Hi,
This method ,i.e, using /dev/urandom should work but there should be
sufficient entropy to generate enough random data. For example, if
you take an octal dump of /dev/urandom (hexdump quits when there is
no more data in the file while od waits for more data), and then dont
touch your machine for a few seconds, it stops - and starts printing
the dump only when you move the mouse or something.
Sorry for being very vague, but I guess the idea should be clear.
Anindya.
On Tue, Mar 08, 2005 at 01:25:23AM +0100, J. wrote:
> On Mon, 7 Mar 2005, Vineet Joglekar wrote:
> > Hi all,
> >
> > Can someone please tell me where can I find and which random/pseudo-random
> > number generator can I use inside the linux kernel? (2.4.28)
>
> I Don't know how this is done for actual use in the kernel itself - So I
> cannot answer that particular question and... I may be way out of my
> league here, but why not use /dev/urandom ? Just to illustrate! I have
> included an example of that below... If it lives up to your idea of
> `cryptographicly secure' - ... ?
>
> > I found out 1 function get_random_bytes() in linux/drivers/char/random.c
> > but thats not what I want.
> >
> > I want a function where I will be supplying a seed to that function as an
> > input,
> > and will get a random number back. If same seed is used, same number
> > should be generated again.
> >
> > Can anybody please help me with that?
> >
> > Thanks and regards,
> >
> > Vineet.
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/types.h>
> #include <unistd.h>
> #include <fcntl.h>
> #include <time.h>
>
> unsigned time_seed(void);
> int get_rand_val(int low, int high);
>
> int main(void) {
> int i = 0;
>
> srand((time_seed()));
>
> for(i = 0; i < 10; i++)
> printf("%d\n", get_rand_val(1, 10));
>
> return 0;
> }
>
> int get_rand_val(int low, int high) {
> int k = 0;
> double d = 0;
>
> d = (double)rand() / ((double)RAND_MAX + 1);
> k = (int)(d * (high - low + 1));
> return(low + k);
> }
>
> unsigned time_seed(void) {
> int retval = 0;
> int fd = 0;
>
> if(open("/dev/urandom", O_RDONLY) == -1) {
> retval = (((int)time(NULL)) & ((1 << 30) - 1)) + getpid();
> } else {
> read(fd, &retval, 4);
> /* positive values only */
> retval = abs(retval) + getpid();
> close(fd);
> }
>
> return retval;
> }
>
> Cheers, J.
>
> --
> http://www.rdrs.net/
>
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