Publish to AWS SNS Topic via C#, works with WP7

PublishAmazonSNSMsg.cs

using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Text;
using System.Net;
using System.Linq;

public class PublishAmazonSnsMsg
{

    public static Uri getRequestUrl(string amzsnshost, string TopicArn, string Message, string AWSAccessKeyId, string privatekey)
    {

        string url;

        string string_to_sign;

        string cannqs;

        List<string> qs = new List<string>();

        List<string> tojoin = new List<string>();

        Dictionary<string, string> parameters = new Dictionary<string, string>();

        HMACSHA256 hmacsha256;

        byte[] keyByte;

        byte[] messageBytes;

        parameters.Add("TopicArn", TopicArn);

        parameters.Add("Message", Message);

        parameters.Add("Timestamp", DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ssZ"));

        parameters.Add("AWSAccessKeyId", AWSAccessKeyId);

        parameters.Add("Action", "Publish");

        parameters.Add("SignatureVersion", "2");

        parameters.Add("SignatureMethod", "HmacSHA256");

        var klist = parameters.Keys.ToList();

        klist.Sort(StringComparer.Ordinal);

        foreach (var key in klist)
        {

            qs.Add(HttpUtility.UrlEncode(key) + "=" + UrlEncode(parameters[key]));

        }

        cannqs = string.Join("&", qs);

        tojoin.Add("GET");

        tojoin.Add(amzsnshost);

        tojoin.Add("/");

        tojoin.Add(cannqs);

        string_to_sign = string.Join("\n", tojoin.ToArray());

        System.Text.UTF8Encoding encoding = new System.Text.UTF8Encoding();

        keyByte = encoding.GetBytes(privatekey);
        
        hmacsha256 = new HMACSHA256(keyByte);

        messageBytes = encoding.GetBytes(string_to_sign);

        var sig = System.Convert.ToBase64String(hmacsha256.ComputeHash(messageBytes));

        //System.Diagnostics.Debug.WriteLine(sig);

        url = "http://" + amzsnshost + "/?" + cannqs + "&Signature=" + UrlEncode(sig);

        //System.Diagnostics.Debug.WriteLine(url);

        return new Uri(url);

    }

    protected static string UrlEncode(string value)
    {
        StringBuilder result = new StringBuilder();

        foreach (char symbol in value)
        {
            if (unreservedChars.IndexOf(symbol) != -1)
            {
                result.Append(symbol);
            }
            else if (reservedChars.IndexOf(symbol) > -1)
            {
                result.Append('%' + String.Format("{0:X2}", (int)symbol));
            }
            else
            {
                result.Append(Uri.EscapeUriString(symbol + "").ToUpper());
            }
        }

        return result.ToString();
    }

    protected static string unreservedChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.-_~";
    
    protected static string reservedChars = "=+:/";


}