A computer-implemented method, performed in a user control device, for generating and transmitting a Command data packet including Command data configured to operate a control unit, the Command data having a plurality of attributes associated therewith, the method comprising, under control of a processor of said user control device: - requesting, from a remote key issuing platform, a time-limited encryption key, and receiving said time-limited encryption key from said key issuing platform, said time-limited encryption key being generated by said key issuing platform using a base key selected according to a specific one or more of said attributes associated with said Command data; - receiving, with said time-limited encryption key from said key issuing platform, a Checksum value representative of at least a subset of said plurality of attributes of said Command data; - encrypting at least said Command data using said time-limited encryption key; - constructing a Command data packet comprising a plain value header and an encrypted Command Payload, said plain value header including said Checksum value; said Command payload comprising at least the encrypted Command Data; and - transmitting said Command data packet to said control unit; characterized in that: • said Checksum value representative of at least a subset of said plurality of attributes of said Command data includes said specific one or more attributes used by said key issuing platform to select the base key; and • said plain value header includes data representative of said subset of said plurality of attributes of said Command data except the specific one or more attributes used by the key issuing platform to select the base key. - requesting, from a remote key issuing platform, a time-limited encryption key, and receiving said time-limited encryption key from said key issuing platform, said time-limited encryption key being generated by said key issuing platform using a base key selected according to a specific one or more of said attributes associated with said Command data; - receiving, with said time-limited encryption key from said key issuing platform, a Checksum value representative of at least a subset of said plurality of attributes of said Command data; - encrypting at least said Command data using said time-limited encryption key; - constructing a Command data packet comprising a plain value header and an encrypted Command Payload, said plain value header including said Checksum value; said Command payload comprising at least the encrypted Command Data; and - transmitting said Command data packet to said control unit; characterized in that: • said Checksum value representative of at least a subset of said plurality of attributes of said Command data includes said specific one or more attributes used by said key issuing platform to select the base key; and • said plain value header includes data representative of said subset of said plurality of attributes of said Command data except the specific one or more attributes used by the key issuing platform to select the base key. - transmitting said Command data packet to said control unit; characterized in that: • said Checksum value representative of at least a subset of said plurality of attributes of said Command data includes said specific one or more attributes used by said key issuing platform to select the base key; and • said plain value header includes data representative of said subset of said plurality of attributes of said Command data except the specific one or more attributes used by the key issuing platform to select the base key. • said Checksum value representative of at least a subset of said plurality of attributes of said Command data includes said specific one or more attributes used by said key issuing platform to select the base key; and • said plain value header includes data representative of said subset of said plurality of attributes of said Command data except the specific one or more attributes used by the key issuing platform to select the base key.