Abstract: To conduct a payment transaction at a merchant's point of sale using a mobile device, the mobile device initiates an authenticated communication session with a payment agent. The payment agent is an entity responsible for facilitating a payment transaction between the merchant and purchaser via their respective financial institutions. During the authenticated communication session, response to an input indicating the user of the mobile device wishes to make a payment, the mobile device generates a unique payment key that is based on at least one unique data of the mobile device. The mobile device transmits the payment key to the payment agent, and then transfers a copy of the payment key to the point of sale system. The merchant's payment system that transmits the payment key to the payment agent in a transaction request.