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BKDECSEC.RVW   980804

"Decrypted Secrets", F. L. Bauer, 1997, 3-540-60418-9, U$39.95
%A   F. L. Bauer
%C   175 Fifth Ave., New York, NY   10010
%D   1997
%G   3-540-60418-9
%I   Springer-Verlag
%O   U$39.95 212-460-1500 800-777-4643
%P   447 p.
%T   "Decrypted Secrets: Methods and Maxims of Cryptology"

Cryptology is the study of the technologies of taking plain, readable
text, turning it into an incomprehensible mishmash, and then
recovering the initial information.  There are two sides to this
study.  Cryptography is the part that lets you garble something, and
then recover it if you have the key.  Cryptanalysis is usually seen as
the "dark side" of the operation, because it is the attempt to get at
the original meaning when you *don't* have the key.  Most current and
popular works on cryptology actually only speak about cryptography. 
For one thing, nobody wants to get into trouble by telling people how
to break encryption.  However, it is also much easier to blithely talk
about key lengths and algorithms and pretend to know what you are
doing if you don't have to understand enough math to try to figure out
how to go about cracking a particular cipher.

Bauer examines both sides, which is an important plus.  If you need to
decide how strong an encryption algorithm or system is, it is
important to know how difficult it might be to break it.

Chapter one looks at Steganography, the science of hiding in plain
sight, or concealing the fact that a message exists at all.  In this
he first demonstrates a wide ranging historical background which is
quite fascinating in its own right.  Basic encryption concepts are
introduced by the same historical background, but move on to a very
dense mathematical discussion of cryptographic characteristics in
chapter two.  Encryption functions are started in chapter three, and
it is delightful to have examples other than Julius Caesar's
substitution code.  Polygraphic substitutions are in chapter four and
the math for advanced substitutions is in chapter five.  Chapter six
introduces transpositions.  Families of alphabets, and rotor
encryptors such as ENIGMA, are reviewed in chapter seven.  Keys are
discussed in chapter eight, ending with a brief look at key
management.  Chapter nine covers the combination of methods resulting
in systems such as DES (Data Encryption Standard).  The basics of
public key encryption is introduced in chapter ten.  The relative
security of encryption is introduced in chapter eleven, leading to
part two.  However, it also ends with a discussion of cryptology and
human rights, concentrating mainly, although not exclusively, on the
US public policy debates.

Part two examines the limits of functions used in cryptography, and
thus the points of attack on encryption systems.  Chapter twelve
calculates complexity, and thus the size of brute force attacks. 
Known plaintext attacks are the basis of chapters thirteen to fifteen,
looking first at general patterns, then at probable words, and finally
at frequencies.  Frequency leads to a discussion of invariance in
chapter sixteen.  Chapter seventeen follows with a look at key
periodicity.  Alignment of alphabets is covered in chapter eighteen. 
Of course, cryptographic users sometimes make mistakes, and chapter
nineteen reviews the different errors and various ways to take
advantage of them.  Chapter twenty one looks at anagrams as an
effective attack on transposition ciphers.  The concluding chapter
muses on the relative effectiveness of attacks and of cryptanalysis
overall.

Those seriously interested in cryptology will really need to be
serious: brush up on your number theory if you want to use this book
for anything.  On the other hand, Bauer's history and vignettes from
the story of codes and the codebreakers are interesting, amusing, and
accessible to anyone.

copyright Robert M. Slade, 1998   BKDECSEC.RVW   980804

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