Question

So I finally found something a little more understable in implementing a AES 128 encryption for a .Net Wcf Service with the same encryption. My problem with it now is that whenever it would try to decrypt the string it would have a step where it does a FromBase64String convert which will give me an error:

static public string DecryptString(string message, string key)
{
    string output = "";
    Rijndael aes = new RijndaelManaged();

    try
    {
        byte[] encrypted = Convert.FromBase64String(message);
        byte[] cipherText = GetCipherText(encrypted);

        aes.Key = Convert.FromBase64String(key);
        aes.Mode = CipherMode.CBC;

        aes.IV = GetIV(encrypted);

        using (MemoryStream ms = new MemoryStream())
        {
            using (ICryptoTransform decryptor = aes.CreateDecryptor())
            {
                using (CryptoStream cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Write))
                {
                    cs.Write(cipherText, 0, cipherText.Length);
                    cs.FlushFinalBlock();

                    byte[] decrypted = ms.ToArray();
                    output = Encoding.UTF8.GetString(decrypted);
                }
            }
        }
    }

The error is:

Index was outside the bounds of the array.

and it happens on the

cs.FlushFinalBlock();

This is the encryption that it produced for the message “heythere” and a key of “25f9e794323b453885f5181f1b624d0b”

0suql40BUGiDoFA4SdXJAA==

This is coming from my .Net encryption:

unNWQfm9RaU/HgKlDNEmoXZaTzsuBoTNsA2UvDKZhc4=

PS For the iPhone encryption of AES 128, this is where I got the codes from:

AES interoperability between .Net and iPhone?

Answer 1

Look at AES Keeping your documents secure article on MSDN and scroll down to the section entitled “Using the AES Class”, “Figure 15 Using AES” has a nice and simple example of encryption / decryption.

P.S. Be aware of padding that is used in certain block cypher (like AES) modes (like CBC), these can be a pain when different systems are talking to each other as padding / block sizes can vary from one system to another… see padding fun

EDIT: Just spotted this little gem… simple-2-way-encryption-for-c-sharp