Hash editor passwords with Argon2id and upgrade old hashes.

Old hashes are replaced at login. Widen the column before deploying:

  ALTER TABLE editors MODIFY password VARCHAR(255) NOT NULL;

publish/addeditor.php

@@ -5,6 +5,8 @@ if ( ! isset($_SERVER['HTTPS'])) {
 require_once("../session.lib.php"); 
 $added = FALSE;
 $csrf_failed = FALSE;
+$hash_failed = FALSE;
+$exists = FALSE;
 if (!isset($_SESSION['editor'])) {
   header("Location: https://xxx.org.za/publish/login");
   return;
@@ -16,11 +18,20 @@ if (!isset($_SESSION['editor'])) {
   $table = "editors";
 
   $username = (string)($_POST['username'] ?? '');
-  $password = password_hash((string)($_POST['password'] ?? ''), PASSWORD_DEFAULT);
+  $password = password_hash((string)($_POST['password'] ?? ''), password_algorithm());
   $email    = (string)($_POST['email'] ?? '');
+  $found = $db->execute_query("SELECT username FROM $table WHERE username = ?", array($username));
   $query = "INSERT INTO $table SET `username` = ?, `password` = ?, `email` = ?";
-  if ($result = $db->execute_query($query, array($username, $password, $email))) {
+  if ($found && $found->fetch_assoc()) {
+    $exists = TRUE;
+  } else if ($result = $db->execute_query($query, array($username, $password, $email))) {
+    // If the password column cut the hash short, the editor could never log in
+    if (password_hash_is_stored($username, $password)) {
       $added = TRUE;
+    } else {
+      $db->execute_query("DELETE FROM $table WHERE username = ?", array($username));
+      $hash_failed = TRUE;
+    }
     $is_admin = TRUE;
   }
   open_db('close');
@@ -54,6 +65,12 @@ if (!isset($_SESSION['editor'])) {
 <?php if ($csrf_failed) { ?>
   <p><strong>Your session has expired. Please try again.</strong></p>
 <?php } ?>
+<?php if ($exists) { ?>
+  <p><strong>An editor with that username already exists.</strong></p>
+<?php } ?>
+<?php if ($hash_failed) { ?>
+  <p><strong>The editor was not added: the editors.password column is too short for the password hash. Widen it to VARCHAR(255).</strong></p>
+<?php } ?>
 
 <form action="<?= form_value("https://xxx.org.za".$_SERVER['REQUEST_URI']) ?>" method="post">
   <?= csrf_field() ?>

publish/login.php

@@ -26,12 +26,15 @@ if (isset($_SESSION['editor'])) {
     $stored_password = $row['password'];
   else  $denied = TRUE;
   $getid->close();
-  open_db('close');
-  $compare_password = $_POST['password'] ?? '';
+  $compare_password = is_string($_POST['password'] ?? NULL) ? $_POST['password'] : '';
   // password_verify() also accepts hashes made by the old crypt() call
   if (!password_verify($compare_password, $stored_password)) {
     $denied = TRUE;
+    open_db('close');
   } else {
+    // Move an old hash to the current algorithm while we have the password
+    rehash_password($username, $compare_password, $stored_password);
+    open_db('close');
     login_editor($username);
     // Keep user logged in with cookie, if they request it
     if (isset($_POST['remember'])) {

session.lib.php

@@ -132,3 +132,44 @@ function login_editor($username) {
   unset($_SESSION['csrf_token']);
   $_SESSION['editor'] = $username;
 }
+
+/*
+ * Password hashing: Argon2id where PHP was built with it, otherwise
+ * bcrypt. Argon2id hashes are about 100 characters long, so the
+ * editors.password column must hold at least that (VARCHAR(255) is best).
+ */
+function password_algorithm() {
+  return defined('PASSWORD_ARGON2ID') ? PASSWORD_ARGON2ID : PASSWORD_BCRYPT;
+}
+
+/*
+ * Store $hash as the password of $username, and return TRUE if the database kept
+ * the whole hash. The database must be open.
+ */
+function store_password_hash($username, $hash) {
+  global $db;
+  $db->execute_query("UPDATE editors SET password = ? WHERE username = ?", array($hash, $username));
+  return password_hash_is_stored($username, $hash);
+}
+
+// TRUE if the database holds exactly $hash for $username
+function password_hash_is_stored($username, $hash) {
+  global $db;
+  $check = $db->execute_query("SELECT password FROM editors WHERE username = ?", array($username));
+  $row = $check ? $check->fetch_assoc() : NULL;
+  return $row && $row['password'] === $hash;
+}
+
+/*
+ * After a successful login, move an old hash (MD5-crypt, bcrypt) to the
+ * current algorithm. If the column is too short and MySQL cut the new
+ * hash, put the old one back so that the editor can still log in.
+ */
+function rehash_password($username, $password, $stored_hash) {
+  if (!password_needs_rehash($stored_hash, password_algorithm()))
+    return;
+  if (!store_password_hash($username, password_hash($password, password_algorithm()))) {
+    store_password_hash($username, $stored_hash);
+    error_log("xxx: could not store a new password hash for $username; widen editors.password");
+  }
+}