AES managed encryption values always end in ==?

Question

I've written an encryption routine built from several methods on the net. I'm currently testing the encryption and have noticed that every encrypted value end in '==' ?

Does anyone know why this might be the case ?

This is the code I'm using. The key is a 32 char value and the IV is a 16 char value.

private static readonly byte[] key = Encoding.Default.GetBytes(getKey());
    private static readonly byte[] iv = Encoding.Default.GetBytes("$ruVe4E!eM#kupuc");

    /// <summary>
    /// 
    /// </summary>
    /// <param name="val"></param>
    /// <returns></returns>
    public static string Encrypt(string val)
    {
        string result = string.Empty;

        var aes = getEncryptionType();

        using (MemoryStream msEncrypt = new MemoryStream())
        {
            using (ICryptoTransform encryptor = aes.CreateEncryptor(key, iv))
            {
                using(CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                {
                    using(StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                    {
                        swEncrypt.Write(val);
                    }
                }
            }
            result = Convert.ToBase64String(msEncrypt.ToArray());
        }
        aes.Clear();
        return result;
    }

getEncryptionType returns an AESManaged class as below:

private static AesManaged getEncryptionType()
    {
        AesManaged aes = new AesManaged();
        aes.Mode = CipherMode.CBC;
        aes.Padding = PaddingMode.PKCS7;
        return aes;
    }

Currently the test method looks like this:

Random rnd = new Random();

                for (int i = 0; i < 50000; i++)
                {
                    int random = rnd.Next(1147483647, int.MaxValue);
                    Guid guid = dal.getToken(CryptoService.Encrypt(random.ToString()));

                    if (i % 100 == 0)
                        addLog(string.Format("{0} new values added", i.ToString()), LogType.Dialog);
                }

Answer 1

That is standard for base 64 encoding. Read the "padding" section of the Wikipedia article for details.

http://en.wikipedia.org/wiki/Base64