How should I implement client side encryption in a

Question

I am trying to implement client side encryption in the jQuery File Upload Plugin. I have tried to follow some information I found along the lines of...

• iterate over the files array,
• replace each item with a Blob representing the encrypted file
• after the encryption is done, invoke the callback

But am struggling I currently have...

   var encryptFiles = function (files, callback) {
        var reader = new FileReader();
        var file = files[0];
        var blob = file.slice(0, file.size);
        reader.readAsBinaryString(blob);
        reader.onload = fileonload;

        function fileonload(event) {
            var result = event.target.result;
            var encrypted = CryptoJS.AES.encrypt(result, "key");
            file.
            callback();
        }

        // iterate over the files array, 
        // replace each item with a Blob representing the encrypted file
        // after the encryption is done, invoke the callback
    }

    $('#fileupload').fileupload({
        add: function (e, data) {
            encryptFiles(data.files, function () {                
                data.submit();
            });
        }
    });

This code successfully reads the file to a blob, then encrypts it but I am unsure how to go about replacing the item with the Blob. Can anyone give me some help.