There are M-Disks. These are CD/DVD/BluRay disks which use a drive with a higher power laser and work by ablating a metal layer, rather than a photosensitive dye as in the lower-powered disks. Regular drives will read both kinds.
For a small amount of data (crypto keys?), consider deep laser engraving on stainless steel. That's very durable. Or even engrave text into stainless steel with a small CNC mill.
You can engrave QR codes, bar codes, etc. But there's a lot to be said for engraving plain text.
Just get a set of alpha numeric punches and blank dog tags for crypto keys. Much cheaper than engraving.
Good answer. A set of punches is about $25, and a manual dog tag stamping machine (set wheel to desired character, pull lever) is about $250. That will get you a tough piece of metal.