SSH rejecting key file with extended attributes

In my .ssh/ directory, when running

$ ssh-add dev Permissions 0755 for 'dev' are too open.

But looking at the dev file

$ ls -lF dev -rw-------@ 1 me staff 1675 Feb 3 09:37 dev

The @ at the end means that there are extended attributes. So I then run $ xattr dev com.apple.metadata:kMDItemWhereFroms com.apple.quarantine

It looks to me that the permissions are what they should be (600) where is the discrepancy coming from, and how do I fix it?