To fix this, you must explicitly define the validationKey in the web.config so that it is identical across all servers in the farm.
Use code with caution.
In the landscape of ASP.NET web application development, security is often a complex tapestry of authentication protocols, authorization checks, and encryption standards. Buried deep within the configuration files lies one of the most critical, yet frequently misunderstood, components of the ASP.NET security infrastructure: the <machineKey> element. machinekey validationkey in web.config
ASP.NET Web Forms relies heavily on View State to maintain state across postbacks. This data is serialized, base-64 encoded, and sent to the client as a hidden field. When the client posts the page back, the server deserializes this data to restore the state.
Never reuse the same machineKey across different applications. If one app is compromised, the attacker could use that key to forge tokens for your other apps. To fix this, you must explicitly define the
It can be used to generate application-specific session IDs, ensuring session variables are isolated between different applications on the same server. Why You Might Need to Configure It
<system.web> <machineKey validationKey="..." decryptionKey="..." validation="SHA1" decryption="AES" /> </system.web> Buried deep within the configuration files lies one
<configuration> <location path="App1"> <system.web> <machineKey validationKey="KEY_FOR_APP1..." validation="SHA256" ... /> </system.web> </location> <location path="App2"> <system.web> <machineKey validationKey="KEY_FOR_APP2..." validation="SHA256" ... /> </system.web> </location> </configuration>
When you create a new ASP.NET project, you rarely see a <machineKey> entry in the web.config . That’s because, by default, ASP.NET generates a automatically on application start.
You can use online tools, but remember: . The operator could record your key and decrypt your live sessions.
Because the keys on Server A and Server B do not match, Server B cannot validate the HMAC generated by Server A. The result is a runtime error, usually the dreaded "Invalid Viewstate" exception, or a forced log-out if the authentication ticket fails validation.