fix: migrating to new key encoding (#598)

Author: maximeroucher

lib/paiement/tools/key_service.dart

@@ -1,3 +1,4 @@
+import 'dart:convert';
 import 'package:cryptography_plus/cryptography_plus.dart';
 import 'package:flutter_secure_storage/flutter_secure_storage.dart';
 
@@ -20,12 +21,13 @@ class KeyService {
     final publicKey = await keyPair.extractPublicKey();
     await _secureStorage.write(
       key: 'privateKey',
-      value: String.fromCharCodes(privateKey),
+      value: base64.encode(privateKey),
     );
     await _secureStorage.write(
       key: 'publicKey',
-      value: String.fromCharCodes(publicKey.bytes),
+      value: base64.encode(publicKey.bytes),
     );
+    await _secureStorage.write(key: 'migrated', value: 'true');
   }
 
   Future saveKeyId(String keyId) async {
@@ -38,8 +40,28 @@ class KeyService {
     if (privateKeyString == null || publicKeyString == null) {
       return null;
     }
-    final privateKey = privateKeyString.codeUnits;
-    final publicKey = publicKeyString.codeUnits;
+    final migrated = await _secureStorage.read(key: 'migrated');
+    if (migrated == null) {
+      final privateKey = privateKeyString.codeUnits;
+      final publicKey = publicKeyString.codeUnits;
+
+      await _secureStorage.write(
+        key: 'privateKey',
+        value: base64.encode(privateKey),
+      );
+      await _secureStorage.write(
+        key: 'publicKey',
+        value: base64.encode(publicKey),
+      );
+      await _secureStorage.write(key: 'migrated', value: 'true');
+      return SimpleKeyPairData(
+        privateKey,
+        publicKey: SimplePublicKey(publicKey, type: KeyPairType.ed25519),
+        type: KeyPairType.ed25519,
+      );
+    }
+    final privateKey = base64.decode(privateKeyString);
+    final publicKey = base64.decode(publicKeyString);
     return SimpleKeyPairData(
       privateKey,
       publicKey: SimplePublicKey(publicKey, type: KeyPairType.ed25519),