You can use the hex value, see this or this
For example from python you could use something like:

param = "\x00\x04\x03\x03"

And then send as GET request (see urllib2 or requests or httplib2)

From URL, before of the hex code you must add the % character

yourpage.html/param=%00%04%03%04

Look also this link

The free ASCIIflow website will let you draw text boxes, text, lines, arrows, freeform lines, erase, import, export, and even undo/redo. What else would one need?

Here is my wonderful creation using this tool:

+-------------------------------+
|                               |
|  My first ASCII box           |
|                               |
+---------+---------------------+
          |
          |
          |
          | My first ever ASCII arrow
          |
          |
          |
+---------v----------------------+
|                                |
|  My second ASCII box           |
+--------------------------------+

Here is a solution not using LINQ, but a for loop, which might be easier to construct and understand:

string text = "vpn123";

var result = new StringBuilder();

for (var i = 0; i < text.Length; i++)
{
    // multiply character code by 5
    var number = text[i] * 5;
    if (char.IsLetter(text[i]) && i > 0 && char.IsLetter(text[i - 1]))
    {
        // if this character is a letter and the previous one also was a letter,
        // add the multiplied value of the previous letter
        number += text[i - 1] * 5;
    }
    result.Append(number);
}

Console.WriteLine(result.ToString());

Prints: 59011501110245250255