title: openssl_encrypt returns false
body: <p>I am trying to encrypt a string using openssl_encrypt in PHP but it keeps returning FALSE.</p>
  
  <pre><code>$encrypted = openssl_encrypt('1234', 'AES-256-CBC', 'kGJeGF2hEQ', OPENSSL_ZERO_PADDING, '1234123412341234');
  </code></pre>
  
  <p>What am I doing wrong?</p>