Hunting and Decrypting EFS Encrypted Files

At home last week, I started doing some preparations for upgrading my home server from Windows Server 2012 R2 to Windows Server 2016. This server was originally installed using Windows Server 2012 R2 Essentials and since, I have performed a Standard edition, edition upgrade on the machine which means that the host has ADDS, ADCS, NPS and some other roles installed as part of the original Essentials server installation. We all know that unbinding ADDS and ADCS can be a bit of a bore which is why nobody in the age of virtualization should be installing ADDS and ADCS on a single server together but that’s by the by.

When I started looking at decommissioning the ADCS role, I noticed that an EFS certificate had been issued to my domain user account. I’ve never knowingly used EFS but the presence of a certificate for that purpose lead me to believe there may be some files out there so I started looking.

EFS was a technology that appeared circa Windows XP to allow users to encrypt files before BitLocker was a thing. It was a nice idea but it was troubled and flawed in that it was enabled by default and users could self-encrypt files without IT having implemented the proper tools to allow them to recover the files when disaster struck.