/* $OpenBSD: arc4random.c,v 1.19 2008/06/04 00:50:23 djm 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.
*
* Here the stream cipher has been modified always to include the time
* when initializing the state. That makes it impossible to
* regenerate the same random sequence twice, so this can't be used
* for encryption, but will generate good random numbers.
*
* RC4 is a registered trademark of RSA Laboratories.
*/
#include <fcntl.h>
#include <limits.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/time.h>
#include "thread_private.h"
/* BIONIC-BEGIN */
/* this lock should protect the global variables in this file */
static pthread_mutex_t _arc4_lock = PTHREAD_MUTEX_INITIALIZER;
#define _ARC4_LOCK() pthread_mutex_lock(&_arc4_lock)
#define _ARC4_UNLOCK() pthread_mutex_unlock(&_arc4_lock)
/* BIONIC-END */
#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 int rs_initialized;
static struct arc4_stream rs;
static pid_t arc4_stir_pid;
static int arc4_count;
static inline u_int8_t arc4_getbyte(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 void
arc4_stir(void)
{
#if 1 /* BIONIC-BEGIN */
int i, fd;
union {
struct timeval tv;
u_int rnd[128 / sizeof(u_int)];
} rdat;
int n;
if (!rs_initialized) {
arc4_init();
rs_initialized = 1;
}
fd = open("/dev/urandom", O_RDONLY);
if (fd != -1) {
read(fd, rdat.rnd, sizeof(rdat.rnd));
close(fd);
}
else
{
/* fd < 0 ? Ah, what the heck. We'll just take
* whatever was on the stack. just add a little more
* time-based randomness though
*/
gettimeofday(&rdat.tv, NULL);
}
arc4_stir_pid = getpid();
arc4_addrandom((void *) &rdat, sizeof(rdat));
#else /* BIONIC-END */
int i, mib[2];
size_t len;
u_char rnd[128];
if (!rs_initialized) {
arc4_init();
rs_initialized = 1;
}
mib[0] = CTL_KERN;
mib[1] = KERN_ARND;
len = sizeof(rnd);
sysctl(mib, 2, rnd, &len, NULL, 0);
arc4_stir_pid = getpid();
arc4_addrandom(rnd, sizeof(rnd));
#endif
/*
* Discard early keystream, as per recommendations in:
* http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
*/
for (i = 0; i < 256; i++)
(void)arc4_getbyte();
arc4_count = 1600000;
}
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]);
}
u_int8_t
__arc4_getbyte(void)
{
u_int8_t val;
_ARC4_LOCK();
if (--arc4_count == 0 || !rs_initialized)
arc4_stir();
val = arc4_getbyte();
_ARC4_UNLOCK();
return val;
}
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;
if (arc4_count <= 0 || !rs_initialized || arc4_stir_pid != getpid())
arc4_stir();
val = arc4_getword();
_ARC4_UNLOCK();
return val;
}
void
arc4random_buf(void *_buf, size_t n)
{
u_char *buf = (u_char *)_buf;
_ARC4_LOCK();
if (!rs_initialized || arc4_stir_pid != getpid())
arc4_stir();
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;
#if (ULONG_MAX > 0xffffffffUL)
min = 0x100000000UL % upper_bound;
#else
/* Calculate (2**32 % upper_bound) avoiding 64-bit math */
if (upper_bound > 0x80000000)
min = 1 + ~upper_bound; /* 2**32 - upper_bound */
else {
/* (2**32 - (x * 2)) % x == 2**32 % x when x <= 2**31 */
min = ((0xffffffff - (upper_bound * 2)) + 1) % upper_bound;
}
#endif
/*
* 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