C# AES-256 Encryption

Question

I am using RijndaelManaged to make a simple encryption/decryption utility. This is working fine, but I am trying to get it integrated with another program which is created in Unix (Oracle). My problem is, for all smaller input string, i am getting the exact same encrypted hex as the Unix code is generation, but for longer strings, half of my encrypted hex is same, but the other half is different:

Unix Output:

012345678901234 - 00984BBED076541E051A239C02D97117 
0123456789012345678 - A0ACE158AD8CF70CEAE8F76AA27F62A30EA409ECE2F7FF84F1A9AF50817FC0C4

Windows Output (my code):

012345678901234 - 00984BBED076541E051A239C02D97117 (same as above)
0123456789012345678 - A0ACE158AD8CF70CEAE8F76AA27F62A3D9A1B396A614DA2C1281AA1F48BC3EBB (half exactly same as above)

My Windows code is:

public string Encrypt(byte[] PlainTextBytes, byte[] KeyBytes, string InitialVector)
        {
            byte[] InitialVectorBytes = Encoding.ASCII.GetBytes(InitialVector);
            RijndaelManaged SymmetricKey = new RijndaelManaged();
            SymmetricKey.Mode = CipherMode.ECB;
            SymmetricKey.Padding = PaddingMode.PKCS7;
            ICryptoTransform Encryptor = SymmetricKey.CreateEncryptor(KeyBytes, InitialVectorBytes);
            MemoryStream MemStream = new MemoryStream();
            CryptoStream CryptoStream = new CryptoStream(MemStream, Encryptor, CryptoStreamMode.Write);
            CryptoStream.Write(PlainTextBytes, 0, PlainTextBytes.Length);
            CryptoStream.FlushFinalBlock();
            byte[] CipherTextBytes = MemStream.ToArray();
            MemStream.Close();
            CryptoStream.Close();
            return ByteToHexConversion(CipherTextBytes);
        }

Unix (PL/SQL) code:

FUNCTION Encrypt_Card (plain_card_id  VARCHAR2)
    RETURN RAW AS
     num_key_bytes      NUMBER := 256/8;        -- key length 256 bits (32 bytes)
     encrypted_raw      RAW (2000);             -- stores encrypted binary text
     encryption_type    PLS_INTEGER :=          -- total encryption type
            DBMS_CRYPTO.ENCRYPT_AES256
          + DBMS_CRYPTO.CHAIN_CBC
          + DBMS_CRYPTO.PAD_PKCS5;

     key_bytes_raw  RAW(64) :=my_hex_key;
    BEGIN



     encrypted_raw := DBMS_CRYPTO.ENCRYPT
           (
              src => UTL_I18N.STRING_TO_RAW (plain_card_id, 'AL32UTF8'),
              typ => encryption_type,
              key => key_bytes_raw
           );


      RETURN encrypted_raw;
    EXCEPTION
    WHEN OTHERS THEN
    dbms_output.put_line (plain_card_id || ' - ' || SUBSTR(SQLERRM,1,100) );
    RETURN HEXTORAW ('EEEEEE');

The only difference i see is use of PKCS5 and PCKS7. But, .NET doesn't have PCKS5.

Answer 1

You use ECB in one case and CBC in the other case.

Answer 2

What abc said and also you don't seem to have any IV (Initialization Vector) in you Unix code at all.

The fact that the first part are the same has to do with the different modes (ECB and CBC). ECB encrypts each block separately while CBC uses the previous block when encrypting the next one.

What happens here is that since you use CBC and do not set an IV the IV is all zeroes.
That means that the first block of ECB encryption and CBC encryption will be the same.
(Since A XOR 0 = A).

You need to make sure you use the same encryption mode in both systems and if you decide on CBC make sure you use the same IV.