Not sure I'm getting you and probably didn't explain myself well. Here's what I mean:
- Host exposes a network share (1-time setup)
- Client mounts the network share (N-time setup, could be automated)
- Client creates a LUKS or VeraCrypt (or something else) file in that network share, secured with their key. The key is generated on the client and it doesn't leave the client or enter the host. (1-time setup)
- Client decrypts the image with their key and mounts it on the client (N-time setup, can be automated)
- Client modifies data in the decrypted vol
- Client unmounts the volume (N-time, not required)
- Client unmounts the network share (N-time, not required)
At no point does the client's key leave their computer and the host only ever sees encrypted data.
Subsequent uses without automation:
- Client mounts network share
- Client decrypts volume
That's at least how I understood OP's suggestion for putting LUKS images on the NAS and that is secure indeed. They're worried about performance.




Cryptomator encrypts files individually right?
E:
For the curious like me, here's how Cryptomator makes a directory with multiple encrypted files appear as a single vol when decrypted. From mount:
It uses its own fuse module to present it as a volume. The real directory has its own file structure:
This looks like a good option. Perhaps more flexible than using LUKS/VeraCrypt file, but those should work too if the underlying dir is on NFS/SAMBA.