--- uuid_prng.c 2005/03/29 19:01:41 1.5
+++ uuid_prng.c 2005/08/30 15:26:07 1.6
@@ -35,9 +35,12 @@
#include <fcntl.h>
#include "uuid_prng.h"
+#include "uuid_md5.h"
struct prng_st {
- int devfd;
+ int dev; /* system PRNG device */
+ md5_t *md5; /* local MD5 PRNG engine */
+ long cnt; /* time resolution compensation counter */
};
prng_rc_t prng_create(prng_t **prng)
@@ -56,14 +59,21 @@
return PRNG_RC_MEM;
/* try to open the system PRNG device */
- (*prng)->devfd = -1;
+ (*prng)->dev = -1;
if ((fd = open("/dev/urandom", O_RDONLY)) == -1)
fd = open("/dev/random", O_RDONLY|O_NONBLOCK);
if (fd != -1) {
fcntl(fd, F_SETFD, FD_CLOEXEC);
- (*prng)->devfd = fd;
+ (*prng)->dev = fd;
}
+ /* initialize MD5 engine */
+ if (md5_create(&((*prng)->md5)) != MD5_RC_OK)
+ return PRNG_RC_INT;
+
+ /* initialize time resolution compensation counter */
+ (*prng)->cnt = 0;
+
/* seed the C library PRNG once */
gettimeofday(&tv, NULL);
pid = getpid();
@@ -72,10 +82,7 @@
^ (unsigned int)pid
^ (unsigned int)tv.tv_sec
^ (unsigned int)tv.tv_usec));
-
- /* crank the PRNG a few times */
- gettimeofday(&tv, NULL);
- for (i = (unsigned int)(tv.tv_sec ^ tv.tv_usec) & 0x1F; i > 0; i--)
+ for (i = (unsigned int)((tv.tv_sec ^ tv.tv_usec) & 0x1F); i > 0; i--)
(void)rand();
return PRNG_RC_OK;
@@ -85,35 +92,59 @@
{
size_t n;
unsigned char *p;
- int cnt;
+ struct {
+ struct timeval tv;
+ long cnt;
+ int rnd;
+ } entropy;
+ unsigned char md5_buf[MD5_LEN_BIN];
+ unsigned char *md5_ptr;
+ size_t md5_len;
+ int retries;
int i;
/* sanity check argument(s) */
if (prng == NULL || data_len == 0)
return PRNG_RC_ARG;
- /* try to gather data from the system PRNG device */
- if (prng->devfd != -1) {
- p = (unsigned char *)data_ptr;
- n = data_len;
- cnt = 0;
+ /* prepare for generation */
+ p = (unsigned char *)data_ptr;
+ n = data_len;
+
+ /* approach 1: try to gather data via stronger system PRNG device */
+ if (prng->dev != -1) {
+ retries = 0;
while (n > 0) {
- i = read(prng->devfd, (void *)p, n);
+ i = read(prng->dev, (void *)p, n);
if (i <= 0) {
- if (cnt++ > 16)
+ if (retries++ > 16)
break;
continue;
}
+ retries = 0;
n -= (unsigned int)i;
p += (unsigned int)i;
- cnt = 0;
}
}
- /* always also apply the weaker PRNG. In case the stronger PRNG device
- based source failed, this is the only remaining randomness, of course */
- for (p = (unsigned char *)data_ptr, n = 0; n < data_len; n++)
- *p++ ^= (unsigned char)(((unsigned int)rand() >> 7) & 0xFF);
+ /* approach 2: try to gather data via weaker libc PRNG API. */
+ while (n > 0) {
+ /* gather new entropy */
+ gettimeofday(&(entropy.tv), NULL);
+ entropy.cnt = prng->cnt++;
+ entropy.rnd = rand();
+
+ /* pass entropy into MD5 engine */
+ md5_update(prng->md5, (void *)&entropy, sizeof(entropy));
+
+ /* store MD5 engine state as PRN output */
+ md5_ptr = md5_buf;
+ md5_len = sizeof(md5_buf);
+ md5_store(prng->md5, (void *)&md5_ptr, &md5_len);
+ for (i = 0; i < MD5_LEN_BIN && n > 0; i++, n--)
+ *p++ ^= md5_buf[i]; /* intentionally no assignment because arbitrary
+ caller buffer content is leveraged, too */
+ }
return PRNG_RC_OK;
}
@@ -125,8 +156,8 @@
return PRNG_RC_ARG;
/* close PRNG device */
- if (prng->devfd != -1)
- close(prng->devfd);
+ if (prng->dev != -1)
+ close(prng->dev);
/* free object */
free(prng);
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