My Sitecore version is 7.2 (150408). I am getting a lot of "Could not decrypt" errors in log files.

ERROR Could not decrypt

valueB932413866B90802C114BA50892879F7B6FABD54309CC8FCF630D72FDBBA7419046DA7C9069650348C5118CF32DFB94756DBA3369CD56EF9DC6AFB432AB83D6A53CA0109D17FDAAF2ABD2C33E40A9B2A7A5DE1C9ABB04279DBE12C3FF97667C0662C366CE77126357671DA3FBEDE831DF9A0E39CDD5981AE711C5EF949BE66480A6FABD0C3EB332D91F6913A86764B1BD92D47A8A9AE27F2F3A31D22C5A87EE5 Exception: System.Web.HttpException Message: Unable to validate data. Source: System.Web at System.Web.Configuration.MachineKeySection.EncryptOrDecryptData(Boolean fEncrypt, Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Boolean useValidationSymAlgo, Boolean

useLegacyMode, IVType ivType, Boolean signData) at System.Web.Security.FormsAuthentication.Decrypt(String encryptedTicket) at Sitecore.Security.Authentication.AuthenticationHelper.GetSavedUser(String cookieName)

What can be the possible reason?


Problem Root Cause

We have also faced some kind of same error. Machine key is used to encrypt/decrypt data like view state. We were having multiple CD servers. As we didn't have the same Machine key on multiple CD servers, this leads to invalid data issue.


You need to set static MachineKey. To set a machine key, add a MachineKey element inside System.Web in your web.config file:

You can review this blog on how to generate machine key https://blogs.msdn.microsoft.com/amb/2012/07/31/easiest-way-to-generate-machinekey/

Also this is known issue article: https://kb.sitecore.net/articles/051243. You can review this also for more information.

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