Trusted Platform Module

What is a Trusted Platform Module?

A Trusted Platform Module (TPM) is a standardised security chip, or a function in processor firmware, that generates and stores cryptographic keys, records measurements of the boot process and can reliably prove those measurements to another party. The specification comes from the Trusted Computing Group (TCG); TPM 1.2 became an international standard in 2009 as ISO/IEC 11889:2009, and TPM 2.0 followed in 2015 as ISO/IEC 11889:2015. In OT, a TPM gives industrial PCs, HMIs, engineering stations, firewalls, gateways and edge devices an identity and key storage that cannot be stolen with a simple disk copy.

Note: in industry the acronym TPM is also used for Total Productive Maintenance, a maintenance philosophy. This article is only about the security chip.

🧠 How does a TPM work?

A TPM is a small, isolated computer with its own processor, memory and firmware. The operating system talks to it through a fixed command set but never gets direct access to the secret keys. The main building blocks are:

• Key hierarchies - TPM 2.0 has three hierarchies: platform, storage and endorsement. Each hierarchy has its own primary key derived from an internal secret. Ordinary keys are created under such a primary key and only leave the chip in encrypted form.
• Endorsement Key (EK) - a unique key per chip, often with an EK certificate from the manufacturer. It lets you prove that you are talking to a genuine TPM.
• Platform Configuration Registers (PCRs) - registers that hold hashes of firmware, bootloader and configuration. The PC Client profile requires at least one bank of 24 PCRs. A PCR cannot be overwritten, only extended: the new value is the hash of the old value plus the new measurement.
• Sealing - a secret is bound to specific PCR values. The TPM only releases it when the system boots in exactly the same state. This is the principle behind BitLocker on Windows and TPM-bound disk encryption on Linux.
• Attestation - using an Attestation Key, the TPM signs a “quote” of the PCR values. A management server compares it with expected values and the measurement log, and can see whether a device started with unmodified firmware.
• Dictionary attack protection - after too many wrong password or PIN attempts, the TPM enters lockout. This makes brute-forcing a short PIN impractical.

A TPM does not itself stop tampered software from starting; Secure Boot blocks that. The TPM measures and remembers what was started (measured boot) and refuses to release keys when that measurement differs.

🔧 What types of TPM exist?

Not every TPM is a separate chip. The form matters a great deal for a risk assessment:

For virtualised SCADA and historian servers you will therefore almost always get a vTPM. It offers the same functions, but the root of trust lies in the hypervisor.

🔄 How does a TPM differ from an HSM and software key storage?

TPM and HSM complement each other. A manufacturer signs firmware with a key held in an HSM (firmware signing); the device verifies that signature at boot and uses its TPM for its own identity.

🏭 What is a TPM used for in industrial environments?

• Disk encryption on engineering stations and laptops - project files and PLC programs are business-critical. With TPM-bound encryption, a stolen drive is unreadable.
• Device identity for 802.1X and VPN - the private key of a client certificate is generated inside the TPM and is non-exportable. An attacker who copies the configuration cannot impersonate that device. Device authentication is thus bound to the hardware.
• Certificates for OPC UA, HTTPS and SSH - application instance certificates and host keys on gateways can be bound to the hardware instead of being kept in a file.
• Integrity of edge devices - with edge computing, devices often sit outside a locked room. Measured boot and remote attestation show whether firmware or the operating system has been changed.
• Zero Trust and conditional access - a management platform only admits a device when its attestation checks out.
• Key storage in embedded systems - many industrial gateways contain a discrete TPM 2.0 or a comparable secure element.

🔐 What do standards and legislation require?

IEC 62443-4-2, the part of the IEC 62443 series with technical requirements for components, does not name TPMs, but many of its requirements can be met directly with one. The enhancements “Hardware security for authenticators” (CR 1.5 RE 1), “Hardware security for public key-based authentication” (CR 1.9 RE 1) and the equivalent for symmetric keys (CR 1.14 RE 1) call for hardware protection of keys at the higher security levels. CR 3.12 and 3.13 cover provisioning the supplier’s and the asset owner’s roots of trust, and EDR/HDR/NDR 3.14 requires integrity and, as an enhancement, authenticity of the boot process. For your ISO 27001 cryptography controls and for the essential requirements of the Cyber Resilience Act, a TPM is a common way to protect keys and integrity demonstrably, although neither mandates a TPM.

⚠️ How secure is a TPM in practice?

A TPM is strong, but not invulnerable. Well-known examples:

What you can learn from this:

1. Include TPM firmware in your patch management - most of these flaws were fixed with firmware updates.
2. Use a pre-boot PIN where physical access is possible. A TPM that releases a key without a PIN does not protect against someone with time, tools and the device in their hands.
3. Combine with physical measures - locked cabinets and hardening remain necessary.
4. Record which devices have which TPM - form, version and firmware version belong in your asset inventory.

🛠️ How do you deploy a TPM step by step?

1. Take inventory - check for each IPC and HMI whether a TPM 2.0 is present and enabled in the UEFI settings. Older devices often have only TPM 1.2 or none at all.
2. Enable UEFI Secure Boot and record the expected PCR values after a clean installation.
3. Turn on disk encryption with a PIN for mobile and physically accessible systems. Store recovery keys centrally and never only on the systems you want to recover with them.
4. Roll out certificates with non-exportable keys through your certificate management for 802.1X, VPN and OPC UA.
5. Plan updates carefully - a BIOS or firmware update can change PCR values. Without preparation, such as temporarily suspending BitLocker, the system asks for the recovery key after the update, which means downtime on a production line.
6. Test recovery - rehearse restoring an encrypted engineering station before you need to do it during an incident.

❓ Frequently asked questions

Is a TPM the same as Total Productive Maintenance?

No, the acronym TPM has two meanings in industry. In cybersecurity, TPM stands for Trusted Platform Module, a chip that protects keys and measures the boot process. Total Productive Maintenance is a maintenance method from manufacturing and has nothing to do with this chip.

Does every industrial PC have a Trusted Platform Module?

No, but newer industrial PCs and panel PCs often include a discrete TPM 2.0 or a firmware TPM in the processor. Older systems sometimes have TPM 1.2 or no TPM at all. Check the datasheet and the UEFI settings, because a TPM is not always enabled by default.

What is the difference between TPM 1.2 and TPM 2.0?

TPM 2.0 supports multiple algorithms, including SHA-256, ECC and AES, whereas TPM 1.2 is tied to SHA-1 and RSA. TPM 2.0 has three key hierarchies instead of one and is required for Windows 11. For new OT systems, TPM 2.0 is the norm.

Does a TPM protect against ransomware?

A TPM does not stop ransomware that encrypts files on a running system using valid privileges. A Trusted Platform Module does help against tampering with firmware and bootloaders and prevents stolen keys from being used on another device. Backups, segmentation and patching therefore remain necessary.

Can a TPM key be copied to a new device?

Non-exportable keys stay inside the TPM and cannot be copied; that is precisely the point. When you replace a device, you therefore create new keys and request new certificates. Always keep disk encryption recovery keys separately, or the data is lost after a motherboard swap.

Is a firmware TPM as secure as a discrete TPM?

A firmware TPM and a discrete TPM each have their own weak spots. A discrete TPM has dedicated isolated hardware but a bus that can be sniffed; a firmware TPM has no external bus but shares hardware with the processor. Both are suitable for most OT applications, provided you keep the firmware up to date and use a PIN where physical access is possible.

📌 In summary

A Trusted Platform Module (TPM) is the hardware foundation for trust in a device: non-copyable keys, measurements of the boot process and attestation. In OT environments, a TPM protects engineering stations, HMIs, gateways and edge devices against key theft and unnoticed firmware changes. It only works well as part of defence in depth, with current firmware, a PIN where needed and well-organised key recovery.

A TPM makes the identity and integrity of an OT device provable, but it does not replace a patch policy, physical security or a recovery procedure.