/*	$$$: arc4random.c 2005/02/08 robert */
/*	$NetBSD: arc4random.c,v 1.5.2.1 2004/03/26 22:52:50 jmc Exp $	*/
/*	$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 <libratbox_config.h>
#include <ratbox_lib.h>

#if !defined(HAVE_OPENSSL) && !defined(HAVE_GNUTLS) && !defined(HAVE_ARC4RANDOM)

#include "arc4random.h"

#ifdef HAVE_GETRUSAGE
#include <sys/resource.h>
#endif



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


static int rs_initialized;
static struct arc4_stream rs;

static inline void arc4_init(struct arc4_stream *);
static inline void arc4_addrandom(struct arc4_stream *, uint8_t *, int);
static void arc4_stir(struct arc4_stream *);
static inline uint8_t arc4_getbyte(struct arc4_stream *);
static inline uint32_t arc4_getword(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, uint8_t *dat, int 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(struct arc4_stream *as)
{
    struct timeval tv;
    pid_t pid;
    int n;
#ifdef _WIN32
    HMODULE lib;
#endif
    /* XXX this doesn't support egd sources or similiar */

    pid = getpid();
    arc4_addrandom(as, (void *)&pid, sizeof(pid));

    rb_gettimeofday(&tv, NULL);
    arc4_addrandom(as, (void *)&tv.tv_sec, sizeof(&tv.tv_sec));
    arc4_addrandom(as, (void *)&tv.tv_usec, sizeof(&tv.tv_usec));
    rb_gettimeofday(&tv, NULL);
    arc4_addrandom(as, (void *)&tv.tv_usec, sizeof(&tv.tv_usec));

#if defined(HAVE_GETRUSAGE) && RUSAGE_SELF
    {
        struct rusage buf;
        getrusage(RUSAGE_SELF, &buf);
        arc4_addrandom(as, (void *)&buf, sizeof(buf));
        memset(&buf, 0, sizeof(buf))
    }
#endif

#if !defined(_WIN32)
    {
        uint8_t rnd[128];
        int fd;
        fd = open("/dev/urandom", O_RDONLY);
        if(fd != -1) {
            read(fd, rnd, sizeof(rnd));
            close(fd);
            arc4_addrandom(as, (void *)rnd, sizeof(rnd));
            memset(&rnd, 0, sizeof(rnd));
        }

    }
#else
    {
        LARGE_INTEGER performanceCount;
        if(QueryPerformanceCounter(&performanceCount)) {
            arc4_addrandom(as, (void *)&performanceCount, sizeof(performanceCount));
        }
        lib = LoadLibrary("ADVAPI32.DLL");
        if(lib) {
            uint8_t rnd[128];
            BOOLEAN(APIENTRY * pfn) (void *, ULONG) =
                (BOOLEAN(APIENTRY *) (void *, ULONG))GetProcAddress(lib,
                        "SystemFunction036");
            if(pfn) {
                if(pfn(rnd, sizeof(rnd)) == TRUE)
                    arc4_addrandom(as, (void *)rnd, sizeof(rnd));
                memset(&rnd, 0, sizeof(rnd));
            }
        }
    }
#endif


    /*
     * Throw away the first N words of output, as suggested in the
     * paper "Weaknesses in the Key Scheduling Algorithm of RC4"
     * by Fluher, Mantin, and Shamir.
     * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps
     * N = 256 in our case.
     */
    for(n = 0; n < 256 * 4; n++)
        arc4_getbyte(as);
}

static inline uint8_t
arc4_getbyte(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(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(void)
{
    if(!rs_initialized) {
        arc4_init(&rs);
        rs_initialized = 1;
    }
    arc4_stir(&rs);
}

void
arc4random_addrandom(uint8_t *dat, int datlen)
{
    if(!rs_initialized)
        arc4random_stir();
    arc4_addrandom(&rs, dat, datlen);
}

uint32_t
arc4random(void)
{
    if(!rs_initialized)
        arc4random_stir();
    return arc4_getword(&rs);
}

#endif