1 .\" $NetBSD: arc4random.3,v 1.9 2011/02/05 00:24:08 wiz Exp $
2 .\" $OpenBSD: arc4random.3,v 1.17 2000/12/21 14:07:41 aaron Exp $
4 .\" Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de>
5 .\" All rights reserved.
7 .\" Redistribution and use in source and binary forms, with or without
8 .\" modification, are permitted provided that the following conditions
10 .\" 1. Redistributions of source code must retain the above copyright
11 .\" notice, this list of conditions and the following disclaimer.
12 .\" 2. Redistributions in binary form must reproduce the above copyright
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14 .\" documentation and/or other materials provided with the distribution.
15 .\" 3. All advertising materials mentioning features or use of this software
16 .\" must display the following acknowledgement:
17 .\" This product includes software developed by Niels Provos.
18 .\" 4. The name of the author may not be used to endorse or promote products
19 .\" derived from this software without specific prior written permission.
21 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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32 .\" Manual page, using -mandoc macros
40 .Nm arc4random_uniform ,
42 .Nm arc4random_addrandom
43 .Nd arc4 random number generator
51 .Fn arc4random_buf "void *buffer" "size_t length"
53 .Fn arc4random_uniform "uint32_t upper_bound"
55 .Fn arc4random_stir "void"
57 .Fn arc4random_addrandom "u_char *dat" "int datlen"
61 function provides a high quality 32-bit pseudo-random
64 seeds itself on a regular basis from the kernel strong random number
65 subsystem described in
67 On each call, an ARC4 generator is used to generate a new result.
70 function uses the ARC4 cipher key stream generator,
71 which uses 8*8 8 bit S-Boxes.
72 The S-Boxes can be in about (2**1700) states.
75 fits into a middle ground not covered by other subsystems such as
76 the strong, slow, and resource expensive random
79 versus the fast but poor quality interfaces described in
91 bytes of ARC4-derived random data.
94 .Fn arc4random_uniform
95 function returns a uniformly distributed random number less than
97 avoiding modulo bias when the upper bound is not a power of two.
101 function reads data from
103 and uses it to permute the S-Boxes via
104 .Fn arc4random_addrandom .
106 There is no need to call
112 automatically initializes itself.
120 was designed by RSA Data Security, Inc.
121 It was considered a trade secret, but not trademarked.
122 Because it was a trade secret, it obviously could not be patented.
123 A clone of this was posted anonymously to USENET and confirmed to
124 be equivalent by several sources who had access to the original cipher.
125 Because of the trade secret situation, RSA Data Security, Inc. can do
126 nothing about the release of the ARC4 algorithm.
129 used to be a trade secret, the cipher is now referred to as
132 These functions first appeared in