Additive Synchronous Stream Ciphers

MPhil Thesis Defence


Title: "Additive Synchronous Stream Ciphers"

By

Miss Wenpei Si


Abstract

Both stream ciphers and block ciphers can be used to provide data 
confidentiality service. Stream ciphers are preferred in many 
applications, since they can destroy statistical properties of natural 
languages to some extent. As an important type of stream ciphers, additive 
synchronous stream ciphers (ASSCs) are simple in structure and could have 
many security properties.

First, we investigate various ASSCs proposed in the past studies and their 
cryptographic aspects, in order to provide a basic knowledge of ASSCs as 
well as their state-of-the-art developments. Some common attacks against 
ASSCs and associated design criteria are examined. The binary ASSCs based 
on natural sequence generators are subsequently overviewed.  The Legendre 
cipher, the two-prime cipher of order 2 and the stream ciphers with 
keystream sequences with three-level autocorrelation are mainly discussed. 
The ASSCs based on other generators are also introduced and briefly 
analysed.

Next, a simple ASSC with proven properties is proposed and examined. Both 
theoretical and experimental results show that this stream cipher is 
secure with respect to a number of possible attacks and has reasonable 
performance. In order to make the stream cipher applicable, we also 
describe some methods of detecting the loss of synchronization and present 
the resynchronization process. The advantage of the stream cipher over 
existing ones is that it has more proven security properties.


Date:			Wednesday, 2 May 2012

Time:			3:00pm – 5:00pm

Venue:			Room 4472
 			Lifts 25/26

Committee Members:	Prof. Cunsheng Ding (Supervisor)
 			Dr. Ke Yi (Chairperson)
 			Dr. Wai-Ho Mow (ECE)


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