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Crypto Tech Reports
The following technical reports are FTPable at
ftp.cs.uow.edu.au
pub/papers
Cheers,
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Yuliang Zheng Email: [email protected]
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
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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.
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