RS-Key v0.4.2

[0.4.2] - 2026-07-25

Changed

• FIDO2 credential IDs are now fingerprint-free — they look random, like a
  YubiKey's. Both credential-ID formats used to carry a fixed cleartext prefix a
  relying party (or a flash dump) could recognise: non-resident boxes led with
  f1d00202, and resident (passkey) ids led with a 10-byte header
  (HMAC(serial)[..4] ‖ f1d00203 ‖ version ‖ 00) whose first four bytes were
  device-specific and identical across every passkey on the device — a
  cross-RP device-correlation handle. New credentials carry neither marker: a
  non-resident box is iv ‖ ciphertext ‖ tag ‖ silent-tag (its key comes from a
  fixed internal label, not an on-wire byte) and a resident id is 42
  pseudo-random per-credential bytes. Backward-compatible: already-registered
  credentials keep working — the authenticator still opens the legacy
  f1d00202 / f1d00203 formats (the AEAD tag and a length-based allowList
  lookup tell the framings apart), so no re-registration is required. The change
  is forward-only: ids issued before the upgrade stay as they were until a site
  is re-registered. bcdDevice → 0x0851.

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Verify a download: https://github.com/TheMaxMur/RS-Key/blob/v0.4.2/docs/supply-chain.md