A data diode is a device which facilitates a unidirectional flow of information. Such devices are used to enforce one-way communication between systems or networks having differing security classifications, for instance. The security classifications may be defined in terms of commercial confidentiality, defence security or any instance where data from a higher classification system should not flow to, or contaminate, a lower classification system. A problem with existing data diode solutions is that they are often reliant on embedded software, which itself is a security risk, since the software itself may be prone to attack or infiltration and this could compromise the entire device, allowing data to flow contrary to the user's intention. Existing data diodes can also be prohibitively expensive, especially those which are certified to a military standard. There therefore exists a need for a simple, inexpensive data diode.

Other techniques rely on physically separate devices, separated by an air gap, which in themselves could pose a security risk.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 shows a multi-network configuration; and

Figure 2 shows a detailed schematic of a data diode according to an embodiment of the invention.

Figure 1 shows a multi-network configuration, comprising three distinct but interconnected networks, 10, 20, 30. Networks 10 and 20 are of a higher classification than network 30, which is of a lower classification. Networks 10 and 20 trust each other and are able to communicate freely in a bidirectional manner, as shown in Figure 1 . Network 30 is of a lower classification and is not permitted to communicate freely with network 10. However, network 30 is required to transmit data to network 10 in a manner which does not permit higher classification data flow in the opposite direction (i.e. from the higher to the lower classification network).

Such a situation may arise in a secure network, where the secure network is required to receive data from a lower classification network, wherein the data may comprise environmental status information or other non-classified data.

Connected between networks 10 and 30 is a data diode 100, which is a physical device via which networks 10 and 30 are interconnected and which permits data to flow in only a single direction i.e. from the lower classification network 30 to the higher classification network 10. Figure 2 shows a detailed schematic of the data diode 100 according to an embodiment of the present invention.

The data diode 100 is operable in a serial data system, whereby the transmitting network is connected at serial data input 130 and the receiving network is connected to serial data output 170. Note that in the embodiments discussed herein, data is always transmitted from a lower classification network to a higher classification network, but it is possible to configure this in the opposite direction, should that be necessary. It is also possible to connect two networks of equal classification, whereby one is not permitted to receive data from the other. The skilled person will readily appreciate the different scenarios which would benefit from a data diode according to an embodiment of the invention.

In the specific embodiment shown in Figure 2, the serial data communication standard in use is RS485, but other serial data may also benefit from embodiments of the invention. Note that in RS485, it is not generally possible to draw any operational power from the signal lines themselves. RS485 is a serial interface of a type known as 'multi-drop' and, as such, it is not always possible to know how many devices are connected to a particular signal line. To ensure signal quality, it is not possible to draw power from the signal lines.

This is in contrast to some other serial interfaces, such as RS232, which are point to point and where it is permissible to draw some operational power for a peripheral device from the signal lines themselves.

Power is therefore provided separately from the signal lines and is derived from a suitable power system, such as 24V DC system, which may be provided as standard on many vessels, for instance, where the data diode may be used. The power input is supplied to power conversion module 1 10, where, using a switching regulator, it is converted to 12V DC for use in other parts of the data diode 100. Power is provided directly from the power conversion module for a first part of the data diode 100, namely the receive portion 100a, comprising serial data transceiver 140. Power is also provided to a power isolation convertor 120. It is important to note that the data diode is provided with power from only a single external power supply.

The power isolation convertor 120 is in the form of a DC-DC convertor and is arranged to provide isolated power to the transmit portion 100b of the data diode 100, comprising serial data transceiver 160. By isolating the power provided to the receive 100a and transmit 100b portions, there can be no backflow of data from the receiving network to the transmitting network via the power lines or connections. This ensures that it is not possible to read or infer any of the data which is passed between the transmit and receive portions, since any perturbations which may occur on the power lines will be removed by the power isolation between said portions.

Data enters the data diode 100 at serial data input 130 on a differential pair of lines connected to the first serial data transceiver 140, which in this embodiment is an RS485 transceiver. The first transceiver 140 converts the input signal (at ±15V DC) to a lower magnitude DC signal voltage (approximately 1 .2V DC), which in turn is used as the driving signal for an optocoupler 150. The optocoupler 150 is operable to provide guaranteed data isolation between the transmitting and receiving networks, in that it physically allows only one-way communication. This is achieved by means of a single transmitter of light (emitter) and a single receiver of light (a photoreceptor), which are encapsulated within the optocoupler component. The light is not visible from the exterior of the component, since this would obviously pose a security risk.

The optocoupler 150 is chosen for convenience, since it is provided in a single physical package. However, functionally, it may be replaced by a separate optical transmitter (emitter) and receiver (detector). The data signal leaving first transceiver 140 is used to energise the light source in the optocoupler 150, with the light thereby generated being detected by the photoreceptor, which then generates a corresponding electronic output signal. It is not physically possible for the photoreceptor to act as an emitter and vice-versa. The output signal thereby generated is supplied to a second serial data transceiver 160, operable to produce the differential voltage necessary to drive the output 170, which is then, in turn, connected to the receiving system.

Due to the data isolation provided by the optocoupler 150 and the power isolation provided by power isolation convertor 120, electronic signals may only pass through the data diode in a single direction, which is determined by the physical configuration and installation of the data diode 100. In other words, there is no requirement to program or configure the device in any way, once installed, and the direction of data flow is determined solely by the physical connections made to the data diode 100. The differential data leaving the data diode output 170 is substantially identical to that arriving at the data diode input 130. By substantially identical, it is meant that the signal leaving output 170 is operable within the same voltage limits as defined by the applicable standard e.g. RS485, and conveying the same information. The substantive difference is that data is physically prevented from travelling 'backwards' through the data diode 100 from the output 170 to the input 130. Embodiments of the invention find particular use in military vehicles, where it is desirable or necessary to provide at least two distinct networks having different security classifications, which must share some information, but where contamination between the networks must be avoided. A particular environment which can benefit from embodiments of the inventions is marine vessels of the surface and submersible type.

Since embodiments of the invention do not require any programming and include no software or firmware elements, they are able to operate without any customised configuration, beyond physically connecting them in circuit. This makes them particularly immune to hacking or phishing attacks. The physical components required are well known and tested to perform to a range of reliability requirements, resulting in a device which can be certified to operate to a range of applicable standards.

Physical connections to the data diode 100 may be provided by standard connectors or by hardwiring the incoming/outgoing connections using screw terminal or similar. The data diode 100 will normally be housed in a secure environment which will prevent or at least hinder tampering with the connections.

The data diode is provided as a unitary device, with suitable packaging to prevent or deter physical compromise. Preferably, any attempt to tamper with the device will be evident or will render the device inoperable.

The electrical connections to the unitary data diode device consist of a data input, a data output and a single power supply. There are no other connections required in order for the data diode to operate. This is advantageous, since no specialised power supply is required over and above that which is customarily provided in the environment in which the data diode is intended to be used.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.