Here’s a scenario, you have a PKI, it all seems to be healthy, but when you try and use the certificates on your client systems, you get ‘unexpected results’
Alternatively, you have issued certificates previously, but when you come to renew, systems fail with ‘unexpected results’
At this point, you might be ready to tear your hair out, or just go home for the night (or the month…). Instead, its worth checking the permissions on the folder where the client OS stores the systems private keys. If the ACL has been changed from the system default, results can be, lets say, unpredictable.
On XP and 2003 systems, the folder in question is “c:documents and settingsall usersapplication datamicrosoftcryptorsamachine keys”. This folder must NOT be inheriting permissions from its parent, and the ACL for the folder should contain Everyone:RW:This Folder Only, Administrators:F:This Folder Only – and nothing else! If you need to grant a service account access to one of the keys, add the account to the ACL on the specific file within the folder. Each file in the folder has explicit permissions defined, which will vary depending on the application that generated it, as a minimum they must include System:F and Administrators:R
Quite why the systems private keys would be stored in the All Users profile, I don’t know, but it has been moved in Vista and Server 2008 to “C:ProgramDataMicrosoftCryptoRSAMachineKeys”, which seems far more logical, and prevents errors where misguided administrators reset the permissions on the entire All Users profile. The ACL structure for the folder and its files remains the same.
A final word of warning – as with anything you read on the web, its always worth checking these ACL’s against a system in your environment that you know to be working, if you have one. It doesn’t matter how much you trust the writer, there’s nothing like the comfort of seeing a working system with your own eyes before you propose a change to hundreds or thousands of systems…
See the next post for info on scripting changes to the ACL’S