Ok, I know that blockchain is public knowledge. But, than, there are experiments like zcash which encrypt sender receiver and amount information and they still work.
I'm considering whether p2p blockchain arbitration service is possible. For example, you want to exchange ETH for BTC. A blockchain generates 2 addresses, one of which is for BTC, other is for ETH. Once both addresses are funded, funds of both are forwarded to the recipients. To do this via blockchain, there should be a secure way to store and use private keys on blockchain.
Is this completely impossible, or are there any indications that one could do something like that?