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>>>>>>>>>>>>>>>>>>>>>>>>>|<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< Yuliang Zheng Email: yuliang@cs.uow.edu.au Centre for Comp Security Research Department of Computer Science Voice: +61 42 21 4331 (office) University of Wollongong +61 42 21 3859 (dept) Wollongong, NSW 2522 AUSTRALIA Fax: +61 42 21 4329 >>>>>>>>>>>>>>>>>>>>>>>>>|<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Preprint No. 94-1 Y. Zheng ``Improved Public Key Cryptosystems Secure against Chosen Ciphertext Attacks'' ABSTRACT This note describes an improvement to the first two of the three public key cryptosystems proposed by Zheng and Seberry, which are provably secure against chosen ciphertext attacks. The improvement removes a shortcoming with the original cryptosystems, which occurs when they are used for both confidentiality and sender authentication purposes. Preprint No. 94-2 J. Seberry, X.M. Zhang and Y. Zheng ``Relationships Among Nonlinearity Criteria'' ABSTRACT An important question in designing cryptographic functions including substitution boxes (S-boxes) is the relationships among the various nonlinearity criteria each of which indicates the strength or weakness of a cryptographic function against a particular type of cryptanalytic attacks. In this paper we reveal, for the first time, interesting connections among the strict avalanche characteristics, differential characteristics, linear structures and nonlinearity of quadratic S-boxes. In addition, we show that our proof techniques allow us to treat in a unified fashion all quadratic permutations, regardless of the underlying construction methods. This greatly simplifies the proofs for a number of known results on nonlinearity characteristics of quadratic permutations. As a by-product, we obtain a negative answer to an open problem regarding the existence of differentially 2-uniform quadratic permutations on an even dimensional vector space. =========================================================================== Newsgroup Co-moderator: Richard Golding, Hewlett-Packard Laboratories compdoc-techreports-request@ftp.cse.ucsc.edu Be sure to send questions about specific reports to the poster, not to the newsgroup. ************************************************** * Allen J. Baum tel. (408)974-3385 * * Apple Computer, 20525 Mariani Ave, MS 305-3B * * Cupertino, CA 95014 baum@apple.com * **************************************************