If I encrypt some files in a folder using EFS, and then I upload such files to a cloud service, will they be encrypted on the cloud?
While the logical answer seems to be yes, I think in reality the answer must be no: because when I upload I am logged-in in the system, where these files are manipulated in a decrypted form...
Here's what I know: when you use EFS, which is what I'd like to do since I only use Windows, the encryption is "transparent" to the user. Files always appear decrypted because I am logged in in the system. My question is: if I use, for example, the Dropbox or the Mega cloud services and upload such files (with their app or through the browser), wouldn't the file be uploaded in a decrypted form, since I am logged in the system? Doesn't EFS only protect files locally?
I think this would work only if I uploaded such files from a different system or account where they appear as encrypted. Am I correct? Or totally misunderstanding how this works?
Yet if I use something like VeraCrypt I am back to square one because such files are encrypted only when inside their container. Once they are copied elsewhere, be it the temp working folder of my cloud sync app or just in the ram, they are decrypted and thus uploaded in such form. Is this also correct?
See, my purpose is to encrypt my local mail folder and then upload it to a backup service. It's a big archive and it's not feasible nor good practice to compress it in an encrypted archive because such archive takes days to upload on my normal second-world home connection, and my could sync service cannot just upload the little chunks of it that need to be updated.