0

See the whole loop

goal: hold the entire field in one mental image
objective Redraw the six-step loop above from memory and say, in one breath, what problem it solves that ordinary encryption cannot.

The idea in spoken language

Event log in the order it happened 1 · measure A 2 · measure B 3 · measure C replay each entry recomputed value from the log alone Security chip the shielded register PCR value read from the chip match log unedited edit one line of the log and the recomputed value no longer matches
The log explains; the register proves. A checker recomputes the register value from the log alone — folding each entry in, in the order it was written — and compares it with the value the chip reports. They agree only if the log is exactly what was measured, because changing a single entry changes everything folded after it.
  • The question it answers: not "is this message real?" but "what software is actually running on that machine over there, right now?" You cannot answer that with a password or a normal secure connection — a hacked machine can lie.
  • Measure before you run: each piece of software takes a fingerprint (a hash) of the next piece before letting it start, and records that fingerprint in the chip. Trust passes down the chain like a relay baton.
  • The register can only grow: you can add a new fingerprint but never erase or overwrite. So a hacker cannot "put back" a clean fingerprint after the fact.
  • The list explains; the register proves: a written log says what was measured; the hardware register proves the log wasn't edited. A checker replays the log and sees if it produces the same register value.
  • The signature seals it: the chip signs the register values together with a fresh random number from the checker. The random number proves the answer is live (not an old recording); the signature proves it came from real hardware.
lab 0 · draw it

Redraw the loop from memory on paper. Label where a fingerprint is taken and where a signature is made. You'll redraw this at the end of every phase and it will get richer each time.

mastery gate 0

In under 3 minutes, no notes: explain to a skeptical friend why a faraway server can't simply "tell you" what it's running, and how this loop makes the answer impossible to fake.