No. Only key holders have access to the data being shared. It is up to you to authorize every share with a key. Single use keys can also be generated. There

No. Only key holders have access to the data being shared. It is up to you to authorize every share with a key. Single use keys can also be generated. There are relays if you need them due to firewalls: "We also provide such additional methods of ensuring connectivity as relay and tracker servers." But you can opt out of this config.