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des算法实现源码

		(Last update: 04-Apr-94 by Dave Barrett)

This package is a DES-compatible encipherment package which makes it easy
to send and receive secret mail through electronic mailers.  

Note: This code is not compatible with Sun's des program; that's why I called 
      it "cipher". Unlike Sun's DES this code preserves the original file size 
      and is also suitable for use in communications protocols (such as my
      deslogin program) where one byte of output occurs as each byte is input.
      As far as I know, this is the only fast implementation of DES in 
      cipher-feedback mode which has the above two properties.

I've changed the code slightly from the previous release to allow compilation 
on MS-DOS and DEC Alpha using the same source code for the DES algorithm;
this sped it up about 15% as well.  Atob and btoa should now work more 
portably.  The code now assumes POSIX/ANSI compliance.  If you are
unfortunate enough to be running a BSD machine without POSIX (unlikely), use 
the -D__BSD flag which changes getkey.c to use BSD <sgtty> instead of Posix.
If the code fails to compile, it's probably for getkey.c.  The rest of the
code is very generic.

I've also included MS-DOS .exe files for atob, btoa and cipher, so that PC
users don't have to have a compiler to use the program.  When using the PC code
don't put any spaces between -option letters and their arguments.  Use the
-d option on cipher to decipher encrypted files.  Input and output from all
these programs is 100% compatable with the unix code.

The most interesting products are:
   cipher (decipher) - the actual encipherment/decipherment program.
   cipher.1	     - the nroff compatible manual page for cipher (please read)
   atob, btoa	     - Binary to ASCII converters from compress 4.0 package
   cmail	     - A script to interface above with your mailer

To install:

Edit the Makefile:
   Change MANDIR and BINDIR as appropriate
   Edit the lines for MS-DOS as appropriate (no changes needed for unix)

   C++ compilers are OK as are ANSI, Non-ANSI and POSIX compilers.
   You may also define CC CCFLAGS and LDFLAGS as appropriate for your machine.

   This code has now been tested on Sun, HP (HP-UX), Dec Alpha, Next  and
   Turbo C++ on MS-DOS.

Type "make"

   You may get some compiler warnings about & in front of an array, an invalid
   pointer combination and optimization problems.  These are OK.  The
   important thing is too see if the testsuite passes.  If it does, the
   make will terminate normally.

Type "make install"

   You may want to read about the "~|" option to the BSD mailer and compose
   "encr" and "decr" scripts.

Send bug reports to "[e-mail]"