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CDC Badge OS

ADR-0011 — Attestation-signed PIN record in R-Memory slot 0

Status: accepted Source: spec 002 (PIN storage); FR-006; components/cdc_core/src/PinManager.cpp

Context

Section titled “Context”

The combined PIN record (badge hash, OpenPGP PW1/PW3 salts/hashes, KDF iteration count, retry flags, and the optional duress PIN material) is stored in TROPIC01 R-Memory slot 0. ECC slot 0 holds the chip-bound P-256 attestation key. The badge-PIN retry counter lives in RAM; only the locked flag and the PW1/PW3 counters are persisted, so a power cycle mid-verify cannot resurrect the badge counter.

Decision

Section titled “Decision”

The PIN record is bound to the device by an attestation signature. On save, PinManager appends a P-256 ECDSA signature over the payload bytes [0..PAYLOAD_SIZE) produced by the chip-bound key in ECC slot 0 (se->ecdsaSign(ATTESTATION_ECC_SLOT, …)). On load, only the signed format is accepted: wrong magic, wrong length, or an invalid signature (verify_payload_signature) causes a silent reinit to defaults, which re-signs the slot freshly.

  • Signature algorithm: ECDSA over P-256 (SECP256R1), 64-byte raw r || s, over SHA-256 of the payload.
  • A regenerated or tampered slot-0 key fails verification and triggers reinit to defaults; this is not migration (per ADR-0005).
  • Random-k ECDSA means re-saving the same payload yields a different signature; only verification matters.

Consequences

Section titled “Consequences”
  • Enables: tamper detection of the PIN record and binding to the specific secure element; an attacker who rewrites slot 0 (e.g. via the pairing key) invalidates the record rather than silently substituting one.
  • Must hold: the attestation key stays in ECC slot 0; the signed format is the only accepted format; load failures reinit to defaults rather than attempting recovery.
  • Cost: each PIN-record save performs an on-chip ECDSA sign; a slot-0 key change wipes PIN state.