/**********************************************************************
  my_crypt.c
 **********************************************************************

  my_crypt - Clone of the UNIX crypt (1) utility.
  Copyright ©2001, Stewart Adcock <stewart@bellatrix.pcl.ox.ac.uk>

  The latest version of this program should be available at:
  http://www.stewart-adcock.co.uk/

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.  Alternatively, if your project
  is incompatable with the GPL, I will probably agree to requests
  for permission to use the terms of any other license.

  This program is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY WHATSOEVER.

  A full copy of the GNU General Public License should be in the file
  "COPYING" provided with this distribution; if not, see:
  http://www.gnu.org/

 **********************************************************************

  synopsis:	Dodgy clone of the dodgy UNIX crypt utility.

  compilation:	try typing something like this with the GNU compiler:
		gcc my_crypt.c -o crypt -lcrypt -Wall -O2

  usage:	crypt [-s] passkey < file > encrypted_file
		crypt [-s] passkey < encrypted_file > file

		Warning: This _IS_ _NOT_ designed to be
		cryptographically secure.  It was solely written as
		a means to decrypt files which were encrypted using
		the legacy UNIX crypt utility.

  Last Updated: 28 May 2003 SAA	Fixed a bug - thanks to Dr A J Bartlett for pointing this out.
		11/06/01 SAA    Clone of UNIX crypt utility.

 **********************************************************************/

#define _XOPEN_SOURCE	/* For crypt() */
#define _ISO99_SOURCE	/* For int32_t */

#include <stdio.h>
#include <stdint.h>	/* Comment out this line for MIPSpro compiler on IRIX, and possibly others. */
#include <stdlib.h>
#include <unistd.h>

#define NUM_ROTORS	256
#define MASK		0377

char	t1[NUM_ROTORS];
char	t2[NUM_ROTORS];
char	t3[NUM_ROTORS];
char	deck[NUM_ROTORS];

char *init(char *key)
  {
  int		ic, i, j, temp;
  unsigned int	random;
  int32_t	seed=123;
  char		*password;

  password = (char *)crypt(key, key);

  for (i=0; i<13; i++) seed = seed*password[i] + i;

  for(i=0;i<NUM_ROTORS;i++)
    {
    t1[i] = i;
    deck[i] = i;
    t2[i] = 0;
    t3[i] = 0;
    }

  for(i=0;i<NUM_ROTORS;i++)
    {
    seed = 5*seed + password[i%13];
    random = seed % 65521;
    j = NUM_ROTORS - i;
    ic = (random&MASK) % j;
    j--;
    random >>= 8;
    temp = t1[ic];
    t1[ic] = t1[j];
    t1[j] = temp;
    if (t3[j]==0)
      {
      ic = (random&MASK) % j;
      while (t3[ic]!=0) ic = (ic+1) % j;
      t3[ic] = j;
      t3[j] = ic;
      }
    }

  for(i=0;i<NUM_ROTORS;i++) t2[t1[i]&MASK] = i;

  return password;
  }


void shuffle(char *deck, char *password)
  {
  int			ic, i, j, temp;
  static int32_t	seed = 123;

  for(i=0;i<NUM_ROTORS;i++)
    {
    seed = 5*seed + password[i%13];
    j = NUM_ROTORS - i;
    ic = ((seed%65521)&MASK)%j;
    j--;
    temp = deck[j];
    deck[j] = deck[ic];
    deck[ic] = temp;
    }

  return;
  }


int main(int argc, char **argv)
  {
  int	i;
  int	n1=0, n2=0, nr1=0, nr2=0;
  int	soption = 0;
  char	*password;

/* Check for the '-s' switch, the only supported option. */
  if (argc > 1 && argv[1][0] == '-' && argv[1][1] == 's')
    {
    argc--;
    argv++;
    soption = 1;
    }

  password = init(argv[1]);

  if (soption)
    {
    while((i=getchar())>=0)
      {
      nr1 = deck[n1]&MASK;
      nr2 = deck[nr1]&MASK;

      i = t2[(t3[(t1[(i+nr1)&MASK]+nr2)&MASK]-nr2)&MASK]-nr1;
      putchar(i);
      n1++;
      if (n1==NUM_ROTORS)
        {
        n1 = 0;
        n2++;
        if(n2==NUM_ROTORS) n2 = 0;

        shuffle(deck, password);
        }
      }
    }
  else
    {
    while((i=getchar())>=0)
      {
      nr1 = n1;

      i = t2[(t3[(t1[(i+nr1)&MASK]+nr2)&MASK]-nr2)&MASK]-nr1;
      putchar(i);
      n1++;
      if (n1==NUM_ROTORS)
        {
        n1 = 0;
        n2++;
        if(n2==NUM_ROTORS) n2 = 0;

        nr2 = n2;
        }
      }
    }

  exit(0);
  }