We have been experiencing a cryptographic exception for several months now.

It simply causes a server warning on logging in or when an AntiforgeryToken is verified. It appears randomly.

I have looked at issues that cause similar error howerver none of them applies to us.

This is the error we are getting:

Error occurred during a cryptographic operation.
   at System.Web.Security.Cryptography.HomogenizingCryptoServiceWrapper.HomogenizeErrors(Func`2 func, Byte[] input)
   at System.Web.Security.Cryptography.HomogenizingCryptoServiceWrapper.Unprotect(Byte[] protectedData)
   at System.Web.Security.FormsAuthentication.Decrypt(String encryptedTicket)
   at Umbraco.Core.StringExtensions.DecryptWithMachineKey(String value)
   at Umbraco.Web.UmbracoHelper.DecryptAndValidateEncryptedRouteString(String ufprt, IDictionary`2& parts)
   at Umbraco.Web.Mvc.RenderRouteHandler.GetFormInfo(RequestContext requestContext)
   at Umbraco.Web.Mvc.RenderRouteHandler.GetHandlerForRoute(RequestContext requestContext, PublishedContentRequest publishedContentRequest)
   at Umbraco.Web.Mvc.RenderRouteHandler.GetHttpHandler(RequestContext requestContext)
   at System.Web.Routing.UrlRoutingModule.PostResolveRequestCache(HttpContextBase context)
   at Umbraco.Web.UmbracoModule.RewriteToUmbracoHandler(HttpContextBase context, PublishedContentRequest pcr)
   at Umbraco.Web.UmbracoModule.ProcessRequest(HttpContextBase httpContext)
   at Umbraco.Web.UmbracoModule.<Init>b__12_3(Object sender, EventArgs e)
   at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)



Request information: 
    Request URL: https://myaccount.mydomain.com:443/umbraco/RenderMvc 
    Request path: /umbraco/RenderMvc 
    User host address: 134.67.123.89
    User:  
    Is authenticated: False 
    Authentication Type:  
    Thread account name: WIN-SOMETHING\IWPD_33(mydomain) 

Thread information: 
    Thread ID: 13 
    Thread account name: WIN-SOMETHING\IWPD_33(mydomain) 
    Is impersonating: False 
    Stack trace:    at System.Web.Security.Cryptography.HomogenizingCryptoServiceWrapper.HomogenizeErrors(Func`2 func, Byte[] input)
   at System.Web.Security.Cryptography.HomogenizingCryptoServiceWrapper.Unprotect(Byte[] protectedData)
   at System.Web.Security.FormsAuthentication.Decrypt(String encryptedTicket)
   at Umbraco.Core.StringExtensions.DecryptWithMachineKey(String value)
   at Umbraco.Web.UmbracoHelper.DecryptAndValidateEncryptedRouteString(String ufprt, IDictionary`2& parts)
   at Umbraco.Web.Mvc.RenderRouteHandler.GetFormInfo(RequestContext requestContext)
   at Umbraco.Web.Mvc.RenderRouteHandler.GetHandlerForRoute(RequestContext requestContext, PublishedContentRequest publishedContentRequest)
   at Umbraco.Web.Mvc.RenderRouteHandler.GetHttpHandler(RequestContext requestContext)
   at System.Web.Routing.UrlRoutingModule.PostResolveRequestCache(HttpContextBase context)
   at Umbraco.Web.UmbracoModule.RewriteToUmbracoHandler(HttpContextBase context, PublishedContentRequest pcr)
   at Umbraco.Web.UmbracoModule.ProcessRequest(HttpContextBase httpContext)
   at Umbraco.Web.UmbracoModule.<Init>b__12_3(Object sender, EventArgs e)
   at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

We are running on a dedicated server. We don't have a machinekey, we don't require it and we won't set it up as this has implications to our member's passwords. We simply can't do it at this stage.

We are running Umbraco 7.15.3.

The error started appearing on version 7.15.1 though some time in November but back then it appeared maybe twice a month, now it is showing up every day several times at least.