/etc/docker/key.json

/etc/docker/key.json 描述信息：

This is the dockerd key for TLS connections.
in web format, that docker uses when connecting to other TLS servers like registries.
It's automatically generated by the docker engine on startup, so there's no risk if deleted. 
You should treat it as sensitive since TLS connections using an exposed key are not secure.

[root@localhost ~]$ cat /etc/docker/key.json 
{
    "crv":"P-256",
    "d":"-o-BHLQyZQDlPUvzOuAFPyoECBHMHApaJCTy2ProBdE",
    "kid":"3ZXC:EHNN:OXY7:SWUD:DBAU:QHU5:PWOX:HDD3:SNQ7:HYQD:HYBI:HXZ4",
    "kty":"EC","x":"CY2phVcW87xBejNSxnAAL2XU-r2vELa_246zaKgNZrU",
    "y":"Ev-JgNcf7PsRXCB7nDW6iASUMOhojRj5SS45ywI6NHQ"
}