I’m a newbie to android dev, right now I implemented an AES on Android and it could encrypt strings with user input passwords. The encryption seems fine and it could omit Base64/Hex encoded strings.
But When I try to decrypt it, the problem comes: With the decryption, the omission always showing me a load of messy characters.
In order to get rid of it, I’ve tried debugging it by define a charset (Like UTF-8) while casting from string to byte[], but no hit, and also tried to encode the omit with base 64 or Hex, but both of them failed.
I’ve also tried to define AES/CBC/PKCS5Padding or just AES while using cipher.getInstance method, but still no go.
It is quite irritating, could you guys help me please?
Forgot to mention that I once asked a similar question https://stackoverflow.com/questions/6727255/aes-decryption-on-android-not-correct , the grammer problem there have been corrected.
And Here’s the code:
For Encryption
public String AESEncrypt(String sKey, String PlainMsg)
throws Exception {
//Try use some Android based alert dialog to catch this exception.
if (sKey == null) {
Log.e("SecureChat", "IllegalArgumentException Catched");
throw new IllegalArgumentException ("NULL Secret NOT ALLOWED!");
}
/*Old Method
//byte[] rawKey = getRawKey(sKey.getBytes("UTF-8"));
byte[] rawKey = getRawKey(sKey.getBytes());
//Encrypt start
SecretKeySpec keySpec = new SecretKeySpec(rawKey, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.ENCRYPT_MODE, keySpec);
//byte[] cipherText = cipher.doFinal(PlainMsg.getBytes("UTF-8"));
byte[] cipherText = cipher.doFinal(PlainMsg.getBytes());
return Base64Encoded(cipherText);
*/
//New Method
byte[] salt = getSalt();
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBEWITHSHA256AND256BITAES-CBC-BC");
KeySpec spec = new PBEKeySpec(sKey.toCharArray(), salt, 1024, 256);
SecretKey tmp = factory.generateSecret(spec);
SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
//Encryption Process
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, secret);
byte[] cipherText = cipher.doFinal(PlainMsg.getBytes());
//return Base64Encoded(cipherText);
//Hex
return toHex(cipherText);
}
For Decryption
public String AESDecrypt(String sKey, String EncryptMsg)
throws Exception {
/*Old Method
//byte[] rawKey = getRawKey(sKey.getBytes("UTF-8"));
byte[] rawKey = getRawKey(sKey.getBytes());
SecretKeySpec keySpec = new SecretKeySpec(rawKey, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, keySpec);
//byte[] plainText = Base64Decoded(EncryptMsg.getBytes("UTF-8"));
byte[] plainText = Base64Decoded(EncryptMsg);
cipher.doFinal(plainText);
return new String(plainText, "UTF-8");
*/
//New Method
byte[] salt = getSalt();
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBEWITHSHA256AND256BITAES-CBC-BC");
KeySpec spec = new PBEKeySpec(sKey.toCharArray(), salt, 1024, 256);
SecretKey tmp = factory.generateSecret(spec);
SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
//byte[] bCipherText = Base64Decoded(EncryptMsg);
//Hex
byte[] bCipherText = toByte(EncryptMsg);
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, secret);
cipher.doFinal(bCipherText);
return new String(bCipherText);
}
private byte[] getSalt() throws NoSuchAlgorithmException {
/*Mark for old key method
//Initialize the KeyGenerator
KeyGenerator kgen = KeyGenerator.getInstance("AES");
SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
sr.setSeed(seed);
//Init for 256bit AES key
kgen.init(Constants.AES_KEY_SIZE, sr);;
SecretKey secret = kgen.generateKey();
//Get secret raw key
byte[] rawKey = secret.getEncoded();
return rawKey;
*/
//New key method with some salt
SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
byte[] ransalt = new byte[20];
random.nextBytes(ransalt);
return ransalt;
}
@Override
public byte[] getRawKey(byte[] seed) throws Exception {
/*Old Method
//Initialize the KeyGenerator
KeyGenerator kgen = KeyGenerator.getInstance("AES");
SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
sr.setSeed(seed);
//Init for 256bit AES key
kgen.init(Constants.AES_KEY_SIZE, sr);
SecretKey secret = kgen.generateKey();
//Get secret raw key
byte[] rawKey = secret.getEncoded();
return rawKey;
*/
return null;
}
/**
*
* @param toBeDecoded
* @return
*/
public byte[] Base64Decoded(String toBeDecoded) {
byte[] decoded = Base64.decode(toBeDecoded, 0);
return decoded;
}
//Hex Mode
public String toHex(String txt) {
return toHex(txt.getBytes());
}
public String fromHex(String hex) {
return new String(toByte(hex));
}
public byte[] toByte(String hexString) {
int len = hexString.length()/2;
byte[] result = new byte[len];
for (int i = 0; i < len; i++)
result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
return result;
}
public String toHex(byte[] buf) {
if (buf == null)
return "";
StringBuffer result = new StringBuffer(2*buf.length);
for (int i = 0; i < buf.length; i++) {
appendHex(result, buf[i]);
}
return result.toString();
}
private final String HEX = "0123456789ABCDEF";
private void appendHex(StringBuffer sb, byte b) {
sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
}
}
I’ve referenced/compared with these code on Stackoverflow:
Android aes encryption pad block corrupted
and
incorrect decryption using AES/CBC/PKCS5Padding in Android
Seems that my problem lies on the charset encoding, but I cannot find out where the problem is.
Any comments/answers are very appreciated!
Thank you for helping me!
This code I wrote works flawlessly. Look at this link below:
http://pocket-for-android.1047292.n5.nabble.com/Encryption-method-and-reading-the-Dropbox-backup-td4344194.html#a4454327
Without looking too carefully at your code I would suggest you should specify the encoding here though I’m not sure if this is the cause of your problems:
and here: