C# to PHP base64 encode/decode

byte[] encbuff = System.Text.Encoding.UTF8.GetBytes("the string");
String enc = Convert.ToBase64String(encbuff);

$data = $_REQUEST['in'];
$raw = base64_decode($data);

byte[] encbuff = System.Text.Encoding.UTF8.GetBytes("the string");
string enc = Convert.ToBase64String(encbuff);
string urlenc = Server.UrlEncode(enc);

$data = $_REQUEST['in'];
$decdata = urldecode($data);
$raw = base64_decode($decdata);

byte[] bytes = new byte[1000];
Console.WriteLine(Convert.ToBase64String(bytes));

this is a <B>long</b>string. and lets make this a3214 ad0-3214 0czcx 909340 zxci 0324#$@#$%%13244513123

dGhpcyBpcyBhIDxCPmxvbmc8L2I+c3RyaW5nLiBhbmQgbGV0cyBtYWtlIHRoaXMgYTMyMTQgYWQwLTMyMTQgMGN6Y3ggOTA5MzQwIHp4Y2kgMDMyNCMkQCMkJSUxMzI0NDUxMzEyMw==

private string HTTPPost(string URL, Dictionary<string, string> FormData)
{

    UTF8Encoding UTF8encoding = new UTF8Encoding();
    string postData = "";

    foreach (KeyValuePair<String, String> entry in FormData)
    {
            postData += entry.Key + "=" + entry.Value + "&";
    }

    postData = postData.Remove(postData.Length - 1);

    //urlencode replace (+) with (%2B) so it will not be changed to space ( )
    postData = postData.Replace("+", "%2B");

    byte[] data = UTF8encoding.GetBytes(postData);

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);

    request.Method = "POST";
    request.ContentType = "application/x-www-form-urlencoded";
    request.ContentLength = data.Length;

    Stream strm = request.GetRequestStream();
    // Send the data.
    strm.Write(data, 0, data.Length);
    strm.Close();

    WebResponse rsp = null;
    // Send the data to the webserver
    rsp = request.GetResponse();

    StreamReader rspStream = new StreamReader(rsp.GetResponseStream());
    string response = rspStream.ReadToEnd();

    return response;

}