setkey - Man Page

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.


#include <stdlib.h>

void setkey(const char *key);


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.

Return Value

No values are returned.


The setkey() function shall fail if:


The functionality is not supported on this implementation.

The following sections are informative.



Application Usage

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.



Future Directions

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

See Also

crypt(), encrypt()

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

Referenced By

crypt(3p), encrypt(3p), stdlib.h(0p).

2017 IEEE/The Open Group POSIX Programmer's Manual