title: PHP - hash_pbkdf2 function
body: <p>I'm trying to do a function to hash passwords with this php function: <a href="http://be.php.net/manual/en/function.hash-pbkdf2.php" rel="noreferrer">http://be.php.net/manual/en/function.hash-pbkdf2.php</a>.</p>
  
  <p>Here is the code:</p>
  
  <pre><code>$hash_algo = "sha256";
  $password = "password";
  $salt = "salt";
  $iterations = 1;
  $length = 1;
  $raw_output = false;
  
  $hash = hash_pbkdf2($hash_algo, $password, $salt, $iterations ,$length ,$raw_output);
  
  echo $hash;
  </code></pre>
  
  <p>I got this error: <strong>Fatal error: Call to undefined function hash_pbkdf2().</strong></p>
  
  <p>How can the function be undefined???</p>
  
  <p>PS: All the values of my variables are set just for testing the function. Obviously the salt will not be "salt", etc.</p>