By default, ASP.NET 4 uses the HMACSHA256 algorithm for hash operations on cookies and view state. It there any simple way to check the current Hash algorithm of ASP membership service?
There are two places (that I know of) to look --
Check your web.config -- you can set the hash for your membership services there which would override the machine settings.
<membership hashAlgorithmType="SHA1">...</membership>
if this doesn't apply to you, then you can check the machineKey in IIS.