Microsoft KB Archive/313091

= How to create keys by using Visual Basic .NET for use in Forms authentication =

Article ID: 313091

Article Last Modified on 10/29/2007

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APPLIES TO


 * Microsoft ASP.NET 1.0
 * Microsoft Visual Basic .NET 2002 Standard Edition
 * Microsoft ASP.NET 1.1
 * Microsoft Visual Basic .NET 2003 Standard Edition

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This article was previously published under Q313091



For a Microsoft Visual C# .NET version of this article, see 312906.

This article refers to the following Microsoft .NET Framework Class Library namespaces:
 * System.Text
 * System.Security.Cryptography

IN THIS TASK
SUMMARY
 * Requirements
 * Create the project
 * Write the code to hash a password
 * Generate the hashes
 * Update the configuration file
 * Troubleshooting

REFERENCES



SUMMARY
This article describes how to create keys to use for encryption, decryption, and validation of Forms authentication cookie data. You can use the keys that you create in this article for the validationKey and the decryptionKey attributes of the  section in the  element in the Machine.config and the Web.config files.

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Requirements
The following list outlines the recommended hardware, software, network infrastructure, and service packs that you need:
 * Microsoft Windows 2000 or Microsoft Windows XP
 * Microsoft .NET Framework
 * Microsoft Internet Information Services (IIS)

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Create the project

 * 1) Start Microsoft Visual Studio .NET.
 * 2) On File menu, point to New, and then click Project.
 * 3) In the Project Types area, click Visual Basic Projects.
 * 4) In the Templates area, click Console Application.
 * 5) In the Name text box, type HashConfigVb, and then click OK.

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Write the code to hash a password
The code in this section reads two arguments that are passed from the command line:
 * The first argument is the number of bytes that is used to create the decryptionKey attribute.
 * The second argument is the number of bytes that is used to create the validationKey attribute.

The code uses a random number generator to create a random number of bytes based on the command-line arguments. After the random bytes are created, the bytes are formatted into a hexadecimal string that is suitable for use in the .config files.

Note The hexadecimal string that is created is twice the size of the value that is passed on the command line. For example, if you specify 24 bytes for a key, the resulting string is 48 bytes in length after the conversion. The valid values for decryptionKey is 8 or 24. This creates a 16 byte key for Data Encryption Standard (DES) or a 48 byte key for Triple DES, respectively. Valid values for validationKey are 20 to 64. This creates keys from 40 to 128 bytes in length after the conversion. The output from the code is an entire  element that you can copy and paste into a Machine.config or a Web.config file.

 Add a new class file named KeyCreator to your Visual Basic project.  Replace the existing code in the KeyCreator.vb file with the following code: Imports System Imports System.Text Imports System.Security.Cryptography

Namespace Crypto Public Class KeyCreator Public Shared Sub CreateMachineKey Dim commandLineArgs As String commandLineArgs = System.Environment.GetCommandLineArgs

Dim decryptionKey As String decryptionKey = CreateKey(System.Convert.ToInt32(commandLineArgs(1))) Dim validationKey As String validationKey = CreateKey(System.Convert.ToInt32(commandLineArgs(2)))

Console.WriteLine(&quot;&quot;, _     validationKey, decryptionKey) End Sub

Public Shared Function CreateKey(numBytes As Integer) As String Dim rng As RNGCryptoServiceProvider = New RNGCryptoServiceProvider Dim buff(numBytes -1) As Byte

rng.GetBytes(buff) Return BytesToHexString(buff) End Function Public Shared Function BytesToHexString(bytes As Byte) As String Dim hexString As StringBuilder = New StringBuilder(64) Dim counter as Integer

For counter = 0 To bytes.Length - 1 hexString.Append(String.Format(&quot;{0:X2}&quot;, bytes(counter))) Next

Return hexString.ToString End Function

End Class End Namespace   Open the Module1.vb file that is created by default, and then add the following code in the Main sub routine: Dim MyKeyCreator As New Crypto.KeyCreator MyKeyCreator.CreateMachineKey  Build the application.</ol>

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Generate the hashes
Run the application from a command prompt, and then pass in two integer values that are the size of the decryption and the validation keys. If you named the console application HashConfigVb.exe, type the following syntax at the command prompt in the Bin directory of the application:

HashConfigVb.exe 24 64

The application should return output that is similar to the following output:

<pre class="fixed_text"><machineKey validationKey=&quot;08CE6B478DCE73..........E566D8AC5D1C045BA60&quot; decryptionKey=&quot;4252D6B2268.........67F451CE65D0F2ABE9BCD3A&quot; validation=&quot;SHA1&quot;/>

Note Because the code uses a random number generator, the output is different each time.

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Update the configuration file

 * 1) Locate the Machine.config or the Web.config file.
 * 2) Locate the <system.web> section in the configuration file.
 * 3) Replace the <machineKey> section with the output from the console application. If the <machineKey> section does not exist, create it.
 * 4) Save the configuration file.
 * 5) Restart IIS on all servers in the Web farm for the Machine.config changes to take effect.

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Troubleshooting
Make sure that the <machineKey> section has identical, explicit keys (that is, do not use the AutoGenerate option for attributes in the <machineKey> section) across the Web farm in the following scenarios:
 * When you use Forms authentication.
 * When you run session state in StateServer mode.
 * When you want ViewState to be available across a Web farm because the enableViewStateMAC attribute is set to True by default.

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