6b97c2e306
libkern in .PATH has too many filename conflicts with libc and my -DNO_CLEAN tinderbox didn't catch that ahead of time. Mea culpa.
228 lines
5.4 KiB
Groff
228 lines
5.4 KiB
Groff
.\"
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.\" Copyright (c) 2015
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.\" Mark R V Murray
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.\" Copyright (c) 2000
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\" "
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.Dd April 16, 2019
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.Dt RANDOM 9
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.Os
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.Sh NAME
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.Nm arc4rand ,
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.Nm arc4random ,
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.Nm arc4random_buf ,
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.Nm is_random_seeded ,
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.Nm random ,
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.Nm read_random ,
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.Nm read_random_uio ,
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.Nm srandom
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.Nd supply pseudo-random numbers
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.Sh SYNOPSIS
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.In sys/libkern.h
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.Ft uint32_t
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.Fn arc4random "void"
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.Ft void
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.Fn arc4random_buf "void *ptr" "size_t len"
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.Ft void
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.Fn arc4rand "void *ptr" "u_int length" "int reseed"
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.Pp
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.In sys/random.h
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.Ft bool
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.Fn is_random_seeded "void"
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.Ft void
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.Fn read_random "void *buffer" "int count"
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.Ft int
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.Fn read_random_uio "struct uio *uio" "bool nonblock"
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.Ss LEGACY ROUTINES
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.In sys/libkern.h
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.Ft void
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.Fn srandom "u_long seed"
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.Ft u_long
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.Fn random "void"
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.Sh DESCRIPTION
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The
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.Fn arc4random
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and
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.Fn arc4random_buf
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functions will return very good quality random numbers, suited for
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security-related purposes.
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Both are wrappers around the underlying
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.Fn arc4rand
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interface.
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.Fn arc4random
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returns a 32-bit random value, while
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.Fn arc4random_buf
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fills
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.Fa ptr
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with
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.Fa len
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bytes of random data.
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.Pp
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The
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.Fn arc4rand
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CSPRNG
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is seeded from the
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.Xr random 4
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kernel abstract entropy device.
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Automatic reseeding happens at unspecified time and bytes (of output)
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intervals.
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A reseed can be forced by passing a non-zero
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.Fa reseed
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value.
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.Pp
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The
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.Fn read_random
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function is used to read entropy directly from the kernel abstract entropy
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device.
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.Fn read_random
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blocks if and until the entropy device is seeded.
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The provided
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.Fa buffer
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is filled with no more than
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.Fa count
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bytes.
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It is strongly advised that
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.Fn read_random
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is not used directly;
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instead, use the
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.Fn arc4rand
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family of functions.
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.Pp
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The
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.Fn is_random_seeded
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function can be used to check in advance if
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.Fn read_random
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will block.
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(If random is seeded, it will not block.)
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.Pp
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The
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.Fn read_random_uio
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function behaves identically to
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.Xr read 2
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on
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.Pa /dev/random .
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The
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.Fa uio
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argument points to a buffer where random data should be stored.
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If
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.Fa nonblock
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is true and the random device is not seeded, this function does not return any
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data.
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Otherwise, this function may block interruptibly until the random device is seeded.
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If the function is interrupted before the random device is seeded, no data is
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returned.
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.Pp
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The legacy
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.Fn random
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function will produce a sequence of numbers that can be duplicated by calling
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.Fn srandom
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with some constant as the
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.Fa seed .
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The legacy
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.Fn srandom
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function may be called with any
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.Fa seed
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value.
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It is strongly advised that the
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.Fn random
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function not be used to generate random numbers.
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See
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.Sx SECURITY CONSIDERATIONS .
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.Sh RETURN VALUES
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The
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.Fn arc4rand
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function uses the Chacha20 algorithm to generate a pseudo-random sequence of
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bytes.
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The
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.Fn arc4random
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function uses
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.Fn arc4rand
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to generate pseudo-random numbers
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in the range from 0 to
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.if t 2\u\s732\s10\d\(mi1.
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.if n (2**32)\(mi1.
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.Pp
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The
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.Fn read_random
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function returns
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the number of bytes placed in
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.Fa buffer .
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.Pp
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.Fn read_random_uio
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returns zero when successful,
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otherwise an error code is returned.
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.Pp
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The legacy
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.Fn random
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function uses
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a non-linear additive feedback random number generator
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employing a default table
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of size 31
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containing long integers
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to return successive pseudo-random
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numbers in the range from 0 to
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.if t 2\u\s731\s10\d\(mi1.
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.if n (2**31)\(mi1.
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The period of this random number generator
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is very large,
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approximately
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.if t 16\(mu(2\u\s731\s10\d\(mi1).
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.if n 16*((2**31)\(mi1).
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.Sh ERRORS
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.Fn read_random_uio
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may fail if:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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.Fa uio
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points to an invalid memory region.
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.It Bq Er EWOULDBLOCK
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The random device is unseeded and
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.Fa nonblock
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is true.
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.El
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.Sh AUTHORS
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.An Dan Moschuk
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wrote
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.Fn arc4random .
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.An Mark R V Murray
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wrote
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.Fn read_random .
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.Sh SECURITY CONSIDERATIONS
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Do not use
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.Fn random
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or
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.Fn srandom
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in new code.
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.Pp
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It is important to remember that the
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.Fn random
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function is entirely predictable.
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It is easy for attackers to predict future output of
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.Fn random
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by recording some generated values.
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We cannot emphasize strongly enough that
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.Fn random
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must not be used to generate values that are intended to be unpredictable.
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