C#: Base64 encoding
<p>Can anyone please let me know where I made a mistake in this code? This code is written in C#.NET. I need to write an algorithm for encoding a string using base64 format using C#.NET, and then decoded with base64_decode() using PHP. Please see the snippit below:</p>

<pre><code>System.Security.Cryptography.RijndaelManaged rijndaelCipher = new System.Security.Cryptography.RijndaelManaged();
rijndaelCipher.Mode = System.Security.Cryptography.CipherMode.CBC;
rijndaelCipher.Padding = System.Security.Cryptography.PaddingMode.Zeros;
rijndaelCipher.KeySize = 256;
rijndaelCipher.BlockSize = 128;

byte[] pwdBytes = System.Text.Encoding.UTF8.GetBytes(_key);
byte[] keyBytes = new byte[16];

int len = pwdBytes.Length;
if (len &gt; keyBytes.Length) len = keyBytes.Length;

System.Array.Copy(pwdBytes, keyBytes, len);

rijndaelCipher.Key = keyBytes;
rijndaelCipher.IV = keyBytes;

System.Security.Cryptography.ICryptoTransform transform = rijndaelCipher.CreateEncryptor();

byte[] plainText = Encoding.UTF8.GetBytes(unencryptedString);
byte[] cipherBytes = transform.TransformFinalBlock(plainText, 0, plainText.Length);

return Convert.ToBase64String(cipherBytes);
</code></pre>
