Midnight Multi Sig Wallet

Inspiration The Midnight Network introduces a privacy-first blockchain with built-in data protection, but there was no standalone wallet extension that could serve as both a personal wallet and a shared treasury management tool. Existing wallet solutions either lacked dApp connectivity or didn't support multi-signature governance. We wanted to build something from scratch that showcases what Midnight enables — private, composable smart contracts with a great user experience. What it does Midnight Multi Sig Wallet is a Chrome Extension (Manifest V3) that serves as a full-featured wallet for the Midnight Network. It supports:

Wallet management — Create or import wallets via BIP-39 mnemonic, with HD key derivation for up to 10 accounts per seed
NIGHT token transfers — Send and receive unshielded NIGHT with automatic DUST (fee token) generation
Multi-sig smart contracts — Deploy and manage N-of-M threshold signature contracts written in Compact. Users can propose transactions, vote to approve, and execute once the threshold is met — ideal for shared treasury management
dApp connector — A full ConnectedAPI v4 implementation with 17 methods, letting web dApps request transfers, sign data, query balances, and more — all requiring explicit user approval through the popup
Multi-network support — Switch between localnet and preprod testnet from the UI How we built it We built the entire extension from scratch in TypeScript (logic) and vanilla JavaScript + CSS (popup UI) — no React, no frameworks. The architecture is a clean three-layer design:
Inpage provider — injected into web pages via content script, exposes window.midnight['midnight-wallet'] to dApps
Content script bridge — thin relay between the page and background via postMessage
Background service worker — the central hub managing the wallet lifecycle, transaction queuing, approval flows, and 40+ message types The multi-sig system is powered by a Compact smart contract compiled to WASM, with ZK proving keys and verifiers loaded directly from the extension bundle. We used Vite with three separate build configs (background+content, inpage, popup) and esbuild for the multi-sig UI module. The wallet SDK from @midnight-ntwrk handles all on-chain operations including HD derivation, transaction building, and ZK proof generation via a proof server. Challenges we ran into
WASM in Chrome MV3 service workers — The Midnight SDK relies heavily on WASM, which requires special CSP headers (wasm-unsafe-eval) and careful bundling with vite-plugin-wasm and top-level await support
Service worker lifecycle — Chrome can kill idle service workers at any time. We had to persist pending dApp requests to chrome.storage.session and gracefully handle "stale" requests that lose their Promise references
Transaction balancing with unknown state — dApps send opaque transaction hex, so we implemented an 18-combination brute-force approach (3 signature states × 3 proof states × 3 binding states × 3 option combos) to deserialize and balance incoming transactions
BigInt serialization — chrome.storage.local can't clone BigInt values, requiring explicit string conversion guards throughout the codebase
Multi-sig witness binding — The Compact contract uses a mutable closure pattern for the secret key witness, requiring careful setSigner() calls before every contract invocation
Network ID patching — A custom Vite plugin was needed to rewrite the midnight-js-network-id module at build time for dynamic network switching Accomplishments that we're proud of
Built a complete Chrome extension wallet from scratch without any existing wallet template or framework
Implemented the full ConnectedAPI v4 with 17 methods and a dApp approval flow that mirrors production-grade wallet UX (pending request queue, badge indicators, stale request handling)
Designed and deployed a multi-sig Compact smart contract with threshold signatures, proposal lifecycle management, and on-chain state queries — all integrated into the extension UI
Created a three-layer architecture with clean separation of concerns across inpage provider, content bridge, and service worker
Wrote extensive architecture documentation (8 arch docs + implementation notes) and built a test dApp for manual connector verification What we learned
Deep understanding of Chrome Extension Manifest V3 architecture, including the service worker lifecycle, content script injection, and postMessage communication patterns
How to work with the Midnight Network SDK — wallet initialization, HD key derivation, transaction building, and ZK proof generation
Compact smart contract development — writing, compiling, and deploying contracts with witness binding patterns and state management
The complexities of building WASM-heavy applications for browser extension contexts, including CSP requirements and module bundling strategies
How to implement a multi-sig governance model on-chain with propose → approve → execute semantics What's next for Midnight Multi Sig Wallet
Multi-sig UI polish — Improve the proposal workflow UX with real-time signer status updates and transaction previews
Shielded transaction support — Extend the multi-sig system to work with Midnight's privacy-preserving Zswap transactions
Event notifications — Push notifications when new proposals are submitted or when thresholds are reached
Contract interaction history — Full audit trail of multi-sig operations (proposals, votes, executions, cancellations)
Additional networks — Support for additional Midnight testnets and eventually mainnet
Unit test coverage — Expand testing beyond the multisig modules to cover the full wallet, background message handling, and inpage provider