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>
Age-check errors previously blocked Buzz startup. Normal app startup now
proceeds immediately; only a valid under-18 response from the current
launch request can restrict access.
Age check enforcement remains disabled at compile time by default.
Builds can opt in with `--dart-define=BUZZ_AGE_GATING_ENABLED=true`.
---------
Signed-off-by: Tom Brow <tomb@block.xyz>
