wiki: correct PCR 16 history - #249
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The change is documentation-only and corrects an inaccurate description; the remaining feedback is a minor consistency tweak (PCR label/“TPM 1/2” spacing).
Pull request overview
Updates the Heads wiki TPM PCR documentation to correct the historical description of PCR 16 and align it with how calcfuturepcr evolved over time.
Changes:
- Replaces the outdated PCR 16 description (“Used for TPM futurecalc of LUKS header…”) with a short history explaining its former scratch usage and current non-use.
- Clarifies the TPM 1 vs TPM 2 PCR choice used historically for
calcfuturepcr, and notes the later shift to replaying fromcbmem -L.
File summaries
| File | Description |
|---|---|
| About/Keys.md | Corrects PCR 16 documentation to reflect historical usage and current behavior (unused). |
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- Comments generated: 1
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| (16): Not measured or read by Heads. Historically used as scratch PCR by | ||
| `calcfuturepcr` on TPM1 (TPM2 used PCR 23); now unused — `calcfuturepcr` | ||
| was rewritten to replay from the `cbmem -L` event log instead. |
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PCR 16 was historically scratch space for calcfuturepcr on TPM1 (PCR 23 on TPM2). calcfuturepcr was later rewritten to replay from cbmem -L event log, eliminating the need for any scratch PCR. PCR 16 is now unused. Extends doc/tpm.md fix (linuxboot/heads#2203). Signed-off-by: Thierry Laurion <insurgo@riseup.net>
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Summary
Extends doc/tpm.md fix (linuxboot/heads#2203) to the wiki.
Changes
PCR 16 description updated from "Used for TPM futurecalc of LUKS header" to accurate history:
calcfuturepcron TPM1 (TPM2 used PCR 23)calcfuturepcrwas later rewritten to replay fromcbmem -Levent log, eliminating the need for any scratch PCREvidence
68cc9d0b132(2017): originaltpm calcfuturepcr -ix 16call inkexec-seal-key.sh80c4a7ea6ea: TPM1 branch used PCR 16, TPM2 used PCR 23d1a18f1f83b:tpmr.shintroduced,calcfuturepcrrewritten toreplay_pcrusingcbmem -Ltpmr.sh:208-230:replay_pcrrejectspcr >= 8, no physical PCR touchedRelated