Constant time for wp_verify_nonce().

Built from https://develop.svn.wordpress.org/trunk@29382


git-svn-id: http://core.svn.wordpress.org/trunk@29160 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/compat.php

@@ -94,3 +94,32 @@ function _json_decode_object_helper($data) {
 		return is_array($data) ? array_map(__FUNCTION__, $data) : $data;
 	}
 }
+
+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;

wp-includes/pluggable.php

@@ -671,7 +671,7 @@ function wp_validate_auth_cookie($cookie = '', $scheme = '') {
 	$key = wp_hash( $username . '|' . $pass_frag . '|' . $expiration . '|' . $token, $scheme );
 	$hash = hash_hmac( 'sha256', $username . '|' . $expiration . '|' . $token, $key );
 
-	if ( hash_hmac( 'sha256', $hmac, $key ) !== hash_hmac( 'sha256', $hash, $key ) ) {
+	if ( ! hash_equals( $hash, $hmac ) ) {
 		/**
 		 * Fires if a bad authentication cookie hash is encountered.
 		 *
@@ -1711,12 +1711,14 @@ function wp_verify_nonce($nonce, $action = -1) {
 	$i = wp_nonce_tick();
 
 	// Nonce generated 0-12 hours ago
-	if ( $nonce === substr( wp_hash( $i . '|' . $action . '|' . $uid . '|' . $token, 'nonce'), -12, 10 ) ) {
+	$expected = substr( wp_hash( $i . '|' . $action . '|' . $uid . '|' . $token, 'nonce'), -12, 10 );
+	if ( hash_equals( $expected, $nonce ) ) {
 		return 1;
 	}
 
 	// Nonce generated 12-24 hours ago
-	if ( $nonce === substr( wp_hash( ( $i - 1 ) . '|' . $action . '|' . $uid . '|' . $token, 'nonce' ), -12, 10 ) ) {
+	$expected = substr( wp_hash( ( $i - 1 ) . '|' . $action . '|' . $uid . '|' . $token, 'nonce' ), -12, 10 );
+	if ( hash_equals( $expected, $nonce ) ) {
 		return 2;
 	}