A new class of unbalanced CAST ciphers and its security analysis

Zhu, Xia (1997) A new class of unbalanced CAST ciphers and its security analysis. Masters thesis, Memorial University of Newfoundland.

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    Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
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Abstract

The original CAST cipher is an efficient and secure private-key block cipher designed to be an alternative to the Data Encryption Standard (DES). In this thesis, we present a new class of unbalanced CAST ciphers which employs the same structure of S-box and round function of the original CAST cipher but has a lower memory requirement. Unbalanced CAST ciphers with one or two 8x32 S-boxes in the round function require only 1/4 or 1/2 the memory of the original CAST cipher, respectively. -- This thesis examines the application of differential and linear cryptanalysis, two of the most powerful methodologies for attacking private-key block ciphers, to the unbalanced CAST ciphers. The results of analysis show that a 48-round unbalanced CAST cipher with one 8 x 32 S-box and a 24-round unbalanced CAST cipher with two 8 x 32 S-boxes, both of which are equivalent to a 12-round original CAST cipher in efficiency, are resistant to both differential and linear cryptanalysis. -- We also investigate the unbalanced CAST ciphers from the perspective of information theory. The results suggest that the maximum static and dynamic input-output bit information leakages for the unbalanced CAST ciphers constructed by 8 x 32 S-boxes are much smaller than for DES. -- The conclusion reached by the thesis is that unbalanced CAST ciphers can be considered to be efficient, secure ciphers which require less memory than the original CAST cipher.

Item Type: Thesis (Masters)
URI: http://research.library.mun.ca/id/eprint/5320
Item ID: 5320
Additional Information: Bibliography: leaves 112-117.
Department(s): Engineering and Applied Science, Faculty of
Date: 1997
Date Type: Submission
Library of Congress Subject Heading: Ciphers; Data encryption (Computer science)

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