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#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdint.h>
#include <unistd.h>
#include "warnp.h"
#include "entropy.h"
/**
* XXX Portability
* XXX We obtain random bytes from the operating system by opening
* XXX /dev/urandom and reading them from that device; this works on
* XXX modern UNIX-like operating systems but not on systems like
* XXX win32 where there is no concept of /dev/urandom.
*/
/**
* entropy_read(buf, buflen):
* Fill the given buffer with random bytes provided by the operating system.
*/
int
entropy_read(uint8_t * buf, size_t buflen)
{
int fd;
ssize_t lenread;
/* Sanity-check the buffer size. */
if (buflen > SSIZE_MAX) {
warn0("Programmer error: "
"Trying to read insane amount of random data: %zu",
buflen);
goto err0;
}
/* Open /dev/urandom. */
if ((fd = open("/dev/urandom", O_RDONLY)) == -1) {
warnp("open(/dev/urandom)");
goto err0;
}
/* Read bytes until we have filled the buffer. */
while (buflen > 0) {
if ((lenread = read(fd, buf, buflen)) == -1) {
warnp("read(/dev/urandom)");
goto err1;
}
/* The random device should never EOF. */
if (lenread == 0) {
warn0("EOF on /dev/urandom?");
goto err1;
}
/* We've filled a portion of the buffer. */
buf += (size_t)lenread;
buflen -= (size_t)lenread;
}
/* Close the device. */
while (close(fd) == -1) {
if (errno != EINTR) {
warnp("close(/dev/urandom)");
goto err0;
}
}
/* Success! */
return (0);
err1:
close(fd);
err0:
/* Failure! */
return (-1);
}
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