the transaction command is then transmitted to the electronic device 200 1 via the usb key 220 1 to be inserted in a message addressed to the creditor such a message can be for example an electronic mail an sms short message service or an mms multimedia messaging service the insertion of the encrypted and signed information in the message addressed to the creditor can be performed automatically by the application used by the debitor to launch the transaction or can be performed by the debitor himself the message can also include the application enabling the creditor to process the message received to perform the transaction the message comprising the encrypted and signed information is then transmitted to the creditor step 410 on receipt of the message step 415 the electronic device of the debitor 200 2 launches preferably automatically the application for processing the message received to perform the transaction this application can be previously installed on the electronic device 200 1 stored in the electronic entity 100 2 and transmitted to the electronic device 200 1 at the request of the latter or automatically when the electronic entity 100 2 is placed close to the usb key 220 2 or transmitted with the message if the electronic entity 100 2 is not close to the usb key 220 2 to enable the exchange of data between these two systems an alert message is preferably displayed on the electronic device 200 2 to prompt the creditor to approach the electronic entity 100 2 of the usb key 220 2 the encrypted.