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/* $OpenBSD: arc4random.c,v 1.7 2003/02/14 17:12:54 deraadt Exp $ */
/*
* Arc4 random number generator for OpenBSD.
* Copyright 1996 David Mazieres <dm@lcs.mit.edu>.
*
* Modification and redistribution in source and binary forms is
* permitted provided that due credit is given to the author and the
* OpenBSD project by leaving this copyright notice intact.
*/
/*
* 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 <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/sysctl.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 int rs_initialized;
static struct arc4_stream rs;
static pid_t arc4_stir_pid;
static inline void
arc4_init(as)
struct arc4_stream *as;
{
int n;
for (n = 0; n < 256; n++)
as->s[n] = n;
as->i = 0;
as->j = 0;
}
static inline void
arc4_addrandom(as, dat, datlen)
struct arc4_stream *as;
u_char *dat;
int datlen;
{
int n;
u_int8_t si;
as->i--;
for (n = 0; n < 256; n++) {
as->i = (as->i + 1);
si = as->s[as->i];
as->j = (as->j + si + dat[n % datlen]);
as->s[as->i] = as->s[as->j];
as->s[as->j] = si;
}
as->j = as->i;
}
static void
arc4_stir(as)
struct arc4_stream *as;
{
int fd;
struct {
struct timeval tv;
u_int rnd[(128 - sizeof(struct timeval)) / sizeof(u_int)];
} rdat;
gettimeofday(&rdat.tv, NULL);
fd = open("/dev/arandom", O_RDONLY);
if (fd != -1) {
read(fd, rdat.rnd, sizeof(rdat.rnd));
close(fd);
} else {
int i, mib[2];
size_t len;
/* Device could not be opened, we might be chrooted, take
* randomness from sysctl. */
mib[0] = CTL_KERN;
mib[1] = KERN_ARND;
for (i = 0; i < sizeof(rdat.rnd) / sizeof(u_int); i ++) {
len = sizeof(u_int);
if (sysctl(mib, 2, &rdat.rnd[i], &len, NULL, 0) == -1)
break;
}
}
/* fd < 0 or failed sysctl ? Ah, what the heck. We'll just take
* whatever was on the stack... */
arc4_stir_pid = getpid();
arc4_addrandom(as, (void *) &rdat, sizeof(rdat));
}
static inline u_int8_t
arc4_getbyte(as)
struct arc4_stream *as;
{
u_int8_t si, sj;
as->i = (as->i + 1);
si = as->s[as->i];
as->j = (as->j + si);
sj = as->s[as->j];
as->s[as->i] = sj;
as->s[as->j] = si;
return (as->s[(si + sj) & 0xff]);
}
static inline u_int32_t
arc4_getword(as)
struct arc4_stream *as;
{
u_int32_t val;
val = arc4_getbyte(as) << 24;
val |= arc4_getbyte(as) << 16;
val |= arc4_getbyte(as) << 8;
val |= arc4_getbyte(as);
return val;
}
void
arc4random_stir()
{
if (!rs_initialized) {
arc4_init(&rs);
rs_initialized = 1;
}
arc4_stir(&rs);
}
void
arc4random_addrandom(dat, datlen)
u_char *dat;
int datlen;
{
if (!rs_initialized)
arc4random_stir();
arc4_addrandom(&rs, dat, datlen);
}
u_int32_t
arc4random()
{
if (!rs_initialized || arc4_stir_pid != getpid())
arc4random_stir();
return arc4_getword(&rs);
}
#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
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