/*
 * Copyright 2003 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*      $OpenBSD: arc4random.c,v 1.6 2001/06/05 05:05:38 pvalchev 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>

#ifdef __GNUC__
#define inline __inline
#else                           /* !__GNUC__ */
#define inline
#endif                          /* !__GNUC__ */

struct arc4_stream {
        uint8_t i;
        uint8_t j;
        uint8_t s[256];
};

int     rs_initialized;
static struct arc4_stream rs;

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;
        size_t    datlen;
{
        int     n;
        uint8_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;
                uint rnd[(128 - sizeof(struct timeval)) / sizeof(uint)];
        }       rdat;

        (void) gettimeofday(&rdat.tv, NULL);
        fd = open("/dev/urandom", O_RDONLY);
        if (fd != -1) {
                (void) read(fd, rdat.rnd, sizeof(rdat.rnd));
                (void) close(fd);
        }
        /* fd < 0 ?  Ah, what the heck. We'll just take
         * whatever was on the stack... */

        arc4_addrandom(as, (void *) &rdat, sizeof(rdat));
}

static inline uint8_t
arc4_getbyte(as)
        struct arc4_stream *as;
{
        uint8_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 uint32_t
arc4_getword(as)
        struct arc4_stream *as;
{
        uint32_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;
        size_t     datlen;
{
        if (!rs_initialized)
                arc4random_stir();
        arc4_addrandom(&rs, dat, datlen);
}

uint32_t
arc4random()
{
        if (!rs_initialized)
                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