Date of Submission


Date of Award


Institute Name (Publisher)

Indian Statistical Institute

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Subject Name



Applied Statistics Unit (ASU-Kolkata)


Roy, Bimal Kumar (ASU-Kolkata; ISI)

Abstract (Summary of the Work)

From time immemorial people have used cryptography for secure communication. Cryptography has decided the fate of many kings and queens as well as the outcome of various wars. It has become all the more important nowadays, with the growing need of electronic communication. We now live in a society where electronic networks pervade all aspects of our professional and private lives. We all use cryptography when we do bank transfers by ATM, or SWIFT, while using the mobile phones and i-phones, SSL protocols or using password protected machines. Though electronic communication is fast and easy, it is vulnerable to security breeches, which are not so widespread in the traditional counterparts. For example we consider writing a letter. A hand-written letter is normally posted in a sealed envelop and delivered to a specified address by the postal service. To read the contents of the letter, the adversary must break open the seal. The recipient can inspect the envelope for damage and can make out if the letter was tampered with by simply inspecting the postmark or the handwriting. However an email is not secure. It passes through a large network of computers. At each router there is a chance of being intercepted. The contents may be read, altered, copied. The recipient has no idea of whether the information has been intercepted. Same situation arises when we transfer money by ATMs, or SWIFT transfers.Cryptography is essentially a collection of mathematical techniques, algorithms and protocols used to render the core information assurance services that are required in electronic communications. The chief services of any cryptographic protocol are confidentiality (hiding the data from the unauthorized users), data integrity (protecting data from manipulation), authentication(verifying the identity), non-repudiation(preventing malicious users to hide their activity).Most cryptographic mechanisms rely on a basic components called keys, which are essentially numbers selected at random from a large space. The security of cryptographic mechanisms rely on the security of the keys contained therein. Since keys form the building block of many cryptographic systems, the secure management of keys form an essential building block of many cryptosystems. The phrase key management describes the entire life cycle of keys, including key generation, methods by which it is sent to the relevant users of the system (key establishment), the techniques that are used to change and refresh it, also called key update and ultimately the means by which it is deleted at the end of its usage calledkey destruction.According to the nature of keys, cryptographic mechanisms can be divided into two broad categories- symmetric mechanisms, in which the same secret key is used for encryption by the sender and decryption by the receiver, and publickey mechanisms in which the sender encrypts the information using a public key. However to decrypt the contents, the receiver has to use her own private keys. There are some mechanisms where both symmetric and public-key mechanisms are used together. Generally public key mechanisms involve huge computational costs. Hence in areas of applications where resources are constrained, symmetric key mechanisms are preferred. One such area of application is sensor networks. Before discussing about sensor networks we look at the key establishment problem in general and key predistribution in particular.


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Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.


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