1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
|
.\"
.\" Copyright (c) 2015
.\" Mark R V Murray
.\" Copyright (c) 2000
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\" "
.Dd March 22, 2021
.Dt RANDOM 9
.Os
.Sh NAME
.Nm arc4rand ,
.Nm arc4random ,
.Nm arc4random_buf ,
.Nm is_random_seeded ,
.Nm random ,
.Nm read_random ,
.Nm read_random_uio
.Nd supply pseudo-random numbers
.Sh SYNOPSIS
.In sys/libkern.h
.Ft uint32_t
.Fn arc4random "void"
.Ft void
.Fn arc4random_buf "void *ptr" "size_t len"
.Ft void
.Fn arc4rand "void *ptr" "u_int length" "int reseed"
.Pp
.In sys/random.h
.Ft bool
.Fn is_random_seeded "void"
.Ft void
.Fn read_random "void *buffer" "int count"
.Ft int
.Fn read_random_uio "struct uio *uio" "bool nonblock"
.Ss LEGACY ROUTINES
.In sys/libkern.h
.Ft u_long
.Fn random "void"
.Sh DESCRIPTION
The
.Fn arc4random
and
.Fn arc4random_buf
functions will return very good quality random numbers, suited for
security-related purposes.
Both are wrappers around the underlying
.Fn arc4rand
interface.
.Fn arc4random
returns a 32-bit random value, while
.Fn arc4random_buf
fills
.Fa ptr
with
.Fa len
bytes of random data.
.Pp
The
.Fn arc4rand
CSPRNG
is seeded from the
.Xr random 4
kernel abstract entropy device.
Automatic reseeding happens at unspecified time and bytes (of output)
intervals.
A reseed can be forced by passing a non-zero
.Fa reseed
value.
.Pp
The
.Fn read_random
function is used to read entropy directly from the kernel abstract entropy
device.
.Fn read_random
blocks if and until the entropy device is seeded.
The provided
.Fa buffer
is filled with no more than
.Fa count
bytes.
It is strongly advised that
.Fn read_random
is not used directly;
instead, use the
.Fn arc4rand
family of functions.
.Pp
The
.Fn is_random_seeded
function can be used to check in advance if
.Fn read_random
will block.
(If random is seeded, it will not block.)
.Pp
The
.Fn read_random_uio
function behaves identically to
.Xr read 2
on
.Pa /dev/random .
The
.Fa uio
argument points to a buffer where random data should be stored.
If
.Fa nonblock
is true and the random device is not seeded, this function does not return any
data.
Otherwise, this function may block interruptibly until the random device is seeded.
If the function is interrupted before the random device is seeded, no data is
returned.
.Pp
The deprecated
.Fn random
function will return a 31-bit value.
It is obsolete and scheduled to be removed in
.Fx 14.0 .
Consider
.Xr prng 9
instead and see
.Sx SECURITY CONSIDERATIONS .
.Sh RETURN VALUES
The
.Fn arc4rand
function uses the Chacha20 algorithm to generate a pseudo-random sequence of
bytes.
The
.Fn arc4random
function uses
.Fn arc4rand
to generate pseudo-random numbers
in the range from 0 to
.if t 2\u\s732\s10\d\(mi1.
.if n (2**32)\(mi1.
.Pp
The
.Fn read_random
function returns
the number of bytes placed in
.Fa buffer .
.Pp
.Fn read_random_uio
returns zero when successful,
otherwise an error code is returned.
.Pp
.Fn random
returns numbers
in the range from 0 to
.if t 2\u\s731\s10\d\(mi1.
.if n (2**31)\(mi1.
.Sh ERRORS
.Fn read_random_uio
may fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
.Fa uio
points to an invalid memory region.
.It Bq Er EWOULDBLOCK
The random device is unseeded and
.Fa nonblock
is true.
.El
.Sh AUTHORS
.An Dan Moschuk
wrote
.Fn arc4random .
.An Mark R V Murray
wrote
.Fn read_random .
.Sh SECURITY CONSIDERATIONS
Do not use
.Fn random
in new code.
.Pp
It is important to remember that the
.Fn random
function is entirely predictable.
It is easy for attackers to predict future output of
.Fn random
by recording some generated values.
We cannot emphasize strongly enough that
.Fn random
must not be used to generate values that are intended to be unpredictable.
|
