GETENTROPY(2)						      BSD System Calls Manual						     GETENTROPY(2)

NAME

     getentropy -- get entropy

SYNOPSIS

     #include <sys/random.h>

     int
     getentropy(void *buf, size_t buflen);

DESCRIPTION

     getentropy() fills a buffer with random data, which can be used as input for process-context pseudorandom generators like arc4random(3).

     The maximum buffer size permitted is 256 bytes.  If buflen exceeds this, an error of EIO will be indicated.

     getentropy() should be used as a replacement for random(4) when random data derived directly from the kernel random byte generator is
     required.	Unlike the random(4) pseudo-devices, it is not vulnerable to file descriptor exhaustion attacks and is available when sandboxed or
     in a chroot, making it more reliable for security-critical applications.

     However, it should be noted that getentropy() is primarily intended for use in the construction and seeding of userspace PRNGs like
     arc4random(3) or CC_crypto(3).  Clients who simply require random data should use arc4random(3), CCRandomGenerateBytes() from CC_crypto(3),
     or SecRandomCopyBytes() from the Security framework instead of getentropy() or random(4)

RETURN VALUES

     Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS

     getentropy() will succeed unless:

     [EINVAL]		The buf parameter points to an invalid address.

     [EIO]		Too many bytes requested, or some other fatal error occurred.

SEE ALSO

     arc4random(3) CC_crypto(3) random(4)

HISTORY

     The getentropy() function appeared in OSX 10.12

BSD
								  October 2 2015							       BSD