Trusted Platform Module (TPM)

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A trusted platform module (TPM) is a separate processor that provides secure hardware-based storage and cryptographic services as specified by ISO/IEC 11889.

• is a cryptoprocessor implemented as a module for a discrete computer platform
• stores encryption keys, hashed passwords, and other user- and platform-identification information.
• During the boot process, the TPM compares hashes of key system state data (system firmware, boot loader, and OS kernel) to ensure they have not been tampered with
• TPM can be enabled or disabled and reset via the system setup program
  • possible to manage it from the OS as well

Uses

• can be used by the OS, processor BIOS, or application (if OS gives access to TPM) to do:
  • Generate private/public key pairs such that the private key never leaves the TPM in plaintext
  • Digitally sign data using a private key stored on the TPM and that never leaves the TPM
    • decreases possibility that key can be stolen by attacker
  • Encrypt data such that it can only be decrypted using the same TPM
  • Verify the state of the machine the TPM is installed on to detect certain forms of tampering
    • e.g. with the BIOS

Private Endorsement Key

• Each TPM microprocessor is hard coded with a unique, unchangeable key, referred to as the endorsement key
• fundamental component of a TPM’s security
• the Private Endorsement Key (PEK) is generated by the TPM manufacturer and burned into the TPM hardware during manufacturing
  • therefor, depends on the security of the TPM manufacturer to ensure that the PEK remains confidential

Versions

• produced to different version specifications
  • 1.2
    • mostly deprecated
  • 2.0
    • not backward compatible with 1.2

Implementation

• 3 ways of implementing TPM:
  • Discrete
    • TPM is implemented as a dedicated chip
    • provides tamper resistance and smallest attack surface
  • Integrated
    • TPM is part of a chipset or CPU that performs other functions
    • not tamper resistant and has a broader attack surface
  • Firmware
    • TPM is implemented in the platform’s low-level operating code
    • depends on the secure enclave function of the CPU or chipset to protect the cryptographic material
    • e.g.,
      • Intel’s Platform Trust Technology (PTT)
      • AMD’s fTPM
    • not tamper-resistant and has broadest attack surface

Info

A virtual TPM can be implemented in a hypervisor to provide a service to virtual machines (VMs).