BTC-E API class

/*
 * Base for making api class for btc-e.com
 * DmT
 * 2012
 */

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

namespace BtceTestApp
{
    class BtceApi
    {
        string key;
        HMACSHA512 hashMaker;

        public BtceApi(string key, string secret)
        {
            this.key = key;
            hashMaker = new HMACSHA512(Encoding.ASCII.GetBytes(secret));
        }

        public string GetInfo()
        {
            return Query(new Dictionary<string, string>()
            {
                { "method", "getInfo" }
            });
        }

        string Query(Dictionary<string, string> args)
        {
            args.Add("nonce", GetNonce().ToString());

            var dataStr = BuildPostData(args);
            var data = Encoding.ASCII.GetBytes(dataStr);

            var request = WebRequest.Create(new Uri("https://btc-e.com/tapi")) as HttpWebRequest;
            if (request == null)
                throw new Exception("Non HTTP WebRequest");

            request.Method = "POST";
            request.Timeout = 15000;
            request.ContentType = "application/x-www-form-urlencoded";
            request.ContentLength = data.Length;

            request.Headers.Add("Key", key);
            var sign = ByteArrayToString(hashMaker.ComputeHash(data)).ToLower();
            request.Headers.Add("Sign", sign);
            var reqStream = request.GetRequestStream();
            reqStream.Write(data, 0, data.Length);
            reqStream.Close();

            var response = request.GetResponse();
            var resStream = response.GetResponseStream();
            var resStreamReader = new StreamReader(resStream);
            var resString = resStreamReader.ReadToEnd();

            return resString;
        }

        static string ByteArrayToString(byte[] ba)
        {
            string hex = BitConverter.ToString(ba);
            return hex.Replace("-", "");
        }

        static string BuildPostData(Dictionary<string, string> d)
        {
            string s = "";
            for (int i = 0; i < d.Count; i++)
            {
                var item = d.ElementAt(i);
                var key = item.Key;
                var val = item.Value;

                s += String.Format("{0}={1}", key, val);

                if (i != d.Count - 1)
                    s += "&";
            }
            return s;
        }

        static DateTime unixEpoch = new DateTime(1970, 1, 1);
        int GetNonce()
        {
            var now = DateTime.UtcNow;
            var dif = now - unixEpoch;
            return (int)dif.TotalSeconds;
        }
    }
}