Research investigation for achieving perfect security is a great challenge. Realization
of the time variant key, key varying from session to session, theorized by Shannon (1949)
for perfect security, is yet to be done. However, a partial implementation is studied
elsewhere (Bhunia et al., 2005) by application of the Automatic Variable Key (AVK) in
which a key is made to vary from session to session. In AVK, session key is made to vary
from session to session based on the data under different algorithm (Prasun et al., 2007;
and Prasun et al., 2008). Application of AVK using RSA and Data Encryption Standard
(DES) is studied where it is found that AVK reduces repetitions in cipher. This is a
significant achievement in reducing the effect of differential attack. In AVK, key varies
from session to session. Keys are obtained as a function of the previous data.
When data/character repeats in a message, the repetition is reflected in cipher if the
key is fixed. The differential attack is due to the repeated code in cipher. To reduce the
differential attack, an attempt is made to reduce the repeated code in cipher even if the
original message has repeated data/character. In AVK, the repeated code is reduced by
variable key(s) generated based on the previous data.
In literature, studies (for example, Jakimoski and Kocarev, 2001) have been made on
the application of chaos theory in key generation and consequent cryptosystem. We
propose to study the application of chaos in AVK with the intention that the abrupt
variation of chaos may further reduce the effect of a differential attack.
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