1.\" $NetBSD: getentropy.3,v 1.4 2022/05/31 13:42:59 riastradh 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.In limits.h 43.Li #define GETENTROPY_MAX 256 44.Sh DESCRIPTION 45.Pp 46The 47.Fn getentropy 48function fills a buffer with high quality random data, suitable for seeding 49cryptographically secure psuedorandom number generators. 50.Pp 51.Fn getentropy 52is only intended for seeding random number generators and is not intended 53for use by regular code which simply needs secure random data. 54For this purpose, please use 55.Xr arc4random 3 . 56.Pp 57The maximum value for 58.Li buflen 59is 256 bytes. 60.Sh IMPLEMENTATION NOTES 61.Fn getentropy 62reads from the 63.Xr sysctl 7 64variable 65.Li kern.arandom . 66.Sh RETURN VALUES 67.Rv -std getentropy 68.Sh ERRORS 69.Fn getentropy 70will succeed unless: 71.Bl -tag -width Er 72.It Bq Er EFAULT 73The 74.Fa buf 75argument points to an invalid memory address. 76.It Bq Er EINVAL 77More than 256 bytes were requested. 78.Sh SEE ALSO 79.Xr arc4random 3 , 80.Xr rnd 4 81.Sh STANDARDS 82The 83.Fn getentropy 84function is non-standard. 85However, it is likely to be included in the next revision of POSIX. 86.Sh HISTORY 87The 88.Fn getentropy 89function first appeared in 90.Ox 5.6 , 91then in 92.Fx 12.0 , 93and 94.Nx 10 . 95