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\!EPSILONLAMBDASET(59,5);
\!PARA; Until recently cryptography \!CIT1(BLOCIP); has been of interest primarily to
the  military  and  diplomatic  communities.  Private individuals and
even commercial organizations have rarely considered it necessary  to
resort \!CIT1(DH1); to encryption for the protection \!CIT1(BARKER); of their communications, and
those that have, have  seldom done \!CIT1(CTT);
 so  with particular care.   Today,
however, several factors have combined to stimulate great interest in
commercial applications.\.

\!PARA; It  has  come to  light  over the  past  two years  that  the
Russians \!CIT1(AUTOM); are monitoring telephones  from their embassy in  Washington
and their \!CIT1(DH2); consulates  in  other parts  of  the  country.   Microwave
antennas intercept telephone  traffic from such  vital places as  the
Capitol building,  and  computer programs  automatically  select  the
conversations of interest \!CIT1(RUSBUG);.\.

\!PARA; Data  communications  are  even more  vulnerable  than  voice
telephony because \!CIT1(BERL);, with voice the  eavesdropper lacks the ability  to
discern the  content  of a  spoken  message, unless  a  costly  human
monitor is employed \!CIT1(AUDTR);, but if  the intercepted material is in  computer
readable form (e.g., Telex), no  such limitation is imposed.  It  has
been reported  \!CIT1(NSABUG);  that  for  some  years  the  National
Security  Agency  (NSA),  in  its  operation  Shamrock,  scanned  all
telegraph and Telex messages passing in and out of the United  States
for keywords.\.

\!PARA; The cost  of eavesdropping  should continue  to decline  with
time \!CIT1(COVKIN);.  There is at present extensive research into speech recognition
\!CIT1(RUSBUG);, and  many communications  will  soon be  carried  on
digitized packet switched networks \!CIT1(PACNET);.  Electronic  mail
and Electronic Funds  Transfer (EFT) are  being \!CIT1(Branstad); developed to  replace
their present day counterparts \!CIT1(BRUN);, and telephone verification of  credit
data is already a reality.\.

\!PARA; As a result, private and commercial interest in  cryptography
has been rising, new  papers have begun to  appear, and the  National
Bureau of  Standards  has  adopted a  standard  cryptographic  system
\!CIT1(NSABUG); for use on sensitive but unclassified data.\.

\!PARA; This paper is intended as an introduction to the  fascinating
but forbidding subject of cryptography.  It provides both a grounding
in the fundamentals and a feel  for the subject to anyone  interested
either in  doing cryptographic  research or  employing  cryptographic
security.  Cryptography is currently an engineering subject in  which
there are more facts and rules  of thumb than theorems or  systematic
developments.  The  text  naturally  reflects this  quality  and,  of
necessity, combines a wide variety of material.\.

\!ENDSEC;