|RANDOM(9)||Kernel Developer's Manual||RANDOM(9)|
*ptr, u_int length,
uio *uio, bool
random() function will by default produce a sequence of numbers that can be duplicated by calling
srandom() with some constant as the seed. The
srandom() function may be called with any arbitrary seed value to get slightly more unpredictable numbers. It is important to remember that the
random() function is entirely predictable, and is therefore not of use where knowledge of the sequence of numbers may be of benefit to an attacker.
arc4rand() function will return very
good quality random numbers, better suited for security-related purposes.
The random numbers from
arc4rand() are seeded from
the entropy device if it is available. Automatic reseeds happen after a
certain timeinterval and after a certain number of bytes have been
delivered. A forced reseed can be forced by passing a non-zero value in the
read_random() function is used to
return entropy directly from the entropy device if it has been loaded. If
the entropy device is not loaded, then the buffer is
ignored and zero is returned. The buffer is filled
with no more than count bytes. It is strongly advised
read_random() is not used; instead use
arc4rand() unless it is necessary to know that no
entropy has been returned.
read_random_uio() function behaves
identically to read(2) on
/dev/random. The uio argument
points to a buffer where random data should be stored. This function only
returns data if the random device is seeded. It blocks if unseeded, except
when the nonblock argument is true.
All the bits returned by
read_random_uio() are usable. For example,
random()&01’ will produce a
random binary value.
arc4random() is a convenience function
arc4rand() to return a 32 bit
random() function uses a non-linear additive feedback random number generator employing a default table of size 31 containing long integers to return successive pseudo-random numbers in the range from 0 to (2**31)−1. The period of this random number generator is very large, approximately 16*((2**31)−1).
arc4rand() function uses the RC4
algorithm to generate successive pseudo-random bytes. The
arc4random() function uses
arc4rand() to generate pseudo-random numbers in the
range from 0 to (2**32)−1.
read_random() function returns the
number of bytes placed in buffer.
read_random_uio() returns zero when
successful, otherwise an error code is returned.
read_random_uio() may fail if:
AUTHORS¶Dan Moschuk wrote
Mark R V Murray wrote
|July 16, 2015||Linux 4.19.0-10-amd64|