Difference between revisions of "Setting the Machine Key"

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m (How to solve Validation of View State MAC failed problem moved to Setting the Machine Key: Setting the machine key solves a range of problems, including but not limited to ViewState MAC validation errors.)
(add to merchant user guide category)
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'''<system.web>''' And paste in the '''<machineKey ... />''' on the next line.  
'''<system.web>''' And paste in the '''<machineKey ... />''' on the next line.  
Save the web.config file.
Save the web.config file.
[[Category:Merchant User Guide]]

Latest revision as of 14:09, 18 August 2009

Sometimes when using ASP.NET enabled website you may get the following error

Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

There are several ways to get around this problem:

  • Host your site on a server that never restarts or recycles! Obviously, this is impossible!
  • Disable ViewstateMac by putting this enableViewStateMac="false" in your web.config. This approach is not 100% secure.
  • Configure ASP.NET to not use Auto-Generated Key but rather a predefined key. This is the preferred method.

The last option, using predefined key, is the most secure and suggested method to use. There is a free Machine Key generator tool available at the following link


In order to generate the key using this tool leave the defaults in place; validation key length 64, encryption key length 24, type sha1. Then click Generate to create a random machine key for you and copy the result.

Now open the web.config file from your site. Find around line which shows <system.web> And paste in the <machineKey ... /> on the next line. Save the web.config file.