I'm trying to write a little something that is not secure. The purpose is to encrypt server-side mp3s so they can't be just downloaded with wget or "save as" and used by the average Joe.
The idea is on the server side, load the mp3, aes-cfb encrypt it, send the key in the header, send the encrypted mp3 in the response body.
Server side is using Go's stdlib and AES-CFB encryption. As first with base64 encoding, then just plain output of the encrypted []byte-s.
Client side I'm using forge to decrypt. I send a xhr, read the arraybuffer, decrypt using forge and write output to the console.
The content of test.txt is "this is just a test and maybe it's working maybe not."
main.go
package main
import (
"net/http"
"io"
"crypto/rand"
"os"
"crypto/aes"
"crypto/cipher"
"fmt"
)
var (
key = "1234567890123456"
fn = "test.txt"
)
func main() {
http.Handle("/file/", http.HandlerFunc(serveFile))
http.Handle("/", http.FileServer(http.Dir("public")))
http.ListenAndServe(":8080", nil)
}
func serveFile(w http.ResponseWriter, r *http.Request) {
file, e := os.Open(fn)
if e != nil {
fmt.Println(e.Error())
return
}
defer file.Close()
fi, _ := file.Stat()
b := make([]byte, fi.Size())
io.ReadFull(file, b)
o := AESencrypt([]byte(key), b)
w.Header().Set("Access-Control-Allow-Origin", "*")
//w.Header().Set("Key", key)
fmt.Println(o)
fmt.Println(len(o))
w.Write(o)
}
func AESencrypt(key []byte, content []byte) []byte {
block, err := aes.NewCipher(key)
if err != nil {
panic(err)
}
ciphertext := make([]byte, aes.BlockSize + len(content))
iv := ciphertext[:aes.BlockSize]
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
panic(err)
}
stream := cipher.NewCFBEncrypter(block, iv)
stream.XORKeyStream(ciphertext[aes.BlockSize:], content)
return ciphertext
}
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>MP3 Player Demo</title>
</head>
<body>
<button onclick="loadFile('1')">Load</button>
<script src="node_modules/node-forge/js/forge.bundle.js"></script>
<script src="assets/reader.js"></script>
</body>
</html>
reader.js
function loadFile(filename) {
//var context = new AudioContext || new webkitAudioContext();
var request = new XMLHttpRequest();
var url = "http://localhost:8080/file/";
request.open("GET", url + filename, true);
request.responseType = "arraybuffer";
request.onload = function () {
var rt = request.response;
console.log(rt);
var decipher = forge.cipher.createDecipher('AES-CFB', forge.util.createBuffer('1234567890123456'));
decipher.start({iv: forge.util.createBuffer('1234567890123456')});
decipher.update(forge.util.createBuffer(rt));
decipher.finish();
console.log(decipher.output);
console.log(decipher.output.bytes());
console.log('--------------');
};
request.send();
}
The result is weird.
It is "properly" decrypted however there's a prefix or garbage of random length with each decrypted result.
3 outputs:
ArrayBuffer { byteLength: 69 } reader.js:10:9
Object { data: "3~æÿK¥=®ªÿÂßthis is just a test…", read: 0, _constructedStringLength: 69 } reader.js:16:9
3~æÿK¥=®ªÿÂßthis is just a test and maybe it's working maybe not. reader.js:17:9
-------------- reader.js:18:9
ArrayBuffer { byteLength: 69 } reader.js:10:9
Object { data: "ÅJÇ9Ë54«ÚV«this is just a test…", read: 0, _constructedStringLength: 69 } reader.js:16:9
ÅJÇ9Ë54«ÚV«this is just a test and maybe it's working maybe not. reader.js:17:9
-------------- reader.js:18:9
ArrayBuffer { byteLength: 69 } reader.js:10:9
Object { data: "ªÕxïÂ`zqA \cýx#this is just a test…", read: 0, _constructedStringLength: 69 } reader.js:16:9
ªÕxïÂ`zqA \cýx#this is just a test and maybe it's working maybe not. reader.js:17:9
-------------- reader.js:18:9
The output here is truncated but it's the same is the test.txt . As you can see it's always prefixed with random garbage.
What am I doing wrong? Is the forge implementation of AES-CFB wrong or Go's? Why are they incompatible? Or why is it that the decryption differs? And if AES-CFB is a standard why are there different implementations?
I also tried gopherjs as an alternative and that works just fine but a) the code size is too big (~3.7MB) and b) I wouldn't know how to play back the decrypted audio using gopherjs. But that's just as an aside.
