Vigenere encode and decode : Vigenere « Security « JavaScript DHTML






Vigenere encode and decode

<html>
  <head>
    <title>Vignere Cipher</title>
    <!--
      CryptoMX Tools
      Copyright (C) 2004 - 2006 Derek Buitenhuis

      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.
    -->
  </head>
  <body bgcolor=#FFFFFF text=#000000>
    <td>
      <script>
function Vigenere (input, key, forward)
{
  if (key == null)
    key = "";
  var alphabet =   "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                 + "abcdefghijklmnopqrstuvwxyz";

  // Validate key:
  key = key . toUpperCase ();
  var key_len = key . length;
  var i;
  var adjusted_key = "";
  for (i = 0; i < key_len; i ++)
  {
    var key_char = alphabet . indexOf (key . charAt (i));
    if (key_char < 0)
      continue;
    adjusted_key += alphabet . charAt (key_char);
  }
  key = adjusted_key;
  key_len = key . length;
  if (key_len == 0)
  {
    alert ('You forgot to supply a key!');
    key = "a";
    key_len = 1;
  }

  // Transform input:
  var input_len = input . length;
  var output = "";
  var key_index = 0;
  var in_tag = false;
  for (i = 0; i < input_len; i ++)
  {
    var input_char = input . charAt (i);
    if (input_char == "<")
      in_tag = true;
    else if (input_char == ">")
      in_tag = false;
    if (in_tag)
    {
      output += input_char;
      continue;
    }
    var input_char_value = alphabet . indexOf (input_char);
    if (input_char_value < 0)
    {
      output += input_char;
      continue;
    }
    var lowercase = input_char_value >= 26 ? true : false;
    if (forward)
      input_char_value += alphabet . indexOf (key . charAt (key_index));
    else
      input_char_value -= alphabet . indexOf (key . charAt (key_index));
    input_char_value += 26;
    if (lowercase)
      input_char_value = input_char_value % 26 + 26;
    else
      input_char_value %= 26;
    output += alphabet . charAt (input_char_value);
    key_index = (key_index + 1) % key_len;

  }
  return output;
}

function runcoder (dir)
{
  document . form . output . value = Vigenere (document . form . input . value, document . form . key . value, dir);
/*  A bug in IE prevents this section from working correctly.
  with (document . form)
  {
    output . value = Vigenere (input . value, key . value, dir);
  }
*/
}
    </script>
    <form name=form>
      <table border cellspacing="2">
        <tr>
          <td>
            Input:<br>
            <input type=button onClick="this.form.input.value='';" value="clear">
          </td>
          <td>
            <textarea name=input rows=10 cols=60 wrap=virtual></textarea>
          </td>
        </tr>
        <tr>
          <td>
            Key:<br>
            <input type=button onClick="this.form.key.value='';" value="clear">
          </td>
          <td>
            <textarea name=key rows=5 cols=60 wrap=virtual></textarea>
          </td>
        </tr>
        <tr>
          <td>Coding direction:</td>
          <td>
            <input type=button value="encode" onClick="runcoder (true);">
            <input type=button value="decode" onClick="runcoder (false);">
          </td>
        </tr>
          <td>
            Output:<br>
            <input type=button onClick="this.form.output.value='';" value="clear">
          </td>
          <td>
            <textarea name=output rows=10 cols=60 wrap=virtual></textarea>
          </td>
        </table>
      </form>
  </body>
</html>






           
       








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