An electronic device generates a dynamic security code for a card transaction, e.g. a card not present transaction. The electronic device receives a user request to generate a dynamic security code. The electronic device sends a time request to a time source and receives a message including a time from the time source. The electronic device determines an authenticity of the message containing the time and computes the dynamic security code based on the time received in the message and a key stored at the electronic device. The electronic device causes the dynamic security code to be displayed on a display of the electronic device. The electronic device may be capable of computing a dynamic security code for a plurality of different cards. The electronic device may be a smart phone, a tablet, or a personal computer.