how to generate validationKey and decryption Key for web.config

[alok pandey]

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 decryptionKey attributes of the <machineKey> section in the
<system.web> element in the web.config file or Machine.config.

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)
Create the project

Create a Visual C# .NET console application:

Start Visual Studio .NET.
On File menu, point to New, and then click Project.
Under Project Types, click Visual C# Projects.
Under Templates, click Console application.
Name the project HashConfigCs.
Click OK.


Write the code to generate the keys

The following code 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. The output
from the code is an entire <machineKey> element that you can copy and
paste into a web.config file.

Add the following code to a .cs file:

using System;
using System.Text;
using System.Security.Cryptography;

namespace Crypto
{
public class KeyCreator
{
public static void Main(String[] args)
{
String[] commandLineArgs =
System.Environment.GetCommandLineArgs();
string decryptionKey =
CreateKey(System.Convert.ToInt32(commandLineArgs[1]));
string validationKey =
CreateKey(System.Convert.ToInt32(commandLineArgs[2]));

Console.WriteLine("<machineKey validationKey=\"{0}\"
decryptionKey=\"{1}\" validation=\"SHA1\"/>", validationKey,
decryptionKey);
}

static String CreateKey(int numBytes)
{
RNGCryptoServiceProvider rng = new
RNGCryptoServiceProvider();
byte[] buff = new byte[numBytes];

rng.GetBytes(buff);
return BytesToHexString(buff);
}

static String BytesToHexString(byte[] bytes)
{
StringBuilder hexString = new StringBuilder(64);

for (int counter = 0; counter < bytes.Length; counter++)
{
hexString.Append(String.Format("{0:X2}",
bytes[counter]));
}
return hexString.ToString();
}
}
}
Generate the hashes

Now you can compile the application.

Run the application from a command prompt by passing in two integer
values that are the size of the decryption and the validation keys.
For example, if you named the console application HashConfigCs.exe,
type the following syntax from the command line in the Bin\debug
directory of the application:

hashconfigcs.exe 24 64
You can expect the application to return output that is similar to the
following output:

<machineKey
validationKey="21F090935F6E49C2C797F69BBAAD8402ABD2EE0B667A8B44EA7DD4374267A75D7AD972A119482D15A4127461DB1DC347C1A63AE5F1CCFAACFF1B72A7F0A281B"

decryptionKey="261F793EB53B761503AC445E0CA28DA44AA9B3CF06263B77"
validation="SHA1"/>

Note Because the code is using a random number generator, the output
is different each time.
Note for Machine.config

Update the configuration file

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

The machineKey section should be the same across the web farm in the
following cases:

When using Forms Authentication.
When you run session state in StateServer mode.
When you want viewstate to be available across a web farm since
enableViewStateMac is turned on by default.