Šepot — end-to-end encrypted messenger

Initial public release. Anonymous on-device identity (no phone number, e-mail, or password), Signal-protocol cryptography (X3DH + PQXDH, Double Ratchet, sealed sender) via libsignal, a metadata-minimizing relay, group chats, disappearing messages, encrypted local storage, optional Tor transport, and a UI localized into Czech, English, German, Russian, and Italian. Monorepo: Flutter client (app/), Rust relay + wire types (rust/), protobuf definitions (proto/), self-host deploy (deploy/). Licensed under AGPL-3.0 with an app-store distribution exception (§7).
2026-07-11 17:06:39 +02:00
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+import 'dart:convert';
+import 'dart:typed_data';
+
+/// Stav přenosu přílohy — čistě lokální (na drát nikdy nejde).
+enum AttachmentTransferState {
+  /// Přijatá zpráva, blob se ještě nezačal stahovat.
+  pending,
+  downloading,
+
+  /// Blob leží (šifrovaný) v lokálním AttachmentStore.
+  ready,
+
+  /// Download/ověření selhalo — UI nabídne opakování.
+  failed,
+}
+
+/// Metadata přílohy. Klíč/nonce/digest dorazily E2E kanálem (relay je
+/// nevidí); v lokální DB žijí uvnitř SQLCipher, takže at-rest jsou
+/// chráněné stejně jako zbytek zpráv.
+///
+/// Wire tvar (pole `att` v content JSON, krátké klíče kvůli obálce):
+///   { bid, k, n, d, s, mime, name?, w?, h?, th? }
+class AttachmentMeta {
+  const AttachmentMeta({
+    required this.blobId,
+    required this.keyB64,
+    required this.nonceB64,
+    required this.digestB64,
+    required this.size,
+    required this.mime,
+    this.name,
+    this.width,
+    this.height,
+    this.thumbB64,
+    this.durationMs,
+    this.state = AttachmentTransferState.pending,
+  });
+
+  final String blobId; // 32 hex znaků (id na relayi i lokálně)
+  final String keyB64; // 32 B per-file AES klíč
+  final String nonceB64; // 12 B GCM nonce
+  final String digestB64; // SHA-256 šifrovaného blobu
+  final int size; // velikost PLAINTEXTU v bajtech
+  final String mime;
+  final String? name; // původní název souboru (dokumenty)
+  final int? width; // rozměry obrázku
+  final int? height;
+  final String? thumbB64; // JPEG náhled — jede UVNITŘ E2E plaintextu
+  final int? durationMs; // délka hlasové zprávy / audia
+  final AttachmentTransferState state;
+
+  bool get isImage => mime.startsWith('image/');
+  bool get isAudio => mime.startsWith('audio/');
+
+  Uint8List get key => base64Decode(keyB64);
+  Uint8List get nonce => base64Decode(nonceB64);
+  Uint8List get digest => base64Decode(digestB64);
+  Uint8List? get thumbnail =>
+      thumbB64 == null ? null : base64Decode(thumbB64!);
+
+  AttachmentMeta copyWith({AttachmentTransferState? state}) {
+    return AttachmentMeta(
+      blobId: blobId,
+      keyB64: keyB64,
+      nonceB64: nonceB64,
+      digestB64: digestB64,
+      size: size,
+      mime: mime,
+      name: name,
+      width: width,
+      height: height,
+      thumbB64: thumbB64,
+      durationMs: durationMs,
+      state: state ?? this.state,
+    );
+  }
+
+  /// Do content JSON zprávy (bez lokálního stavu).
+  Map<String, dynamic> toWire() => {
+        'bid': blobId,
+        'k': keyB64,
+        'n': nonceB64,
+        'd': digestB64,
+        's': size,
+        'mime': mime,
+        if (name != null) 'name': name,
+        if (width != null) 'w': width,
+        if (height != null) 'h': height,
+        if (thumbB64 != null) 'th': thumbB64,
+        if (durationMs != null) 'dur': durationMs,
+      };
+
+  /// Z content JSON příchozí zprávy. Remote input — tvary se validují
+  /// (blob_id formát hlídá AttachmentStore, tady rozsahy a typy).
+  factory AttachmentMeta.fromWire(Map<String, dynamic> wire) {
+    final size = wire['s'] as int;
+    if (size <= 0 || size > 512 * 1024 * 1024) {
+      throw const FormatException('implausible attachment size');
+    }
+    return AttachmentMeta(
+      blobId: wire['bid'] as String,
+      keyB64: wire['k'] as String,
+      nonceB64: wire['n'] as String,
+      digestB64: wire['d'] as String,
+      size: size,
+      mime: wire['mime'] as String,
+      name: wire['name'] as String?,
+      width: wire['w'] as int?,
+      height: wire['h'] as int?,
+      thumbB64: wire['th'] as String?,
+      durationMs: wire['dur'] as int?,
+      state: AttachmentTransferState.pending,
+    );
+  }
+
+  /// Lokální perzistence (SQLCipher) — wire tvar + stav.
+  Map<String, dynamic> toJson() => {
+        ...toWire(),
+        'state': state.name,
+      };
+
+  factory AttachmentMeta.fromJson(Map<String, dynamic> json) {
+    final base = AttachmentMeta.fromWire(json);
+    final stateName = json['state'] as String?;
+    return base.copyWith(
+      state: AttachmentTransferState.values.asNameMap()[stateName] ??
+          AttachmentTransferState.pending,
+    );
+  }
+}