Some embodiments relate to a data processing method comprising selecting a key from a plurality of previously stored keys, depending on at least on predefined criterion relating to at least one current value of at least one given repository. Other embodiments relate to a reception method comprising receiving second data obtained by applying, to first obtained data, a first cryptographic function using a key selected from a plurality of previously stored keys, depending on at least one predefined criterion relating to a current value of at least one given repository and for obtaining the first data by applying, to the second received data, a second cryptographic function using a second key associated with the selected key. Further embodiments relate to a processing device and a reception device that respectively implement the processing method and the reception method.