What is Reverse mode?

[physkets]

Hi, I hope this isn't a stupid question.

Could someone explain to me what exactly "reverse mode" is?
The documentation states that: "In reverse mode, gocryptfs provides an encrypted view of a plain-text directory. The primary use-case are encrypted backups."
( https://nuetzlich.net/gocryptfs/reverse_mode_crypto/ )

What exactly does that mean?

[lquenti]

lets say you have a dropbox or whatever sync that just looks whats there, and then syncs it up. Then you could reverse mount it in that magic directory.

Or, you reverse mount a directory, and then click "upload directory" in your cloud backup web form.

[lquenti]

i.e. you get a "virtual" cipher folder without needing to actually have the duplicated storage on disk.

[physkets]

I'm sorry, I'm afraid I still don't get it.

I mostly understand what it is to 'mount' a filesystem or some such, which is to take something that is raw binary data/objects, and make it readable/writable.

Now what is it to 'reverse mount'?
And what do you mean by 'magic directory'?

Is it that the data actually only lives on the cloud, and then like say gvfs allows mounting a Google Drive of OneDrive folder, this also mounts that at a local location?

If yes, so then I assume this is good for when there you only want one source/storage location, and it is just 'accessed' from everywhere else?

And if all of that is correct, then why does this scenario need AES-SIV encryption instead of the AES-GCM variety?

[rfjakob]

"reverse mount" here is an abbreviation of "gocryptfs reverse mode mount".

Aes-siv because it's deterministic, aes-gcm is not.