This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       Decoding  need not be implemented in all environments. This is related to government restrictions in some
       countries on encryption and decryption routines. Historical practice has been to ship a different version
       of the encryption library without the decryption feature in the  routines  supplied.  Thus  the  exported
       version of encrypt() does encoding but not decoding.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical  and  Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE  and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                        SETKEY(3POSIX)

       The  setkey()  function  provides access to an implementation-defined encoding algorithm. The argument of
       setkey() is an array of length 64 bytes containing only the bytes with numerical value of  0  and  1.  If
       this  string is divided into groups of 8, the low-order bit in each group is ignored; this gives a 56-bit
       key which is used by the algorithm. This is the key that shall be used with the  algorithm  to  encode  a
       string block passed to encrypt().

       The  setkey()  function  shall  not  change the setting of errno if successful. An application wishing to
       check for error situations should set errno to 0 before  calling  setkey().   If  errno  is  non-zero  on
       return, an error has occurred.

       The setkey() function need not be thread-safe.

       The setkey() function shall fail if:

       ENOSYS The functionality is not supported on this implementation.

       Thefollowingsectionsareinformative.

       None.

       A future version of the standard may mark this interface as obsolete or remove it altogether.

       setkey — set encoding key (CRYPT)

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       None.

       No values are returned.

crypt(), encrypt()

       The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

       #include <stdlib.h>

       void setkey(const char *key);