 
Summary: 2/4/09 9:49 AMCryptanalyze This  New York Times
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November 7, 1999
Cryptanalyze This
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:
Doubleday. $24.95.
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, 300digit) number and tries to factor it to find the original
