Evil Maid Attack, TPM 2.0 PCR Bank & LUKS2/BitLocker Hardening Planner (2026)

Coined by Joanna Rutkowska, an Evil Maid attack occurs when an adversary gains brief unattended physical access to a powered-off device (e.g., in a hotel room). In traditional Linux setups, the `/boot` partition (containing the kernel and initramfs that prompt for your LUKS password) is unencrypted. The attacker replaces the initramfs with a trojanized version that logs your passphrase on the next boot.

A Unified Kernel Image bundles the Linux kernel, initramfs, and kernel command line into a single PE binary signed with your personal Secure Boot key (`sbctl`). During boot, UEFI verifies the signature (measured into PCR 7) and measures the UKI into PCR 11. If an attacker alters `/boot` or kernel parameters (`init=/bin/sh`), the PCR hash changes and the TPM 2.0 chip refuses to unseal the LUKS2 volume key.

When BitLocker or LUKS2 is configured for silent TPM-only unlock (without a pre-boot PIN), the TPM automatically releases the Volume Master Key over the motherboard's discrete SPI or LPC bus as soon as the boot chain passes PCR checks. On laptops with discrete TPM chips, an attacker can tap the SPI pins with a logic analyzer and read the cleartext key in seconds unless `tpm2-pin=yes` / BitLocker Pre-Boot PIN is required.

Binding directly to PCR 4 (raw bootloader code hash) means every routine kernel or systemd update changes the PCR digest and breaks TPM unlock. By binding to PCR 7 (Secure Boot authority state) and using signed PCR 11 policies (`systemd-measure`), any kernel signed by your enrolled private key unlocks seamlessly while unsigned tampering is blocked.

Legacy LUKS1 used PBKDF2-HMAC-SHA256, which only consumes a few kilobytes of memory and can be parallelized across thousands of GPU shaders. LUKS2 defaults to Argon2id—a memory-hard key derivation function that requires up to 1–4 GB of dedicated RAM per password guess, neutralizing GPU brute-force acceleration.