fixes #1236 - handle browser/extension/add-on causing a double page load, invalidating the token in the form; refactor Nonce class out of Piwik.php

git-svn-id: http://dev.piwik.org/svn/trunk@1981 59fd770c-687e-43c8-a1e3-f5a4ff64c105

1 files changed, 81 insertions, 0 deletions

diff --git a/core/Nonce.php b/core/Nonce.php
new file mode 100644
index 0000000000..44d67195f7
--- /dev/null
+++ b/core/Nonce.php
@@ -0,0 +1,81 @@
+<?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 comines 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
+		$ns = new Zend_Session_Namespace($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)
+	{
+		$ns = new Zend_Session_Namespace($id);
+		$nonce = $ns->nonce;
+
+		// validate token
+		if(empty($cnonce) || $cnonce !== $nonce)
+		{
+			return false;
+		}
+
+		// validate referer
+		$referer = Piwik_Url::getReferer();
+		if(!empty($referer) && (Piwik_Url::getLocalReferer() === false))
+		{
+			return false;
+		}
+
+		return true;
+	}
+}