Code Challenge for Nerdery .Net Newsletter #2

CodeChallenge_20150512.cs

using System;
using Newtonsoft.Json;
using System.Linq;
using System.Text;
using System.Web;
using System.Security.Cryptography;

public class Program
{
	static string INPUT = @"{
""author_name"": ""Robert Jordan"",
""book_title"": ""Knife of Dreams"",
""series"": ""The Wheel of Time, Book 11"",
""publisher"": ""Tor Fantasy"",
""published_date"": ""November 28, 2006""
}";
	public static void Main()
	{
		Console.Out.WriteLine(GenerateQuerystring(INPUT));
	}

	public static string GenerateQuerystring(string input)
	{
		var book = JsonConvert.DeserializeObject<Book>(input);
		var result = new StringBuilder();
		foreach (var property in typeof (Book).GetProperties().OrderBy(x => x.Name))
		{
			result.Append(property.Name);
			result.Append("=");
			result.Append(HttpUtility.UrlEncode(property.GetValue(book).ToString()));
			result.Append("&");
		}

		result.Append("timestamp=");
		result.Append(GetUnixTimestamp());
		result.Append("&signature=");
		result.Append(HttpUtility.UrlEncode(Hash(result.ToString() + "1234MySuperSecretKey4321")));
		return result.ToString();
	}

	public static string Hash(string input)
	{
		var temp = Encoding.UTF8.GetBytes(input);
		using (SHA1Managed sha1 = new SHA1Managed())
		{
			var hash = sha1.ComputeHash(temp);
			return Convert.ToBase64String(hash);
		}
	}

	public static long GetUnixTimestamp()
	{
		var timeSpan = (DateTime.UtcNow - new DateTime(1970, 1, 1));
		return (long)timeSpan.TotalSeconds;
	}

	public class Book
	{
		public string author_name { get; set; }

		public string book_title { get; set; }

		public string series { get; set; }

		public string publisher { get; set; }

		//This should be a DateTime (but and we're not doing any Date maths)
		//but would require adding a ton of complexity to the reflection logic above.
		public string published_date { get; set; }
	}
}

Just a thought, but wouldn't you want to create the signature hash before appending the '&signature=' param, to not include the param in the hash too?

...
    result.Append("timestamp=");
    result.Append(GetUnixTimestamp());
    var signature = HttpUtility.UrlEncode(Hash(result.ToString() + "1234MySuperSecretKey4321"));
    result.Append("&signature=");
    result.Append(signature);
    return result.ToString(); // generates: CX5NjWdEJI7oF%2bkj8xBNCfkgs%2b0%3d

Instead of

...
    result.Append("timestamp=");
    result.Append(GetUnixTimestamp());
    result.Append("&signature=");
    result.Append(HttpUtility.UrlEncode(Hash(result.ToString() + "1234MySuperSecretKey4321")));
    return result.ToString(); //generates: RiDSg2bTWGUi4WISKjDUAo2mK7Q%3d