A system for ascertaining identity of a customer based on a single card carried by the customer. The card bears a machine-readable code, which is transmitted to a database at a remote location. The database locates a record associated with the code, which contains one or more account numbers. Associated with each account number is a Personal Identification Number, PIN. (It is possible that all PINs are identical.) The customer selects an account number, and is asked for a PIN. If the PIN given by the customer matches that of the account number, the customer is concluded to be the valid owner of the account, and a transaction is allowed to proceed.