Keys Not Included: recovering the signing keys for US driver's license barcodes

Original Article ↗ Hacker News Discussion ↗

Researchers show that US driver’s license barcodes using ECDSA signatures allow the issuing state’s public keys to be recovered from the signed data, enabling third parties to verify whether barcodes were produced by a real DMV system. Commenters clarify that only public (verification) keys are exposed—not private signing keys—so this doesn’t enable forging licenses, but it does highlight both the value of standardizing cryptographic verification for IDs and the limitations of current barcode-based designs that don’t cover photos and are easy to copy. The conversation broadens into comparisons with NFC-based passports, privacy concerns around mandatory ID scanning and data brokers, and the challenge of explaining public‑key cryptography accurately to non-experts.

Nature of the “recovered keys”

  • Several commenters note the HN subtitle is misleading: only public keys are recovered, not signing (private) keys.
  • The blog explicitly says these are public keys, usable for verification only, not forgery.
  • Some object to phrasing like “key that produced the signature,” arguing that only the private key “produces” a signature and imprecise language confuses readers.

Cryptographic concepts & analogies

  • Much discussion centers on how to explain public‑key cryptography:
    • Many argue “key” and “lock” analogies are poor or misleading, especially for asymmetric crypto.
    • Alternatives suggested: “public address,” “signature,” “verification key,” or “secret vs identity.”
    • Others defend imperfect analogies as useful teaching tools, if later refined with real math.

ID barcodes, verification, and forgery

  • Enthusiasm: Signing barcodes is seen as a clear security upgrade over unsigned data and as a better design than some app‑based ID schemes.
  • Skepticism:
    • The barcode does not include or sign the photo. A forger could pair a real barcode with a fake front and photo.
    • Proper verification should compare machine‑readable data to printed data; some dispute whether that’s always necessary in practice.
    • Commercial ID scanners often log, correlate, and do “anti‑passback” checks, raising both security and privacy issues.

NFC chips, biometric documents, and mDL

  • Many argue NFC smartcards (as in passports and some EU IDs) are superior:
    • They can store photos and do nonce‑based challenge‑response, preventing simple copying.
    • Some propose removing printed photos entirely and forcing electronic verification; others worry about constant scanning and data retention.
  • Mobile driver’s licenses and wallet‑integrated “verifiable credentials” are seen as the likely future in banking and onboarding, though there is concern about:
    • Reliance on proprietary ecosystems (e.g., specific phone wallet platforms).
    • States’ and vendors’ ability to protect private keys.

Currency, e‑cash, and blind signatures

  • One line of discussion wonders if similar signatures could secure paper money.
  • Critics note static signed data on notes is easy to copy; proper anti‑counterfeiting would need NFC and online checks.
  • Debate over blind signatures:
    • Some stress they provide strong privacy but require immediate redemption and are ill‑suited to physical cash.
    • Others clarify that preventing duplication depends on protocol design and secrecy of signed data.

Privacy, vendors, and governance

  • Concern that private vendors now handle signed ID data for many states, seeing full PII with no real opt‑out.
  • Some call for legal limits on outsourcing and data sale, and for wider adoption of standardized, verifiable signatures on IDs.