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Prof. Vijay Varadharajan PhD

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Some cryptographic techniques for secure data communication

This thesis investigates conventional and public key cryptographic techniques for secure data communication.

Block and stream cipher methods to provide secure communication over an insecure channel are discussed with particular reference to the Data Encryption Standard (DES) algorithm. A microprocessor based data encryption interface unit has· been designed and constructed using the DES to provide both communication and file security. Several chaining techniques using the system have also been investigated enabling a study of their error characteristics, speed of operation, level of security and their ability to overcome difficulties due to data redundancy and structure. A statistical analysis ·of the randomness of the output sequences in each of these techniques has been made. Furthermore, the developed system can be used on the Prestel public network allowing storage and retrieval of completely and partly encrypted frames of information on the Prestel database.

The use of such a DES based encryption system in a communication network poses problems with regard to key distribution since· the keys used need to be distributed to the users over a secure, separate channel. Several methods of key distribution including the use of public key systems are discussed.

Extensions of the Rivest-Shamir-Adleman (RSA) public key scheme to matrix rings, polynomial rings and algebraic number fields have been proposed. These extensions indicate that rings other than the ring of rational integers can be used to construct public key systems with the factorization trapdoor property. The security of such systems again relies on the difficulty of factorizing a large integer.

An extension of the Diffie-Hellman public key distribution system to matrix rings is proposed. Short cycling attacks against the exponentiation system in GF(2n) have been analysed and are shown to be equivalent to a random search procedure. A hybrid system using exponentiation in GF(2n) for key distribution and the DES for data security has been implemented and the advantage of normal basis representation in the computation of the exponentiation in GF(2n) is examined.

The role of permutation polynomials in the design of public key systems has also been investigated. In particular, it is shown that secure public key systems can be designed using Dickson permutation polynomials and Redei rational functions. Further the complexity of public key systems can be increased by combining the permutation polynomials under the law of composition.

Prof. Vijay Varadharajan

Director of studies: Dr Colin T Stockel
Other supervisors: Mr Peter W Sanders, Dr R W K Odoni (original DoS Dr G Wade)

Journal papers

Secure communications between microcomputer systems
Sanders P, Varadharajan V
Computer Communications, vol.6, no.5, October, 1983
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1 Journal papers

1 publication(s) - all categories.