How to encrypt connection string in web.config . In order to not expose connection string to outside world.
Protecting Connection Strings and Other Configuration Information (C#)
Configuration information for ASP.NET applications is commonly stored in an XML file named
Web.config
. Over the course of these tutorials we have updated the Web.config
a handful of times. When creating the Northwind
Typed DataSet in the first tutorial, for example, connection string information was automatically added to Web.config
in the <connectionStrings>
section. Later, in the Master Pages and Site Navigation tutorial, we manually updatedWeb.config
, adding a <pages>
element indicating that all of the ASP.NET pages in our project should use theDataWebControls
Theme.
Since
Web.config
may contain sensitive data such as connection strings, it is important that the contents ofWeb.config
be kept safe and hidden from unauthorized viewers. By default, any HTTP request to a file with the.config
extension is handled by the ASP.NET engine, which returns the This type of page is not served message shown in Figure 1. This means that visitors cannot view your Web.config
file s contents by simply entering http://www.YourServer.com/Web.config into their browser s Address bar.
But what if an attacker is able to find some other exploit that allows her to view your
Web.config
file s contents? What could an attacker do with this information, and what steps can be taken to further protect the sensitive information within Web.config
? Fortunately, most sections in Web.config
do not contain sensitive information. What harm can an attacker perpetrate if they know the name of the default Theme used by your ASP.NET pages?
Certain
Web.config
sections, however, contain sensitive information that may include connection strings, user names, passwords, server names, encryption keys, and so forth. This information is typically found in the followingWeb.config
sections:<appSettings>
<connectionStrings>
<identity>
<sessionState>
In this tutorial we will look at techniques for protecting such sensitive configuration information. As we will see, the .NET Framework version 2.0 includes a protected configurations system that makes programmatically encrypting and decrypting selected configuration sections a breeze.
Note: This tutorial concludes with a look at Microsoft s recommendations for connecting to a database from an ASP.NET application. In addition to encrypting your connection strings, you can help harden your system by ensuring that you are connecting to the database in a secure fashion.
Step 1: Exploring ASP.NET 2.0 s Protected Configuration Options
ASP.NET 2.0 includes a protected configuration system for encrypting and decrypting configuration information. This includes methods in the .NET Framework that can be used to programmatically encrypt or decrypt configuration information. The protected configuration system uses the provider model, which allows developers to choose what cryptographic implementation is used.
The .NET Framework ships with two protected configuration providers:
RSAProtectedConfigurationProvider
- uses the asymmetric RSA algorithm for encryption and decryption.DPAPIProtectedConfigurationProvider
- uses the Windows Data Protection API (DPAPI) for encryption and decryption.
Since the protected configuration system implements the provider design pattern, it is possible to create your own protected configuration provider and plug it into your application. See Implementing a Protected Configuration Provider for more information on this process.
The RSA and DPAPI providers use keys for their encryption and decryption routines, and these keys can be stored at the machine- or user-level. Machine-level keys are ideal for scenarios where the web application runs on its own dedicated server or if there are multiple applications on a server that need to share encrypted information. User-level keys are a more secure option in shared hosting environments where other applications on the same server should not be able to decrypt your application s protected configuration sections.
In this tutorial our examples will use the DPAPI provider and machine-level keys. Specifically, we will look at encrypting the
<connectionStrings>
section in Web.config
, although the protected configuration system can be used to encrypt most any Web.config
section. For information on using user-level keys or using the RSA provider, consult the resources in the Further Readings section at the end of this tutorial.
Note: The
RSAProtectedConfigurationProvider
and DPAPIProtectedConfigurationProvider
providers are registered in the machine.config
file with the provider names RsaProtectedConfigurationProvider
andDataProtectionConfigurationProvider
, respectively. When encrypting or decrypting configuration information we will need to supply the appropriate provider name (RsaProtectedConfigurationProvider
orDataProtectionConfigurationProvider
) rather than the actual type name (RSAProtectedConfigurationProvider
and DPAPIProtectedConfigurationProvider
). You can find themachine.config
file in the $WINDOWS$\Microsoft.NET\Framework\version\CONFIG
folder.Step 2: Programmatically Encrypting and Decrypting Configuration Sections
With a few lines of code we can encrypt or decrypt a particular configuration section using a specified provider. The code, as we will see shortly, simply needs to programmatically reference the appropriate configuration section, call its
ProtectSection
or UnprotectSection
method, and then call the Save
method to persist the changes. Moreover, the .NET Framework includes a helpful command line utility that can encrypt and decrypt configuration information. We will explore this command line utility in Step 3.
To illustrate programmatically protecting configuration information, let s create an ASP.NET page that includes buttons for encrypting and decrypting the
<connectionStrings>
section in Web.config
.
Start by opening the
EncryptingConfigSections.aspx
page in the AdvancedDAL
folder. Drag a TextBox control from the Toolbox onto the Designer, setting its ID
property to WebConfigContents
, its TextMode
property toMultiLine
, and its Width
and Rows
properties to 95% and 15, respectively. This TextBox control will display the contents of Web.config
allowing us to quickly see if the contents are encrypted or not. Of course, in a real application you would never want to display the contents of Web.config
.
Beneath the TextBox, add two Button controls named
EncryptConnStrings
and DecryptConnStrings
. Set their Text properties to Encrypt Connection Strings and Decrypt Connection Strings .
At this point your screen should look similar to Figure 2.
Next, we need to write code that loads and displays the contents of
Web.config
in the WebConfigContents
TextBox when the page is first loaded. Add the following code to the page s code-behind class. This code adds a method named DisplayWebConfig
and calls it from the Page_Load
event handler when Page.IsPostBack
isfalse
:protected void Page_Load(object sender, EventArgs e)
{
// On the first page visit, call DisplayWebConfig method
if (!Page.IsPostBack)
DisplayWebConfig();
}
private void DisplayWebConfig()
{
// Reads in the contents of Web.config and displays them in the TextBox
StreamReader webConfigStream =
File.OpenText(Path.Combine(Request.PhysicalApplicationPath, "Web.config"));
string configContents = webConfigStream.ReadToEnd();
webConfigStream.Close();
WebConfigContents.Text = configContents;
}
The
DisplayWebConfig
method uses the File
class to open the application s Web.config
file, the StreamReader
class to read its contents into a string, and the Path
class to generate the physical path to the Web.config
file. These three classes are all found in the System.IO
namespace. Consequently, you will need to add a using
System.IO
statement to the top of the code-behind class or, alternatively, prefix these class names with System.IO.
.
Next, we need to add event handlers for the two Button controls
Click
events and add the necessary code to encrypt and decrypt the <connectionStrings>
section using a machine-level key with the DPAPI provider. From the Designer, double-click each of the Buttons to add a Click
event handler in the code-behind class and then add the following code:protected void EncryptConnStrings_Click(object sender, EventArgs e)
{
// Get configuration information about Web.config
Configuration config =
WebConfigurationManager.OpenWebConfiguration(Request.ApplicationPath);
// Let's work with the <connectionStrings> section
ConfigurationSection connectionStrings = config.GetSection("connectionStrings");
if (connectionStrings != null)
// Only encrypt the section if it is not already protected
if (!connectionStrings.SectionInformation.IsProtected)
{
// Encrypt the <connectionStrings> section using the
// DataProtectionConfigurationProvider provider
connectionStrings.SectionInformation.ProtectSection(
"DataProtectionConfigurationProvider");
config.Save();
// Refresh the Web.config display
DisplayWebConfig();
}
}
protected void DecryptConnStrings_Click(object sender, EventArgs e)
{
// Get configuration information about Web.config
Configuration config =
WebConfigurationManager.OpenWebConfiguration(Request.ApplicationPath);
// Let's work with the <connectionStrings> section
ConfigurationSection connectionStrings =
config.GetSection("connectionStrings");
if (connectionStrings != null)
// Only decrypt the section if it is protected
if (connectionStrings.SectionInformation.IsProtected)
{
// Decrypt the <connectionStrings> section
connectionStrings.SectionInformation.UnprotectSection();
config.Save();
// Refresh the Web.config display
DisplayWebConfig();
}
}
The code used in the two event handlers is nearly identical. They both start by getting information about the current application s
Web.config
file via the WebConfigurationManager
class s OpenWebConfiguration
method. This method returns the web configuration file for the specified virtual path. Next, the Web.config
file s<connectionStrings>
section is accessed via the Configuration
class s GetSection(sectionName)
method, which returns a ConfigurationSection
object.
The
ConfigurationSection
object includes a SectionInformation
property that provides additional information and functionality regarding the configuration section. As the code above shows, we can determine whether the configuration section is encrypted by checking the SectionInformation
property s IsProtected
property. Moreover, the section can be encrypted or decrypted via the SectionInformation
property sProtectSection(provider)
and UnprotectSection
methods.
The
ProtectSection(provider)
method accepts as input a string specifying the name of the protected configuration provider to use when encrypting. In the EncryptConnString
Button s event handler we pass DataProtectionConfigurationProvider into the ProtectSection(provider)
method so that the DPAPI provider is used. The UnprotectSection
method can determine the provider that was used to encrypt the configuration section and therefore does not require any input parameters.
After calling the
ProtectSection(provider)
or UnprotectSection
method, you must call the Configuration
object s Save
method to persist the changes. Once the configuration information has been encrypted or decrypted and the changes saved, we call DisplayWebConfig
to load the updated Web.config
contents into the TextBox control.
Once you have entered the above code, test it by visiting the
EncryptingConfigSections.aspx
page through a browser. You should initially see a page that lists the contents of Web.config
with the <connectionStrings>
section displayed in plain-text (see Figure 3).
Now click the Encrypt Connection Strings button. If request validation is enabled, the markup posted back from the
WebConfigContents
TextBox will produce an HttpRequestValidationException
, which displays the message, A potentially dangerous Request.Form
value was detected from the client. Request validation, which is enabled by default in ASP.NET 2.0, prohibits postbacks that include un-encoded HTML and is designed to help prevent script-injection attacks. This check can be disabled at the page- or application-level. To turn it off for this page, set theValidateRequest
setting to false
in the @Page
directive. The @Page
directive is found at the top of the page s declarative markup.<%@ Page ValidateRequest="False" ... %>
For more information on request validation, its purpose, how to disable it at the page- and application-level, as well as how to HTML encode markup, see Request Validation - Preventing Script Attacks.
After disabling request validation for the page, try clicking the Encrypt Connection Strings button again. On postback, the configuration file will be accessed and its
<connectionStrings>
section encrypted using the DPAPI provider. The TextBox is then updated to display the new Web.config
content. As Figure 4 shows, the<connectionStrings>
information is now encrypted.
The encrypted
<connectionStrings>
section generated on my computer follows, although some of the content in the <CipherData>
element has been removed for brevity:<connectionStrings
configProtectionProvider="DataProtectionConfigurationProvider">
<EncryptedData>
<CipherData>
<CipherValue>AQAAANCMnd8BFdERjHoAwE/...zChw==</CipherValue>
</CipherData>
</EncryptedData>
</connectionStrings>
Note: The
<connectionStrings>
element specifies the provider used to perform the encryption (DataProtectionConfigurationProvider
). This information is used by the UnprotectSection
method when the Decrypt Connection Strings button is clicked.
When the connection string information is accessed from
Web.config
- either by code we write, from a SqlDataSource control, or the auto-generated code from the TableAdapters in our Typed DataSets - it is automatically decrypted. In short, we do not need to add any extra code or logic to decrypt the encrypted<connectionString>
section. To demonstrate this, visit one of the earlier tutorials at this time, such as the Simple Display tutorial from the Basic Reporting section (~/BasicReporting/SimpleDisplay.aspx
). As Figure 5 shows, the tutorial works exactly as we would expect it, indicating that the encrypted connection string information is being automatically decrypted by the ASP.NET page.
To revert the
<connectionStrings>
section back to its plain-text representation, click the Decrypt Connection Strings button. On postback you should see the connection strings in Web.config
in plain-text. At this point your screen should look like it did when first visiting this page (see in Figure 3).
Step 3: Encrypting Configuration Sections Using aspnet_regiis.exe
The .NET Framework includes a variety of command line tools in the
$WINDOWS$\Microsoft.NET\Framework\version\
folder. In the Using SQL Cache Dependencies tutorial, for instance, we looked at using the aspnet_regsql.exe
command line tool to add the infrastructure necessary for SQL cache dependencies. Another useful command line tool in this folder is the ASP.NET IIS Registration tool (aspnet_regiis.exe
). As its name implies, the ASP.NET IIS Registration tool is primarily used to register an ASP.NET 2.0 application with Microsoft s professional-grade Web server, IIS. In addition to its IIS-related features, the ASP.NET IIS Registration tool can also be used to encrypt or decrypt specified configuration sections in Web.config
.
The following statement shows the general syntax used to encrypt a configuration section with the
aspnet_regiis.exe
command line tool:aspnet_regiis.exe -pef section physical_directory -prov provider
section is the configuration section to encrypt (like connectionStrings ), the physical_directory is the full, physical path to the web application s root directory, and provider is the name of the protected configuration provider to use (such as DataProtectionConfigurationProvider ). Alternatively, if the web application is registered in IIS you can enter the virtual path instead of the physical path using the following syntax:
aspnet_regiis.exe -pe section -app virtual_directory -prov provider
The following
aspnet_regiis.exe
example encrypts the <connectionStrings>
section using the DPAPI provider with a machine-level key:aspnet_regiis.exe -pef
"connectionStrings" "C:\Websites\ASPNET_Data_Tutorial_73_CS"
-prov "DataProtectionConfigurationProvider"
Similarly, the
aspnet_regiis.exe
command line tool can be used to decrypt configuration sections. Instead of using the -pef
switch, use -pdf
(or instead of -pe
, use -pd
). Also, note that the provider name is not necessary when decrypting.aspnet_regiis.exe -pdf section physical_directory
-- or --
aspnet_regiis.exe -pd section -app virtual_directory
Note: Since we are using the DPAPI provider, which uses keys specific to the computer, you must run
aspnet_regiis.exe
from the same machine from which the web pages are being served. For example, if you run this command line program from your local development machine and then upload the encrypted Web.config file to the production server, the production server will not be able to decrypt the connection string information since it was encrypted using keys specific to your development machine. The RSA provider does not have this limitation as it is possible to export the RSA keys to another machine.Understanding Database Authentication Options
Before any application can issue
SELECT
, INSERT
, UPDATE
, or DELETE
queries to a Microsoft SQL Server database, the database first must identify the requestor. This process is known as authentication and SQL Server provides two methods of authentication:- Windows Authentication - the process under which the application is running is used to communicate with the database. When running an ASP.NET application through Visual Studio 2005 s ASP.NET Development Server, the ASP.NET application assumes the identity of the currently logged on user. For ASP.NET applications on Microsoft Internet Information Server (IIS), ASP.NET applications usually assume the identity of
domainName
\MachineName
ordomainName
\NETWORK SERVICE
, although this can be customized. - SQL Authentication - a user ID and password values are supplied as credentials for authentication. With SQL authentication, the user ID and password are provided in the connection string.
Windows authentication is preferred over SQL authentication because it is more secure. With Windows authentication the connection string is free from a username and password and if the web server and database server reside on two different machines, the credentials are not sent over the network in plain-text. With SQL authentication, however, the authentication credentials are hard-coded in the connection string and are transmitted from the web server to the database server in plain-text.
These tutorials have used Windows authentication. You can tell what authentication mode is being used by inspecting the connection string. The connection string in
Web.config
for our tutorials has been:Data Source=.\SQLEXPRESS; AttachDbFilename=|DataDirectory|\NORTHWND.MDF; Integrated Security=True; User Instance=True
The Integrated Security=True and lack of a username and password indicate that Windows authentication is being used. In some connection strings the term Trusted Connection=Yes or Integrated Security=SSPI is used instead of Integrated Security=True , but all three indicate the use of Windows authentication.
The following example shows a connection string that uses SQL authentication. Note the credentials embedded within the connection string:
Server=serverName; Database=Northwind; uid=userID; pwd=password
Imagine that an attacker is able to view your application s
Web.config
file. If you use SQL authentication to connect to a database that is accessible over the Internet, the attacker can use this connection string to connect to your database through SQL Management Studio or from ASP.NET pages on their own website. To help mitigate this threat, encrypt the connection string information in Web.config
using the protected configuration system.
Note: For more information on the different types of authentication available in SQL Server, see Building Secure ASP.NET Applications: Authentication, Authorization, and Secure Communication. For further connection string examples illustrating the differences between Windows and SQL authentication syntax, refer toConnectionStrings.com.
Summary
By default, files with a
.config
extension in an ASP.NET application cannot be accessed through a browser. These types of files are not returned because they may contain sensitive information, such as database connection strings, usernames and passwords, and so on. The protected configuration system in .NET 2.0 helps further protect sensitive information by allowing specified configuration sections to be encrypted. There are two built-in protected configuration providers: one that uses the RSA algorithm and one that uses the Windows Data Protection API (DPAPI).
In this tutorial we looked at how to encrypt and decrypt configuration settings using the DPAPI provider. This can be accomplished both programmatically, as we saw in Step 2, as well as through the
aspnet_regiis.exe
command line tool, which was covered in Step 3. For more information on using user-level keys or using the RSA provider instead, see the resources in the Further Reading section.
Happy Programming!
Further Reading
For more information on the topics discussed in this tutorial, refer to the following resources:
- Building Secure ASP.NET Application: Authentication, Authorization, and Secure Communication
- Encrypting Configuration Information in ASP.NET 2.0 Applications
- Encrypting
Web.config
Values in ASP.NET 2.0 - How To: Encrypt Configuration Sections in ASP.NET 2.0 Using DPAPI
- How To: Encrypt Configuration Sections in ASP.NET 2.0 Using RSA
- The Configuration API in .NET 2.0
- Windows Data Protection
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