freebsd-dev/lib/libc/gen/arc4random.c
Xin LI 91868665a9 Discard first 3072 bytes of RC4 keystream, this is a bandaid
that allows us to work on switching to a more modern PRNG.

Submitted by:	Steven Chamberlain <steven pyro eu org>
Approved by:	so
2017-03-14 06:00:44 +00:00

303 lines
6.1 KiB
C

/* $OpenBSD: arc4random.c,v 1.24 2013/06/11 16:59:50 deraadt Exp $ */
/*
* Copyright (c) 1996, David Mazieres <dm@uun.org>
* Copyright (c) 2008, Damien Miller <djm@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* Arc4 random number generator for OpenBSD.
*
* This code is derived from section 17.1 of Applied Cryptography,
* second edition, which describes a stream cipher allegedly
* compatible with RSA Labs "RC4" cipher (the actual description of
* which is a trade secret). The same algorithm is used as a stream
* cipher called "arcfour" in Tatu Ylonen's ssh package.
*
* RC4 is a registered trademark of RSA Laboratories.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "namespace.h"
#include <fcntl.h>
#include <limits.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/param.h>
#include <sys/sysctl.h>
#include <sys/time.h>
#include <pthread.h>
#include "libc_private.h"
#include "un-namespace.h"
#ifdef __GNUC__
#define inline __inline
#else /* !__GNUC__ */
#define inline
#endif /* !__GNUC__ */
struct arc4_stream {
u_int8_t i;
u_int8_t j;
u_int8_t s[256];
};
static pthread_mutex_t arc4random_mtx = PTHREAD_MUTEX_INITIALIZER;
#define RANDOMDEV "/dev/random"
#define KEYSIZE 128
#define _ARC4_LOCK() \
do { \
if (__isthreaded) \
_pthread_mutex_lock(&arc4random_mtx); \
} while (0)
#define _ARC4_UNLOCK() \
do { \
if (__isthreaded) \
_pthread_mutex_unlock(&arc4random_mtx); \
} while (0)
static int rs_initialized;
static struct arc4_stream rs;
static pid_t arc4_stir_pid;
static int arc4_count;
extern int __sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp,
void *newp, size_t newlen);
static inline u_int8_t arc4_getbyte(void);
static void arc4_stir(void);
static inline void
arc4_init(void)
{
int n;
for (n = 0; n < 256; n++)
rs.s[n] = n;
rs.i = 0;
rs.j = 0;
}
static inline void
arc4_addrandom(u_char *dat, int datlen)
{
int n;
u_int8_t si;
rs.i--;
for (n = 0; n < 256; n++) {
rs.i = (rs.i + 1);
si = rs.s[rs.i];
rs.j = (rs.j + si + dat[n % datlen]);
rs.s[rs.i] = rs.s[rs.j];
rs.s[rs.j] = si;
}
rs.j = rs.i;
}
static size_t
arc4_sysctl(u_char *buf, size_t size)
{
int mib[2];
size_t len, done;
mib[0] = CTL_KERN;
mib[1] = KERN_ARND;
done = 0;
do {
len = size;
if (__sysctl(mib, 2, buf, &len, NULL, 0) == -1)
return (done);
done += len;
buf += len;
size -= len;
} while (size > 0);
return (done);
}
static void
arc4_stir(void)
{
u_char rdat[KEYSIZE];
int i;
if (!rs_initialized) {
arc4_init();
rs_initialized = 1;
}
if (arc4_sysctl(rdat, KEYSIZE) != KEYSIZE) {
/*
* The sysctl cannot fail. If it does fail on some FreeBSD
* derivative or after some future change, just abort so that
* the problem will be found and fixed. abort is not normally
* suitable for a library but makes sense here.
*/
abort();
}
arc4_addrandom(rdat, KEYSIZE);
/*
* Discard early keystream, as per recommendations in:
* "(Not So) Random Shuffles of RC4" by Ilya Mironov.
*/
for (i = 0; i < 3072; i++)
(void)arc4_getbyte();
arc4_count = 1600000;
}
static void
arc4_stir_if_needed(void)
{
pid_t pid = getpid();
if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != pid) {
arc4_stir_pid = pid;
arc4_stir();
}
}
static inline u_int8_t
arc4_getbyte(void)
{
u_int8_t si, sj;
rs.i = (rs.i + 1);
si = rs.s[rs.i];
rs.j = (rs.j + si);
sj = rs.s[rs.j];
rs.s[rs.i] = sj;
rs.s[rs.j] = si;
return (rs.s[(si + sj) & 0xff]);
}
static inline u_int32_t
arc4_getword(void)
{
u_int32_t val;
val = arc4_getbyte() << 24;
val |= arc4_getbyte() << 16;
val |= arc4_getbyte() << 8;
val |= arc4_getbyte();
return val;
}
void
arc4random_stir(void)
{
_ARC4_LOCK();
arc4_stir();
_ARC4_UNLOCK();
}
void
arc4random_addrandom(u_char *dat, int datlen)
{
_ARC4_LOCK();
if (!rs_initialized)
arc4_stir();
arc4_addrandom(dat, datlen);
_ARC4_UNLOCK();
}
u_int32_t
arc4random(void)
{
u_int32_t val;
_ARC4_LOCK();
arc4_count -= 4;
arc4_stir_if_needed();
val = arc4_getword();
_ARC4_UNLOCK();
return val;
}
void
arc4random_buf(void *_buf, size_t n)
{
u_char *buf = (u_char *)_buf;
_ARC4_LOCK();
arc4_stir_if_needed();
while (n--) {
if (--arc4_count <= 0)
arc4_stir();
buf[n] = arc4_getbyte();
}
_ARC4_UNLOCK();
}
/*
* Calculate a uniformly distributed random number less than upper_bound
* avoiding "modulo bias".
*
* Uniformity is achieved by generating new random numbers until the one
* returned is outside the range [0, 2**32 % upper_bound). This
* guarantees the selected random number will be inside
* [2**32 % upper_bound, 2**32) which maps back to [0, upper_bound)
* after reduction modulo upper_bound.
*/
u_int32_t
arc4random_uniform(u_int32_t upper_bound)
{
u_int32_t r, min;
if (upper_bound < 2)
return 0;
/* 2**32 % x == (2**32 - x) % x */
min = -upper_bound % upper_bound;
/*
* This could theoretically loop forever but each retry has
* p > 0.5 (worst case, usually far better) of selecting a
* number inside the range we need, so it should rarely need
* to re-roll.
*/
for (;;) {
r = arc4random();
if (r >= min)
break;
}
return r % upper_bound;
}
#if 0
/*-------- Test code for i386 --------*/
#include <stdio.h>
#include <machine/pctr.h>
int
main(int argc, char **argv)
{
const int iter = 1000000;
int i;
pctrval v;
v = rdtsc();
for (i = 0; i < iter; i++)
arc4random();
v = rdtsc() - v;
v /= iter;
printf("%qd cycles\n", v);
}
#endif