Winnow

A private, opinionated, modern Bitcoin wallet for iOS — 100% Swift, one dependency.

Public beta on TestFlight — signet by default.

• Pure P2P by default. The read side is BIP157/158 compact block filters served by full-node peers — no server ever learns your addresses. Bounded mempool windows (short full-relay subscriptions while the Receive or Send screen is open) give 0-conf payment detection and propagation tracking without any server. Design papers, framed around the phone: docs/.
• Taproot only. P2TR receiving (BIP86); no legacy address types, no ECDSA signing paths.
• Two modern multisig flavors. MuSig2 (BIP327) n-of-n vaults and script-path k-of-n (multi_a, BIP387/388), coordinated over PSBTv2 (BIP370/371/373).
• Silent payments, send-side (BIP352): pay reusable sp1… codes.
• One runtime dependency: swift-secp256k1 (Bitcoin Core's libsecp256k1), pinned.
• Optional esplora fast path — off by default, behind an explicit privacy warning in Settings.

Layout

Architecture invariant: all logic lives in the SPM package, where it is tested; the app target is a thin shell. No wallet, protocol, or crypto logic may move into WinnowApp — if the UI needs something, expose it from a library.

• Sources/BitcoinCore — crypto, keys (BIP39/32/86), Taproot (BIP341), descriptors (BIP380/387/389/390), MuSig2 (BIP327), silent payments (BIP352)
• Sources/BitcoinP2P — wire protocol, peers, header chain, BIP157 filter sync, tx broadcast
• Sources/BlockchainBackend — opt-in esplora client (never contacted unless enabled)
• Sources/WalletCore — wallet/vault actors, sighash + signing, PSBTv2, coin selection, fee policy, import bundles
• Sources/WinnowApp — the iOS app (SwiftUI, iOS 17+)
• docs/ — design papers (phone, read, write, vaults, import) + webpage
• Scripts/ — icon generation, App Store Connect API tooling, TestFlight pipeline

Build & test

swift build
DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer swift test   # 203 tests, official BIP vectors
/opt/homebrew/bin/xcodegen && open WinnowApp.xcodeproj                # iOS app

Default network for development is signet. Point the app at your own filter-serving node (Settings → Manual peers); the node needs blockfilterindex=1 and peerblockfilters=1.