<?php
/**
 * Piwik - Open source web analytics
 *
 * @link http://piwik.org
 * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
 * @version $Id$
 *
 * @category Piwik
 * @package Piwik
 */

/**
 * Nonce class.
 *
 * A cryptographic nonce -- "number used only once" -- is often recommended as part of a robust defense against cross-site request forgery (CSRF/XSRF).
 * Desrable characteristics: limited lifetime, uniqueness, unpredictability (pseudo-randomness).
 *
 * We use a session-dependent nonce with a configurable expiration that combines and hashes:
 * - a private salt because it's non-public
 * - time() because it's unique
 * - a mix of PRNGs (pseudo-random number generators) to increase entropy and make it less predictable
 *
 * @package Piwik
 */
class Piwik_Nonce
{
	/**
	 * Generate nonce
	 *
	 * @param string  $id   Unique id to avoid namespace conflicts, e.g., ModuleName.ActionName
	 * @param int     $ttl  Optional time-to-live in seconds; default is 5 minutes
	 * @return string  Nonce
	 */
	static public function getNonce($id, $ttl = 300)
	{
		// save session-dependent nonce
		$ns = new Piwik_Session_Namespace($id);
		$nonce = $ns->nonce;

		// re-use an unexpired nonce (a small deviation from the "used only once" principle, so long as we do not reset the expiration)
		// to handle browser pre-fetch or double fetch caused by some browser add-ons/extensions
		if(empty($nonce))
		{
			// generate a new nonce
			$nonce = md5(Piwik_Common::getSalt() . time() . Piwik_Common::generateUniqId());
			$ns->nonce = $nonce;
			$ns->setExpirationSeconds($ttl, 'nonce');
		}

		return $nonce;
	}

	/**
	 * Verify nonce and check referrer (if present, i.e., it may be suppressed by the browser or a proxy/network).
	 *
	 * @param string  $id      Unique id
	 * @param string  $cnonce  Nonce sent to client
	 * @return bool  true if valid; false otherwise
	 */
	static public function verifyNonce($id, $cnonce)
	{
		$ns = new Piwik_Session_Namespace($id);
		$nonce = $ns->nonce;

		// validate token
		if(empty($cnonce) || $cnonce !== $nonce)
		{
			return false;
		}

		// validate referer
		$referer = Piwik_Url::getReferer();
		if(!empty($referer) && !Piwik_Url::isLocalUrl($referer))
		{
			return false;
		}

		// validate origin
		$origin = self::getOrigin();
		if(!empty($origin) &&
			($origin == 'null'
			|| !in_array($origin, self::getAcceptableOrigins())))
		{
			return false;
		}

		return true;
	}

	/**
	 * Discard nonce ("now" as opposed to waiting for garbage collection)
	 *
	 * @param string  $id  Unique id
	 */
	static public function discardNonce($id)
	{
		$ns = new Piwik_Session_Namespace($id);
		$ns->unsetAll();
	}

	/**
	 * Get ORIGIN header, false if not found
	 *
	 * @return string|false
	 */
	static public function getOrigin()
	{
		if(!empty($_SERVER['HTTP_ORIGIN']))
		{
			return $_SERVER['HTTP_ORIGIN'];
		}
		return false;
	}

	/**
	 * Returns acceptable origins (not simply scheme://host) that
	 * should handle a variety of proxy and web server (mis)configurations,.
	 *
	 * @return array
	 */
	static public function getAcceptableOrigins()
	{
		$host = Piwik_Url::getCurrentHost(null);
		$port = '';

		// parse host:port
		if(preg_match('/^([^:]+):([0-9]+)$/D', $host, $matches))
		{
			$host = $matches[1];
			$port = $matches[2];
		}

		if(empty($host))
		{
			return array();
		}

		// standard ports
		$origins[] = 'http://'.$host;
		$origins[] = 'https://'.$host;

		// non-standard ports
		if(!empty($port) && $port != 80 && $port != 443)
		{
			$origins[] = 'http://'.$host.':'.$port;
			$origins[] = 'https://'.$host.':'.$port;
		}

		return $origins;
	}
}