adminandClaude Opus 4.7 ef00afb14e fix(firmware/lib): validate HMAC secret length and hex format before signing ...

hmac_sign() previously trusted whatever secret_hex came out of NVS:
- Lengths >128 chars overflowed the fixed 64-byte stack buffer in
  hex_to_bytes (out_len was unbounded).
- Non-hex characters were silently decoded to 0 via strtol with no
  end-pointer check, producing signatures under a corrupted key.
- Empty secrets fell through to mbedtls_md_hmac_starts with len=0.

flash_device.py now rejects malformed --hmac-secret at provision time,
but hmac_sign should also refuse to sign under a malformed key regardless
of how it ended up in NVS (legacy provisioning, partial flash, etc.).

Add length, hex-charset, and even-length validation; make hex_to_bytes
return bool and have hmac_sign return empty HString on any failure
(callers already treat empty as failure via post_json_once).

Found via adversarial review (run 2026-05-01-202910, both reviewers).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-01 15:36:06 -07:00

..

hmac.cpp

fix(firmware/lib): validate HMAC secret length and hex format before signing

2026-05-01 15:36:06 -07:00

hmac.h

fix: HMAC format — match server POST\npath\ntimestamp\nsha256(body) scheme

2026-04-14 10:47:13 -07:00