program enkripsi vigenere cipher dengan html

buat agan yang lagi mempelajari enkripsi, saya punya program yang saya dapat dari internet... nih dia silakan copy kode di bawah, terus paste di dalam teks editor seperti notepad, simpan dengan ekstensi html..

kode program

<html>

<head>

    <title>Vignere Cipher</title>

    

</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>