87 lines
2.1 KiB
Groff
87 lines
2.1 KiB
Groff
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.\" $OpenBSD: getentropy.2,v 1.8 2015/01/31 00:20:12 schwarze Exp $
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.\"
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.\" Copyright (c) 2018 Conrad Meyer <cem@FreeBSD.org>
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.\" Copyright (c) 2014 Theo de Raadt
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 24, 2018
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.Dt GETENTROPY 3
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.Os
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.Sh NAME
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.Nm getentropy
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.Nd get entropy
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn getentropy "void *buf" "size_t buflen"
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.Sh DESCRIPTION
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.Fn getentropy
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fills a buffer with high-quality random data.
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.Pp
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The maximum
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.Fa buflen
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permitted is 256 bytes.
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.Pp
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If it does not produce an error,
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.Fn getentropy
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always provides the requested number of bytes of random data.
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.Pp
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Similar to reading from
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.Pa /dev/urandom
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just after boot,
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.Fn getentropy
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may block until the system has collected enough entropy to seed the CSPRNG.
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.Sh IMPLEMENTATION NOTES
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The
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.Fn getentropy
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function is implemented using
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.Xr getrandom 2 .
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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.Fn getentropy
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will succeed unless:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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The
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.Fa buf
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parameter points to an
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invalid address.
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.It Bq Er EIO
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Too many bytes requested, or some other fatal error occurred.
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.El
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.Sh SEE ALSO
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.Xr arc4random 3 ,
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.Xr getrandom 2 ,
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.Xr random 4
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.Sh STANDARDS
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.Fn getentropy
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is non-standard.
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It is present on
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.Ox
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and Linux.
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.Sh HISTORY
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The
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.Fn getentropy
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function appeared in
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.Ox 5.6 .
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The
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.Fx
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libc compatibility shim first appeared in
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.Fx 12.0 .
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