29 Add encrypted metadata support

lib/src/v2/models/destination.dart

@@ -11,6 +11,7 @@ class Destination {
 
   DestinationType? type;
   String? zkId;
+  String? encryptedDek;
 
   Destination({
     required this.value,
@@ -19,6 +20,7 @@ class Destination {
     this.isEncrypted = false,
     this.type,
     this.zkId,
+    this.encryptedDek,
   });
 
   factory Destination.fromJson(Map<String, dynamic> json) => Destination(
@@ -27,6 +29,7 @@ class Destination {
         isZk: json['zk'] as bool? ?? false,
         type: DestinationType.fromJson(json['type'] as String?),
         zkId: json['zk_id'] as String?,
+        encryptedDek: json['encrypted_dek'] as String?,
       );
 
   Map<String, dynamic> toJson() => {
@@ -35,5 +38,6 @@ class Destination {
         'zk': isZk,
         if (type != null) 'type': type!.jsonValue,
         if (zkId != null) 'zk_id': zkId,
+        if (encryptedDek != null) 'encrypted_dek': encryptedDek,
       };
 }

lib/src/v2/models/payment.dart

@@ -13,6 +13,10 @@ class Payment {
   Platform? parentPlatform;
   String? btcPayServerPluginVersion;
 
+  /// Runtime-only flag set by [BrantaService] after metadata decryption.
+  /// Not serialized to/from JSON.
+  bool isMetadataDecrypted = false;
+
   Payment({
     this.description,
     required this.destinations,

lib/src/v2/services/branta_service.dart

@@ -69,9 +69,9 @@ class BrantaService implements IBrantaService {
 
     final keys = <String, String>{};
     for (final payment in payments) {
-      await _decryptDestinations(payment.destinations, lookupValue, encryptionKey, null, keys);
+      await _decryptDestinations(payment, lookupValue, encryptionKey, null, keys);
       for (final value in additionalHashValues) {
-        await _decryptHashZkDestinations(payment.destinations, value, keys);
+        await _decryptHashZkDestinations(payment, value, keys);
       }
     }
 
@@ -82,21 +82,22 @@ class BrantaService implements IBrantaService {
   }
 
   Future<void> _decryptHashZkDestinations(
-    List<Destination> destinations,
+    Payment payment,
     String plainValue,
     Map<String, String> keys,
   ) async {
     final hashZkType = plainValue.getHashZkType();
     if (hashZkType == null) return;
 
     final key = plainValue.toNormalizedHash();
-    for (final destination in destinations) {
+    for (final destination in payment.destinations) {
       if (!destination.isZk || destination.type != hashZkType) continue;
       try {
         destination.value = await _aesEncryption.decrypt(destination.value, key);
         destination.isEncrypted = false;
         final zkId = destination.zkId;
         if (zkId != null) keys.putIfAbsent(zkId, () => key);
+        await _tryDecryptMetadata(payment, destination, key);
       } catch (_) {
         // Key didn't match this destination — leave it encrypted.
       }
@@ -136,7 +137,7 @@ class BrantaService implements IBrantaService {
 
     final keys = <String, String>{};
     for (final payment in payments) {
-      await _decryptDestinations(payment.destinations, normalizedDestination, destinationEncryptionKey, hashZkType, keys);
+      await _decryptDestinations(payment, normalizedDestination, destinationEncryptionKey, hashZkType, keys);
     }
 
     return PaymentsResult(
@@ -146,13 +147,13 @@ class BrantaService implements IBrantaService {
   }
 
   Future<void> _decryptDestinations(
-    List<Destination> destinations,
+    Payment payment,
     String destinationValue,
     String? encryptionKey,
     DestinationType? hashZkType,
     Map<String, String> keys,
   ) async {
-    for (final destination in destinations) {
+    for (final destination in payment.destinations) {
       destination.isEncrypted = destination.isZk;
       if (!destination.isZk) continue;
 
@@ -163,6 +164,7 @@ class BrantaService implements IBrantaService {
           destination.isEncrypted = false;
           final zkId = destination.zkId;
           if (zkId != null) keys.putIfAbsent(zkId, () => encryptionKey);
+          await _tryDecryptMetadata(payment, destination, encryptionKey);
         } catch (_) {
           // Key didn't match — leave it encrypted.
         }
@@ -173,13 +175,30 @@ class BrantaService implements IBrantaService {
           destination.isEncrypted = false;
           final zkId = destination.zkId;
           if (zkId != null) keys.putIfAbsent(zkId, () => key);
+          await _tryDecryptMetadata(payment, destination, key);
         } catch (_) {
           // Key didn't match — leave it encrypted.
         }
       }
     }
   }
 
+  Future<void> _tryDecryptMetadata(
+    Payment payment,
+    Destination destination,
+    String keyUsed,
+  ) async {
+    final encryptedDek = destination.encryptedDek;
+    if (encryptedDek == null || payment.metadata == null || payment.isMetadataDecrypted) return;
+    try {
+      final dek = await _aesEncryption.decrypt(encryptedDek, keyUsed);
+      payment.metadata = await _aesEncryption.decrypt(payment.metadata!, dek);
+      payment.isMetadataDecrypted = true;
+    } catch (_) {
+      // DEK decryption failed — leave metadata as-is.
+    }
+  }
+
   @override
   Future<AddPaymentResult> addPaymentAsync(Payment payment, {BrantaClientOptions? options}) async {
     final privacy = _resolvePrivacy(options);
@@ -189,6 +208,12 @@ class BrantaService implements IBrantaService {
       );
     }
 
+    String? dek;
+    if (payment.metadata != null && payment.destinations.any((d) => d.isZk)) {
+      dek = _secretGenerator.generate();
+      payment.metadata = await _aesEncryption.encrypt(payment.metadata!, dek, deterministicNonce: false);
+    }
+
     final secret = _secretGenerator.generate();
     final encryptedToKey = <String, String>{};
 
@@ -202,6 +227,9 @@ class BrantaService implements IBrantaService {
           deterministicNonce: _secretGenerator.deterministicNonce,
         );
         encryptedToKey[destination.value] = secret;
+        if (dek != null) {
+          destination.encryptedDek = await _aesEncryption.encrypt(dek, secret, deterministicNonce: false);
+        }
       } else {
         final hashZkType = destination.value.getHashZkType();
         if (hashZkType == null) {
@@ -213,6 +241,9 @@ class BrantaService implements IBrantaService {
         final key = normalizedValue.toNormalizedHash();
         destination.value = await _aesEncryption.encrypt(normalizedValue, key, deterministicNonce: true);
         encryptedToKey[destination.value] = key;
+        if (dek != null) {
+          destination.encryptedDek = await _aesEncryption.encrypt(dek, key, deterministicNonce: false);
+        }
       }
     }