43,803 research outputs found
Return-Map Cryptanalysis Revisited
As a powerful cryptanalysis tool, the method of return-map attacks can be
used to extract secret messages masked by chaos in secure communication
schemes. Recently, a simple defensive mechanism was presented to enhance the
security of chaotic parameter modulation schemes against return-map attacks.
Two techniques are combined in the proposed defensive mechanism: multistep
parameter modulation and alternative driving of two different transmitter
variables. This paper re-studies the security of this proposed defensive
mechanism against return-map attacks, and points out that the security was much
over-estimated in the original publication for both ciphertext-only attack and
known/chosen-plaintext attacks. It is found that a deterministic relationship
exists between the shape of the return map and the modulated parameter, and
that such a relationship can be used to dramatically enhance return-map attacks
thereby making them quite easy to break the defensive mechanism.Comment: 11 pages, 7 figure
A Mathematical Model for the Dynamics and Synchronization of Cows
We formulate a mathematical model for daily activities of a cow (eating,
lying down, and standing) in terms of a piecewise affine dynamical system. We
analyze the properties of this bovine dynamical system representing the single
animal and develop an exact integrative form as a discrete-time mapping. We
then couple multiple cow "oscillators" together to study synchrony and
cooperation in cattle herds. We comment on the relevant biology and discuss
extensions of our model. With this abstract approach, we not only investigate
equations with interesting dynamics but also develop interesting biological
predictions. In particular, our model illustrates that it is possible for cows
to synchronize \emph{less} when the coupling is increased.Comment: to appear in Physica
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