FPGA data diodes for hardware-based OT cybersecurity

Critical networks often need to send operational data outward. A substation may forward status data to a control center. A factory may send production metrics to a historian. A facility may share logs with monitoring tools. These connections are useful because they support visibility, reporting, maintenance, and better decision-making.

The challenge is to make that data movement precise. In process or OT environments, communication patterns are usually more predictable than in general IT networks. Devices often talk to known systems, using known protocols, for known purposes. That makes OT a strong fit for controlled, one-way data transfer and allowlist-based security approaches.

A data diode addresses the direction of communication: data can move from the protected OT side to the outside network, but not back in. An FPGA-based data diode goes a step further. It does not only enforce direction. It can also inspect and process outbound traffic in hardware before allowing it to move forward.

What makes FPGA different?

FPGA stands for Field-Programmable Gate Array. The easiest way to understand it is this comparison: A CPU runs instructions. An FPGA becomes a circuit.

A software-based security system typically processes traffic by running code on a general-purpose processor. Packets arrive, software evaluates them, and the system decides what to do next. With an FPGA, engineers configure its internal logic so the chip performs specific tasks as hardware circuits. For packet handling, that means certain checks can happen directly in hardware rather than through a conventional software path.

This matters in OT cybersecurity because traffic at the boundary is often repetitive and well defined. If the expected flow is known, the inspection logic can be designed around that expected behavior. For example, an FPGA-based inspection layer may evaluate packet headers, protocol fields, data length, message format, expected value ranges, time intervals, data types, and approved communication patterns. Instead of treating every packet as an open-ended software decision, the system can compare outbound traffic against predetermined logic. If the packet matches the expected pattern, it can move forward. If it does not, it can be dropped or flagged.

In short, the core benefit of FPGAs or hardware logic is the ability to enforce both direction and expected behavior.

Direction alone is not the whole story

Traditional data diode discussions often focus on physical one-way movement. That is important. Removing the return path is a strong architectural control, especially when OT data needs to be shared with systems outside the protected zone.

But in many real deployments, the next question is just as important: What exactly should be allowed to leave?

A basic one-way path can prevent inbound communication, but it may not fully answer whether the outbound traffic is expected, properly formatted, or aligned with the operational use case. FPGA-based inspection adds another layer of control. It can help verify that outbound data follows the intended protocol behavior before it crosses the boundary.

This is especially useful for industrial protocols because their behavior is often structured. A temperature value, voltage reading, status message, alarm, or file transfer may have an expected format and range. If a value should appear as a certain data type at a certain interval, those details can become part of the inspection logic. The technical advantage is not just speed. It is specificity.

The know-how: Translating OT behavior into hardware logic

The most interesting part of FPGA-based data diode technology is not simply that it uses hardware. The real value comes from translating operational knowledge into hardware-enforced rules, which requires understanding the environment, including:

• Which systems are allowed to send data?
• Which protocols are being used?
• What message types are expected?
• What values are reasonable?
• How often should certain data appear?
• Which fields matter for validation?
• What should happen when traffic does not match the expected pattern?

For example, if a substation device sends a measurement every minute, the expected interval can be part of the validation model. If a field should contain an INT16 value within a known range, that can also be checked. If traffic appears in the correct protocol but carries abnormal content, hardware-level inspection can help identify the mismatch. This is where company know-how becomes important. FPGA-based protection is not only a chip-level feature. It depends on protocol knowledge, deployment experience, and the ability to define meaningful rules with the customer.

In practice, the process should be collaborative. Engineering and OT teams know how the process behaves. Security teams know what must be controlled. The technology provider brings protocol expertise and implementation knowledge. Together, they can define what “expected traffic” really means.

Why hardware inspection helps performance

OT environments value predictability. A security function should not introduce unnecessary uncertainty into communications that support operations. Because FPGA logic is implemented in hardware, it can support fast and consistent packet handling for defined inspection tasks. Instead of pushing every decision through a general-purpose software stack, the system can perform selected checks at the hardware level. This can support:

• Lower processing overhead
• More predictable inspection behavior
• Efficient handling of approved traffic
• Reduced dependence on complex software rule chains
• Clearer separation between expected and unexpected flows

That does not mean software has no role. Many unidirectional gateway architectures still use software components for protocol handling, data replication, logging, or management. But FPGA logic is valuable because it can place key enforcement functions closer to the hardware path.

For critical networks, this creates a practical balance: software can support usability and integration, while hardware logic supports deterministic enforcement.

A more precise boundary for OT data

FPGA-based data diode technology is best understood as a boundary-control mechanism. It combines three ideas:

1. One-way movement: Data moves from the protected OT side toward the receiving side.
2. Hardware-enforced logic: Key traffic-handling functions are implemented directly in FPGA hardware.
3. Protocol-aware validation: Outbound traffic can be checked against expected formats, fields, values, and behavior.

This makes the technology especially relevant for OT networks, where communication is often stable enough to define with precision. The goal achieved? Data movement becomes more intentional. Operational data can still reach historians, monitoring platforms, dashboards, or reporting systems, but the pathway is limited, inspected, and aligned with known traffic patterns.

Secure data movement, built around expected behavior

OT cybersecurity is strongest when it reflects how the environment actually works. If the systems, protocols, values, and intervals are known, they can be used to build more precise controls. For organizations that need visibility beyond the OT network boundary, FPGA-based data diode technology offers one-way transfer with hardware-level inspection, designed around predictable operational communication.

A conventional data diode answers: “Can traffic come in?” An FPGA-based approach can also help answer: “Is the outgoing traffic what we expect?” It is a practical way to move the right data, in the right direction, under the right conditions.