One of the often heard criticisms of Bitcoin concerns the relatively long waiting period before a transaction is confirmed: 10 minutes on average. This raises the question how Bitcoin will ever be useful in brick-and-mortar stores where you don’t want to wait for 10 minutes (on average, the time between blocks can be over half an hour!) with your groceries or before you get your coffee. As it turns out, while the security of a confirmed transaction is unmatched, even an unconfirmed transaction is already very useful. And there are techniques that can be used to enhance the security of these so-called 0-confirmation (0-conf) transactions.