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<title>[29384] branches/3.9: Constant time for wp_verify_nonce().</title>
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<div id="msg">
<dl class="meta">
<dt>Revision</dt> <dd><a href="http://core.trac.wordpress.org/changeset/29384">29384</a></dd>
<dt>Author</dt> <dd>nacin</dd>
<dt>Date</dt> <dd>2014-08-06 05:41:12 +0000 (Wed, 06 Aug 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Constant time for wp_verify_nonce().
Merges <a href="http://core.trac.wordpress.org/changeset/29382">[29382]</a> to the 3.9 branch.
Adds a second copy of hash_equals() to pluggable.php in case compat.php is not copied over in an update. (The general goal is no cross-file dependencies for minor releases.)</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#branches39srcwpincludescompatphp">branches/3.9/src/wp-includes/compat.php</a></li>
<li><a href="#branches39srcwpincludespluggablephp">branches/3.9/src/wp-includes/pluggable.php</a></li>
</ul>
<h3>Property Changed</h3>
<ul>
<li><a href="#branches39">branches/3.9/</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<span class="cx">Index: branches/3.9
</span><span class="cx">===================================================================
</span><del>--- branches/3.9 2014-08-06 05:25:55 UTC (rev 29383)
</del><ins>+++ branches/3.9 2014-08-06 05:41:12 UTC (rev 29384)
</ins><a id="branches39"></a>
<div class="propset"><h4>Property changes: branches/3.9</h4>
<pre class="diff"><span>
</span></pre></div>
<a id="svnmergeinfo"></a>
<div class="modfile"><h4>Modified: svn:mergeinfo</h4></div>
<span class="cx"> /branches/3.1:18031
</span><span class="cx"> /branches/3.3:20543
</span><span class="cx"> /branches/3.4:21757
</span><del>-/trunk:18512,28158,28161,28163,28165-28166,28168-28169,28171-28174,28176-28187,28189-28191,28193-28195,28203,28219,28223,28266,28269,28275-28276,28280,28284
</del><ins>+/trunk:18512,28158,28161,28163,28165-28166,28168-28169,28171-28174,28176-28187,28189-28191,28193-28195,28203,28219,28223,28266,28269,28275-28276,28280,28284,29382
</ins><span class="cx">\ No newline at end of property
</span><a id="branches39srcwpincludescompatphp"></a>
<div class="modfile"><h4>Modified: branches/3.9/src/wp-includes/compat.php (29383 => 29384)</h4>
<pre class="diff"><span>
<span class="info">--- branches/3.9/src/wp-includes/compat.php 2014-08-06 05:25:55 UTC (rev 29383)
+++ branches/3.9/src/wp-includes/compat.php 2014-08-06 05:41:12 UTC (rev 29384)
</span><span class="lines">@@ -94,3 +94,32 @@
</span><span class="cx"> return is_array($data) ? array_map(__FUNCTION__, $data) : $data;
</span><span class="cx"> }
</span><span class="cx"> }
</span><ins>+
+if ( ! function_exists( 'hash_equals' ) ) :
+/**
+ * Compare two strings in constant time.
+ *
+ * This function was added in PHP 5.6.
+ * It can leak the length of a string.
+ *
+ * @since 3.9.2
+ *
+ * @param string $a Expected string.
+ * @param string $b Actual string.
+ * @return bool Whether strings are equal.
+ */
+function hash_equals( $a, $b ) {
+ $a_length = strlen( $a );
+ if ( $a_length !== strlen( $b ) ) {
+ return false;
+ }
+ $result = 0;
+
+ // Do not attempt to "optimize" this.
+ for ( $i = 0; $i < $a_length; $i++ ) {
+ $result |= ord( $a[ $i ] ) ^ ord( $b[ $i ] );
+ }
+
+ return $result === 0;
+}
+endif;
</ins><span class="cx">\ No newline at end of file
</span></span></pre></div>
<a id="branches39srcwpincludespluggablephp"></a>
<div class="modfile"><h4>Modified: branches/3.9/src/wp-includes/pluggable.php (29383 => 29384)</h4>
<pre class="diff"><span>
<span class="info">--- branches/3.9/src/wp-includes/pluggable.php 2014-08-06 05:25:55 UTC (rev 29383)
+++ branches/3.9/src/wp-includes/pluggable.php 2014-08-06 05:41:12 UTC (rev 29384)
</span><span class="lines">@@ -647,7 +647,7 @@
</span><span class="cx"> $key = wp_hash($username . $pass_frag . '|' . $expiration, $scheme);
</span><span class="cx"> $hash = hash_hmac('md5', $username . '|' . $expiration, $key);
</span><span class="cx">
</span><del>- if ( hash_hmac( 'md5', $hmac, $key ) !== hash_hmac( 'md5', $hash, $key ) ) {
</del><ins>+ if ( ! hash_equals( $hash, $hmac ) ) {
</ins><span class="cx"> /**
</span><span class="cx"> * Fires if a bad authentication cookie hash is encountered.
</span><span class="cx"> *
</span><span class="lines">@@ -1658,11 +1658,17 @@
</span><span class="cx"> $i = wp_nonce_tick();
</span><span class="cx">
</span><span class="cx"> // Nonce generated 0-12 hours ago
</span><del>- if ( substr(wp_hash($i . $action . $uid, 'nonce'), -12, 10) === $nonce )
</del><ins>+ $expected = substr( wp_hash( $i . '|' . $action . '|' . $uid . '|' . $token, 'nonce'), -12, 10 );
+ if ( hash_equals( $expected, $nonce ) ) {
</ins><span class="cx"> return 1;
</span><ins>+ }
+
</ins><span class="cx"> // Nonce generated 12-24 hours ago
</span><del>- if ( substr(wp_hash(($i - 1) . $action . $uid, 'nonce'), -12, 10) === $nonce )
</del><ins>+ $expected = substr( wp_hash( ( $i - 1 ) . '|' . $action . '|' . $uid . '|' . $token, 'nonce' ), -12, 10 );
+ if ( hash_equals( $expected, $nonce ) ) {
</ins><span class="cx"> return 2;
</span><ins>+ }
+
</ins><span class="cx"> // Invalid nonce
</span><span class="cx"> return false;
</span><span class="cx"> }
</span><span class="lines">@@ -2200,3 +2206,35 @@
</span><span class="cx"> }
</span><span class="cx"> endif;
</span><span class="cx">
</span><ins>+if ( ! function_exists( 'hash_equals' ) ) :
+/**
+ * Compare two strings in constant time.
+ *
+ * This function is NOT pluggable. It is in this file (in addition to
+ * compat.php) to prevent errors if, during an update, pluggable.php
+ * copies over but compat.php does not.
+ *
+ * This function was added in PHP 5.6.
+ * It can leak the length of a string.
+ *
+ * @since 3.9.2
+ *
+ * @param string $a Expected string.
+ * @param string $b Actual string.
+ * @return bool Whether strings are equal.
+ */
+function hash_equals( $a, $b ) {
+ $a_length = strlen( $a );
+ if ( $a_length !== strlen( $b ) ) {
+ return false;
+ }
+ $result = 0;
+
+ // Do not attempt to "optimize" this.
+ for ( $i = 0; $i < $a_length; $i++ ) {
+ $result |= ord( $a[ $i ] ) ^ ord( $b[ $i ] );
+ }
+
+ return $result === 0;
+}
+endif;
</ins></span></pre>
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