[ticket/12352] Add passwords driver for passwords that should be converted

This driver will only be used for getting the new $CP$ prefix that will signal
that the hash is a legacy hash that needs to be converted.

PHPBB3-12352

phpBB/phpbb/passwords/driver/convert_password.php

@@ -0,0 +1,50 @@
+<?php
+/**
+*
+* @package phpBB3
+* @copyright (c) 2014 phpBB Group
+* @license http://opensource.org/licenses/gpl-2.0.php GNU General Public License v2
+*
+*/
+
+namespace phpbb\passwords\driver;
+
+/**
+* @package passwords
+*/
+class convert_password extends base
+{
+	const PREFIX = '$CP$';
+
+	/**
+	* @inheritdoc
+	*/
+	public function get_prefix()
+	{
+		return self::PREFIX;
+	}
+
+	/**
+	* @inheritdoc
+	*/
+	public function hash($password, $user_row = '')
+	{
+		return false;
+	}
+
+	/**
+	* @inheritdoc
+	*/
+	public function check($password, $hash, $user_row = array())
+	{
+		return false;
+	}
+
+	/**
+	* @inheritdoc
+	*/
+	public function get_settings_only($hash, $full = false)
+	{
+		return false;
+	}
+}