What are the three key questions that a distributed consensus mechanism needs to answer? What are Bitcoin’s answers to these questions?

1) Who maintains the ledger of transactions? -> The blockchain does. It is a decentralized system so the system itself maintains the ledger of transactions. 2) Who has authority over which transactions are valid? -> The signature (private & public key) is checked by peers and by proof-of-work the blocks are validated. A transaction is valid when the signature is set by the corresponding private key, this can be checked by using the public key. Once the transactions are sent to the network, 51% of the nodes need to validate, by proof-of-work mining, in order for the block to be send to the blockchain. 3) Who creates new currency? -> Miners generate BTC through a competitive and decentralized process called the mining process. This process involves individuals that are rewarded by the network for their services. BTC miners are processing transactions and securing the network using specialized hardware and are collecting new BTC in exchange.