Backlog

May 24, 2026 · View on GitHub

Open work items beyond the current ship state. Items are grouped by theme; ordering within a section is rough priority (highest first) but most items are independent.

1. Audit-driven hardening (highest priority)

Real defense-in-depth wins deferred because the original threat model didn't make them blocking.

1.1 M&D-backed PIN counters for OpenPGP PW1 / PW3 / RC — ✅ DONE (Phase 8 M4)

Landed in commits leading up to 561e040 (schema PG7R). pin_md_kernel extracted to firmware/src/tropic/pin_md_kernel.{c,h}; OpenPGP wrappers live in firmware/src/openpgp/openpgp_pin_md.{c,h} using M&D slots 8-16 and R-mem slots 50/51/52 (per-PIN state). pgp_pin.c VERIFY routes through M&D first. Bootstrap path wipes M&D state on schema bump to avoid PIN brick. Acceptance verified by tools/validate-pin-md.sh.

1.2 M&D-KEK wrap for X25519 dec priv key

The X25519 dec key for gpg --decrypt lives in R-mem slot 1 byte 180-211 (Trezor Safe 7 pattern). Anyone with SH0 + L3 session can read it. Wrap it with a PW1-derived KEK released only via M&D — mirrors Trezor's PIN-encrypted-seed design.

Implementation sketch (~200 LOC, reuses landed M&D framework):

KEK = HMAC(PW1-hash, M&D-derived-secret) — pin_md_kernel already exposes the M&D-derived-secret hook needed for this.
Stored ciphertext = AES-GCM(dec_priv, KEK)
On PSO:DEC: verify PW1 (consumes M&D slot via §1.1's landed wrappers), derive KEK, decrypt priv, perform ECDH, zeroize all on return.

§1.1's framework already landed in Phase 8 M4, so this is unblocked.

1.3 cpp-reviewer audit followups

The Phase 6 cpp-reviewer audit caught 2 MEDIUMs that were tagged as deferred. Re-read the audit report (in archive/phases-1-7 branch STATUS.md entry) and address what still applies post-Phase-7.

2. WebAuthn / FIDO2 polish

2.1 credProps extension — ✅ DONE (Phase 8 M2)

Landed in commit bcff8fb. CTAP2 MakeCredential now parses incoming extensions.credProps request and emits the rk flag in the attestation extension map. webauthn.io shows device-bound credential of unknown discoverability no more.

2.2 hidraw udev rule for FIDO — ✅ DONE (Phase 8 M1)

Landed in commit bcff8fb. nixos/tropic.nix now installs a udev rule tagging cafe:4001 with ID_SECURITY_TOKEN=1 + group access to plugdev, so libfido2 / browsers see the dongle without a manual rule.

3. Configurable policies (Yubikey-class)

3.1 authenticatorConfig (CTAP2.1 command 0x0D)

Runtime toggles for Force-UV / alwaysUv / etc. Currently all options are compile-time. CTAP2.1 §6.11. Requires PIN auth.

3.2 credProtect per-credential UV

Per-credential UV requirement (CTAP2.1 §11.1.2). Some RPs (Google, Microsoft) request credProtect: 3 for high-value credentials.

3.3 PIN protocol v2 token permissions

Scope-limited PIN tokens — token authorizes only specific operations (e.g. credential management read but not delete). CTAP2.1 §6.5.5.7.

3.4 OpenPGP touch policy — ✅ PARTIAL (Phase 8 M3, GLOBAL only)

Landed in commit 98486f4 + bcff8fb. Global on/off touch toggle implemented and enforced in PSO:CDS, PSO:DEC, INTERNAL_AUTHENTICATE. Defaults to ON (user-presence required for every signing op).

Still TODO — per-slot policy + cached mode: Yubikey-style per-key granularity (sig / dec / aut independent) and the "cached (1 touch per session)" mode. Maps to OpenPGP DOs D6/D7/D8 properly. Current impl is one boolean for all 3 slots.

4. OpenPGP card polish

4.1 gpg --card-status display anomaly verification

Post-flash, run gpg-connect-agent "SCD RESTART" then gpg --debug 0x0009 --card-status to capture the trace. Confirm whether "Max. PIN lengths: 0 0 0" and "PIN retry: 0 0 0" actually resolved post-flash (expected: yes, because the schema bump forced clean defaults). If anomalies persist, file an upstream gnupg bug with the captured trace.

4.2 AID manufacturer ID cosmetic

gpg --card-status shows "Manufacturer: unknown" because 0x4E58 ("NX") isn't in gnupg's hardcoded table. Options:

Keep 0x4E58 — accept cosmetic display
Swap to 0xFF02 for spec-defined "unmanaged S/N range" label
Patch upstream gnupg to recognize 0x4E58 as "nixtropic"

Option 2 is one-line change but invalidates existing card state and requires TERMINATE+ACTIVATE.

4.3 Default language pref

write_activated_defaults zeroes OFF_LANG. Could optionally write 'e' 'n' so gpg --card-status shows "Language: en" out of the box. Trivial.

4.4 PIV applet

A second smartcard applet (alongside OpenPGP) adding pkcs11 + Windows smartcard logon use cases. firmware/src/ccid/apdu_dispatch.c is structured to accept a second applet — just needs AID-based routing wired in.

4.5 OpenPGP attestation slot (Yubikey-compat)

Yubikey 5.2.3+ adds a vendor extension: an extra "attestation" key slot beyond the standard 3 (sig/dec/aut). Verified at runtime by ykman openpgp keys attest <slot> — the device signs a statement that the user-facing key was generated on-device (not imported), and the resulting X.509 attestation is rooted in a Yubico-issued CA cert. Useful for compliance scenarios that must distinguish HW-generated keys from imported ones.

What it needs on our side:

One more TROPIC01 ECC slot (we have headroom — slot 28 or repurpose one FIDO slot, since 29 FIDO creds is generous).
An on-device-burned attestation CA (Ed25519 key + cert), or per-device unique attestation key signed at provisioning.
Vendor APDU INS 0xF1 (Yubikey-compat) returning the X.509 cert chain.
ykman / gpg --card-edit interop testing.

References:

Cost: ~1 KB flash + 1 ECC slot + one-time provisioning step.

5. Publishing / Nixpkgs upstreaming

5.1 Nixpkgs upstream PR

Package metadata: firmware as fixed-output, lt-util as a library, NixOS module.

5.2 pid.codes VID:PID allocation

Currently using cafe:4001 (TinyUSB demo VID:PID). For public release get a pid.codes allocation (free for open hardware), then submit upstream PR to libccid to add the new VID:PID to its known-readers list — eliminates the runtime Info.plist patch.

5.3 TROPIC01 TRNG SP 800-90B compliance

Before any public production / security claims, verify TRNG entropy against SP 800-90B. Tropic Square App Note ODN_TR01_app_008 documents the chip's TRNG architecture.

5.4 Rust CLI

Direct dongle control beyond what lt-util provides — credential enumeration, FIDO reset, OpenPGP card init, validate orchestration.

6. Bug followups + maintenance

6.1 picocom termios hang on TinyUSB CDC

SET_LINE_CODING race when picocom opens our CDC interface. Workaround documented; underlying fix in TinyUSB upstream pending.

6.2 Validate scripts: substring matching for `--reader`

Older opensc-tool versions don't support substring matching on --reader nixtropic; current scripts pin --reader 0 to avoid this. Detect opensc-tool version + fall back to substring when supported.

6.3 Windows compatibility pass

Runtime use (FIDO2, OpenPGP, CDC) should auto-bind via in-box Win10/11 class drivers. Needs: scdaemon.conf docs (same disable-ccid + pcsc-shared as Linux, via Gpg4win), DFU flashing recipe (Zadig + dfu-util OR STM32CubeProgrammer), README "Windows setup" section, HW-in-the-loop verification on Win10 22H2 + Win11. No firmware changes expected.

7. Performance / flash budget

Current firmware.elf text = 218856 B / 256 KB (83.5%) post-Phase-8 (M&D PIN counters + global touch + credProps + udev rule landed). ~37 KB headroom.

§1.2 M&D-KEK wrap for X25519 dec priv key: ~3-5 KB (shares framework with the already-landed §1.1 wrappers). PIV applet (§4.4): ~15-25 KB (also fits). Attestation slot (§4.5): ~1 KB.

If we exceed budget:

Drop USE_PRECOMPUTED_CP=0 (P-256 base point caching) — current setting saves 74 KB at the cost of ECDH speed; could trade some back.
Move trezor_crypto's nist256p1.c precomputed table to flash-stored blob with on-demand access (slower + more complex ECDH).
Strip unused libtropic functions via LTO + -fdata-sections.

Out of scope

These come up regularly but belong elsewhere:

Other TROPIC01 dev kits (RPi shield, Arduino shield) — this project is TS1302-specific.
RSA support — locked out by flash budget. Users who need RSA have other devices.
FIDO Alliance AAGUID registration — $25k/year not viable for an open-source project.