CRYPT(C)                             UNIX System V



     Name
          crypt - encode/decode


     Syntax
          crypt [ password ]
          crypt [-k]


     Description
          The crypt command reads from the standard input  and  writes
          to  the standard output.  The password is a key that selects
          a particular transformation.  If no argument is given, crypt
          demands a key from the terminal and turns off printing while
          the key is being typed in.  If the -k option is used,  crypt
          will  use  the  key  assigned  to  the  environment variable
          CRYPTKEY.  The crypt command encrypts and decrypts with  the
          same key:

               crypt key <clear >cypher
               crypt key <cypher | pr

          Files encrypted by crypt are compatible with  those  treated
          by   the   editors  ed(C),  edit(C),  ex(C),  and  vi(C)  in
          encryption mode.

          The security of encrypted files depends  on  three  factors:
          the  fundamental method must be hard to solve; direct search
          of the key space must  be  infeasible;  ``sneak  paths''  by
          which  keys  or  clear  text  can  become  visible  must  be
          minimized.

          The crypt command implements a  one-rotor  machine  designed
          along the lines of the German Enigma, but with a 256-element
          rotor.  Methods of attack on such machines  are  known,  but
          not  widely;  moreover the amount of work required is likely
          to be large.

          The transformation of a key into the  internal  settings  of
          the  machine is deliberately designed to be expensive, i.e.,
          to take a substantial  fraction  of  a  second  to  compute.
          However,  if  keys  are restricted to (say) three lower-case
          letters, then encrypted files can be read by expending  only
          a substantial fraction of five minutes of machine time.

          If the key is an  argument  to  the  crypt  command,  it  is
          potentially   visible   to   users   executing  ps(C)  or  a
          derivative.  To minimize this possibility, crypt takes  care
          to  destroy  any  record  of the key immediately upon entry.
          The choice of keys and key security are the most  vulnerable
          aspect of crypt.


     Files
          /dev/tty  for typed key


     See Also
          ed(C), edit(C), ex(C), makekey(C), ps(C), stty(C), vi(C)


     Notes
          If two or  more  files  encrypted  with  the  same  key  are
          concatenated  and  an attempt is made to decrypt the result,
          only the contents of the first of the original files will be
          decrypted correctly.

          Distribution  of  the  crypt  libraries  and  utilities   is
          regulated  by  the  U.S. Government and are not available to
          sites outside of the  United  States  and  its  territories.
          Because  we  cannot control the destination of the software,
          these utilities are not included in  the  standard  product.
          If  your site is within the U.S. or its territories, you can
          obtain the crypt software through your  product  distributor
          or reseller.


     (printed 2/15/90)                                   CRYPT(C)