M Tech Dissertations

Permanent URI for this collectionhttp://drsr.daiict.ac.in/handle/123456789/3

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Subject: search.filters.subject.Cryptography

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Now showing 1 - 5 of 5
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    Performance analysis of TCP over enhanced UMTS network
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2008) Mathur, Rahul; Jotwani, Naresh D.
    The increase in demand and overwhelming response of 3G mobile networks has made it a technology which would drive the future of mobile communication. On the other hand the popularity of the Internet has also increased with type of services it is providing. Internet mainly relies on TCP/IP protocol which is the backbone of almost all NRT packet services. The designer of TCP made it for wired networks only, so it lacks the capability to handle the wireless nature of the link. The performance decreases when the error in the wireless link occurs in burst. To recover error more reliably wireless link uses some recovery mechanism at the link layer like ARQ. The error recovery by doing retransmission at the link layer may increase the latency and adds to the overall RTT of packet. TCP treats these sudden increase in delays as a congestion indication, and starts it congestion recovering mechanism which indeed not required here. TCP lowers the number of packet to be transmitted by lowering the Congestion Window and hence causing a degraded performance. Many solutions have been proposed to alleviate the problem. But all have some flaws at their own level. Introduction of HSDPA in 3G UMTS system, has raised up some hopes regarding TCP performance. The technical features that HSDPA has brought proven to be a performance enhancer for TCP. The effect of ARQ delay is minimized by the introduction of a new error mechanism at the physical layer. This error mechanism uses the principles of chase combining and incremental redundancy to increase the probability of successful decoding of the data block. The TTI duration has been changed from 10ms to 2ms so that overall delay reduces to a great extent. More efficient algorithms have been proposed to cope with the time varying channel conditions which can be utilized to schedule users to maintain an optimal use of system resources. The thesis investigates the influence of these features and also the effect they imposes on TCP performance.
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    Effect of channel asymmetry on reputation based cooperation mechanisms in mobile ad-hoc networks
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2008) Vasavada, Tejas; Srivastava, Sanjay
    Enforced cooperation among MANET nodes is an active research issue. In applications, where the users have different goals and there is no central authority to control them, users may become selfish. These nodes may not forward packets sent by others and thus affect the basic functionality of the network. One proposed class of protocols to handle such scenarios is based on reputation functions. In reputation based schemes, nodes maintain reputation values of other nodes. Reputation value of a node is high for nodes that forward the received packets and low otherwise. Nodes with very low reputation values are identified as selfish nodes and isolated from network operations. In such schemes, every node has to observe whether its neighbour is forwarding packets or not. A node after sending a packet to its neighbour to forward further, increases reputation of neighbour if it overhears the same packet from the neighbour. If it does not overhear the packet, reputation of neighbour is reduced. This is the basic method to observe whether neighbour node is cooperative or not. Here basic assumption is that the channel between two neighbour nodes is always symmetric. This assumption does not hold true due to two reasons: (1) Nodes are moving. Neighbour node may have forwarded the packet but by the time it forwards, either observing node or neighbour or both might move out of each others range. (2) Even if both are in each others range, due to multipath fading, observing node may not overhear the packets forwarded by neighbour node. Thus sometimes even honest nodes may be considered selfish and isolated due to this asymmetry. This reduces throughput of honest nodes. In this thesis work we have examined the probability of channel asymmetry as a function of ratio r(of inter node distance and transmission range), for given values of relative average velocity of nodes V and Ricean parameter K. Ricean parameter K represents type of the environment i.e. obstructed or unobstructed. We have proposed an enhancement of existing reputation protocol OCEAN. In the enhanced protocol, observing node probabilistically updates reputation of neighbour when it does not overhear. This probabilistic update takes into account probability of channel asymmetry. We have tried to minimize false positives, i.e. honest nodes being detected as selfish. We have shown through simulations that false negatives, i.e. selfish nodes being detected as honest, do not increase much. We have also shown that how false positives and false negatives change as degree of dishonesty of selfish nodes change. At last, we have shown that throughput levels of honest nodes in original OCEAN protocol and modified OCEAN protocol are almost same.
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    Secure and efficient key assignment scheme for dynamic access control in a hierarchy
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2006) Vadnala, Praveen Kumar; Mathuria, Anish M.
    The users belonging to an organization are often assigned different access permissions depending on their security class. In this situation, the users belonging to a higher security class are allowed access to the information accessible to the users belonging to a lower security class, but the opposite is not allowed. In the past two decades, many cryptographic solutions to the hierarchical access control problem have been proposed. This thesis classifies the existing schemes depending upon different properties such as type of hierarchy, key derivation method, the range of applications, etc. A comparative analysis of some prominent schemes is presented. Attacks are proposed on an existing scheme due to Yang and Li. A modification is proposed to avoid the attacks and improve the efficiency of the scheme. The modified scheme is proved to be secure using a security model proposed by Wu and Wei. A countermeasure is proposed to overcome an attack on an existing time-bound scheme due to Tzeng.
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    Technique to improve revocation mechanism and enhancement of CA's services
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2004) Thacker, Grishma D.; Jadhav, Ashish
    Public Key Cryptography [PKC] is becoming popular in the world of security because of its promising features like authentication and non-repudiation along with integrity and data confidentiality. It has been possible to achieve an electronic equivalent of hand written signatures that are considered to be the most common method of providing identity proof in a non-electronic world, thanks to PKC techniques. Public Key Infrastructure [PKI] is a technology that supports PKC to achieve its intended services by implementing PKC concepts. It is considered to be one of the potential technologies for the future of e-business and e-governance. Digital certificates are one of the most important components of PKI. They are issued and signed by a trusted third party named Certification Authority to provide trust worthy binding between the entity and its public key, thus, they impute trust in the public key of a claimant. The certificate has predefined validity period after which they expire. But sometimes during its valid lifetime due to certain events, the certificate doesn't remain valid. A need arises to declare its invalidity implying withdrawal of trust that was imputed in it at the time of issuance. This event is called 'revocation' of the certificate. The information regarding this event of revocation has to propagate to the entire community that might use the certificate in question for its important transaction. 'Certificate Revocation' is one of the key issues in PKI because security of any transaction relies on the validity of the certificate used in it. Hence, the status of these certificates in terms of 'valid' / 'non- valid' becomes important information to be processed, conveyed, acquired, and managed securely. There are many mechanisms proposed for the certificate revocation information distribution. My primary concern is to focus on some of these mechanisms and to provide some solution for this problem. I've proposed a method named "Staggered CRLs". It uses delta CRLs and shows how a CA can avoid generation of signature over the voluminous CRL and still can provide more timely information than the traditional CRL. CRLs are issued along with delta CRLs with 'slight' modification. The method avoids prefixing of next update time of CRL and makes it dynamic based on some other criteria. It provides more timely information at lesser frequency of CRL. My second proposal is about how a CA can enhance its services to the user community. I suggest to go beyond merely providing revocation information about the certificate and to add more value to the CA services by providing further information about the certificates.
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    Classification of quantum cryptography
    (Dhirubhai Ambani Institute of Information and Communication Technology, 2004) Acharya, Jaykumari; Jadhav, Ashish
    Modern Classical Cryptography is divided into two parts. The first part is Asymmetric (public-key) cryptography and the second is Symmetric (private or secret-key) cryptography. In spite of its popularity public-key cryptography has major flaws. Fast factoring algorithms or computers with fast processing power can break the public-key cryptographic system. In the case of private key cryptography, it is expensive to distribute the key via a trusted carrier or personal meetings. So, to overcome these drawbacks of classical cryptography, a cryptographic scheme based on the principles of quantum physics was developed. Quantum Cryptography provides unconditional security. Quantum cryptographic systems are provably secure systems that uses public channel for the distribution of the secret key. To get unconditional security quantum cryptography uses the principles of quantum physics like No-cloning theorem, Heisenberg’s uncertainty principle and quantum entanglement. Here, Classification of Quantum Cryptography is proposed. Quantum Cryptography is an alternative for the Classical Cryptography especially to have unconditional security. Classification may help the designer for an appropriate choice of the quantum cryptographic techniques.