smart phones, computers or any other usual networking technologies, but they are the normal things and appliances in our daily lives, such as refrigerators. Smart things are mostly resource-constrained and power-limited so the former ways of securing networks cannot be applicable in IoT. Thus, Security bootstrapping has is introduced a solution for establishing... 

Design of anonymous authentication scheme is one of the most important challenges in Vehicular Ad hoc Networks (VANET). Most of the existing schemes have high computational and communication overhead and they do not meet security requirements. Recently, Azees et al. have introduced an Efficient Anonymous Authentication with Conditional Privacy-Preserving (EAAP) scheme for VANET and claimed that it is secure. We show that this protocol is vulnerable against replay attack, impersonation attack and message modification attack. Also, we show that the messages sent by a vehicle are linkable. Therefore, an adversary can easily track the vehicles. In addition, it is shown that vehicles face with... 

The Internet of Things (IoT) is rapidly expanding as an emerging concept. The connection of billions of objects and human beings creates serious challenges. Security is one of the major challenges faced by the Internet of Things, and a standardized scheme to meet security requirements has not yet been introduced. Authentication and privacy preserving users is one of the important security requirements. In this thesis, a user and a message authentication scheme in the Internet of Things are introduced, which simultaneously preserving the conditional privacy of the users. The scheme that proposed on Identity Based signature, in the verification phase user signature is verified Simultaneous,... 

Vehicle Ad-hoc Network (VANET) is a type of mobile Ad-hoc network (MANETs) which vehicles are mobile nodes of this network and it can be used for various applications such as secure data sharing between vehicles, sending road information to vehicles, traffic controlling and reducing road accidents, also primary types of these networks are implemented in some systems such as “Waze” and “Balad”. On the other hand, if the security requirments are not provide in these networks, attackers can use this network to cause disruptions in this network, including intentional accidents, so providing security requirements in these networks seems necessary. Data authentication and preserving privacy of the... 

IoT security is an important step in the rapid development of its applications and ser-vices. Many security protocols have been defined to maintain security at higher communication layers, such as the transport layer and the application layer, but with the advent of quantum computers due to high-speed parallel computing, the previous methods are no longer secure and we have to establish security at lower layers such as the physical layer. The efficiency of IoT devices depends on the reliability of their message transmission. Cyber-attacks such as data injection, eavesdropping and man-in-the-middle can lead to security challenges. In this study, we propose a new deep learning based component... 

Nowadays, intelligent transportation systems have become possible and practical with the help of vehicular ad-hoc networks. This network is a subset of mobile ad-hoc networks introduced and studied separately due to its unique properties. With the help of vehicular ad-hoc networks, the level of road and drivers safety is increased and safety messages can be sent to road side units or other vehicles, so real-time is one of the main requirements of these networks. Other advantages of implementing such networks include providing entertainment and internet access services.On the other hand, these networks face various challenges, including routing data packets, preserving security requirements,...