feat: import Chinese-localized Buzz source snapshot

Signed-off-by: cls_宁波本机 <908705107@qq.com>

mobile/lib/features/pairing/pairing_crypto.dart

@@ -0,0 +1,164 @@
+import 'dart:typed_data';
+
+import '../../shared/crypto/ecdh.dart';
+import '../../shared/crypto/hkdf.dart';
+
+/// Derive session ID from session secret.
+/// session_id = HKDF-SHA256(IKM=session_secret, salt="", info="nostr-pair-session-id", L=32)
+Uint8List deriveSessionId(Uint8List sessionSecret) {
+  return hkdf(
+    sessionSecret,
+    Uint8List(0), // empty salt
+    Uint8List.fromList('nostr-pair-session-id'.codeUnits),
+    32,
+  );
+}
+
+/// Derive SAS code and SAS input from ECDH shared secret and session secret.
+/// sas_input = HKDF-SHA256(IKM=ecdh_shared, salt=session_secret, info="nostr-pair-sas-v1", L=32)
+/// sas_code = be_u32(sas_input[0..4]) % 1_000_000
+(int, Uint8List) deriveSas(Uint8List ecdhShared, Uint8List sessionSecret) {
+  final sasInput = hkdf(
+    ecdhShared,
+    sessionSecret,
+    Uint8List.fromList('nostr-pair-sas-v1'.codeUnits),
+    32,
+  );
+
+  // be_u32 from first 4 bytes.
+  final code =
+      ((sasInput[0] << 24) |
+          (sasInput[1] << 16) |
+          (sasInput[2] << 8) |
+          sasInput[3]) %
+      1000000;
+
+  return (code, sasInput);
+}
+
+/// Format a SAS code as a 6-digit zero-padded string.
+String formatSas(int code) => code.toString().padLeft(6, '0');
+
+/// Derive transcript hash binding all session parameters.
+/// transcript = session_id || source_pubkey || target_pubkey || sas_input (128 bytes)
+/// transcript_hash = HKDF-SHA256(IKM=transcript, salt=session_secret, info="nostr-pair-transcript-v1", L=32)
+Uint8List deriveTranscriptHash(
+  Uint8List sessionId,
+  Uint8List sourcePubkey,
+  Uint8List targetPubkey,
+  Uint8List sasInput,
+  Uint8List sessionSecret,
+) {
+  final transcript = Uint8List(128);
+  transcript.setRange(0, 32, sessionId);
+  transcript.setRange(32, 64, sourcePubkey);
+  transcript.setRange(64, 96, targetPubkey);
+  transcript.setRange(96, 128, sasInput);
+
+  return hkdf(
+    transcript,
+    sessionSecret,
+    Uint8List.fromList('nostr-pair-transcript-v1'.codeUnits),
+    32,
+  );
+}
+
+/// Parse a `nostrpair://` QR URI.
+({
+  String sourcePubkey,
+  Uint8List sessionSecret,
+  List<String> relays,
+  int version,
+})
+parseNostrpairUri(String uri) {
+  if (uri.length > 2048) {
+    throw FormatException('URI exceeds 2048-character limit');
+  }
+
+  if (!uri.startsWith('nostrpair://')) {
+    throw const FormatException('URI must start with nostrpair://');
+  }
+
+  final rest = uri.substring('nostrpair://'.length);
+  final qIdx = rest.indexOf('?');
+  if (qIdx < 0) {
+    throw const FormatException('Missing query string');
+  }
+
+  final pubkeyHex = rest.substring(0, qIdx);
+  final query = rest.substring(qIdx + 1);
+
+  // Validate pubkey: 64 lowercase hex chars.
+  if (pubkeyHex.length != 64 || !_isLowercaseHex(pubkeyHex)) {
+    throw const FormatException('Pubkey must be 64 lowercase hex chars');
+  }
+
+  // Parse query params.
+  String? secretHex;
+  final relays = <String>[];
+  int? version;
+
+  for (final pair in query.split('&')) {
+    final eqIdx = pair.indexOf('=');
+    if (eqIdx < 0) continue;
+    final key = pair.substring(0, eqIdx);
+    final value = pair.substring(eqIdx + 1);
+    switch (key) {
+      case 'secret':
+        secretHex = value;
+      case 'relay':
+        relays.add(Uri.decodeComponent(value));
+      case 'v':
+        version = int.tryParse(value);
+    }
+  }
+
+  // Default version to 1.
+  version ??= 1;
+  if (version != 1) {
+    throw FormatException(
+      'Unsupported protocol version $version. Please update the app.',
+    );
+  }
+
+  // Validate secret.
+  if (secretHex == null ||
+      secretHex.length != 64 ||
+      !_isLowercaseHex(secretHex)) {
+    throw const FormatException('Secret must be 64 lowercase hex chars');
+  }
+  final sessionSecret = hexToBytes(secretHex);
+
+  // Reject all-zeros.
+  if (sessionSecret.every((b) => b == 0)) {
+    throw const FormatException('Session secret must not be all zeros');
+  }
+
+  if (relays.isEmpty) {
+    throw const FormatException('At least one relay URL is required');
+  }
+
+  // Validate relay URLs.
+  for (final relay in relays) {
+    final parsed = Uri.tryParse(relay);
+    if (parsed == null || (parsed.scheme != 'wss' && parsed.scheme != 'ws')) {
+      throw FormatException('Invalid relay URL: $relay');
+    }
+  }
+
+  return (
+    sourcePubkey: pubkeyHex,
+    sessionSecret: sessionSecret,
+    relays: relays,
+    version: version,
+  );
+}
+
+bool _isLowercaseHex(String s) {
+  for (final c in s.codeUnits) {
+    if (!((c >= 0x30 && c <= 0x39) || (c >= 0x61 && c <= 0x66))) {
+      return false;
+    }
+  }
+  return true;
+}