feat(useragent): initial connection impl

useragent/lib/features/identity/pk_manager.dart

@@ -0,0 +1,16 @@
+enum KeyAlgorithm {
+  rsa, ecdsa, ed25519
+}
+
+// The API to handle without storing the private key in memory. 
+//The implementation will use platform-specific secure storage and signing capabilities.
+abstract class KeyHandle {
+  KeyAlgorithm get alg;
+  Future<List<int>> sign(List<int> data);
+  Future<List<int>> getPublicKey();
+}
+
+abstract class KeyManager {
+  Future<KeyHandle?> get();
+  Future<KeyHandle> create();
+}

useragent/lib/features/identity/simple_ed25519.dart

@@ -0,0 +1,93 @@
+import 'dart:convert';
+
+import 'package:cryptography/cryptography.dart';
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+import 'package:arbiter/features/identity/pk_manager.dart';
+
+final storage = FlutterSecureStorage(
+  aOptions: AndroidOptions.biometric(
+    enforceBiometrics: true,
+    biometricPromptTitle: 'Authentication Required',
+  ),
+  mOptions: MacOsOptions(
+    accessibility: KeychainAccessibility.unlocked_this_device,
+    label: "Arbiter",
+    description: "Confirm your identity to access vault",
+    synchronizable: false,
+    accessControlFlags: [
+      AccessControlFlag.userPresence,
+    ],
+    usesDataProtectionKeychain: true,
+  ),
+);
+
+final processor = Ed25519();
+
+class SimpleEd25519 extends KeyHandle {
+  final SimpleKeyPair _keyPair;
+
+  SimpleEd25519({required SimpleKeyPair keyPair}) : _keyPair = keyPair;
+
+  @override
+  KeyAlgorithm get alg => KeyAlgorithm.ed25519;
+
+  @override
+  Future<List<int>> getPublicKey() async {
+    final publicKey = await _keyPair.extractPublicKey();
+    return publicKey.bytes;
+  }
+
+  @override
+  Future<List<int>> sign(List<int> data) async {
+    final signature = await processor.sign(data, keyPair: _keyPair);
+    return signature.bytes;
+  }
+}
+
+class SimpleEd25519Manager extends KeyManager {
+  static const _storageKey = "ed25519_identity";
+  static const _storagePublicKey = "ed25519_public_key";
+
+  @override
+  Future<KeyHandle> create() async {
+    final storedKey = await get();
+    if (storedKey != null) {
+      return storedKey;
+    }
+
+    final newKey = await processor.newKeyPair();
+    final rawKey = await newKey.extract();
+
+    final keyData = base64Encode(rawKey.bytes);
+    await storage.write(key: _storageKey, value: keyData);
+
+    final publicKeyData = base64Encode(rawKey.publicKey.bytes);
+    await storage.write(key: _storagePublicKey, value: publicKeyData);
+
+    return SimpleEd25519(keyPair: newKey);
+  }
+
+  @override
+  Future<KeyHandle?> get() async {
+    final storedKeyPair = await storage.read(key: _storageKey);
+    if (storedKeyPair == null) {
+      return null;
+    }
+
+    final publicKeyData = await storage.read(key: _storagePublicKey);
+    final publicKeyRaw = base64Decode(publicKeyData!);
+    final publicKey = SimplePublicKey(
+      publicKeyRaw,
+      type: processor.keyPairType,
+    );
+
+    final keyBytes = base64Decode(storedKeyPair);
+    final keypair = SimpleKeyPairData(
+      keyBytes,
+      publicKey: publicKey,
+      type: processor.keyPairType,
+    );
+
+    return SimpleEd25519(keyPair: keypair);
+  }
+}