213 lines
4.9 KiB
Groff
213 lines
4.9 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 July 16, 2015
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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 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 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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.Ft void
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.Fn arc4rand "void *ptr" "u_int length" "int reseed"
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.Ft uint32_t
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.Fn arc4random "void"
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.Pp
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.In sys/random.h
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.Ft int
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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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.Sh DESCRIPTION
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The
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.Fn random
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function will by default produce
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a sequence of numbers
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that can be duplicated
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by calling
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.Fn srandom
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with some constant
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as the
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.Fa seed .
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The
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.Fn srandom
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function may be called with any arbitrary
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.Fa seed
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value to get slightly more unpredictable numbers.
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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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and is therefore not of use where
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knowledge of the sequence of numbers
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may be of benefit to an attacker.
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.Pp
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The
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.Fn arc4rand
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function will return very good quality random numbers,
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better suited
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for security-related purposes.
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The random numbers from
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.Fn arc4rand
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are seeded from the entropy device
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if it is available.
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Automatic reseeds happen
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after a certain timeinterval
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and after a certain number of bytes
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have been delivered.
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A forced reseed
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can be forced
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by passing a non-zero
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value in the
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.Fa reseed
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argument.
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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 return entropy directly from the entropy device
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if it has been loaded.
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If the entropy device is not loaded, then
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the
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.Fa buffer
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is ignored
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and zero is returned.
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The
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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;
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instead use
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.Fn arc4rand
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unless it is
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necessary to know
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that no entropy
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has been returned.
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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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This function only returns data if the random device is seeded.
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It blocks if unseeded,
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except when the
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.Fa nonblock
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argument is true.
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.Pp
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All the bits returned by
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.Fn random ,
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.Fn arc4rand ,
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.Fn read_random ,
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and
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.Fn read_random_uio
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are usable.
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For example,
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.Sq Li random()&01
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will produce a random binary value.
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.Pp
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The
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.Fn arc4random
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is a convenience function which calls
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.Fn arc4rand
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to return a 32 bit pseudo-random integer.
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.Sh RETURN VALUES
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The
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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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.Pp
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The
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.Fn arc4rand
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function uses the RC4 algorithm
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to generate successive pseudo-random 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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.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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