Encrypt/decrypt byte array > 256 bytes using AES-128

Question

The following code encrypts a byte array SOURCE_DATA using AES-128 to another byte array ENCRYPTED_DATA, and then decrypts it again to DECRYPTED_DATA. With a byte array size of <= 256 bytes, the code works just fine, but if the byte array is longer, DECRYPTED_DATA only contains zeros after byte 256 and is not equal to the SOURCE_DATA array. What am I missing?

Output:

Source Data: ...fbfcfdfeff0001
Decrypted Data: ...fbfcfdfeff0000

Code:

// Create data array with size greater 256 bytes
byte[] SOURCE_DATA = new byte[257];     
for (int i=0;i<SOURCE_DATA.length; i++) {
    SOURCE_DATA[i] = (byte)((i+1) & 0xff);
}

// Init ciphers
Cipher encC = Cipher.getInstance("AES/ECB/PKCS5Padding");
Cipher decC = Cipher.getInstance("AES/ECB/PKCS5Padding");
encC.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(new byte[] {0,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6}, "AES"));                  
decC.init(Cipher.DECRYPT_MODE, new SecretKeySpec(new byte[] {0,1,2,3,4,5,6,7,8,9,1,2,3,4,5,6}, "AES"));          

// Encrypt
ByteArrayOutputStream bos = new ByteArrayOutputStream();
CipherOutputStream cos = new CipherOutputStream(bos, encC);
DataOutputStream dos = new DataOutputStream(cos);

dos.write(SOURCE_DATA, 0, SOURCE_DATA.length);
dos.close();

byte[] ENCRYPTED_DATA = bos.toByteArray();

// Decrypt
ByteArrayInputStream bis = new ByteArrayInputStream(ENCRYPTED_DATA);
CipherInputStream cis = new CipherInputStream(bis, decC);
DataInputStream dis = new DataInputStream(cis);

byte[] DECRYPTED_DATA = new byte[SOURCE_DATA.length];
dis.read(DECRYPTED_DATA, 0, DECRYPTED_DATA.length);
cis.close();

System.out.println("Source Data:    "+toHex(SOURCE_DATA));
System.out.println("Decrypted Data: "+toHex(DECRYPTED_DATA));

"What am I missing?" The block length of the cipher algorithm? — Hot Licks, Jul 03 '12 at 20:43
@CodeInChaos I just tried CBC with IV (according to [this post](http://stackoverflow.com/questions/1440030/how-to-implement-java-256-bit-aes-encryption-with-cbc) and the problem remains the same. — binwiederhier, Jul 03 '12 at 21:15
@kv3980 My questions weren't about your immediate problem, but about why you chose weak crypto. — CodesInChaos, Jul 03 '12 at 21:17
Your immediate problem is probably related to lack of flushing or partial reading. But I don't know enough about the java APIs you use to answer that. — CodesInChaos, Jul 03 '12 at 21:20
@kv3980: welcome to your first *question* on stackoverflow :) Please don't put the answers within the question, let the site do the work - you found the "accept" button nicely it seems. — Maarten Bodewes, Jul 03 '12 at 23:41

score 1 · Accepted Answer · answered Jul 03 '12 at 20:48

1

Try using DataInputStream.readFully (i.e. you are only reading part of the result, which is why you always call InputStream.read in a while loop).

answered Jul 03 '12 at 20:48

jtahlborn

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This was indeed the problem. The problem had nothing to do with the cipher-padding or mode of operation, but was simply related to the misuse of the `DataInputStream`. I updated the solution above. – binwiederhier Jul 03 '12 at 21:29
My "updated solution" was rolled back, so in short, this did the trick: `dis.readFully(DECRYPTED_DATA);` – binwiederhier Jul 11 '13 at 12:08

Encrypt/decrypt byte array > 256 bytes using AES-128

1 Answers1