code: public static function decryptWithAppendedTag($K, $IV, $Ciphertext = null, $A = null, $tag_length = 128)
      {
          $tag_length_in_bits = $tag_length / 8;
          $C = mb_substr($Ciphertext, 0, -$tag_length_in_bits, '8bit');
          $T = mb_substr($Ciphertext, -$tag_length_in_bits, null, '8bit');
  
          return self::decrypt($K, $IV, $C, $A, $T);
      }
docs: This method should be used if the tag is appended at the end of the ciphertext.
  It is used by some AES GCM implementations such as the Java one.
  
  @param string      $K          Key encryption key
  @param string      $IV         Initialization vector
  @param string|null $Ciphertext Data to encrypt (null for authentication)
  @param string|null $A          Additional Authentication Data
  @param int         $tag_length Tag length
  
  @return string
  
  @see self::encryptAndAppendTag