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Tom Brow 4ff02bf03b perf(mobile): sign events with native libsecp256k1 on iOS and Android (#8654) 
Mobile signs every Nostr event (sends, relay AUTH, media auth headers,
preference writes) in pure Dart on the UI isolate. On an iPhone SE (2nd
gen, Profile build) one BIP-340 signature costs about 10.7 ms and
deriving the public key another 5.6 ms, so a burst of signed writes
drops frames.

This adds `mobile/packages/buzz_secp256k1`, a small FFI package that
builds vendored bitcoin-core/libsecp256k1 v0.8.0 (ecdh, extrakeys,
schnorrsig modules) through a Dart build hook, so the same C and the
same Dart API ship on iOS and Android with no platform bridge code. All
13 `nostr.Event.from` signing sites now go through `signNostrEvent`,
which keeps the `nostr` package's event-id serialization and moves only
key derivation and signing to native code. Calls stay synchronous.

The package also exposes `schnorrVerify` and `ecdhX`; follow-up PRs move
verification and the NIP-44 conversation key over. Incoming relay events
are still not verified, unchanged by this PR.

Safety: the signing context is randomized once per isolate, secret keys
and keypairs are wiped from the native scratch buffer after each call,
aux randomness comes from `Random.secure()`, and the static verify
context runs libsecp256k1's self test before first use.

### Validation

- Added tests: BIP-340 official vectors and native-vs-pure-Dart
differential tests in the package; `event_signing_test.dart` signs with
64 random keys and checks pubkey, event id and signature against the
existing `nostr` builder and verifier, plus malformed-key rejection.
- Full mobile analyze and test suite pass locally.
- Builds: iOS release (framework ~1.3 MB) and Android debug APK with the
library for arm64-v8a, armeabi-v7a and x86_64 (~1.2–1.3 MB each).
- On-device (iPhone SE 2nd gen, Profile, median per op): sign 10,736 µs
→ 41 µs, derive pubkey 5,580 µs → 16.5 µs, full signed event 10,744 µs →
65 µs. Event-id JSON and SHA-256 are 23 µs, so they stay in Dart.
- Device, iOS (iPhone SE 2nd gen, Profile): `buzz_secp256k1.framework`
embedded; the signed-in app authenticated to a real community relay,
loaded channels and history, and paged older messages. No native-asset
or secp256k1 errors in the console.
- Device, Android (emulator, debug): APK contains `libbuzz_secp256k1.so`
and loads it. Against a local mock relay that verifies with the
pure-Dart `nostr` package, the app's NIP-42 AUTH, NIP-98 `POST /query`
headers, and kind 20001/30078 events all verified.
- Blossom GET auth, iOS: the dev relay returns 401 for unauthenticated
`/media/` GETs. From inside the running app, the production
`MediaGetAuthService.headersFor()` header for a nonexistent hash got 404
(accepted, file missing), compared with 401 without it. The community
has no relay-hosted image, so none was rendered.


buzz-review-completed (agent review, Codex and security review clean;
device validation above; human app test not applicable under the mobile
testing exception)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Signed-off-by: Tom Brow <tomb@block.xyz>
Co-authored-by: george <973be878edd6d4f79692a3827f20a6f7fe0ed0362f269ff6b6ba8867033d7d8e@sprout-oss.stage.blox.sqprod.co>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-28 16:28:26 -07:00
..
buzz_secp256k1
perf(mobile): sign events with native libsecp256k1 on iOS and Android (#8654)
2026-10-28 16:28:26 -07:00
README.md
perf(mobile): sign events with native libsecp256k1 on iOS and Android (#8654)
2026-10-28 16:28:26 -07:00

README.md

Native packages

Local Dart packages that wrap a native C library through dart:ffi. Each one compiles its library from vendored source with a Dart build hook (hook/build.dart), so Flutter's native assets support builds it for every target (iOS, Android, and the host for flutter test). No CocoaPods, Gradle, or CMake plugin wiring is involved.

Layout

packages/<name>/
  pubspec.yaml          # depends on hooks, code_assets, native_toolchain_c, ffi
  hook/build.dart       # CBuilder.library over the vendored sources
  third_party/<lib>/    # pinned upstream subset + VENDORED.md (tag, sha256)
  src/*.c               # optional shims when the upstream API needs adapting
  lib/src/bindings.dart # @Native leaf bindings, @DefaultAsset = the hook's assetName
  lib/<name>.dart       # small typed Dart API that owns memory and validation
  test/                 # upstream test vectors where they exist

Adding a library

  1. Vendor the smallest source subset from a tagged upstream release and record the tag and tarball sha256 in third_party/<lib>/VENDORED.md. Do not edit vendored files.
  2. Mirror the upstream build system's compile definitions in hook/build.dart.
  3. Bind only the symbols the app needs. Mark calls isLeaf: true unless they call back into Dart, and keep callbacks in C shims so the bindings work in any isolate.
  4. Add the package to mobile/pubspec.yaml as a path: dependency.

Packages

  • buzz_secp256k1: bitcoin-core/libsecp256k1 (BIP-340 Schnorr, ECDH).