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#+title: Hardware Modules
#+date: 2026-06-08 Mon
#+author: W. Kosior
#+email: wkosior@agh.edu.pl
* Hardware Security Module
- key generation
- secrets store
- cryptographic operations
- non-exportable keys
- sample uses
- malware-resistant SSH keys
- DNSSEC signing
- cryptocurrency transactions
- rng
- TOTP/HOTP
- https://www.iana.org/dnssec/ceremonies
- API (PKCS#11 or other)
* HSM Types
- PCIe
- USB
- smart card
- virtualized/emulated
- wire protocol often proprietary, non-standard
* HSM Diversity
- firmware-based?
- updatable?
- display?
- input device (e.g., fingerprint reader)?
* PKCS#11
- RSA Laboratories
- slot
- token
- label, serial
- PIN
* PKCS#11, Cont.
- RSA Laboratories
- slot
- token
- label, serial
- PIN
- mechanism (cipher + hash function + block mode)
- capabilities
- parameters
- object classes
- keys
- domain parameters
- certs
- object attributes (class-specific)
- sessions
* SIM Cards
- K
- symmetric cryptography
- user-operator shared secret
- 128-bit
* Measured Boot
- Secure Boot → verify software to be booted
- Measured Boot → attest what has been booted
* Trusted Platform Module
- "Trusted" Computing Group
- aka HSM integrated with hardware
- sample uses
- BitLocker/LUKS
- SSH
- GPG
- file integrity
- rng
* Trusted Platform Module, Cont.
- "Trusted" Computing Group
- aka HSM integrated with hardware
- sample uses
- BitLocker/LUKS
- SSH
- GPG
- file integrity
- rng
- eSIM
* TPM Versions
- TPM 1.0-1.2
- SHA1, 2048-bit RSA
- TPM 2.0
- algorithm-agnostic (in practice: SHA256, ECC, AES)
- =/sys/class/tpm/tpm0/tpm_version_major=
* Interfaces
- TCG specification
- SAPI
- ESAPI
- FAPI
- tpm-tools (CLI)
- https://tpm2-tools.readthedocs.io
* TPM Types
discrete TPM*
integrated TPM
firmware TPM
virtual TPM
* TPM Entities
- types
- objects
- *keys*
- data
- NVRAM indexes
- Platform Configuration Registers (PCRs)
- hierarchies
- …
- handles (4 bytes)
- objects & NVRAM indexes can be removed
* TPM Hierarchies
- collections of entities
- defined hierarchies
- endorsement/privacy
- remote attestation (device state confirmation)
- platform
- use by motherboard manufacturer
- storage/owner
- most uses
- null/ephemeral
- entities not persisted
* PCRs
- extending (concatenate+hash)
- banks (hash algorithm)
- =tpm2_pcrlist=
- =tpm2_pcrread=
* Firmware-Extended PCRs
| 0 | "Core system firmware executable code" | e.g., UEFI BIOS code |
| 1 | "Core System Firmware data" | e.g., UEFI BIOS settings |
| 2 | "Extended or pluggable executable code" | e.g., option ROMs |
| 3 | "Extended or pluggable firmware data" | |
| 4 | "Boot Manager Code and Boot Attempts" | e.g., bootloader code |
| 5 | "Boot Manager Configuration and Data" | e.g., bootloader config, part table |
| 6 | "Resume from S4 and S5 Power State Events" | |
| 7 | "Secure Boot State" | e.g., PK, KEK, db |
Based on: https://wiki.archlinux.org/title/Trusted_Platform_Module
* Other PCRs
| 8-16 | defined by OS | e.g., kernel, kernel command line, initrd(s) |
| 23 | "Application support" | resettable by the OS |
* TPM Entity Sealing
- particular PCR values
- PCR values signed with configured key
* TPM Keys
- derivation
- storing not needed
- endorsement key (& cert)
* TPM NVRAM
- data entities
- size
- attributes
- 0x10000000-0x1fffffff
- reading&writing
- =tpm2_nvreadpublic=
- =tpm2_nvdefine=
- =tpm2_nvwrite=
- =tpm2_nvread=
- =tpm2_nvundefine=
* TPM NVRAM Entity Locking
- =tpm2_nvwritelock=
- =tpm2_nvreadlock=
* TPM Authorization
- password (single-command sessions)
- HMAC (shared secret)
- Enhanced Authorization (policy)
* side-channel attacks
- bus snooping (passive, discrete TPM)
- MITM (active, discrete TPM)
- desolder-and-move (active, discrete TPM)
- fault injection (active)
- spectre-like? (firmware TPM)
- power analysis
* TPM Encrypted Commands / Response Buffers
- unbound, bound, salted
- first parameter only
* Application Support for TPM (2.0)
- LUKS
- systemd-cryptenroll
- SSH
- https://github.com/Foxboron/ssh-tpm-agent
- others
- https://github.com/tpm2-software/tpm2-pkcs11
- PGP
- GnuPG (since 2.3, 2021)
* "Secure" Boot for Firmware
- Intel TXT
- using TPM to verify UEFI firmware (and more)
- one-time-programmable fuses
- motherboard vendor's public key
- firmware signing
- AMD PSP
- Intel Boot Guard
* Trusted/Treacherous Execution Environment
- remote attestation (of hardware by software vendor)
- encrypted memory regions
- application not inspectable by host OS
- IO (e.g., PCIe) not interceptible by host OS
- sample use: client-attested VM hosting
- Intel Software Guard Extensions (SGX)
- application-level
- deprecated on consumer PCs
- AMD Secure Encrypted Virtualization
- encryption of guest-selected memory pages
- also server CPUs
- Intel Trust Domain Extensions
- shared & private VM memory
- also server CPUs
- ARM TrustZone
* Dangers
- inability to exercise fair use rights (DRM)
- media backup
- software reverse engineering
- elimination of competition
- inability to audit/fix
- no software freedom :c
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