How to fix “Could not decrypt” errors in log files

Question

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?

Answer 1

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.

Solution:

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.