  In many of the cryptography applications like password or IP address
encryption schemes, symmetric cryptography is useful. In these relatively
simpler applications of cryptography, asymmetric cryptography is difficult to
justify on account of the computational and implementation complexities
associated with asymmetric cryptography. Symmetric schemes make use of a single
shared key known only between the two communicating hosts. This shared key is
used both for the encryption as well as the decryption of data. This key has to
be small in size besides being a subset of a potentially large keyspace making
it convenient for the communicating hosts while at the same time making
cryptanalysis difficult for the potential attackers. In the present work, an
abstract Rossler nonlinear dynamical machine has been described first. The
Rossler system exhibits chaotic dynamics for certain values of system
parameters and initial conditions. The chaotic dynamics of the Rossler system
with its apparently erratic and irregular characteristics and extreme
sensitivity to the initial conditions has been used for the design of the
cryptographic key in an attempt to increase the confusion and the challenge for
the potential attackers.
