Backing up & restoring individual encrypted files?

Bert, you may need to raise this specific question directly with Acronis about the effect of backing up encrypted files / folders using Windows EFS.

I have never used Windows EFS and it is only available in the Pro or Enterprise versions of Windows, so will only be available to some users here, not all. It is also old technology that dates back to Windows 2000 when it was first introduced.

Doing a partition backup that includes EFS encrypted files will depend on whether the user who encrypted the files is the same user who is performing the backup or not?  If it is the same user, then from what I understand, the files may be stored as unencrypted in the backup by virtue of the encryption being transparent when the user / owner is signed in.  If the backup is done by a different user then the files should be stored as encrypted because these files are not available to that different user.

One issue that may arise is whether the partition being backed up is the OS partition or not, as my understanding is that the encryption keys are stored with the OS and these are required in order to allow the decryption of the files / folders.  This becomes an issue if you restore the encrypted files / folders to a different computer where the original user / owner is not known and therefore there are no decryption keys available to give access to the data.

My personal rule of thumb - if the folder is encrypted with anything else at the time of backup, I assume it's not going to be recoverable because the encryption, if doing it's job, should prevent anything from being able to back it up as well, unless doing a complete sector-by-sector backup of the entire drive.

If you really want to test, use a small test folder and enable the EFS on it with just a couple of small test files already inside - make sure the folder is locked with EFS and run a backup of the folder with Acronis.  Restore the folder from Acronis to a new temporary\test location.  See if you can unlock the folder with EFS and get access to the files inside.  If you can, can you actually open those test files (.txt or .doc or whatever you want to use).  

Doing a test is probably the only sure way to know; things in Windows don't always work as documented, even if you can find the documentation.

Couple that with the fact that my understanding of "partition backups" has always been hazy at best. Maybe they're not as magical as I imagine.

Next time I have the backup media mounted, it shouldn't take more than a few minutes to find out what's going on.

Well, it worked as I'd hoped. I've been doing partition backups, and was able to recover an EFS encrypted file to a new directory (on the same machine) and it retained its encrypted state, and I was able to read it. I've been backing up those EFS files for years, never having to restore any of them and never even thinking about it. I'm glad everything just works now that I finally tested this out.

The problem of recovering EFS files to a different machine or replacement disk is addressed by making backups of the certificates/keys used to encrypt the files and installing those keys on the new computer or disk. If a full restore of the original mass storage complement is done, that wouldn't be needed.

I currently have my and my wife's certificates backed up on several pieces of external media kept in what I hope are secure places. I try to remember to make fresh backups from time to time to protect against bit rot. 

Don't have the first clue how any of this works on Windows 10.

EFS is an entirely different layer of encrytion than say Bitlocker is.  You can think of it this way, Bitlocker uses a hardware layer for encryption whereas EFS uses a software layer of protection.

The most secure way to encrypt data is with Bitlocker or an equivelent.  EFS has shortcomings which render it less secure.  So if you want to truly keep data secure use Bitlocker or another hardware type encryption.