OTP example

<?php
/*
Copyright (C) 2003 Enders Web Development
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.
This program is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with
this program; if not, write to the
Free Software Foundation, Inc.,
59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
Author Email: tomender@ptd.net
Author Post:
J. Thomas Enders
PO Box 663
Gilbert, PA 18331, USA
*/
error_reporting(E_ALL);

if(!isset($_POST['key'])) {$_POST['key'] = '';}
if(!isset($_POST['plaintext'])) {$_POST['plaintext'] = '';}
if(!isset($_POST['ciphertext'])) {$_POST['ciphertext'] = '';}

$parse = false;
$error = '';
if(isset($_POST['encrypt']) || isset($_POST['decrypt'])) {
 $parse = true;
 if((isset($_POST['encrypt']) || isset($_POST['decrypt']))) {
   if($_POST['key'] == '') {
    $error .= "ERROR: You must enter a key to encrypt or decrypt text.<br />\n";
    $parse = false;
   } elseif(!preg_match("^[a-z]+$/i^",$_POST['key'])) {
    $error .= "ERROR: The key (" . $_POST['key'] . ") can only contain letters.<br />\n";
    $parse = false;
   }
  }
  if(isset($_POST['encrypt']) && $_POST['plaintext'] == '') {
   $error .= "ERROR: You must enter pleantext to encrypt.<br />\n";
   $parse = false;
  } elseif (isset($_POST['decrypt']) && $_POST['ciphertext'] == '') {
   $error .= "ERROR: You must enter ciphertext to decrypt.<br />\n";
   $parse = false;
  }
 }
 if ($parse && isset($_POST['encrypt'])) {
  $_POST['ciphertext'] = encrypt($_POST['key'],$_POST['plaintext']);
 } elseif ($parse && isset($_POST['decrypt'])) {
  $_POST['plaintext'] = decrypt($_POST['key'],$_POST['ciphertext']);
 }
 echo '<?xml version="1.0" encoding="UTF-8"?>' . "\n";
?>
<!--
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
 <title>Vernam Cipher</title>
 <style type="text/css">
   body {
    font-family: arial,helvetica,_sans;
    font-size: 11pt;
    color: #000000;
    background-color: #FFFFEE;
   }

   div.dataScrubbing {
    position: absolute;
    padding: 5px;
    background-color: #EEFFFF;
    border-width: 1px;
    border-color: #888899;
    border-style: solid;
    color: #990000;
    width: 375px;
   }

   div.inputArea {
    background-color: #FFFFFF;
    position: absolute;
    padding: 5px;
    border-width: 1px;
    border-color: #000000;
    border-style: solid;
    width: 380px;
   }

   input,textarea {
    font-family: arial,helvetica,_sans;
    font-size: 11pt;
    color: #000000;
    background-color: #EEFFFF;
    border-width: 1px;
    border-color: #889999;
    border-style: solid;
   }
 </style>
</head>
 <body>
  <h1>Vernam Cipher</h1>
-->
  <?php
   if($error != '') {
    echo '<div class="dataScrubbing">' . "\n";
    echo $error;
    echo "</div>\n";
    echo "<div><br /><br /></div>\n";
   }
?>
<!--
<div class="inputArea">
  <form method="post" action="">
    Enter the key: <input type="text" name="key" size="20" value="<?php $_POST['key'] ?>" /><br />
    Plaintext:<br />
    <textarea name="plaintext" cols="50" rows="5"><?php $_POST['plaintext'] ?></textarea><br />
    Ciphertext:<br />
    <textarea name="ciphertext" cols="50" rows="5"><?php $_POST['ciphertext'] ?></textarea><br /><br />
    <input type="submit" name="encrypt" value="Encrypt" />&nbsp;&nbsp;
    <input type="submit" name="decrypt" value="Decrypt" />
  </form>
</div>
</body>
</html>
-->
<?php
 function encrypt($key,$text) {
  $key = strtolower($key);
  preptext($text,'enc');
  $key .= $text;
  $retval = '';
  for($i=0;$i<strlen($text);$i++) {
   $cur_char = ord(substr($text,$i,1)) - 97;
   $cur_key = ord(substr($key,$i,1)) - 97;
   $retval .= chr(($cur_char + $cur_key)%26 + 65);
  }
  return $retval;
 }

 function decrypt($key,$text) {
  $key = strtoupper($key);
  preptext($text,'dec');
  $retval = '';
  $i_inc = strlen($key);
  $str_len = strlen($text);
  $retval = '';
  for($i=0;$i<$str_len;$i = $i + $i_inc) {
   $key .= strtoupper(substr($retval,($i-$i_inc),$i_inc));
   for($j=0;$j<$i_inc;$j++) {
    $cur_char = ord(substr($text,($i+$j),1)) - 65;
    $cur_key = ord(substr($key,($i+$j),1)) - 65;
    $cur_dec = $cur_char - $cur_key;
    if($cur_dec > -1) {$cur_dec = $cur_dec + 97;}
    else {$cur_dec = (26 + $cur_dec)+ 97;}
    if(($i+$j) < $str_len) {$retval .= chr($cur_dec);}
   }
  }
  return $retval;
 }
 function preptext(&$text,$direction = 'enc') {
  $direction = strtolower($direction);
   if($direction != 'enc' && $direction != 'dec') {
    warn("preptext called with an inappropriate direction value.");
   }
   switch ($direction) {
    case 'enc';
     $text = strtolower($text);
     $low_bound = 95;
     $high_bound = 122;
    break;
    case 'dec';
     $text = strtoupper($text);
     $low_bound = 65;
     $high_bound = 90;
   }

   $t_len = strlen($text);
   for($i=0;$i<$t_len;$i++) {
    if(ord(substr($text,$i,1)) < $low_bound ||
    ord(substr($text,$i,1)) > $high_bound) {
     $text = substr($text,0,$i) . substr($text,($i+1));
     $t_len--;
    }
   }
 }
?>