Merge branch 'soru/export-key-as-string' into 'main'

feat: Add a way to string-encode a recovery key

Closes #140

See merge request famedly/famedlysdk!634

lib/encryption/ssss.dart

@@ -142,6 +142,24 @@ class SSSS {
         OLM_RECOVERY_KEY_PREFIX.length + SSSS_KEY_LENGTH));
   }
 
+  static String encodeRecoveryKey(Uint8List recoveryKey) {
+    final keyToEncode = <int>[];
+    for (final b in OLM_RECOVERY_KEY_PREFIX) {
+      keyToEncode.add(b);
+    }
+    keyToEncode.addAll(recoveryKey);
+    var parity = 0;
+    for (final b in keyToEncode) {
+      parity ^= b;
+    }
+    keyToEncode.add(parity);
+    // base58-encode and add a space every four chars
+    return base58
+        .encode(keyToEncode)
+        .replaceAllMapped(RegExp(r'.{4}'), (s) => '${s.group(0)} ')
+        .trim();
+  }
+
   static Uint8List keyFromPassphrase(String passphrase, PassphraseInfo info) {
     if (info.algorithm != AlgorithmTypes.pbkdf2) {
       throw Exception('Unknown algorithm');
@@ -596,6 +614,9 @@ class OpenSSSS {
 
   bool get isUnlocked => privateKey != null;
 
+  String get recoveryKey =>
+      isUnlocked ? SSSS.encodeRecoveryKey(privateKey) : null;
+
   Future<void> unlock(
       {String passphrase, String recoveryKey, String keyOrPassphrase}) async {
     if (keyOrPassphrase != null) {

test/encryption/ssss_test.dart

@@ -112,6 +112,17 @@ void main() {
       expect(await handle.getStored('best animal'), 'foxies');
     });
 
+    test('encode / decode recovery key', () async {
+      final key = Uint8List.fromList(SecureRandom(32).bytes);
+      final encoded = SSSS.encodeRecoveryKey(key);
+      final decoded = SSSS.decodeRecoveryKey(encoded);
+      expect(key, decoded);
+
+      final handle = client.encryption.ssss.open();
+      await handle.unlock(recoveryKey: SSSS_KEY);
+      expect(handle.recoveryKey, SSSS_KEY);
+    });
+
     test('cache', () async {
       final handle =
           client.encryption.ssss.open(EventTypes.CrossSigningSelfSigning);