Hash the password for an unknown username at login.

An unknown username got a fast answer, which showed which usernames exist.

publish/login.php

@@ -29,14 +29,13 @@ if (isset($_SESSION['editor'])) {
   $getid = $db->execute_query($query, array($username)) or db_fail();
   $row = $getid->fetch_assoc();
 
-  $stored_password = '';
+  $stored_password = NULL;
   if (isset($row))
-    $stored_password = $row['password'];
+    $stored_password = (string)$row['password'];
   else  $denied = TRUE;
   $getid->close();
   $compare_password = is_string($_POST['password'] ?? NULL) ? $_POST['password'] : '';
-  // password_verify() also accepts hashes made by the old crypt() call
-  if (!password_verify($compare_password, $stored_password)) {
+  if (!editor_password_valid($compare_password, $stored_password)) {
     $denied = TRUE;
     record_login_failure($username);
     open_db('close');

session.lib.php

@@ -211,6 +211,21 @@ function password_hash_is_stored($username, $hash) {
   return $row && $row['password'] === $hash;
 }
 
+/*
+ * TRUE if $password matches $stored_hash. For an unknown editor
+ * ($stored_hash is NULL), it hashes the password anyway, so that the
+ * answer takes as long as for a wrong password, and does not show which
+ * usernames exist.
+ */
+function editor_password_valid($password, $stored_hash) {
+  if ($stored_hash === NULL) {
+    password_hash($password, password_algorithm());
+    return FALSE;
+  }
+  // password_verify() also accepts hashes made by the old crypt() call
+  return password_verify($password, $stored_hash);
+}
+
 /*
  * After a successful login, move an old hash (MD5-crypt, bcrypt) to the
  * current algorithm. If the column is too short and MySQL cut the new

tests/php/Unit/PasswordTest.php

@@ -23,6 +23,30 @@ class PasswordTest extends TestCase {
     $this->assertSame(defined('PASSWORD_ARGON2ID') ? PASSWORD_ARGON2ID : PASSWORD_BCRYPT, password_algorithm());
   }
 
+  public function testEditorPasswordValid(): void {
+    $hash = password_hash('secret', password_algorithm());
+    $this->assertTrue(editor_password_valid('secret', $hash));
+    $this->assertFalse(editor_password_valid('wrong', $hash));
+    $this->assertFalse(editor_password_valid('', ''));
+    $this->assertFalse(editor_password_valid('secret', NULL));
+    $this->assertFalse(editor_password_valid('', NULL));
+  }
+
+  // A fast answer for an unknown username would show which usernames exist
+  public function testAnUnknownEditorTakesAsLongAsAWrongPassword(): void {
+    $hash = password_hash('secret', password_algorithm());
+    $time = function ($stored) {
+      $best = INF;
+      for ($i = 0; $i < 3; $i++) {
+        $start = hrtime(TRUE);
+        editor_password_valid('wrong', $stored);
+        $best = min($best, hrtime(TRUE) - $start);
+      }
+      return $best;
+    };
+    $this->assertGreaterThan($time($hash) / 2, $time(NULL));
+  }
+
   public function testHashIsStoredAndChecked(): void {
     $this->addEditor('old');
     $hash = password_hash('secret', password_algorithm());