The encrypt() function shall provide access to an implementation-defined
encoding algorithm. The key generated by setkey() is used to encrypt
the string block with encrypt().
The block argument to encrypt() shall be an array of length 64
bytes containing only the bytes with values of 0 and 1. The array is modified
in place to a similar array using the key set by setkey(). If
edflag is 0, the argument is encoded. If edflag is 1, the
argument may be decoded (see the APPLICATION USAGE section); if the argument
is not decoded, errno shall be set to [ENOSYS].
The encrypt() 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 encrypt(). If errno is non-zero
on return, an error has occurred.
The encrypt() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
Historical implementations of the encrypt() function used a rather
primitive encoding algorithm.
In some environments, decoding might not be implemented. This is related to some
Government restrictions 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, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 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