I know movies are often not the best reference however in MI3: Ghost Protocol they used highly encrypted data vaults backed by hard currency. This is not a far fetched idea. http://en.wikipedia.org/wiki/Digital_gold_currency
(I know wickepedia is not the best of sources but it gives you an idea) As you had already mentioned Regulators perhaps a Guild that has a presence per planet or system that can exchange for a fee local currency from the standardized encrypted data vault funds. Each vault would contain all the information on amount of hard currency in each individual or corporate account , transactions, withdraws and so on so forth and each guild would use specialized couriers with even more specialized encrypted data vaults to update a centralized database on regularly scheduled occasions to circumvent communication breakdowns.