/*
* 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 (for instance 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 <sys/cdefs.h>
__FBSDID("$FreeBSD: src/lib/libc/gen/arc4random.c,v 1.10 2004/03/24 14:44:57 green Exp $");
#include <sys/types.h>
#include <sys/time.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
struct arc4_stream {
u_int8_t i;
u_int8_t j;
u_int8_t s[256];
};
#define RANDOMDEV "/dev/urandom"
#define THREAD_LOCK()
#define THREAD_UNLOCK()
static struct arc4_stream rs;
static int rs_initialized;
static int rs_stired;
static inline u_int8_t arc4_getbyte(struct arc4_stream *);
static void arc4_stir(struct arc4_stream *);
static inline void
arc4_init(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(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;
}
}
static void
arc4_stir(struct arc4_stream *as)
{
int fd, n;
struct {
struct timeval tv;
pid_t pid;
u_int8_t rnd[128 - sizeof(struct timeval) - sizeof(pid_t)];
} rdat;
gettimeofday(&rdat.tv, NULL);
rdat.pid = getpid();
fd = open(RANDOMDEV, O_RDONLY, 0);
if (fd >= 0) {
(void) read(fd, rdat.rnd, sizeof(rdat.rnd));
close(fd);
}
/* fd < 0? Ah, what the heck. We'll just take whatever was on the
* stack... */
arc4_addrandom(as, (void *) &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
* suggestions in the paper "(Not So) Random Shuffles of RC4"
* by Ilya Mironov.
*/
for (n = 0; n < 1024; n++)
arc4_getbyte(as);
}
static inline u_int8_t
arc4_getbyte(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(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);
}
static void
arc4_check_init(void)
{
if (!rs_initialized) {
arc4_init(&rs);
rs_initialized = 1;
}
}
static void
arc4_check_stir(void)
{
if (!rs_stired) {
arc4_stir(&rs);
rs_stired = 1;
}
}
u_int32_t
arc4random()
{
u_int32_t rnd;
THREAD_LOCK();
arc4_check_init();
arc4_check_stir();
rnd = arc4_getword(&rs);
THREAD_UNLOCK();
return (rnd);
}
#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
