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Query string encryption for ASP.NET

, 15 Nov 2014 CPOL
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Clear text query strings are a potential security threat for your web application. Thus, query strings should always be encrypted.

Introduction

Using query strings to send data from the browser to the server is a widespread approach. Giving the visitor of a web application the opportunity of modifying query strings by transmitting them in clear text, is certainly a potential security threat.

Thus, I encourage developers to encrypt query strings, even if they do not contain confidential data. However, I am aware that it is still possible to alternate an encrypted query string, but with an appropriate exception handling, this is harmless.

Background

To keep this article simple, I used a contradictable encryption (DES encoding), though any cutting-edge encryption can be easily applied to the samples given.

Using the code

So, let's get down to business. The main part of the presented solution consists of a HttpModule which decrypts the query string and hence provides the page request with the ordinary unencrypted query strings:

using System;
using System.Web;
using System.Web.Configuration;

namespace HelveticSolutions.QueryStringEncryption
{
    /// <summary>
    /// Http module that handles encrypted query strings.
    /// </summary>
    public class CryptoQueryStringUrlRemapper : IHttpModule
    {
        #region IHttpModule Members

        /// <summary>
        /// Initialize the http module.
        /// </summary>
        /// <param name="application">Application,
        ///           that called this module.</param>
        public void Init(HttpApplication application)
        {
            // Attach the acquire request state event
            // to catch the encrypted query string
            application.AcquireRequestState += application_AcquireRequestState;
        }

        public void Dispose()
        {}
    
        #endregion

        /// <summary>
        /// Event, that is called when the application acquires the request state.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        public void application_AcquireRequestState(object sender, EventArgs e)
        {
            // Get http context from the caller.
            HttpApplication application = (HttpApplication) sender;
            HttpContext context = application.Context;

            // Check for encrypted query string
            string encryptedQueryString = context.Request.QueryString["request"];
            if (!string.IsNullOrEmpty(encryptedQueryString))
            {
                // Decrypt query strings
                string cryptoKey = WebConfigurationManager.AppSettings["CryptoKey"];
                string decryptedQueryString = 
                  CryptoQueryStringHandler.DecryptQueryStrings(encryptedQueryString, 
                                                               cryptoKey);
                context.Server.Transfer(
                  context.Request.AppRelativeCurrentExecutionFilePath + 
                  "?" + decryptedQueryString);
            }
        }
    }
}

As you might have noticed, if there is an encrypted query string for the current request, the module automatically terminates the execution of the current page and internally starts execution of a new request on the server.

The next step is to register the HttpModule in the web.config file:

<httpModules>
    <add name="CryptoQueryStringUrlRemapper" 
      type="HelveticSolutions.QueryStringEncryption.CryptoQueryStringUrlRemapper"/>
</httpModules>

Last but not least, do not forget to encrypt query strings before sending them back to the server:

private void PrepareSendButton()
{
    NameValueCollection queryStrings = new NameValueCollection();
    queryStrings.Add("param1", "Test1");
    queryStrings.Add("param2", "Test2");
    queryStrings.Add("param3", "Test3");

    // Encrypt query strings
    string encryptedString = CryptoQueryStringHandler.EncryptQueryStrings(
      queryStrings, WebConfigurationManager.AppSettings["CryptoKey"]);
    btnSendParams.PostBackUrl = string.Concat("~/Default.aspx?", encryptedString);
}

As outlined earlier in this article, the encryption class can be easily replaced by any other encryption class. A full running sample can be downloaded above.

Important issue

The method DecryptQueryStrings in the CryptoQueryStringHandler contains the following line :

return Encryption64.Decrypt(encryptedStrings.Replace(" ", "+"), key); 

For unknown reasons, the request replaces every '+' character in the query with an empty character.

History

  • 30.04.2008 - First version (deleted -> was not possible to modify, why ever...).
  • 01.05.2008 - Re-released updated article.
  • 08.05.2008 - BeginRequest event in the HttpModule changed to AcquireRequestState in order to support Session data.
  • 11th November 2014 - Namespace corrected

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Michael Ulmann
Architect Helvetic Solutions
Australia Australia
MCAD, MCPD Web Developer 2.0, MCPD Enterprise Developer 3.5
 
My company: Helvetic Solutions
My blog: Sitecore Experts
 
Hopp Schwiiz Smile | :)

Comments and Discussions

 
QuestionIntegrity != Confidentiality - wrong security service PinmemberMember 841817317-Nov-14 4:20 
Question"500 - Internal server error" when running it on the server Pinmemberfniles28-Aug-13 6:22 
SuggestionQuery String encryption does not work when page is post back. Pinmembereli86200614-Mar-13 3:45 
GeneralRe: Query String encryption does not work when page is post back. PinmemberFarhad Hazraty Eini24-Apr-13 19:58 
Questionproblem when page postback event fire, it shows plain text in Url Pinmemberjitendra77719-Oct-11 20:52 
AnswerRe: problem when page postback event fire, it shows plain text in Url Pinmembereli86200614-Mar-13 3:46 
GeneralFor unknown reasons, the request replaces every '+' character in the query with an empty character. Pinmemberya3mro28-Jul-10 11:15 
GeneralA code free approach PinmemberZiad J.khan26-Mar-10 1:52 
GeneralOutput Caching not working in conjunction with query string encryption. Pinmemberjellyfish728-Sep-09 14:35 
GeneralSerious issue with encoding Pinmembersrouss3-Jun-09 0:57 
GeneralThere is a major problem with this approach PinmemberOrionDR20-Mar-09 6:44 
QuestionCan still alter query string and decryption goes through and returs invalid charactors PinmemberNimendra29-Sep-08 20:55 
GeneralAuto-Encrypting QueryStrings before Response PinmemberRuchit Surati8-May-08 10:51 
GeneralRe: Auto-Encrypting QueryStrings before Response Pinmembercijothomas10-Jul-09 4:59 
GeneralRe: Auto-Encrypting QueryStrings before Response PinmemberRuchit S.10-Jul-09 5:21 
GeneralRe: Auto-Encrypting QueryStrings before Response Pinmemberthewazz17-Nov-14 9:53 
GeneralSession State PinmemberAllan Eagle7-May-08 5:14 
GeneralRe: Session State PinmemberMichael Ulmann7-May-08 18:47 
GeneralQuerystring decrypting on postback PinmemberLordGentle6-May-08 10:25 
GeneralRe: Querystring decrypting on postback PinmemberMichael Ulmann6-May-08 13:10 
GeneralRe: Querystring decrypting on postback Pinmemberkraazee118-Jul-11 9:02 
RantCompletely unnecessary PinmemberTrumpi1-May-08 1:10 
GeneralRe: Completely unnecessary PinmemberAndyM772-May-08 7:52 
I think you're missing the point, the goal is to hide the data from the user, did you really not understand that?
GeneralRe: Completely unnecessary PinmemberMR_SAM_PIPER7-May-08 15:33 
GeneralRe: Completely unnecessary PinmemberMichael Ulmann7-May-08 18:32 
GeneralRe: Completely unnecessary PinmemberMatt Sollars13-May-08 4:18 
GeneralRe: Completely unnecessary Pinmemberwk63313-May-08 5:29 
GeneralNo Completely Pinmember Clickok 2-May-08 12:50 
GeneralRe: No Completely PinmemberMichael Ulmann2-May-08 14:53 
GeneralRe: Completely unnecessary (really necessary) Pinmembersides_dale7-May-08 11:19 
GeneralRe: Completely unnecessary Pinmemberinetfly1238-May-08 2:59 
AnswerRe: Completely unnecessary Pinmembermeaningoflights7-Jan-09 19:48 
GeneralRe: Completely unnecessary PinmemberJonathan C Dickinson6-Jan-09 0:49 

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