Custom reCaptcha Validation

using System;
using System.Collections.Generic;
using System.Web;

using System.IO;
using System.Net;

/// <summary>
/// Summary description for reCaptchaValidation
/// </summary>
public class reCaptchaValidation
{
    private string challenge, response, privateKey, ip;
    private IWebProxy proxy;


    public reCaptchaValidation(string clientIP, string privateKey, string challenge, string response) : this(null, clientIP, privateKey, challenge, response) { }

	public reCaptchaValidation(IWebProxy proxy, string clientIP, string privateKey, string challenge, string response)
	{
        this.proxy = proxy;
        this.ip = clientIP;
        this.privateKey = privateKey;
        this.challenge = challenge;
        this.response = response;
	}

    private bool _errored;
    public bool IsErrored
    {
        get
        {
            return _errored;
        }
    }

    private Exception _ex;
    public Exception Exception
    {
        get
        {
            return _ex;
        }
    }

    private string _vr;
    public string ValidationResult
    {
        get
        {
            return _vr;
        }
    }

    public bool Validate()
    {
        try
        {
            string post = "privatekey=" + HttpUtility.UrlEncode(privateKey) + "&remoteip=" + HttpUtility.UrlEncode(ip) + "&challenge=" + HttpUtility.UrlEncode(challenge) + "&response=" + HttpUtility.UrlEncode(response);

            WebRequest wr = HttpWebRequest.Create("http://www.google.com/recaptcha/api/verify");
            wr.Method = "POST";

            if (proxy != null)
                wr.Proxy = proxy;

            wr.ContentLength = post.Length;
            wr.ContentType = "application/x-www-form-urlencoded";
            using (StreamWriter sw = new StreamWriter(wr.GetRequestStream()))
            {
                sw.Write(post);
                sw.Close();
            }

            HttpWebResponse resp = (HttpWebResponse)wr.GetResponse();
            using (StreamReader sr = new StreamReader(resp.GetResponseStream()))
            {
                string valid = sr.ReadLine();
                if (valid != null)
                {
                    if (valid.ToLower().Trim() == "false")
                    {
                        string errorcode = sr.ReadLine();

                        if (errorcode != null)
                        {
                            if (errorcode.ToLower().Trim() != "incorrect-captcha-sol")
                            {
                                _vr = errorcode;
                                _errored = true;
                                return false;
                            }
                        }
                    }

                    return (valid.ToLower().Trim() == "true");
                }
                else _vr = "empty web service response";

                sr.Close();
                return false;
            }
        }
        catch (Exception caught)
        {
            _errored = true;
            _ex = caught;
        }
        return false;
    }
}