Javascript - Make a Text Encryption Program

This is a simple HTML application scripted in JavaScript which can encrypt and decrypt the text entered into a text box using the given password. The encryption algorithm is really simple and the output is in only uppercase alphabet letters and numbers. The drawback of the program is that it will double the length of the string when encrypting. Don't use this encryption program as the only source of security for important data.

To make the encryption program save the following code with .hta extension using notepad.

<style>

textarea {
  width: 500;
  height: 200;
  background-color: E0E0E0;
  color: #0000FF;
}

input {
  font-family: Courier New;
}

.button {
  width: 500;
  height: 40;
}

b {
  font-size: 15pt;
  color: #303030;
}

body {
  background-color: #808080;
  font-family: Courier New;
}

table {
  border-color: #A0A0A0;
  background-color: #C0C0C0;
}

</style>

<script>

function resize() {
  var width = 560;
  var height = 520;
  window.resizeTo(width, height);
}

function validate(ID) {
  pswd = document.getElementById("pass").value;
  if (parseInt(pswd) != pswd) {
    alert("Please enter a numeric password!");
  } else {
    pswd = parseInt(pswd) % 255;
  if (ID == 1) {
    encode(pswd);
  } else {
    decode(pswd);
  }
  }
}

function encode(pswd) {
  var text = document.getElementById("box").value;
  var alph = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
  document.getElementById("box").value = "";
  for (var i = 0; i < text.length; i++) {
    var cnum = (text.charCodeAt(i) + pswd) % 255;
    var num = cnum % 26;
    var count = 0;
    var tst = num;
    while (tst != cnum) {
      tst += 26;
      count += 1;
    }
    document.getElementById("box").value += alph[num] + count;
  }
  alert("Text successfully encrypted! Please don't forget your password!");
}

function decode(pswd) {
  var text = document.getElementById("box").value;
  document.getElementById("box").value = "";
  for (var i = 0; i < text.length; i += 2) {
    var num = text.charCodeAt(i) - 65;
    var chk = text.charAt(i + 1);
    var count = 0;
    while (count != chk) {
      num += 26;
      count += 1;
    }
    num = num - pswd;
    while (num <= 0) {
      num += 255;
    }
    document.getElementById("box").value += String.fromCharCode(num);
  }
  alert("Code decrypted successfully!");
}

function help() {
  document.getElementById("box").value = "";
  document.getElementById("box").value += "XBCrypt - Free Online Cryption Service\n";
  document.getElementById("box").value += "--------------------------------------\n\n";
  document.getElementById("box").value += "Encrypting text:\n";
  document.getElementById("box").value += "----------------\n\n";
  document.getElementById("box").value += "* Type in the text or copy-paste it into the text box.\n";
  document.getElementById("box").value += "* Type in a numeric password into the password field.\n";
  document.getElementById("box").value += "* Press Encrypt button.\n";
  document.getElementById("box").value += "* Wait until the text is encrypted.\n";
  document.getElementById("box").value += "* If the text is long it would take sometime.\n\n";
  document.getElementById("box").value += "WARNING: DO NOT FORGET THE PASSWORD YOU USED FOR ENCRYPTION!\n\n";
  document.getElementById("box").value += "Decrypting the code:\n";
  document.getElementById("box").value += "--------------------\n\n";
  document.getElementById("box").value += "* Cope-paste the code into the text box.\n";
  document.getElementById("box").value += "* Enter the password used to create the code.\n";
  document.getElementById("box").value += "* Press Decrypt button.\n";
  document.getElementById("box").value += "* Wait until the code is deciphered.\n";
  document.getElementById("box").value += "* It may take sometime if the code is long.\n\n";
  document.getElementById("box").value += "WARNING: IF YOU USE AN INCORRECT PASSWORD THE CODE WON'T BE DECODED CORRECTLY!\n\n";
}

</script>

<html>
  <head>
    <title>XBCrypt - Free Online Text Cryption</title>
    <HTA:APPLICATION
      APPLICATIONNAME="TextCrypt"
      ID="TextCrypt"
      VERSION="1.0"
      MAXIMIZEBUTTON="no"
      ICON="favicon.ico"
      SCROLL="no" />
  </head>
  <body onload="resize()">
    <table cellpadding="2" align="center" border="7">
      <caption><hr><b>XBCrypt - Text Cryption</b><hr></caption>
      <tr>
        <td align="center">Password: <input type="text" id="pass"></td>
      </tr>
      <tr>
        <td align="center"><textarea id="box"></textarea></td>
      </tr>
      <tr>
        <td><input type="button" id="BTNE" class="button" value="Encode" onclick="validate(1)"></td>
      </tr>
      <tr>
        <td><input type="button" id="BTND" class="button" value="Decode" onclick="validate(2)"></td>
      </tr>
      <tr>
        <td align="center">XBCrypt | By #XByte | Copyright © 2013 | <span style="cursor:pointer;color:#0000FF" onclick="help()">help</span></td>
      </tr>
    </table>
</body>
</html>

We have also released a VBScript version of this program. You may want to check it out here. If you liked this program please remember to leave a like and your feedback.