How to encrypt and decrypt Query-string

Below is the code to encrypt and decrypt whole website querystrings without doing any coding in each page of website. You have to do nothing except copying and pasting this code in your website. The procedure consists of 3 steps.
Step 1)
Create a new file in App_code folder with the name QueryStringModule.cs
Step 2)
Copy this whole code in the file named QueryStringModule.cs

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Text;
/// Summary description for QueryStringModule
///
public class QueryStringModule : IHttpModule
{
// private ILog m_Logger = LogManager.GetLogger(typeof(QueryStringModule));
#region IHttpModule Members
public void Dispose()
{
// Nothing to dispose
}
public void Init(HttpApplication context)
{
context.BeginRequest += new EventHandler(context_BeginRequest);
}
#endregion
private const string PARAMETER_NAME = "enc=";
private const string ENCRYPTION_KEY = "key";
void context_BeginRequest(object sender, EventArgs e)
{
HttpContext context = HttpContext.Current;
string query = string.Empty;
string path = string.Empty;
try
{
if (context.Request.Url.OriginalString.Contains("aspx") && context.Request.RawUrl.Contains("?"))
{
query = ExtractQuery(context.Request.RawUrl);
path = GetVirtualPath();
if (query.StartsWith(PARAMETER_NAME, StringComparison.OrdinalIgnoreCase))
{
// Decrypts the query string and rewrites the path.
string rawQuery = query.Replace(PARAMETER_NAME, string.Empty);
string decryptedQuery = Decrypt(rawQuery);
context.RewritePath(path, string.Empty, decryptedQuery);
}
else if (context.Request.HttpMethod == "GET")
{
// Encrypt the query string and redirects to the encrypted URL.
// Remove if you don't want all query strings to be encrypted automatically.
string encryptedQuery = Encrypt(query);
context.Response.Redirect(path + encryptedQuery, false);
}
}
}
catch (Exception ex)
{
// m_Logger.Error("An error occurred while parsing the query string in the URL: " + path, ex);
context.Response.Redirect("~/index.aspx");
}
}
///

/// Parses the current URL and extracts the virtual path without query string.
///

/// The virtual path of the current URL.
private static string GetVirtualPath()
{
string path = HttpContext.Current.Request.RawUrl;
path = path.Substring(0, path.IndexOf("?"));
path = path.Substring(path.LastIndexOf("/") + 1);
return path;
}
///

/// Parses a URL and returns the query string.
///

/// The URL to parse.
/// The query string without the question mark.
private static string ExtractQuery(string url)
{
int index = url.IndexOf("?") + 1;
return url.Substring(index);
}
#region Encryption/decryption
///

/// The salt value used to strengthen the encryption.
///

private readonly static byte[] SALT = Encoding.ASCII.GetBytes(ENCRYPTION_KEY.Length.ToString());
///

/// Encrypts any string using the Rijndael algorithm.
///

/// The string to encrypt.
/// A Base64 encrypted string.
private static string Encrypt(string inputText)
{
RijndaelManaged rijndaelCipher = new RijndaelManaged();
byte[] plainText = Encoding.Unicode.GetBytes(inputText);
PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(ENCRYPTION_KEY, SALT);
using (ICryptoTransform encryptor = rijndaelCipher.CreateEncryptor(SecretKey.GetBytes(32), SecretKey.GetBytes(16)))
{
using (MemoryStream memoryStream = new MemoryStream())
{
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
{
cryptoStream.Write(plainText, 0, plainText.Length);
cryptoStream.FlushFinalBlock();
return "?" + PARAMETER_NAME + Convert.ToBase64String(memoryStream.ToArray());
}
}
}
}
///

/// Decrypts a previously encrypted string.
///

/// The encrypted string to decrypt.
/// A decrypted string.
private static string Decrypt(string inputText)
{
RijndaelManaged rijndaelCipher = new RijndaelManaged();
byte[] encryptedData = Convert.FromBase64String(inputText);
PasswordDeriveBytes secretKey = new PasswordDeriveBytes(ENCRYPTION_KEY, SALT);
using (ICryptoTransform decryptor = rijndaelCipher.CreateDecryptor(secretKey.GetBytes(32), secretKey.GetBytes(16)))
{
using (MemoryStream memoryStream = new MemoryStream(encryptedData))
{
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
{
byte[] plainText = new byte[encryptedData.Length];
int decryptedCount = cryptoStream.Read(plainText, 0, plainText.Length);
return Encoding.Unicode.GetString(plainText, 0, decryptedCount);
}
}
}
}
#endregion
}

Step 3)
Add a line in the web.config file as below.
if your web application is running on IIS 5 or 6 then write
<system.web>
<httpModules>
<add type="QueryStringModule" name="QueryStringModule"/>
</httpModules>
</system.web>
But if your web application is running on IIS 7 then write
<system.webServer>
<modules>
<add type="QueryStringModule" name="QueryStringModule"/>
</modules>
</system.webServer>

Happy Coding…