An electrical circuit including a controllable oscillator, a transmission line and a control loop. Thus, the dusting brush can be operated easily and conveniently, thereby facilitating the user operating the dusting brush. The microlens array and the light-source receiver are arranged so that when each of the light sources is arranged on the light-source receiver there is associated therewith exactly one of the microlenses. A data valid signal propagating with valid data adds further selection, such that only stages with valid data are stalled. The host device receives the re-encrypted symmetric key from the key management server, decrypts it using the host private key, and decrypts the encrypted VMI using the symmetric key.