I've been trying to decrypt an ArrayBuffer object using CryptoJS, but so far it always returns a blank WordArray. The files (images) are encrypted in an iOS and Android app, sent to a server, and downloaded in this web app to be decrypted and displayed. The iOS and Android apps are able to decrypt the files without problems, so there's nothing wrong with the encryption process.
The files are downloaded with an XMLHttpRequest
with responseType
set to arraybuffer
. Here's my code so far:
// Decrypt a Base64 encrypted string (this works perfectly)
String.prototype.aesDecrypt = function(key) {
var nkey = CryptoJS.enc.Hex.parse(key.sha256());
return CryptoJS.AES.decrypt(this.toString(), nkey, {
iv: CryptoJS.enc.Hex.parse('00000000000000000000000000000000'),
mode: CryptoJS.mode.CBC,
padding: CryptoJS.pad.Pkcs7
}).toString(CryptoJS.enc.Utf8);
}
// Decrypt a plain encrypted ArrayBuffer (this is the problem, it always outputs an empty WordArray)
ArrayBuffer.prototype.aesDecrypt = function(key) {
// Get key
if (!key) return null;
var nkey = CryptoJS.enc.Hex.parse(key.sha256());
// Get input (if I pass the ArrayBuffer directly to the create function, it returns
// a WordList with sigBytes set to NaN)
//var input = CryptoJS.lib.WordArray.create(this);
var input = CryptoJS.lib.WordArray.create(new Uint8Array(this));
// Decrypt
var output = CryptoJS.AES.decrypt(input, nkey, {
iv: CryptoJS.enc.Hex.parse('00000000000000000000000000000000'),
mode: CryptoJS.mode.CBC,
padding: CryptoJS.pad.Pkcs7
});
// Output is an empty WordList
console.log("Output: ", output);
}
Another question I have is how do you convert a WordArray
to an ArrayBuffer
?
The conversion of ArrayBuffer -> WordArray
has been discussed in CryptoJS's issue 46. For that reason a TypedWordArray
where you can also pass an ArrayBuffer
has been added.
To use that additionally include the following script:
<script src="http://crypto-js.googlecode.com/svn/tags/3.1/build/components/lib-typedarrays.js"></script>
Then you can simply do:
var wordArray = CryptoJS.lib.WordArray.create(arrayBuffer);
/* perform decryption of `wordArray` */
To reconvert the resulting decryptedWordArray
to an ArrayBuffer
, the simplest approach would probably be, to first convert it to a Base64-String
(as discussed here) and then decode that String to the desired ArrayBuffer
(see here). The whole procedure would look something like this:
dcWordArray = ... // your decrypted WordArray
dcBase64String = dcWordArray.toString(CryptoJS.enc.Base64); // to Base64-String
dcArrayBuffer = base64DecToArr(dcBase64String).buffer; // to ArrayBuffer
Edit:
For a more efficient conversion (no intermediate Base64String
necessary) check out Aletheios answer to that question (the function wordToByteArray(wordArray)
and then do .buffer
).