kirakira

A mobile client for Smol Mail, the minimalist end-to-end encrypted mail protocol: one Ed25519 identity, five operations, Noise_NX transport, sealed and signed messages. The sibling of the reference CLI client (../smolmail) and the browser client (../gsmol) — everything they do, in an Android app.

How it works

app (all crypto, all keys)  ⇄  smolmaild (TCP :1961, Noise_NX)

There is no bridge and no server-side account: the Noise session, sealing, signing, pinning and trust-on-first-use all run on the device. The seed lives in Hive app storage — the phone's app sandbox is the trust boundary, as with the CLI client's identity.key file.

First use

1. Create an identity (or restore from a seed) and back the seed up — it is the only secret.
2. Pin your home server's public key, obtained from the operator through a trusted channel (SPEC.md §4: registration and fetching refuse unpinned servers).
3. Register an address, then fetch. Restoring a seed on a new device? Enter the address alongside the seed — or "Recall" from settings — and it rebinds by RESOLVE + key check, without re-registering.

What it implements

• Identity (§2): one 32-byte seed; the X25519 agreement keys are derived from the Ed25519 keypair. Superseded seeds are kept after rotation, since mail sealed to them is readable with nothing else.
• Addressing (§3): short user@host[:1961] and self-certifying smol://user@host/key addresses; base32 fingerprints.
• Trust (§4, §8): server keys pinned explicitly; mismatch aborts the handshake; registration and fetching require a pin.
• Mail (§5): sealed and signed envelopes with 1 KiB padding, flat frontmatter bodies, sent copies sealed to self. Fetch verifies id and signature before acknowledging — anything unreadable stays on the server.
• Contacts: outgoing mail carries a signed Reply-To field with the sender's full smol:// address (an "anonymous" switch omits it); a first-contact claim binds only when its key matches the message's signer, and never over an address already pinned to a different key. The contacts screen shows each bound key with its trust badge and the keys it displaced — the only local record that a contact rotated — and a re-resolve applies §8: a chain-validated rotation is accepted and announced, an unexplained key change is refused until verified out of band. Trust warnings (unpinned sessions, rotations) persist on screen until dismissed, as the spec's §4/§8 messages demand.
• Rotation (§7): rotate with a signed certificate; contacts accept the change from the chain.
• Backup: settings can export the inbox, sent mail, contacts and server pins to one shareable file (and import it back) — the same JSON shape as gsmol's export, so backups move between the two clients. It never contains the seed, which has its own reveal-and-copy flow. Import never overwrites a pin or contact that already differs locally; malformed entries are skipped and counted.

Layout

lib/smol/crypto.dart     SHA-2, HKDF, ChaCha20-Poly1305, X25519, Ed25519, §2 conversions
lib/smol/noise.dart      Noise_NX_25519_ChaChaPoly_SHA256 initiator
lib/smol/proto.dart      addresses, seal/unseal, frontmatter, rotation, op framing
lib/smol/transport.dart  TCP byte pipe (dart:io)
lib/smol/store.dart      Hive: identity, pins, contacts, sealed mail, export/import
lib/smol/config.dart      deploy-time preset server pin (--dart-define)
lib/smol/client.dart     connect/fetch/send/register/rotate flows
lib/presentation/       the UI (Riverpod + auto_route)
test/smol_test.dart     byte-exact vectors + protocol cases
test/store_test.dart    contact key history, import
test/widget_test.dart   UI smoke test
test/e2e_test.dart      live round-trip against smolmaild

The crypto is pure Dart, mirroring gsmol's dependency-free modules, so test/vectors.json — generated from the reference stack (PyNaCl, noiseprotocol) by ../gsmol/test/gen_vectors.py — pins every operation byte for byte.

Run and verify

devbox run analyze
devbox run test

Then flutter run with a device or emulator attached. test/e2e_test.dart additionally runs a live round-trip (register, send to self, fetch, unseal, drain) against ../smolmail/smolmaild.py on 127.0.0.1:1961, and self-skips when no server is listening.

Not verified here: clicking through the app on a real device — the logic under every button is what the tests exercise, as with gsmol.

Notes and limits

• No server push or notifications in v1 (SPEC.md §13): tap fetch.
• The seed sits in app storage: a compromised device is game over, same as a stolen identity.key file for the CLI client.
• Rotation is not revocation (§7): a stolen key can rotate onward and the chain validates. The settings screen surfaces rotations instead of applying them invisibly; out-of-band re-verification is the only defence.

License

Distributed under the MIT License; see LICENSE.md.