I think spoofing will be difficult unless you can dump the key from a specific AirTag (already done, but it's a manual process involving disassembly and advance

I think spoofing will be difficult unless you can dump the key from a specific AirTag (already done, but it's a manual process involving disassembly and advanced skills and equipment). Replay attacks may be possible, but we will have to wait to see if the protocol is entirely passive. The iPhone could broadcast a challenge to the AirTag and transmit the signed response and response delay. The delay should be fairly tightly bounded. The AirTags do have a clock as I understand it, but drift is inevitable, so it wouldn't be a tight bound.