The problem of course is the payee can't verify that one of the owners did not doublespend the coin. A common solution is to introduce a trusted central authority, or mint, that checks every transaction for double spending. After each transaction, the coin must be returned to the mint to issue a new coin, and only coins issued directly from the mint are trusted not to be double-spent.The problem with this solution is that the fate of the entire money system depends on the company running the mint, with every transaction having to go through them, just like a bank.We need a way for the payee to know that the previous owners did not sign any earliertransactions. For our purposes, the earliest transaction is the one that counts, so we don't careabout later attempts to double-spend. The only way to confirm the absence of a transaction is to be aware of all transactions. In the mint based model, the mint was aware of all transactions and decided which arrived first. To accomplish this without a trusted party, transactions must be publicly announced [1], and we need a system for participants to agree on a single history of the order in which they were received. The payee needs proof that at the time of each transaction, the majority of nodes agreed it was the first received.
解读：实际来说这就不是一个币，它只是一个数字签名，随之而来的二个问题，我怎么确认我是否有那么多钱？怎么确认我没把同一笔钱刚给同时给2个人？传统现金交易不会有这样的问题，传统第三方中介也不会有这样的问题。因为都是第三方来背书。第一个问题是追溯来解决，每一次交易都在链上，很简单就能查到。第二问题，比特币交易需要全网广播，如果双花，那么就会有2条交易信息，最后实际以多数人接受到的那条为主。就像在一个透明的房子里，A给B转账必须要说出来，大家都听到记录，A再想给其他C转账的时候，大家大都能看到你没钱了，不做数，只有被大多数人认可的交易才生效。
