Add functionality to extract a decrypted collection key

lib/core/configuration.dart

@@ -22,11 +22,13 @@ class Configuration {
   static const hasOptedForE2EKey = "has_opted_for_e2e_encryption";
   static const foldersToBackUpKey = "folders_to_back_up";
   static const keyKey = "key";
+  static const secretKeyKey = "secret_key";
   static const keyAttributesKey = "key_attributes";
 
   SharedPreferences _preferences;
   FlutterSecureStorage _secureStorage;
   String _key;
+  String _secretKey;
   String _documentsDirectory;
   String _tempDirectory;
   String _thumbnailsDirectory;
@@ -40,6 +42,7 @@ class Configuration {
     new io.Directory(_tempDirectory).createSync(recursive: true);
     new io.Directory(_thumbnailsDirectory).createSync(recursive: true);
     _key = await _secureStorage.read(key: keyKey);
+    _secretKey = await _secureStorage.read(key: secretKeyKey);
   }
 
   Future<KeyAttributes> generateAndSaveKey(String passphrase) async {
@@ -71,6 +74,7 @@ class Configuration {
       Sodium.bin2base64(encryptedSecretKeyData.nonce),
     );
     await setKey(Sodium.bin2base64(key));
+    await setSecretKey(Sodium.bin2base64(keyPair.sk));
     await setKeyAttributes(attributes);
     return attributes;
   }
@@ -176,10 +180,23 @@ class Configuration {
     }
   }
 
+  Future<void> setSecretKey(String secretKey) async {
+    _secretKey = secretKey;
+    if (secretKey == null) {
+      await _secureStorage.delete(key: secretKeyKey);
+    } else {
+      await _secureStorage.write(key: secretKeyKey, value: secretKey);
+    }
+  }
+
   Uint8List getKey() {
     return _key == null ? null : Sodium.base642bin(_key);
   }
 
+  Uint8List getSecretKey() {
+    return _secretKey == null ? null : Sodium.base642bin(_secretKey);
+  }
+
   String getDocumentsDirectory() {
     return _documentsDirectory;
   }

lib/services/collections_service.dart

@@ -1,18 +1,26 @@
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:dio/dio.dart';
+import 'package:flutter_sodium/flutter_sodium.dart';
 import 'package:logging/logging.dart';
 import 'package:photos/core/configuration.dart';
 import 'package:photos/db/collections_db.dart';
 import 'package:photos/models/collection.dart';
+import 'package:photos/services/user_service.dart';
+import 'package:photos/utils/crypto_util.dart';
 
 class CollectionsService {
   final _logger = Logger("CollectionsService");
 
   CollectionsDB _db;
+  Configuration _config;
+  UserService _userService;
 
   CollectionsService._privateConstructor() {
     _db = CollectionsDB.instance;
+    _config = Configuration.instance;
+    _userService = UserService.instance;
   }
 
   static final CollectionsService instance =
@@ -46,6 +54,19 @@ class CollectionsService {
     });
   }
 
+  Uint8List getCollectionKey(Collection collection) {
+    final encryptedKey = Sodium.base642bin(collection.encryptedKey);
+    if (collection.ownerID == _config.getUserID()) {
+      return CryptoUtil.decryptSync(encryptedKey, _config.getKey(),
+          Sodium.base642bin(collection.keyDecryptionNonce));
+    } else {
+      return CryptoUtil.openSealSync(
+          encryptedKey,
+          Sodium.base642bin(_config.getKeyAttributes().publicKey),
+          _config.getSecretKey());
+    }
+  }
+
   Future<List<Collection>> getCollections(int sinceTime) {
     return Dio()
         .get(

lib/utils/crypto_util.dart

@@ -123,6 +123,18 @@ class CryptoUtil {
     }
   }
 
+  static Uint8List decryptSync(
+    Uint8List cipher,
+    Uint8List key,
+    Uint8List nonce,
+  ) {
+    final args = Map<String, dynamic>();
+    args["cipher"] = cipher;
+    args["nonce"] = nonce;
+    args["key"] = key;
+    return cryptoSecretboxOpenEasy(args);
+  }
+
   static EncryptionResult encryptChaCha(Uint8List source, Uint8List key) {
     final initPushResult =
         Sodium.cryptoSecretstreamXchacha20poly1305InitPush(key);
@@ -205,4 +217,9 @@ class CryptoUtil {
   static Future<KeyPair> generateKeyPair() async {
     return Sodium.cryptoBoxKeypair();
   }
+
+  static Uint8List openSealSync(
+      Uint8List input, Uint8List publicKey, Uint8List secretKey) {
+    return Sodium.cryptoBoxSealOpen(input, publicKey, secretKey);
+  }
 }