Summary: 2/4/09 9:49 AMCryptanalyze This - New York Times
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November 7, 1999
By ROBERT OSSERMAN
THE CODE BOOK
The Evolution of Secrecy
From Mary Queen of Scots
to Quantum Cryptography.
By Simon Singh.
Illustrated. 402 pp. New York:
A very old joke -- one that does not quite work in written form -- goes, ''If 9W is the answer, what is the
question?'' One reason mathematicians are fond of this joke (whose punch line is below) is that it is a
perfect example of an ''inverse problem,'' one that arises when one knows the outcome of some process and
needs to deduce what led to it. Coding and decoding -- or in Greek terminology, cryptography and
cryptanalysis -- are perfect examples of direct and inverse problems. They share the basic features of both:
the inverse problem is generally far more difficult to solve, and there may not be a unique answer. A direct
operation playing a major part in current cryptography involves multiplying together two large numbers.
The inverse takes the resulting even larger (say, 300-digit) number and tries to factor it to find the original