# case · 02 / 04 · 2024
● betamacOSiOSe2eeswift
Lynkboard — copy on your Mac, paste on your iPhone in under one second.
role
sole engineer · all platforms
stack
swift 5.9 · supabase · cryptokit
timeline
q2 — q4 2024
status
beta · phases 0–5 complete
#01 · the problem
// brief
Universal Clipboard is iCloud-only and sends your clipboard to Apple's servers.
Developers copy API keys, tokens, and sensitive snippets constantly. Routing those through a cloud server — even Apple's — is a non-starter when you care about operational security.
LAN-first sync with E2EE fallback was the only acceptable architecture.
// constraints
- < 1s lanclipboard syncs on local network instantly
- e2ee alwaysserver stores only opaque ciphertext
- qr pairingkey exchange via physical proximity only
- offline-okfull history works without internet
- share extios share extension reuses same grdb stack
#02 · system design
LAN-first. Cloud fallback. Always encrypted.
clients
· macOS menu bar
· iOS app
· iOS share extension
encrypt · seal
lan transport
· multipeer connectivity
· bonjour discovery
· 200ms timeout
cryptography
· chacha20poly aead
· curve25519 keypairs
· qr key exchange
relay fallback
supabase relay
· postgrest http post
· realtime websocket
· phoenix protocol
storage
· grdb · sqlite
· keychain keypairs
· app group container
layer · 01
transport
MultipeerConnectivity for LAN — symmetric advertise+browse, sub-200ms pairing. Supabase relay as automatic fallback on cellular.
layer · 02
cryptography
ChaChaPoly AEAD seals payloads before leaving the device. Server stores ciphertext+nonce only. Group key never touches the wire in plaintext.
layer · 03
shared core
ClipboardCore Swift Package shared across Mac, iOS app, and Share Extension — zero duplication. Port/adapter pattern behind protocol interfaces.
#03 · engineering highlights
Zero-SDK realtime. Phoenix over URLSession.
1// LAN-first, relay fallback actor
2actor SyncCoordinator {
3 func sync(_ entry: ClipEntry) async {
4 let sealed = try box.seal(entry)
5 if await lan.isReachable {
6 try await lan.send(sealed)
7 } else {
8 try await relay.post(sealed)
9 }
10 }
11}
// what makes it different
phoenix ws — no sdk
Supabase Realtime WebSocket implemented natively over URLSessionWebSocketTask. Zero SDK dependency on the client.
qr pairing
Curve25519 keypair exchange via QR code — secure channel established by physical device proximity alone.
share extension
iOS Share Extension writes directly to the shared SQLite via app group, reusing the same GRDB stack with zero duplication.
menu bar native
macOS LSUIElement process — no Dock icon. NSPasteboard polling at 0.5s, global Shift+Cmd+V hotkey.
#04 · where it stands
<1s
lan sync latency
e2ee
chacha20poly aead
3 targets
mac · ios · share ext
phases 0–5
complete · storekit next