Instead of metal, can we not use bones instead to craft keys, if you can make a curved hook and sure a simple key would work, right?
My idea would be to change the key system all together.
Keys and Gates are passwords, when a gate is created you give the gate a password, you get a pre-made key with the password on it. Key password must match gate password to open.
The password on the key is set and unchangeable, the password on the gate can be changed (wood/bone resource) + use of the current correct key will change the gate lock (password) and issue a new key. Now you have a current key and old key (mostly useless).
Furthering the idea, have bone keys and metal keys. (Metal for metal locks too)
Passwords on bone keys and locks are limited to 4 characters, passwords on metal keys limited to 8 characters.
You can guess where this is heading.
Allow it possible to craft keys to a password, so you can make duplicate, or if you know a friends password craft your own key!
Opens the possibility of key cracking skill/picklocking, where if a key fails to open it says which letters are in the right place, and which letters are right but in wrong place, a classic mini puzzle game.
Obviously using just letters, a 4 letter password (all lower case) is 456,976 combinations.
Abuse is possible, if someone cracks your gate password they could fit a new lock

But on the plus side if you loose your key and you still know the password, grab a few bones and remake it. Obviously if someone fines the lost key maybe they could find your gate!.