I've looked around stack to find an answer to my problem and yet nothing did work.
What im trying to achive is to encrypte XML file that is downloaded in ASYNCtask and later on decrypt it.
What I've already checked:
-Generated key is the same when encrypring and decrypting and saved in sharedpreferenced with Base64.
-IV is the same since at the moment its in static variable for testing purposes.
-Cipher is set to AES/CBC/PKCS5Padding
-Key is set to AES
The error appear in decryptXml() at line:
byte[] decrypted = cipher.doFinal(bytes);
Im all out of ideas and nothing seems to work. I hope some of u can find mistake in my code. Thanks for help!
CODE:
genetateKey()
SharedPreferences sharedPreferences = context.getSharedPreferences(GENERATED_KEY, Context.MODE_PRIVATE);
String keyStr = sharedPreferences.getString(GENERATED_KEY, null);
if (keyStr == null) {
final int outputKeyLength = 128;
SecureRandom secureRandom = new SecureRandom();
KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
keyGenerator.init(outputKeyLength, secureRandom);
SecretKey key = keyGenerator.generateKey();
byte[] bytes = key.getEncoded();
keyStr = Base64.encodeToString(bytes, Base64.DEFAULT);
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString(GENERATED_KEY, keyStr);
editor.commit();
return key.toString();
} else {
return keyStr;
}
XML encryption:
connection = (HttpURLConnection) url.openConnection();
connection.connect();
SecretKey secretKey = getSecretKey(context);
SecretKeySpec secretKeySpec = new SecretKeySpec(secretKey.getEncoded(), "AES");
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
spec = generateIv(cipher.getBlockSize());
cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, spec);
input = connection.getInputStream();
cis = new CipherInputStream(input, cipher);
String FILEPATH = context.getFilesDir().getParentFile().getPath();
File file = new File(FILEPATH, "/download/" + id + "/");
if (!file.exists()) {
file.mkdirs();
}
xmlFile = new File(FILEPATH + "/download/" + id + "/", "xmldata.xml");
output = new FileOutputStream(xmlFile);
cos = new CipherOutputStream(output, cipher);
byte data[] = new byte[4096];
int count;
while ((count = cis.read(data)) != -1) {
if (isCancelled()) throw new TaskCanceledException();
cos.write(data, 0, count);
progress = -1;
publishProgress();
}
if (isCancelled()) throw new TaskCanceledException();
Decryption:
public String decryptXml() {
String data = null;
File file = new File(context.getFilesDir().getParentFile().getPath() + "/download/" + id + "/xmldata.xml");
int size = (int) file.length();
byte[] bytes = new byte[size];
try {
SecretKeySpec secretKeySpec = new SecretKeySpec(getSecretKey(context).getEncoded(), "AES");
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, DownloadBookAsyncTask.spec);
BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
bis.read(bytes, 0, bytes.length);
bis.close();
byte[] decrypted = cipher.doFinal(bytes);
}
getSecretKey():
public SecretKey getSecretKey(Context context){
SharedPreferences sharedPreferences = context.getSharedPreferences(DashboardFragment.GENERATED_KEY, Context.MODE_PRIVATE);
String stringKey = sharedPreferences.getString(DashboardFragment.GENERATED_KEY, null);
byte[] encodedKey = Base64.decode(stringKey, Base64.DEFAULT);
return new SecretKeySpec(encodedKey, 0, encodedKey.length, "AES");
}
EDIT
Adding IV generator method
public AlgorithmParameterSpec generateIv(int size) throws NoSuchAlgorithmException {
AlgorithmParameterSpec ivspec;
byte[] iv = new byte[size];
new SecureRandom().nextBytes(iv);
ivspec = new IvParameterSpec(iv);
return ivspec;
}