FIELD

The invention relates to a security device and a field bus system to support a secure communication by means of a field bus.

BACKGROUND

Communication security in information and communication technology is now playing an increasingly important role in the entire cyberspace and thus also in industrial automation technology.

From the EP 2 940 541 A2, a measure is known with which a secure communication can be offered to a conventional device within a micro network (Microgrid). For this purpose, a security device is connected between a conventional local device and a remote connection, which is formed as a BITW (bump-in-the-wire) device. Such BITW devices are switched on and managed as separate and independent units.

Existing field bus network protocols such as Modbus, PROFONET, Ethernet/IP, HART or Foundation Field bus protocols do not contain any security mechanisms or functions, i.e. security mechanisms with which communication links between two or more subscribers can be protected against external attacks, for example. Known security functions that ensure communication security and, in particular, the protection of the exchange of information between subscribers are, for example, authentication algorithms. Algorithms for integrity protection or encryption and decryption algorithms. Up to now, the known field bus networks have been protected with the help of firewalls or application gateways arranged in the periphery, so that trustworthy zones are created within which communication, however, is insecure.

From the DE 102 48 100A1 a security-related device for the connection of field devices to a security-related field bus is known. For this purpose, a field bus plug, which has a security-related field bus interface that enables the transfer of security-related signals via the field bus to a control system. The security-related signals correspond to the required security categories and thus safety aspects. In addition, the field bus plug has a security-related, field bus-neutral device interface to which a security field device with a security-related, field bus-neutral field bus interface can be connected. Thanks to the special field bus plug, which has both a security-related, field bus-neutral field bus station and a security-related, but field bus-dependent field bus interface, field devices only have to be developed for a security-related, field bus-neutral field bus interface.

SUMMARY

The invention is based on the object to create a security device and a field bus system with which it is possible to give field bus subscribers, that do not have a security function, the possibility to communicate securely via a field bus.

The technical problem mentioned above is solved by the features of claim1.

Accordingly, a security device is provided for the support of a secure communication via a field bus. The security device has a connecting apparatus for the direct coupling of the security device to a field bus-formed network interface of a field bus subscriber which is not formed for a secure communication via the field bus. This means that the field bus subscriber does not have any security functionality for safeguarding a communication. In other word: the field bus subscriber that does not have a security functionality for securing a communication, is not technically capable to protect an information exchange between itself and at least one other field bus subscriber.

The security device is formed in such a way that in the coupled state between the security device and the field bus subscriber, which is not formed for secure communication via the field bus, there is a link in such a way that after disconnection or damage to the coupling, the proper operation of the security device is reversibly or irreversibly blocked. The security device also has a network interface for connecting the security device to the field bus. The security device further has a transmitting and receiving apparatus which is formed to securely transfer data coming from a directly coupled field bus subscriber which is not formed for secure communication via the field bus according to a predetermined security protocol. Furthermore, the transmitting and receiving apparatus is formed to receive, via the field bus, data determined for the field bus subscriber according to the predetermined security protocol and to deliver them to the field bus subscriber as non-secure.

A predetermined security protocol is a protocol that protects a communication link or information exchange between two or more subscribers. For example, the predetermined security protocol regulates authentication, integrity protection, data encryption or data decryption. Thus, the security device is preferably formed to perform an authentication method and/or to perform at least one cryptographic algorithm according to the predetermined security protocol to ensure secure communication, e.g. protected against external attacks.

Depending on the predetermined security protocol, the transmitting and receiving apparatus can also be formed for decrypting encrypted data received via the field bus and for encrypting data to be transferred from a connected field bus subscriber which is not formed for secure communication via the field bus.

In order to execute cryptographic algorithms, the security device can have a secure storage apparatus for storing cryptographic keys. Programs for the execution of security functions according to the predetermined security protocol can also be stored in the secure storage apparatus.

At this point it should already be mentioned that the security device can be adapted to changing security protocols for communication security. For this purpose, the security device can have a programming interface that allows appropriate programming of the security device. However, it is also conceivable that the security device can be updated via the field bus.

Advantageously, the security device has a control apparatus and a monitoring apparatus formed to monitor the link between the security device and a connected field bus subscriber. The control apparatus is formed to block the appropriate operation of the security device in response to an error signal from the monitoring apparatus. Such an error signal can be triggered by the security device if the security device is disconnected appropriately, i.e. without damage, or by force from the coupled field bus subscriber.

An advantageous further embodiment provides that the security device is integrated in a plug connector, in particular in an RJ45 plug.

Advantageously, the control apparatus can be formed to erase at least one of the cryptographic keys saved in the secure storage apparatus and/or irreversibly or reversibly block the connecting apparatus and/or the network interface of the security device in response to an error signal from the monitoring apparatus.

Due to this measure it is ensured that the security device can only, if at all, continue to be operated if a disconnection or damage of the coupling with the field bus subscriber is determined, when an operator releases the security device again, e.g. if the previously deleted cryptographic keys are resaved and/or the locked network interface and/or connecting apparatus is unlocked.

Expediently, the power supply of the security device occurs via the field bus, for example, by means of the known Power-Over-Ethernet technology, and/or by means of an internal power supply source and/or via a connected field bus subscriber and/or by means of Energy Harvesting technologies.

In the case that a field bus subscriber which is not formed for secure communication via the field bus and which is already coupled to the security device is to be enabled for non-secure communication via the field bus, the transmitting apparatus and receiving apparatus can be formed to transparently conduct data from the connected field bus subscriber to the field bus.

Preferably, a field device or a control device can be linked to the security device as a field bus subscriber.

The predetermined security protocol contains several defined security functions, such as authentication functions, encryption functions and integrity backup functions, which can be deployed as a separate protocol stack or integrated in a field bus protocol.

The above-mentioned technical problem is also solved by the features of claim12.

Accordingly, a field bus system is provided for the support of secure communication via a field bus. The field bus system comprises a field bus, at least one first field bus subscriber which has a network interface formed for switching on to the field bus, wherein the at least one first field bus subscriber is not formed for secure communication via the field bus. The at least one first field bus subscriber is connected to a security device which has been previously defined, wherein the security device is formed for secure communication according to a predetermined security protocol.

Advantageously, the at least one field bus subscriber and the security device coupled thereto are managed in the field bus system as a single field bus subscriber, for example if a common address is assigned to the at least one field bus subscriber and the security device coupled thereto.

Advantageously, a second field bus subscriber is connected to the field bus which is formed for secure communication with the security device of the at least one first field bus subscriber according to the predetermined security protocol.

In order to establish a stable and reliable coupling between the at least one first field bus subscriber and the at least one security device, the security device is detachably or non-detachably linked to the at least one first field bus subscriber. A detachable link is understood to be, for example, a bolted joint, whereas a non-detachable link can be, for example, a riveted, weld or adhesive joint.

According to an advantageous embodiment, at least one first field bus subscriber can be formed as a field device or control device and at least one second field bus subscriber as a field device or control device. A field device can, for example, be a sensor or actuator, while a control device can, for example, be a PLC (Programmable Logic Controller) or a DCS (Distributed Control System).

