An online commerce system facilitates online commerce over a public network using an online commerce card. The "card" does not exist in physical form, but instead exists in digital form. The online commerce card is issued electronically to a customer by an issuing institution. The issued card is assigned a permanent customer account number that is maintained on behalf of the customer at the issuing institution to remove the risk of the number being lost or s stolen. When the customer desires to conduct an online transaction, the customer asks the issuing institution to issue a transaction number for a single transaction. The issuing institution generates a temporary transaction number and associates it with the permanent account number in a data record. The customer receives the transaction number and submits that number to the merchant as a proxy for the customer account number. The transaction number looks like a real card number and the merchant handles the transaction number in the same manner as any regular credit card number. When the merchant submits an request for authorization, the issuing institution recognizes the number as a transaction number for an online commerce card. The issuing institution references the customer account number, using the transaction number as an index, and processes the authorization request using the real customer account number in place of the proxy number. Once the authorization request is processed, the issuing institution once again exchanges the transaction number for the customer account number and sends an authorization reply back to the merchant under the transaction number.