1.\" $NetBSD: getentropy.3,v 1.2 2020/05/07 12:55:06 wiz Exp $ $ 2.\" 3.\" Copyright (c) 2020 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Nia Alarie. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd May 1, 2020 31.Dt GETENTROPY 3 32.Os 33.Sh NAME 34.Nm getentropy 35.Nd fill a buffer with high quality random data 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In unistd.h 40.Ft int 41.Fn getentropy "void *buf" "size_t buflen" 42.Sh DESCRIPTION 43The 44.Fn getentropy 45function fills a buffer with high quality random data, suitable for seeding 46cryptographically secure pseudo-random number generators. 47.Pp 48.Fn getentropy 49is only intended for seeding random number generators and is not intended 50for use by regular code which simply needs secure random data. 51For this purpose, please use 52.Xr arc4random 3 . 53.Pp 54The maximum value for 55.Li buflen 56is 256 bytes. 57.Sh IMPLEMENTATION NOTES 58.Fn getentropy 59reads from the 60.Xr sysctl 7 61variable 62.Li kern.arandom . 63.Sh RETURN VALUES 64The 65.Fn getentropy 66function returns 0 on success, and \-1 if an error occurred. 67.Sh ERRORS 68.Fn getentropy 69will succeed unless: 70.Bl -tag -width Er 71.It Bq Er EFAULT 72The 73.Fa buf 74argument points to an invalid memory address. 75.It Bq Er EIO 76Too many bytes were requested. 77.El 78.Sh SEE ALSO 79.Xr arc4random 3 , 80.Xr rnd 4 81.Sh STANDARDS 82The 83.Fn getentropy 84function is non-standard. 85.Sh HISTORY 86The 87.Fn getentropy 88function first appeared in 89.Ox 5.6 , 90then in 91.Fx 12.0 , 92and 93.Nx 10 . 94