Verified Boot on Chrome OS and How to do it yourself
summary
Chrome OS boots a read-only firmware that verifies an updatable, signed firmware which in turn verifies a signed kernel and a dm-verify root hash, providing rollback protection via TPM and RSA-signed chains (Chrome uses 8k RSA for initial keys, U-Boot supports RSA-2048). Upstream U-Boot (2013.07) adds signature support using the FIT image container and make_image/bootm flow, plus optional hardware hashing; dm-verity protects the read-only root. Verification costs ~6 ms on a BeagleBone, ~6 KB extra code (RSA ~2 KB), and the demos boot successfully.
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chapters (24)
- 0:00Introduction
- 3:46Why do we do Verified Boot
- 4:55Requirements
- 6:48Hashing
- 7:57Public Key Cryptography
- 8:52TPM
- 9:48Root of Trust
- 11:17How Verified Boot Works
- 17:57User Space
- 19:57How to do Verified Boot
- 23:19How to sign an image
- 26:07Inplace signing
- 29:05Code size
- 29:57Performance
- 30:32Summary
- 31:20Demo
- 35:22Other features
- 36:56In summary
- 37:25Questions
- 39:52Root Hash
- 43:04Blocking the Book
- 43:32Block Size
- 44:18Objectives of Chrome OS
- 45:27GPL
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