ASP.NET Syntax   ASP.NET Configuration Sections

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Configures keys to use for encryption and decryption of Forms authentication cookie data. This section can be declared at the machine, site, and application levels but not at the subdirectory level.

<machineKey 
   validationKey = "autogenerate | value" 
   decryptionKey = "autogenerate | value"
   validation = "SHA1 | MD5 | 3DES" />

The <machineKey> tag supports three attributes.

Attribute	Option	Description
validationKey		Specifies the key used for validation.
	AutoGenerate	Specifies that ASP.NET generates a random key and stores it in the Local Security Authority ( LSA ). The AutoGenerate option is the default value.
	value	Specifies a manually assigned validation key. This value must be manually set to ensure consistent configuration across a network of Web servers ( a Web farm ). The key must be a minimum of 40 characters ( 20 bytes ) and a maximum of 128 characters ( 64 bytes ) long. If keys shorter than the maximum length are used, they should be created by a truly random means, such as by using RNGCryptoServiceProvider. The recommended key length is 128 hexadecimal characters.
decryptionKey		Specifies the type of encryption used for validation.
	AutoGenerate	Specifies that ASP.NET generates a random key and stores it in the Local Security Authority ( LSA ). The AutoGenerate option is the default value.
	value	Specifies a manually assigned validation key. This value must be manually set to ensure consistent configuration across a Web farm. The key must be a minimum of 40 characters ( 20 bytes ) and a maximum of 128 characters ( 64 bytes ) long. If keys shorter than the maximum length are used, they should be created by a strong random means, such as by using RNGCryptoServiceProvider. The recommended key length is 128 hexadecimal characters.
validation		Specifies the type of encryption used for data validation.
	SHA1	Specifies that ASP.NET uses SHA1 encryption.
	MD5	Specifies that ASP.NET uses MD5 encryption.
	3DES	Specifies that ASP.NET uses Triple-DES ( 3DES ) encryption. When 3DES is selected, forms authentication defaults to SHA1. When the validation attribute is set to 3DES, the view state validation technique uses 3DES encryption.

The following example sets both the validationKey and the decryptionKey keys to AutoGenerate.

<machineKey validationKey = "AutoGenerate"
   decryptionKey = "AutoGenerate"
   validation = "SHA1" />

ASP.NET Configuration   MachineKeySection Class