FR: Modernize ERC-4527 (QR transmission protocol) and build a reference implementation

Summary

ERC-4527 "QR Code transmission protocol for wallets" has been Stagnant since its creation (Created: 2021-12-07, no activity for 6+ months). The standard describes an offline/air-gapped QR-code request–response protocol between dApps/watch-only wallets and offline signers (e.g. Keystone, AirGap Vault, Ngrave), built on BC-UR (Blockchain Commons Uniform Resources).

Meanwhile the underlying ecosystem (BC-UR + crypto-* / eth-* UR types) has kept evolving and is shipping in real hardware wallets — so the formal ERC is out of sync with practice. This issue proposes to (1) modernize the ERC and (2) provide a reference implementation in this repo.

Motivation

• The protocol works and is interoperable in shipping wallets, but the ERC text is frozen at 2021 and marked Stagnant, so there is no authoritative, up-to-date spec to point to.
• There is no canonical, vendor-neutral reference implementation that demonstrates the full round-trip (dApp shows QR → offline signer scans → signer shows QR → dApp scans back).
• ERCRef's mission explicitly covers both ERC drafting discussions and reference implementations — this is squarely in scope.

Scope

Part 1 — Modernize the ERC

• Move the proposal out of Stagnant (reopen as Draft / Review).
• Reconcile the spec with the current BC-UR registry and the UR types actually used in production (eth-sign-request, eth-signature, crypto-hdkey, crypto-account, etc.).
• Cover modern signing payloads beyond legacy txs: EIP-1559 typed txs, personal_sign, EIP-712 eth_signTypedData_v4, and EIP-4337 UserOperations.
• Specify multi-part / animated QR (UR fragmentation) behavior and versioning.
• Add interoperability notes vs. WalletConnect (online relay) to clarify the air-gapped niche.
• Update references, test vectors, and security considerations.

Part 2 — Reference implementation (this repo)

• Off-chain TS/JS reference lib demonstrating encode/decode of the UR request/response types (build on the maintained BC-UR libraries, e.g. @ngraveio/bc-ur / @keystonehq/bc-ur-registry-eth).
• A minimal demo dApp: render an animated request QR and read back a signed-response QR via webcam.
• Test vectors covering each payload type (legacy/1559 tx, personal_sign, EIP-712, UserOp).
• Round-trip / interop tests; document which hardware signers were verified against.
• README + usage docs, wired into the @ercref/contracts packaging conventions.

Notes / open questions

• ERC-4527 is primarily an off-chain transmission protocol, so the "reference implementation" here is a TS/JS library + demo rather than a Solidity contract — confirm desired home/layout in this repo.
• Decide whether to align directly with BC-UR as the normative dependency, or to re-specify the UR types inline in the ERC.
• Coordinate with original author(s) and current BC-UR / hardware-wallet implementers before re-submitting upstream.

References

• ERC-4527: https://eips.ethereum.org/EIPS/eip-4527
• BC-UR (Blockchain Commons Uniform Resources): https://github.com/BlockchainCommons/Research/blob/master/papers/bcr-2020-005-ur.md