BREAKING SECURE BOOT WITHOUT BREAKING THE CRYPTO

Summary from the TLDR InfoSec newsletter

A signature check alone doesn't prove a device is safe. This post breaks secure boot into four failure buckets: did the check run, did it cover the right bytes, was the signer authorized, and do those bytes still run at execution time? It walks through Qualcomm's PBL/XBL-SC/TME chain, Android Verified Boot, DICE key derivation, and RATS attestation roles. Real CVEs illustrate each bucket: CVE-2019-2278 let a rejected keystore still verify a boot image, CVE-2023-48425 chains an AVB failure into a full bypass on a retail Chromecast, and CVE-2021-1931 lets one signed image authorize a different one.