Trusted Platform Module (TPM)

A dedicated physical computing device that safeguards and manages digital keys for strong authentication and provides cryptoprocessing. Unlike a TPM, which is typically a single chip on a motherboard, an HSM is a removable or external module designed for high-volume cryptographic operations.

• Key distinction: HSMs are general-purpose crypto accelerators; TPMs are platform-integrity anchors
• HSMs often come as PCIe cards or network-attached appliances
• Used for SSL/TLS termination, code signing, and database encryption
• TPMs are bound to a specific platform; HSMs can serve multiple systems

A process by which a platform's firmware, bootloader, and operating system components are cryptographically hashed and the measurements are stored in a TPM's Platform Configuration Registers (PCRs). This creates an immutable, tamper-evident log of the boot chain.

• Each stage measures the next before executing it
• Measurements are extended into PCRs using the TPM's hash algorithm
• Enables remote attestation by providing a signed quote of PCR values
• Forms the foundation of the TPM's integrity measurement architecture

A mechanism by which a TPM produces a cryptographically signed report (a quote) of its Platform Configuration Registers, allowing a remote verifier to determine whether the platform is in a trusted state. This is the TPM's primary value proposition for zero-trust architectures.

• The TPM signs PCR values with its Attestation Identity Key (AIK)
• The verifier compares the quote against known-good reference measurements
• Enables policy-based access control: only trusted devices gain network access
• Critical for device health verification in enterprise deployments

A secure, isolated area within a main processor that guarantees code and data loaded inside are protected with respect to confidentiality and integrity. While a TPM is a passive co-processor, a TEE is an active execution environment.

• Examples: Intel SGX, AMD SEV, ARM TrustZone
• TEEs run entire applications in encrypted memory enclaves
• TPMs store keys and report integrity; TEEs execute sensitive workloads
• Often used together: TPM verifies platform state, TEE processes sensitive data
• TEEs protect against privileged software attacks; TPMs protect against physical tampering

Special shielded memory locations within a TPM that store integrity measurements in a tamper-resistant manner. PCRs cannot be written directly; values are extended using a cryptographic hash operation that irreversibly incorporates new measurements.

• PCR extension formula: New PCR = Hash(Old PCR || New Measurement)
• Typically 24 PCRs per bank, each assigned to specific boot components
• PCR 0: Core system firmware; PCR 7: Secure Boot policy
• The cumulative nature ensures the final value reflects the entire boot sequence
• Resetting PCRs requires a platform reboot, preventing runtime tampering

Two fundamental TPM operations for data protection. Binding encrypts data with a TPM's public key so only that specific TPM can decrypt it. Sealing goes further by cryptographically tying decryption to a specific platform state defined by PCR values.

• Sealed data can only be unsealed when PCRs match the specified policy
• Enables BitLocker-style disk encryption: keys are sealed to a known-good boot state
• If malware modifies the bootloader, PCR values change and the key remains locked
• Binding provides device-specific encryption without state conditions
• Both operations ensure keys never leave the TPM in plaintext