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#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdint.h>
#include <stdlib.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 reader state. At present it holds a file descriptor for
* /dev/urandom, but in the future this structure may gain other OS-dependent
* state, e.g. a Windows Handle.
*/
struct entropy_read_cookie {
int fd;
};
/**
* entropy_read_init(void):
* Initialize the ability to produce random bytes from the operating system,
* and return a cookie.
*/
struct entropy_read_cookie *
entropy_read_init(void)
{
struct entropy_read_cookie * er;
/* Allocate cookie. */
if ((er = malloc(sizeof(struct entropy_read_cookie))) == NULL) {
warnp("malloc");
goto err0;
}
/* Open /dev/urandom. */
if ((er->fd = open("/dev/urandom", O_RDONLY)) == -1) {
warnp("open(/dev/urandom)");
goto err1;
}
/* Success! */
return (er);
err1:
free(er);
err0:
/* Failure! */
return (NULL);
}
/**
* entropy_read_fill(er, buf, buflen):
* Fill the given buffer with random bytes provided by the operating system
* using the resources in ${er}.
*/
int
entropy_read_fill(struct entropy_read_cookie * er, uint8_t * buf,
size_t buflen)
{
ssize_t lenread;
/* Sanity checks. */
assert(er != NULL);
assert(buflen <= SSIZE_MAX);
/* Read bytes until we have filled the buffer. */
while (buflen > 0) {
if ((lenread = read(er->fd, buf, buflen)) == -1) {
warnp("read(/dev/urandom)");
goto err0;
}
/* The random device should never EOF. */
if (lenread == 0) {
warn0("EOF on /dev/urandom?");
goto err0;
}
/* We've filled a portion of the buffer. */
buf += (size_t)lenread;
buflen -= (size_t)lenread;
}
/* Success! */
return (0);
err0:
/* Failure! */
return (-1);
}
/**
* entropy_read_done(er):
* Release any resources used by ${er}.
*/
int
entropy_read_done(struct entropy_read_cookie * er)
{
/* Sanity check. */
assert(er != NULL);
/* Close the device. */
while (close(er->fd) == -1) {
if (errno != EINTR) {
warnp("close(/dev/urandom)");
goto err1;
}
}
/* Clean up. */
free(er);
/* Success! */
return (0);
err1:
free(er);
/* Failure! */
return (-1);
}
/**
* 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)
{
struct entropy_read_cookie * er;
/* Sanity-check the buffer size. */
assert(buflen <= SSIZE_MAX);
/* Open /dev/urandom. */
if ((er = entropy_read_init()) == NULL) {
warn0("entropy_read_init");
goto err0;
}
/* Read bytes until we have filled the buffer. */
if (entropy_read_fill(er, buf, buflen)) {
warn0("entropy_read_fill");
goto err1;
}
/* Close the device. */
if (entropy_read_done(er)) {
warn0("entropy_read_done");
goto err0;
}
/* Success! */
return (0);
err1:
entropy_read_done(er);
err0:
/* Failure! */
return (-1);
}
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