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36 .Nm is_random_seeded ,
40 .Nd supply pseudo-random numbers
46 .Fn arc4random_buf "void *ptr" "size_t len"
48 .Fn arc4rand "void *ptr" "u_int length" "int reseed"
52 .Fn is_random_seeded "void"
54 .Fn read_random "void *buffer" "int count"
56 .Fn read_random_uio "struct uio *uio" "bool nonblock"
66 functions will return very good quality random numbers, suited for
67 security-related purposes.
68 Both are wrappers around the underlying
72 returns a 32-bit random value, while
85 kernel abstract entropy device.
86 Automatic reseeding happens at unspecified time and bytes (of output)
88 A reseed can be forced by passing a non-zero
94 function is used to read entropy directly from the kernel abstract entropy
97 blocks if and until the entropy device is seeded.
100 is filled with no more than
103 It is strongly advised that
105 is not used directly;
112 function can be used to check in advance if
115 (If random is seeded, it will not block.)
119 function behaves identically to
125 argument points to a buffer where random data should be stored.
128 is true and the random device is not seeded, this function does not return any
130 Otherwise, this function may block interruptibly until the random device is seeded.
131 If the function is interrupted before the random device is seeded, no data is
136 function will return a 31-bit value.
137 It is obsolete and scheduled to be removed in
142 .Sx SECURITY CONSIDERATIONS .
146 function uses the Chacha20 algorithm to generate a pseudo-random sequence of
152 to generate pseudo-random numbers
153 in the range from 0 to
154 .if t 2\u\s732\s10\d\(mi1.
160 the number of bytes placed in
164 returns zero when successful,
165 otherwise an error code is returned.
169 in the range from 0 to
170 .if t 2\u\s731\s10\d\(mi1.
179 points to an invalid memory region.
180 .It Bq Er EWOULDBLOCK
181 The random device is unseeded and
192 .Sh SECURITY CONSIDERATIONS
197 It is important to remember that the
199 function is entirely predictable.
200 It is easy for attackers to predict future output of
202 by recording some generated values.
203 We cannot emphasize strongly enough that
205 must not be used to generate values that are intended to be unpredictable.