A method for secure data transmission between a first device and a second device (5A, 5B, 5C); the method comprising the following steps: a) establishing a secure communication channel between the first device and the second device (5A, 5B, 5C) through a handshaking process using a secure transmission protocol, which provides confidentiality and integrity of the data transmitted over the secure transmission channel, as well as identity of the first device and second device, between which the transmission takes place; b) once said secure communication channel has been established, transmitting a set of symmetric encryption keys (sekj(k)) from the first device to the second device under secure transmission conditions using said secure transmission protocol through the secure communication channel, and storing the set of symmetric encryption keys (sekj) in respective protected storage memory areas at the fist device and at the second device (5A, 5B, 5C); c) once the set of symmetric encryption keys (sekj(k)) have been transmitted from the first device to the second device, closing the secure communication channel; and wherein, when the second device (5A, 5B, 5C) is required to transmit data to the first device, the following steps are performed: d) selecting one of said symmetric encryption keys (sekj(k)) at the second device (5A, 5B, 5C); e) generating a data bunch at the second device (5A, 5B, 5C) and encrypting the data bunch with the selected symmetric encryption key (sekj(k)); f) establishing a communication channel between the second device and the first device without said handshaking process, and transmitting the encrypted data bunch from the second device (5A, 5B, 5C) to the first device; g) decrypting the encrypted data bunch at the first device using the selected symmetric encryption key (sekj(k)). a) establishing a secure communication channel between the first device and the second device (5A, 5B, 5C) through a handshaking process using a secure transmission protocol, which provides confidentiality and integrity of the data transmitted over the secure transmission channel, as well as identity of the first device and second device, between which the transmission takes place; b) once said secure communication channel has been established, transmitting a set of symmetric encryption keys (sekj(k)) from the first device to the second device under secure transmission conditions using said secure transmission protocol through the secure communication channel, and storing the set of symmetric encryption keys (sekj) in respective protected storage memory areas at the fist device and at the second device (5A, 5B, 5C); c) once the set of symmetric encryption keys (sekj(k)) have been transmitted from the first device to the second device, closing the secure communication channel; d) selecting one of said symmetric encryption keys (sekj(k)) at the second device (5A, 5B, 5C); e) generating a data bunch at the second device (5A, 5B, 5C) and encrypting the data bunch with the selected symmetric encryption key (sekj(k)); f) establishing a communication channel between the second device and the first device without said handshaking process, and transmitting the encrypted data bunch from the second device (5A, 5B, 5C) to the first device; g) decrypting the encrypted data bunch at the first device using the selected symmetric encryption key (sekj(k)).