Preserve backupCredentialRequest across rereg

service/src/main/java/org/whispersystems/textsecuregcm/storage/Accounts.java

@@ -304,6 +304,11 @@ public class Accounts extends AbstractDynamoDbStore {
 
       accountToCreate.setVersion(existingAccount.getVersion());
 
+      // Carry over the old backup id commitment. If the new account claimer cannot does not have the secret used to
+      // generate their backup-id, this credential is useless, however if they can produce the same credential they
+      // won't be rate-limited for setting their backup-id.
+      accountToCreate.setBackupCredentialRequest(existingAccount.getBackupCredentialRequest());
+
       final List<TransactWriteItem> writeItems = new ArrayList<>();
 
       // If we're reclaiming an account that already has a username, we'd like to give the re-registering client

service/src/test/java/org/whispersystems/textsecuregcm/storage/AccountsTest.java

@@ -416,6 +416,23 @@ class AccountsTest {
         Collections.emptyList()).toCompletableFuture().join());
   }
 
+  @Test
+  void testReclaimAccountPreservesBcr() {
+    final String e164 = "+14151112222";
+    final UUID existingUuid = UUID.randomUUID();
+    final Account existingAccount =
+        generateAccount(e164, existingUuid, UUID.randomUUID(), List.of(generateDevice(DEVICE_ID_1)));
+    existingAccount.setBackupCredentialRequest(TestRandomUtil.nextBytes(32));
+    createAccount(existingAccount);
+    final Account secondAccount =
+        generateAccount(e164, UUID.randomUUID(), UUID.randomUUID(), List.of(generateDevice(DEVICE_ID_1)));
+
+    reclaimAccount(secondAccount);
+
+    final Account reclaimed = accounts.getByAccountIdentifier(existingUuid).get();
+    assertThat(reclaimed.getBackupCredentialRequest()).isEqualTo(existingAccount.getBackupCredentialRequest());
+  }
+
   @Test
   void testReclaimAccount() {
     final String e164 = "+14151112222";