Platform Configuration Registers, or PCRs, are special values inside a Trusted Platform Module (TPM). During boot, trusted components such as the bootloader, kernel, or firmware are measured, and those measurements extend the PCRs. Because each new measurement changes the register state, PCRs act like a running fingerprint of the platform’s startup chain.
In cyber security, PCRs matter because TPM-backed features often use them to decide whether to release a sealed key. If the PCR values match the expected boot state, the TPM may unlock disk or system secrets; if they do not, it can refuse access. This is what makes PCRs central to measured boot and disk encryption defenses. Attackers try to abuse weak measurement policies by altering a boot stage that is not included in the PCR checks, so the TPM still trusts a system that has changed. Defenders use PCRs to bind secrets to a known-good boot path, but only if every meaningful boot component is measured.