/*
 * 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.
 */

/*
 * $FreeBSD: /usr/local/www/cvsroot/FreeBSD/src/lib/libc/gen/arc4random.c,v 1.10.8.1 2006/11/18 21:35:13 ache Exp $
 * Modified for Atheme by Jilles Tjoelker
 * $Id: arc4random.C,v 1.1 2007/07/19 08:24:56 pippijn Exp $
 */

#include "atheme.h"

#ifndef HAVE_ARC4RANDOM

struct arc4_stream
{
  unsigned char i;
  unsigned char j;
  unsigned char s[256];
};

#define	RANDOMDEV	"/dev/urandom"

static struct arc4_stream rs;
static int rs_initialized;
static int rs_stired;
static int arc4_count;

static inline unsigned char 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, unsigned char *dat, int datlen)
{
  int n;
  unsigned char 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;
    unsigned char 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, (unsigned char *) &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++)
    (void) arc4_getbyte (as);
  arc4_count = 400000;
}

static inline unsigned char
arc4_getbyte (struct arc4_stream *as)
{
  unsigned char 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 unsigned int
arc4_getword (struct arc4_stream *as)
{
  unsigned int 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)
    return;

  arc4_init (&rs);
  rs_initialized = 1;
}

static void
arc4_check_stir (void)
{
  if (!rs_stired || --arc4_count == 0)
    {
      arc4_stir (&rs);
      rs_stired = 1;
    }
}

void
arc4random_stir ()
{
  arc4_check_init ();
  arc4_stir (&rs);
}

void
arc4random_addrandom (unsigned char *dat, int datlen)
{
  arc4_check_init ();
  arc4_check_stir ();
  arc4_addrandom (&rs, dat, datlen);
}

unsigned int
arc4random (void)
{
  unsigned int rnd;

  arc4_check_init ();
  arc4_check_stir ();
  rnd = arc4_getword (&rs);

  return (rnd);
}

/* vim:cinoptions=>s,e0,n0,f0,{0,}0,^0,=s,ps,t0,c3,+s,(2s,us,)20,*30,gs,hs
 * vim:ts=8
 * vim:sw=8
 * vim:noexpandtab
 */

#endif /* !HAVE_ARC4RANDOM */