试图让用户可以更改他们的密码，但由于密码是加密的，用户不能更改它没有输入加密的密码第一。
当用户点击“更改密码”时，他们会被发送到change.php，然后返回到profile.php？error=wrong\u pw
不习惯散列密码，因为到目前为止我只使用php做过“简单”的站点，没有任何安全性。这也是为什么这很容易被黑客利用的原因。
更改.php

<?php
session_start();

require 'dbc.php';
if (!isset($_POST['password']) || !isset($_POST['newpassword']) ||   !isset($_POST['renewpassword'])) {
header('Location: ../profile.php?error=wrong_info');
exit();
}

$user = $_SESSION['id'];
$password = $_POST['password'];
$newpassword = $_POST['newpassword'];
$renewpassword = $_POST['renewpassword'];
$sql = "SELECT * FROM users WHERE id='$user' AND pwd='$password'";
$result = mysqli_query($conn, $sql);
if($row = mysqli_fetch_assoc($result)){

if($newpassword == $renewpassword){
if($newpassword != ""){
  $newsql = "UPDATE users SET pwd='$newpassword' WHERE id='$user'";
  $newresult = mysqli_query($conn, $newsql);
  header('Location: ../index.php');

}
else{
  header('Location: ../profile.php?error=empty');
  exit();
}

} 
else{
header('Location: ../profile.php?error=match');
exit();
}

} else{

header('Location: ../profile.php?error=wrong_pw');
}

配置文件.php

<?php require "inc/header.inc.php"; ?>
<?php
if(isset($_GET['u'])){
$u = $_GET['u'];
}else{
$u = $_SESSION['id'];
}

$sql = "SELECT * FROM users WHERE id='$u'";
$result = mysqli_query($conn, $sql);
$user = mysqli_fetch_assoc($result);

?>

<div class="container mt-3">
<table class="table">
<tr>
  <th>Email</th>
  <th>Username</th>
  <?php
    if ($u === $_SESSION['id']) {
      echo "<th>Password</th>";
    }
  ?>
</tr>
<tr>
  <td><?php echo $user['email']; ?></td>
  <td><?php echo $user['uid']; ?></td>
  <?php
    if ($u === $_SESSION['id']) {
      echo '<th><a href="javascript:;" class="btn btn-danger" data-toggle="modal" data-target="#leModal">Change</a></th>';
    }
  ?>
</tr>
</table>
</div>
 <form action="change_theme.php" method="post">
 <center><button class="btn btn-primary themebutton" type="submit" value="Change theme" action="change_theme.php">Change theme</button></center>
 </form>
 <div class="modal fade" id="leModal" tabindex="-1" role="dialog" aria-labelledby="exampleModalLabel" aria-hidden="true">
<div class="modal-dialog" role="document">
<div class="modal-content">
  <div class="modal-header">
    <h5 class="modal-title" id="exampleModalLabel">Change Password</h5>
    <button type="button" class="close" data-dismiss="modal" aria-label="Close">
      <span aria-hidden="true">&times;</span>
    </button>
  </div>
  <div class="modal-body">
    <form class="article_q" action="engine/change.php" method="post">
      <input type="hidden" name="user" value="<?php echo $_SESSION['id']; ?>">
      <input type="password" name="password" placeholder="Current Password"><br><br>
      <input type="password" name="newpassword" placeholder="New Password"><br><br>
      <input type="password" name="renewpassword" placeholder="Re:Password"><br><br>
      <button class="btn btn-danger" value="submit">Save</button>
  </div>
  <div class="modal-footer">
    </form>
  </div>
</div>
</div>
</div>
<?php require "inc/footer.inc.php"; ?>