Trusted Platform Module (TPM)

The TPM records cryptographic hashes of every firmware and software component loaded during the boot sequence into Platform Configuration Registers (PCRs). This process, known as Measured Boot, creates an immutable, tamper-proof log of the system's startup state. The TPM's PCRs cannot be arbitrarily overwritten; they can only be extended with a new hash, ensuring the historical record of the boot chain is preserved for later verification.

The TPM contains a True Random Number Generator (TRNG) that harvests entropy from thermal noise and other physical phenomena to produce non-deterministic keys. It can generate and securely store RSA-2048 and ECC key pairs within its shielded hardware boundary. Crucially, private keys are never exposed to the host operating system, making them immune to software-based exfiltration attacks.

A TPM can create a unique, unclonable identity for the physical machine. The Endorsement Key (EK) is a unique RSA key pair burned into the TPM during manufacturing, establishing a root identity for the platform's entire lifecycle. For privacy, the TPM generates anonymous Attestation Identity Keys (AIKs) derived from the EK, allowing a platform to prove it is a genuine device with a valid TPM without revealing its specific identity across different services.

The TPM 2.0 specification defines a standardized command set for interacting with the module. Key command groups include:

• Startup & Self-Test: Initializing the TPM and verifying its internal integrity.
• Session Management: Establishing encrypted and salted command paths to the TPM.
• Object Management: Creating, loading, and evicting keys and data objects from the TPM's limited non-volatile memory.
• Asymmetric & Symmetric Primitives: Performing RSA decryption, ECDSA signing, and HMAC operations entirely within the secure hardware.

The immutable foundation of a system's security architecture. A TPM often serves as the HRoT, providing the first link in the chain of trust. It contains cryptographic keys and secure storage that are physically resistant to tampering, ensuring that all subsequent boot stages can be verified against an uncompromised anchor. Without a verified HRoT, all higher-level software attestations are fundamentally untrustworthy.

The process by which a TPM records the cryptographic hash of every firmware and software component loaded during startup. These measurements are stored in shielded Platform Configuration Registers (PCRs). The TPM's design prevents falsification; you cannot write arbitrary values to a PCR, only extend them with a new hash. This log allows a remote server to verify the exact software state of the machine through remote attestation.

A mechanism where a client machine proves its identity and software integrity to a challenger. The TPM signs a quote of its PCR values using an Attestation Identity Key (AIK). This allows a server to verify that the client is running an approved OS and firmware stack before granting network access or releasing secrets. It is the core protocol for enforcing Zero-Trust policies at the hardware level.

A complementary standard to Measured Boot. While Measured Boot records the state, Secure Boot enforces it. The firmware checks the digital signature of each boot component against a database of trusted keys. If a component is unsigned or signed by a revoked key, execution halts. This prevents bootkits and unauthorized operating systems from loading, ensuring the TPM only measures a trusted environment.

A secure area of the main processor that isolates sensitive computation. While a TPM is a discrete, passive chip for key storage and measurement, a TEE like Intel SGX or ARM TrustZone actively executes code in a hardware-encrypted memory region. Modern architectures often combine a discrete TPM for platform state with a TEE for running confidential AI workloads, providing layered defense.

A modern standard that layers boot states to create a compound device identity without requiring a discrete TPM chip. DICE starts with a Unique Device Secret (UDS) and cryptographically derives new keys based on the hash of each firmware layer. This enables secure boot and remote attestation in highly constrained, low-cost IoT devices where a full TPM might be impractical.