3.8 Configure MachineKey Validation Method - .Net 3.5 - Default


The machineKey element of the ASP.NET web.config specifies the algorithm and keys that ASP.NET will use for encryption. The Machine Key feature can be managed to specify hashing and encryption settings for application services such as view state, Forms authentication, membership and roles, and anonymous identification.

The following validation methods are available:
o Advanced Encryption Standard (AES) is relatively easy to implement and requires little memory. AES has a key size of 128, 192, or 256 bits. This method uses the same private key to encrypt and decrypt data, whereas a public-key method must use a pair of keys
o Message Digest 5 (MD5) is used for digital signing of applications. This method produces a 128-bit message digest, which is a compressed form of the original data
o Secure Hash Algorithm (SHA1) is considered more secure than MD5 because it produces a 160-bit message digest
o Triple Data Encryption Standard (TripleDES) is a minor variation of Data Encryption Standard (DES). It is three times slower than regular DES but can be more secure because it has a key size of 192 bits. If performance is not a primary consideration, consider using TripleDES

It is recommended that AES or SHA1 methods be configured for use at the global level.

Setting the validation property to AES will provide confidentiality and integrity protection to the viewstate. AES is the strongest encryption algorithm supported by the validation property. Setting the validation property to SHA1 will provide integrity protection to the viewstate. SHA1 is the strongest hashing algorithm supported by the validation property.


Machine key encryption can be set by using the UI, running appcmd.exe commands, by editing configuration files directly, or by writing WMI scripts. To set the Machine Key encryption at the global level using an appcmd.exe command:
%systemroot%\system32\inetsrv\appcmd set config /commit:WEBROOT /section:machineKey /validation:SHA1

Note: When Appcmd.exe is used to configure the <machineKey> element at the global level in IIS, the /commit:WEBROOT switch must be included so that configuration changes are made to the root web.config file instead of ApplicationHost.config.

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