Protection device and dongle and method for using the same

A method for suspending a physical protection of an object achieved by a protection device, comprising the following steps:

• establishing a first data connection between the protection device and a dongle;
• establishing a second data connection between a host device and the dongle;
• establishing a third data connection between the host device and a public transaction directory;
• receiving by the host device via the second data connection at least a first public key, a second public key, a third public key and a signed combined identifier incorporating at least the first public key and the second public key, wherein the second public key is different from the first public key, wherein the third public key is different from the first public key and from the second public key, wherein the signed combined identifier is signed with a third private key, which third private key is cryptographically associated with the third public key;
• requesting by the host device via the third data connection a search of transactions associated with the signed combined identifier within the public transaction directory;
• authenticating by the host device at least the first public key and the second public key using a signature of the signed combined identifier and using the third public key;
• authenticating by the host device the protection device using the first public key;
• authenticating by the host device the dongle using the second public key;
• responsive to determining that the search of the public transaction directory yields at least one transaction and that the first public key and second public key are authentic and that the protection device is authentic and that the dongle is authentic, sending by the host device an unlock request to the dongle via the second data connection;
• receiving by the dongle the unlock request;
• generating, in reaction to receiving the unlock request, by the dongle an unlock command;
• signing by the dongle the generated unlock command using a second private key, which is cryptographically associated with the second public key and stored in an internal memory of the dongle;
• sending by the dongle the signed unlock command via the first data connection to the protection device;
• receiving by the protection device the signed unlock command via the first data connection from the dongle;
• authenticating by the protection device the received unlock command using a signature of the received unlock command and using the second public key;
• responsive to determining that the received unlock command is authentic, controlling by the protection device an actuator of the protection device to suspend the physical protection of the protected object.