C# - symetrische verschlüsselung via stream

/*
* die verschlüsselung läuft über einen stream transformer
* verschlüsselung: inputstream -plain-> cryptotransformer -encrypted-> outputstream
* entschlüsselung: inputstream -encrypted-> cryptotransformer -plain-> outputstream
* erzeugen des IV/Keys = Rijndael rj = Rijndael.Create();
*/
             public Stream SymetricDeEncryption(bool encrypt, Stream input, Stream output, byte[] key, byte[] iv)
        {
            int buffSize = 1024;
            Rijndael rj = Rijndael.Create();
            rj.IV = iv;
            rj.Key = key;
            ICryptoTransform streamTransformer = null;
            if (encrypt)
            {
                streamTransformer = rj.CreateEncryptor(key, iv);
            }
            else
            {
                streamTransformer = rj.CreateDecryptor(key, iv);
            }
            using (CryptoStream cs = new CryptoStream(input, streamTransformer, CryptoStreamMode.Read))
            {
                int bytesRead = 0;
                byte[] buff = new byte[buffSize];
                do
                {
                    bytesRead = cs.Read(buff, 0, buffSize);
                    output.Write(buff, 0, bytesRead);
                }
                while (bytesRead > 0);
            }
            return output;
        }