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1) Use __packed attr on rdat structure to make it exact 128 bytes.

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2) Use gettimeofday() and getpid() only if reading from /dev/urandom
fails or impossible.
3) Discard N bytes on very first initialization only (i.e. don't
discard on re-stir).
4) Reduce N from 1024 to 512 as really suggested in the
"(Not So) Random Shuffles of RC4" paper:
http://research.microsoft.com/users/mironov/papers/rc4full.pdf
This commit is contained in:
Andrey A. Chernov 2008-07-21 21:57:30 +00:00
parent 99d803b98f
commit a08f5d95ec
1 changed files with 17 additions and 10 deletions
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27
lib/libc/gen/arc4random.c
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@ -106,34 +106,41 @@ arc4_addrandom(u_char *dat, int datlen)
static void
arc4_stir(void)
{
int fd, n;
int fd, n, done;
struct {
struct timeval tv;
pid_t pid;
u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)];
} rdat;
} __packed rdat;
gettimeofday(&rdat.tv, NULL);
rdat.pid = getpid();
fd = _open(RANDOMDEV, O_RDONLY, 0);
done = 0;
if (fd >= 0) {
(void)_read(fd, rdat.rnd, sizeof(rdat.rnd));
if (_read(fd, &rdat, sizeof(rdat)) == sizeof(rdat))
done = 1;
(void)_close(fd);
}
/* fd < 0? Ah, what the heck. We'll just take whatever was on the
/* !done? Ah, what the heck. We'll just take whatever was on the
* stack... */
if (!done) {
gettimeofday(&rdat.tv, NULL);
rdat.pid = getpid();
}
arc4_addrandom((u_char *)&rdat, sizeof(rdat));
/*
* Throw away the first N bytes of output, as suggested in the
* paper "Weaknesses in the Key Scheduling Algorithm of RC4"
* by Fluher, Mantin, and Shamir. N=1024 is based on
* by Fluher, Mantin, and Shamir. N=512 is based on
* suggestions in the paper "(Not So) Random Shuffles of RC4"
* by Ilya Mironov.
*/
for (n = 0; n < 1024; n++)
(void)arc4_getbyte();
if (rs_initialized != 1) {
for (n = 0; n < 512; n++)
(void)arc4_getbyte();
rs_initialized = 1;
}
arc4_count = 1600000;
}
@ -170,7 +177,7 @@ arc4_check_init(void)
{
if (!rs_initialized) {
arc4_init();
rs_initialized = 1;
rs_initialized = 2;
}
}