None of your examples make any sense to me.  It seems like it&#x27;d be a lot easier and safer to simply piggyback on the existing Bitcoin blockchain.  To use your trivial example of a two person blockchain, what are you trying to do?  If we trust each other already, then we don&#x27;t need a blockchain, we just need signed transactions.  If we don&#x27;t trust each other then having our own private blockchain solves nothing, as whoever has more processing power can perform a 51% attack on the network, deny the other person&#x27;s transactions, and double-spend your own.  Having a blockchain makes no sense in this context.<p>That&#x27;s why you use the biggest existing blockchain, not a separate one.  There&#x27;s no way in hell I can cheat you if we do our transactions on the Bitcoin blockchain, because I can&#x27;t beat the overall hashing power of the system, but I sure as hell can beat your hashing power if we have a blockchain that&#x27;s only for two people, or just for a neighborhood.