I can't decrypt AES
My colleague encrypts data using AES-256 without a vector using the node module.js aes-js. Accordingly, the key is a 32-dimensional array, and the encrypted string is a string.
In Java Android, I'm trying to do something like
public static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
byte[] decrypted = cipher.doFinal(encrypted);
return decrypted;
}
But I always get an error -
javax.crypto.IllegalBlockSizeException: last block incomplete in decryption
But in the TextView I drive in this way
byte[] key = new byte[]{83, 63, (byte) 180, (byte) 178, (byte) 169, 38, 21, 10, 62, (byte) 160, (byte) 216, (byte) 191, 122, 13, 55, 68, (byte) 181, 4, (byte) 180, 20, 8, 117, (byte) 138, 36, 51, 26, 7, 90, 3, (byte) 184, 47, 17};
TextView t = findViewById(R.id.text);
try {
t.setText(Decrypt.decrypt(key, "cc1e55b3a5c6fbcc22c67bcafbb2e2704e25c9db8959f4a9d6570666d73fb15c49139b".getBytes()).toString());
} catch (GeneralSecurityException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
This is how a colleague encrypts and decrypts at home
let encrypt = function(text, key){
if(!key){
key = KEY;
}
let encryptionBlock = new aes.ModeOfOperation.ctr(key, new aes.Counter(100));
return aes.utils.hex.fromBytes(encryptionBlock.encrypt(aes.utils.utf8.toBytes(text)))
}
And decryption
let decrypt = function(text, key){
if(!key){
key = KEY;
}
let encryptionBlock = new aes.ModeOfOperation.ctr(key, new aes.Counter(100));
return aes.utils.utf8.fromBytes(encryptionBlock.decrypt(aes.utils.hex.toBytes(text)))
}
How do I decipher this text? I have already tried many ways. Thank you in advance
2 answers
At least 2 things you are doing wrong:
-
"...".getBytes(). Encrypted data is binary data, not a string. You should get the bytes from the hex string, not the bytes from the characters. - Even if you do the first one correctly, you have an encrypted message length of 35 bytes. In AES, it must be a multiple of the block size, i.e. 16 bytes. So Java throws an exception.
I do not know how your encrypted message was received, but it is definitely not received a standard AES application. So I can't tell you how to decipher it.
After updating the question.
In the case of CTR, you need to do this:
byte[] ciphertext = new byte[] { 113, (byte)202, 74, (byte)141, 19 };
byte[] key = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 };
byte[] counter = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 100 };
SecretKeySpec skeySpec = new SecretKeySpec(key, "AES");
Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");
IvParameterSpec ctrParameter = new IvParameterSpec(counter);
cipher.init(Cipher.DECRYPT_MODE, skeySpec, ctrParameter);
byte[] plain = cipher.doFinal(ciphertext);
System.out.println(new String(plain, StandardCharsets.UTF_8));
Outputs hello. Note the counter array. The last byte is 100, which corresponds to the counter specified in the nodejs code.
I can also add that using the same counter with the same key is a very large security hole, an attacker will be able to decrypt the message even without knowing the key.
Try this:
public static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
final byte[] bt = new byte[16];
Arrays.fill(bt, (byte)0);
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding");
cipher.init(Cipher.DECRYPT_MODE, skeySpec, bt);
return cipher.doFinal(encrypted);
}