PHP - file encryption/decryption

Davide Airaghi April 27, 2018 2 min read
To have some sort of privacy while sending/receiving messages (or files) using encryption is the first choice. Below you can find a very simple PHP web application that allows you to encrypt/decrypt a file using your web browser (and a web server hosting the page).
<?php

$ALGORITHM = 'AES-128-CBC';
$IV    = '12dasdq3g5b2434b';

$error = '';

if (isset($_POST) && isset($_POST['action'])) {
  
  $password   = isset($_POST['password']) && $_POST['password']!='' ? $_POST['password'] : null;
  $action = isset($_POST['action']) && in_array($_POST['action'],array('c','d')) ? $_POST['action'] : null;
  $file     = isset($_FILES) && isset($_FILES['file']) && $_FILES['file']['error'] == UPLOAD_ERR_OK ? $_FILES['file'] : null;
  
  if ($password === null) {
    $error .= 'Invalid Password<br>';
  }
  if ($action === null) {
    $error .= 'Invalid Action<br>';
  }
  if ($file === null) {
    $error .= 'Errors occurred while elaborating the file<br>';
  }
  
  if ($error === '') {
  
    $contenuto = '';
    $nomefile  = '';
  
    $contenuto = file_get_contents($file['tmp_name']);
    $filename  = $file['name'];
  
    switch ($action) {
      case 'c':
        $contenuto = openssl_encrypt($contenuto, $ALGORITHM, $password, 0, $IV);
        $filename  = $filename . '.crypto';
        break;
      case 'd':
        $contenuto = openssl_decrypt($contenuto, $ALGORITHM, $password, 0, $IV);
        $filename  = preg_replace('#\.crypto$#','',$filename);
        break;
    }
    
    if ($contenuto === false) {
      $error .= 'Errors occurred while encrypting/decrypting the file ';
    }
    
    if ($error === '') {
    
      header("Pragma: public");
      header("Pragma: no-cache");
      header("Cache-Control: no-store, no-cache, must-revalidate, max-age=0");
      header("Cache-Control: post-check=0, pre-check=0", false);
      header("Expires: 0");
      header("Content-Type: application/octet-stream");
      header("Content-Disposition: attachment; filename=\"" . $filename . "\";");
      $size = strlen($contenuto);
      header("Content-Length: " . $size);
      echo $contenuto;    
      die;
      
    }
  
  }
  
}


?>
<html>
  <head>
    <title>Encrypt/Decrypt file</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css">
  </head>
  <body>
    <div class="container">
      <div class="row">
        <div class="col-12" >
          <h1>Utility to encrypt/decrypt a file</h1>
        </div>
      </div>
      <?php if ($error != '') { ?>
      <div class="row">
        <div class="col-12 alert alert-danger" role="alert">
          <?php echo ($error); ?>
        </div>
      </div>
      <?php } ?>
      <form class="form" enctype="multipart/form-data" method="post" id="form1" name="form1" auto-complete="off">
        <div class="form-row">
          <div class="form-group">
            <label for="file">File</label>
            <input type="file" name="file" id="file" placeholder="Choose a file" required class="form-control-file"/>
          </div>
        </div>
        <div class="form-row">
          <div class="form-group">
            <label for="password">Password</label>
            <input type="password" name="password" id="password" placeholder="Insert password" required class="form-control" />
          </div>
        </div>
        <div class="form-row">
          <div class="form-group">
            <label for="action">Action</label>
            <select name="action" id="action" required class="form-control">
              <option value="">-- Choose --</option>
              <option value="c">Encrypt</option>
              <option value="d">Decrypt</option>
            </select>
          </div>
        </div>
        <div class="form-row">
          <button type="submit" class="btn btn-primary" onclick="setTimeout('document.form1.reset();',1000)">Execute</button>
          <button type="reset" class="btn btn-reset">Reset</button>
         </div>
      </form>
    </div>
    <script type="text/javascript" src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
    <script type="text/javascript" src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.bundle.min.js"></script>
  </body>
</html>
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