It is a database which stores: - Serial numbers and hashes of public keys of clients who have activated this serial number (**users can authorize with it**) - Serial number expiration dates and dates of the last connection using this serial number (**is used for calculating expiration date for every serial number**). - Hashes of [[3. Conditional Transactions|conditional transactions]] for each client. That is, if several clients have authorized with a serial number, each will have its own set of transactions (**conditional transactions are necessary for providing advanced VPN service, when client wants to choose service provider by his own, these kind of transactions are tied to the client**). - [[orders|Order]] limits which are minimum and maximum allowed number of units in an order, and maximum allowed cost per unit (**this is important to avoid some over and low prices in the market, providing fair service**). - User's reports (**we always collect data about all technical problems and user cases to make our service better**). - Node list for clients (**these nodes are collected in one list because they will be offered to the client as service providers**). When you buy a serial key, the payment gate provides it for you.