The invention relates to an electronic circuit comprising: a first random-access data storage element, a processing module designed to delete the first storage element, and an access terminal which is connected to the processing module and receives a first power signal supplied by a first power source external to the electronic circuit. The circuit also includes a second random-access storage element in which a key is stored, said key being used to encrypt the data and a second power source which is built into the electronic circuit and supplies a second power signal to the processing module. The processing module is designed to detect an unauthorized access attempt by comparing the first and second power signals and to delete the key when the processing module is powered by the second power source.