getentropy(3)
- NetBSD Manual Pages
GETENTROPY(3) NetBSD Library Functions Manual GETENTROPY(3)
NAME
getentropy -- generate uniform random seeds from system entropy for cryp-
tography
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
int
getentropy(void *buf, size_t buflen);
#include <limits.h>
#define GETENTROPY_MAX 256
DESCRIPTION
The getentropy function fills buf with exactly buflen independent uniform
random bytes derived from the system's entropy pool.
The output of getentropy is meant to be unpredictable to an adversary and
fit for use in cryptography. See CAVEATS below.
getentropy is meant for seeding random number generators, not for direct
use by applications; most applications should use arc4random(3).
buflen must be at most 256.
RETURN VALUES
The getentropy() function returns the value 0 if successful; otherwise
the value -1 is returned and the global variable errno is set to indicate
the error.
ERRORS
getentropy() will succeed unless:
[EFAULT] The buf argument points to an invalid memory address.
[EINVAL] More than 256 bytes were requested.
CAVEATS
Security can only be guaranteed relative to whatever unpredictable physi-
cal processes or secret seed material are available to the system; see
entropy(7).
On systems which have no hardware random number generator and which have
not had secret seed material loaded, NetBSD makes a reasonable effort to
incorporate samples from various physical processes available to it that
might be unpredictable from random jitter in timing.
However, the getentropy interface alone can make no security guarantees
without a physical system configuration that includes random number gen-
eration hardware or secret seed material from such hardware on another
machine.
SEE ALSO
arc4random(3), rnd(4), entropy(7)
STANDARDS
The getentropy() function is nonstandard. However, it is likely to be
included in the next revision of POSIX.
HISTORY
The getentropy() function first appeared in OpenBSD 5.6, then in
FreeBSD 12.0, and in NetBSD 10.0.
NetBSD 10.0 February 28, 2023 NetBSD 10.0
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