Looking at encrypted Dropbox Alternative Sync.com, anyone know anything about it.

See here:
https://support.apple.com/en-us/HT202303

Found by googling:
is icloud drive encrypted


If you want an overtly encrypted drive, is there a reason that you can't make an encrypted disk image in sparsebundle format (use Disk Utility.app), put it in your Dropbox folder, and then use that? Notwithstanding that you'd have to mount it to use it, and thus enter your password, is there a reason that won't work?

If you don't know what a sparse bundle is, see here:
https://en.wikipedia.org/wiki/Sparse_image

 

You don't have to constantly make them. Simply make one and keep using it. The sparse bundle format ensures it consumes no more space than needed.

You can arrange to open the disk image automatically at login (Login Items). To do this, the password must be stored in your keychain. This means the security of the encrypted disk image is only as good as the security of your keychain file. That is, a stored key or password has different risks than one that's not stored.

Finally, iCloud Drive is encrypted, according to the link I pointed at.
Does that meet your needs?


Please explain what you intend to defend against. Encryption is a defense (defensive tactic). It defends against certain things, and not others. If you apply encryption as a defense against the wrong thing, it can be completely useless or nearly so.

 

No, that's incorrect.

The disk image is created as read-write. It then acts exactly like any "external disk".

A read-only disk image is exactly that: read-only. While that may be what you're familiar with, such as from installing software, it's certainly not the only kind of disk image there is.

I suggest doing a few trials with Disk Utility. First, make a read-write disk image. It doesn't need to be encrypted yet. Mount it. Put files on it. Delete files from it. Put other files on it. Unmount it. Copy it to a USB thumb drive, or to the Dropbox folder. Open it there. Observe that all the files you copied to it are still there.

After you understand disk images in general, then you can make an encrypted read-write sparse bundle disk image. It should work the same as the unencrypted one, except for the password. And if you store the password in your keychain (an optional checkbox in the mounting dialog), then it will work exactly the same until you lock your keychain or delete the password from it.

 

The recipient would need to mount the disk image located in the Dropbox folder.

As before, I suggest that you try this to see what happens. Try it first with an unencrypted disk image, then with an encrypted one. The disk image need not be large. Just put a handful of small to medium files on it. Then try it and see what happens.

If there are problems, you're in the best position to see them and identify them, because you're the only person who knows how you want the process to work.