Building Secure ASP.NET Applications: Authentication, Authorization, and Secure Communication

The registry represents one possible location for an application to store database connection strings. Although individual registry keys can be secured with Windows access control lists (ACLs), for added security you should store encrypted connection strings.

This How To describes how to store an encrypted database connection string in the registry and retrieve it from an ASP.NET Web application. It uses the generic encryption and decryption managed class library created in How to: Create an Encryption Library, which can be found in Reference section of this guide.

If you have not already created the encryption class library assembly, do so before continuing with the current How To.

For more information about other locations and ways of securely storing database connection strings, see Storing Database Connection Strings Securely in Chapter 12, "Data Access Security."

Notes

• The connection string, initialization vector and key used for encryption will be stored in the registry as named values beneath the following registry key.

  HKEY_LOCAL_MACHINE\Software\TestApplication
  

• The initialization vector and key must be stored in order to allow the connection string to be decrypted.

Requirements

The following items describe the recommended hardware, software, network infrastructure, skills and knowledge, and service packs you will need.

• Microsoft?Windows?2000 operating system
• Microsoft Visual Studio?.NET development system

The procedures in this article also require that you have knowledge of the Microsoft Visual C#?development tool.

Summary

This How To includes the following procedures:

1. Store the Encrypted Data in the Registry
2. Create an ASP.NET Web Application

1. Store the Encrypted Data in the Registry

This procedure creates a Windows application that will be used to encrypt a sample database string and store it in the registry.

To store the encrypted data in the registry

1. Start Visual Studio .NET and create a new C# Windows project called EncryptionTestApp.
2. Add an assembly reference to the Encryption.dll assembly.

   To create this assembly, you must perform the steps described in How To: Create an Encryption Library in the Reference section of this guide.

3. Add the following using statements to the top of Form1.cs beneath the existing using statements.

   using Encryption;
   using System.Text;
   using Microsoft.Win32;
   

4. Add the controls in Table 1 to Form1 and arrange them as illustrated in Figure 1.

   Table 1. EncryptionTestApp controls

   Control	Text	ID
   Label	Connection String:
   TextBox		txtConnectionString
   Label	Key:
   TextBox		txtKey
   Label	Initialization Vector:
   TextBox		txtInitializationVector
   Label	Encrypted String
   TextBox		txtEncryptedString
   Label	Decrypted String
   TextBox		txtDecryptedString
   Button	Encrypt	btnEncrypt
   Button	Decrypt	btnDecrypt
   Button	Write Registry Data	btnWriteRegistryData

   

   Figure 1. Encryption Test Harness dialog box

5. Set the Text property of txtConnectionString to

   "Server=local; database=pubs; uid=Bob; pwd=Password"
   

6. Set the Text property of txtKey to

   "0123456789012345"
   

   The key length is 16 bytes to suite the Triple DES encryption algorithm.

7. Set the Text property of Form1 to

   "Encryption Test Harness"
   

8. Double-click the Encrypt button to create a button click event handler and add the following code to the event handler.

   try
   {
     // Create the encryptor object, specifying 3DES as the
     // encryption algorithm
     Encryptor enc = new Encryptor(EncryptionAlgorithm.TripleDes);
     // Get the connection string as a byte array
     byte[] plainText = 
       Encoding.ASCII.GetBytes(txtConnectionString.Text);
     byte[] key = Encoding.ASCII.GetBytes(txtKey.Text);
   
     // Perform the encryption
     byte[] cipherText = enc.Encrypt(plainText, key);
     // Store the intialization vector, as this will be required
     // for decryption
     txtInitializationVector.Text = Encoding.ASCII.GetString(enc.IV);
   
     // Display the encrypted string
     txtEncryptedString.Text = Convert.ToBase64String(cipherText);
   }
   catch(Exception ex)
   {
     MessageBox.Show("Exception encrypting: " + ex.Message, 
                     "Encryption Test  Harness");
   }
   

9. Return to Form1 in Designer mode and double-click the Decrypt button to create a button click event handler.
10. Add the following code to the Decrypt button event handler.

    try
    {
      // Set up the Decryptor object
      Decryptor dec = new Decryptor(EncryptionAlgorithm.TripleDes);
    
      // Set the Initialization Vector
      dec.IV = Encoding.ASCII.GetBytes(txtInitializationVector.Text);
    
      byte[] key = Encoding.ASCII.GetBytes(txtKey.Text);
      // Perform the decryption
      byte[] plainText =  dec.Decrypt(Convert.FromBase64String(
                                      txtEncryptedString.Text),
                                      key);
    
      // Display the decrypted string.
      txtDecryptedString.Text = Encoding.ASCII.GetString(plainText);
    }
    catch(Exception ex)
    {
      MessageBox.Show("Exception decrypting. " + ex.Message, 
                      "Encryption Test Harness");
    }
    

11. Return to Form1 in Designer mode and double-click the Write Registry Data button to create a button click event handler.
12. Add the following code to the event handler.

    // Create registry key and named values
    RegistryKey rk = Registry.LocalMachine.OpenSubKey("Software",true);
    rk = rk.CreateSubKey("TestApplication");
    
    // Write encrypted string, initialization vector and key to the 
      registry
    rk.SetValue("connectionString",txtEncryptedString.Text);
    rk.SetValue("initVector",Convert.ToBase64String(
               Encoding.ASCII.GetBytes(txtInitializationVector.Text)));
    rk.SetValue("key",Convert.ToBase64String(Encoding.ASCII.GetBytes(
                                             txtKey.Text)));
    MessageBox.Show("The data has been successfully written to the 
      registry");
    

13. Run the application, and then click Encrypt.

    The encrypted connection string is displayed in the Encrypted String field.

14. Click Decrypt.

    The original string is displayed in the Decrypted String field.

15. Click Write Registry Data.
16. In the message box, click OK.
17. Run regedit.exe and view the contents of the following key.

    HKLM\Software\TestApplication
    

    Confirm that encoded values are present for the connectionString, initVector and key named values.

18. Close regedit and the test harness application.

2. Create an ASP.NET Web Application

This procedure develops a simple ASP.NET Web application that will retrieve the encrypted connection string from the registry and decrypt it.

To create an ASP.NET application

1. Create a new Visual C# ASP.NET Web Application called EncryptionWebApp.
2. Add an assembly reference to the Encryption.dll assembly.

   To create this assembly, you must perform the steps described in How To: Create an Encryption Library in the Reference section of this guide.

3. Open Webform1.aspx.cs and add the following using statements at the top of the file beneath the existing using statements.

   using Encryption;
   using System.Text;
   using Microsoft.Win32;
   

4. Add the controls listed in Table 2 to WebForm1.aspx.

   Table 2: WebForm1.aspx controls

   Control	Text	ID
   Label		lblEncryptedString
   Label		lblDecryptedString
   Button	Get Connection String	btnGetConnectionString

5. Double-click the Get Connection String button to create a button click event handler.
6. Add the following code to the event handler.

   RegistryKey rk = Registry.LocalMachine.OpenSubKey(
                                   @"Software\TestApplication",false);
   lblEncryptedString.Text = (string)rk.GetValue("connectionString");
   
   string initVector = (string)rk.GetValue("initVector");
   string strKey = (string)rk.GetValue("key");
   
   Decryptor dec = new Decryptor(EncryptionAlgorithm.TripleDes );
   dec.IV = Convert.FromBase64String(initVector);
   
   // Decrypt the string
   byte[] plainText = dec.Decrypt(Convert.FromBase64String(
                                  lblEncryptedString.Text), 
                                  Convert.FromBase64String(strKey));
   
   lblDecryptedString.Text = Encoding.ASCII.GetString(plainText);
   

7. On the Build menu, click Build Solution.
8. Right-click Webform1.aspx in Solution Explorer, and then click View in Browser.
9. Click Get Connection String.

   The encrypted and decrypted connection strings are displayed on the Web form.

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