TheCodeBreakers
Shannon is
suggesting that noise is analogous to encipherment. "The chief
differences in the two cases," he wrote, "are: first, that the operation of
the enciphering transformation is generally of a more complex nature
than the perturbing noise in a channel; and, second, the key for a
secrecy system is usually chosen from a finite set of possibilities while
the noise in a channel is more often continually introduced, in effect
chosen from an infinite set."
When Carl W. Helstrom, author of Statistical Theory of Signal
Detection, was asked whether the techniques of isolating signals from
noise had any relevance to crypt-analysis, he replied: "I suspect that the
analogy between the enciphering rule of 'key' and random noise will not
prove very fruitful. It seems to me more appropriate to regard the
encipherment as a filtering of the original message to produce a
transformed version. The 'filter' is a definite transformation rule, but the
analyst doesn't know what it is.
annaabi.ee 
