#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

void usage(char *);

int main(int argc, char *argv[]){
  int fdin, fdout;
  int strlen, i, c;
  int cryptFlag=0, decryptFlag=0,seekFlag=0;
  int seekOffset=50688;
  char *infile=NULL, *outfile=NULL;
  char inbuff[8192];
  char outbuff[8192];

  
  while ((c = getopt(argc, argv, "cdhi:o:s:")) != EOF){
    switch (c) {
      case 'c':
        cryptFlag++;
        break;
      case 'd':
        decryptFlag++;
        break;
      case 'i':
        infile = optarg;
        break;
      case 'o':
        outfile = optarg;
        break;
      case 's':
        seekOffset = atoi(optarg);
        break;
      case 'h':
        usage(argv[0]);
        break;
      default:
        usage(argv[0]);
        break;
    }
  }
      
  if ((cryptFlag && decryptFlag) || (!cryptFlag && !decryptFlag)){
    printf("Must specify either -c or -d but not both\n");
    usage(argv[0]);
  }

  if (infile){
    fdin = open(infile, O_RDONLY);
    if (fdin == -1){
      perror("open infile");
    }
  } else {
    fdin = STDIN_FILENO;
  }

  if (outfile){
    fdout = open(outfile, O_WRONLY|O_CREAT|O_EXCL, 0644);
    if (fdout == -1){
      perror("open outfiel");
    }
  } else {
    fdout = STDOUT_FILENO;
  }

  memset(inbuff, '\0', sizeof(inbuff));
  memset(outbuff, '\0', sizeof(outbuff));

  if (decryptFlag)
    lseek(fdin, seekOffset, SEEK_SET);

  while ((strlen = read(fdin, inbuff, sizeof(inbuff))) != 0){

    for (i=0; i < strlen ; i++){
      if (cryptFlag){
        if (!(i % 2))
          outbuff[i] = (inbuff[i] + 0x44) & 0xff;
        else
          outbuff[i] = (inbuff[i] + 0x63) & 0xff;
      } else {
        if (!(i % 2))
          outbuff[i] = inbuff[i] - 0x44;
        else
          outbuff[i] = inbuff[i] - 0x63;
      }
    }

    write(fdout, outbuff, strlen);
  }

  close(fdin);
  close(fdout);

  return(0);
} 

void usage(char *progname){

  char *c;
 
  c = strrchr(progname, '/');
  if (c)
    c++;
  else
    c = progname;

  printf("Usage: %s -cd[h] [-i infile] [-o outfile] [-s seek] \n", c);
  printf("  Shell-lock {en,de}coder by mudge@l0pht.com and _lumpy\n");
  printf("    -c  encrypt\n");
  printf("    -d  decrypt\n");
  printf("    -h  help\n");
  printf("    -i <file> input file\n");
  printf("    -o <file> output file\n");
  printf("    -s <offset> seed offset [defaults to 50688]\n");
  exit(1);
}