Encrypt/Decrypt database file in Android with FileInputStream/Cipher

Question

I'm using Cipher/CipherInputStream to encrypt and decrypt a database file(sqlite) in Android to backup it.
When I use the FileInputStream without Cipher, it works very well. But when I use the Cipher, the file encrypt successfuly, but when I decrypt(restore) it, the database doesn't decrypt to the original "source code".
The original caracteres(source code) seems to be an ideogram/hieroglyphs/kanjis(I don't know), and when I encrypt and decrypt, the "source code" is sql(english) restored O.O
That makes the 'database corrupted'

Only to clarify

Backup

File dbFile = new File(PATH_DB);

FileInputStream fileInputStream = new FileInputStream(PATH_DB);

FileOutputStream outputStream = new FileOutputStream(PATH_BKP);

byte[] s = Arrays.copyOf(KEY_DATABASE.getBytes(),16);
SecretKeySpec sks = new SecretKeySpec(s, "AES");

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
cipher.init(Cipher.ENCRYPT_MODE, sks);

CipherOutputStream cos = new CipherOutputStream(outputStream, cipher);

//Transferencia dos dados do inputfile para o output
byte[] buffer = new byte[1024];
int length;
while ((length = fileInputStream.read(buffer))!= -1) {
    cos.write(buffer,0,length);
}

//Fecha as streams
cos.flush();
cos.close();
fileInputStream.close();

Restore:

FileInputStream fis = new FileInputStream(PATH_BKP);

FileOutputStream fos = new FileOutputStream(PATH_DB);

byte[] s = Arrays.copyOf(KEY_DATABASE.getBytes(),16);
SecretKeySpec sks = new SecretKeySpec(s, "AES");

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
cipher.init(Cipher.DECRYPT_MODE, sks);

CipherInputStream cis = new CipherInputStream (fis, cipher);

byte[] buffer = new byte[1024];
int length;
while ((length = cis.read(buffer)) != -1) {
    fos.write(buffer, 0, length);
}

fos.flush();
fos.close();
cis.close();

Artjom B. · Accepted Answer · 2016-09-25 07:57:45Z

CBC mode needs an initialization vector (IV) to operate. This IV is not a secret value, but it has to be unpredictable (read: randomly chosen). In order for the decryption to work, you must use the same IV. Otherwise, the first block will be corrupted. A common way to solve this is to write the IV in front of the ciphertext.

If you call Cipher#init without an IvParameterSpec as the third argument, the IV will be automatically generated for you. If you don't store it, it will be lost.

During encryption

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
cipher.init(Cipher.ENCRYPT_MODE, sks);

outputStream.write(cipher.getIV()); // store the generated IV

CipherOutputStream cos = new CipherOutputStream(outputStream, cipher);

During decryption

byte[] iv = new byte[16]; // 16 is the block size of AES
if (fis.read(iv) != 16) {
    throw new Exception("Incomplete IV"); // TODO: rename to a different exception
}

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
cipher.init(Cipher.DECRYPT_MODE, sks, new IvParameterSpec(iv));

CipherInputStream cis = new CipherInputStream (fis, cipher);

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