Code:
$(function(){
var body = $('body'),
stage = $('#stage'),
back = $('a.back');
/* Step 1 */
$('#step1 .encrypt').click(function(){
body.attr('class', 'encrypt');
// Go to step 2
step(2);
});
$('#step1 .decrypt').click(function(){
body.attr('class', 'decrypt');
step(2);
});
/* Step 2 */
$('#step2 .button').click(function(){
// Trigger the file browser dialog
$(this).parent().find('input').click();
});
// Set up events for the file inputs
var file = null;
$('#step2').on('change', '#encrypt-input', function(e){
// Has a file been selected?
if(e.target.files.length!=1){
alert('Please select a file to encrypt!');
return false;
}
file = e.target.files[0];
if(file.size > 5120*5120){
alert('Please choose files smaller than 5mb, otherwise you may crash your browser. \nThis is a known issue. .');
return;
}
step(3);
});
$('#step2').on('change', '#decrypt-input', function(e){
if(e.target.files.length!=1){
alert('Please select a file to decrypt!');
return false;
}
file = e.target.files[0];
step(3);
});
/* Step 3 */
$('a.button.process').click(function(){
var input = $(this).parent().find('input[type=password]'),
a = $('#step4 a.download'),
password = input.val();
input.val('');
if(password.length<5){
alert('Please choose a longer password!');
return;
}
// The HTML5 FileReader object will allow us to read the
// contents of the selected file.
var reader = new FileReader();
if(body.hasClass('encrypt')){
// Encrypt the file!
reader.onload = function(e){
// Use the CryptoJS library and the AES cypher to encrypt the
// contents of the file, held in e.target.result, with the password
var encrypted = CryptoJS.AES.encrypt(e.target.result, password);
// The download attribute will cause the contents of the href
// attribute to be downloaded when clicked. The download attribute
// also holds the name of the file that is offered for download.
a.attr('href', 'data:application/octet-stream,' + encrypted);
a.attr('download', file.name + '.encrypted');
step(4);
};
// This will encode the contents of the file into a data-uri.
// It will trigger the onload handler above, with the result
reader.readAsDataURL(file);
}
else {
// Decrypt it!
reader.onload = function(e){
var decrypted = CryptoJS.AES.decrypt(e.target.result, password)
.toString(CryptoJS.enc.Latin1);
if(!/^data:/.test(decrypted)){
alert("Invalid pass phrase or file! Please try again.");
return false;
}
a.attr('href', decrypted);
a.attr('download', file.name.replace('.encrypted',''));
step(4);
};
reader.readAsText(file);
}
});
/* The back button */
back.click(function(){
// Reinitialize the hidden file inputs,
// so that they don't hold the selection
// from last time
$('#step2 input[type=file]').replaceWith(function(){
return $(this).clone();
});
step(1);
});
// Helper function that moves the viewport to the correct step div
function step(i){
if(i == 1){
back.fadeOut();
}
else{
back.fadeIn();
}
// Move the #stage div. Changing the top property will trigger
// a css transition on the element. i-1 because we want the
// steps to start from 1:
stage.css('top',(-(i-1)*100)+'%');
}
});
People here dont usually provide the benefit of the doubt. 
