message integrity

lib/chat/cubits/reconciliation/message_integrity.dart

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+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:protobuf/protobuf.dart';
+import 'package:veilid_support/veilid_support.dart';
+import '../../../proto/proto.dart' as proto;
+
+class MessageIntegrity {
+  MessageIntegrity._({
+    required TypedKey author,
+    required VeilidCryptoSystem crypto,
+  })  : _author = author,
+        _crypto = crypto;
+  static Future<MessageIntegrity> create({required TypedKey author}) async {
+    final crypto = await Veilid.instance.getCryptoSystem(author.kind);
+    return MessageIntegrity._(author: author, crypto: crypto);
+  }
+
+  ////////////////////////////////////////////////////////////////////////////
+  // Public interface
+
+  Future<Uint8List> generateMessageId(proto.Message? previous) async {
+    if (previous == null) {
+      // If there's no last sent message,
+      // we start at a hash of the identity public key
+      return _generateInitialId();
+    } else {
+      // If there is a last message, we generate the hash
+      // of the last message's signature and use it as our next id
+      return _hashSignature(previous.signature);
+    }
+  }
+
+  Future<void> signMessage(
+    proto.Message message,
+    SecretKey authorSecret,
+  ) async {
+    // Ensure this message is not already signed
+    assert(!message.hasSignature(), 'should not sign message twice');
+    // Generate data to sign
+    final data = Uint8List.fromList(utf8.encode(message.writeToJson()));
+
+    // Sign with our identity
+    final signature = await _crypto.sign(_author.value, authorSecret, data);
+
+    // Add to the message
+    message.signature = signature.toProto();
+  }
+
+  Future<bool> verifyMessage(proto.Message message) async {
+    // Ensure the message is signed
+    assert(message.hasSignature(), 'should not verify unsigned message');
+    final signature = message.signature.toVeilid();
+
+    // Generate data to sign
+    final messageNoSig = message.deepCopy()..clearSignature();
+    final data = Uint8List.fromList(utf8.encode(messageNoSig.writeToJson()));
+
+    // Verify signature
+    return _crypto.verify(_author.value, data, signature);
+  }
+
+  ////////////////////////////////////////////////////////////////////////////
+  // Private implementation
+
+  Future<Uint8List> _generateInitialId() async =>
+      (await _crypto.generateHash(_author.decode())).decode();
+
+  Future<Uint8List> _hashSignature(proto.Signature signature) async =>
+      (await _crypto.generateHash(signature.toVeilid().decode())).decode();
+  ////////////////////////////////////////////////////////////////////////////
+  final TypedKey _author;
+  final VeilidCryptoSystem _crypto;
+}