[project @ Documentation and removal of silly low-entropy entropy sources from CryptUtil]

1 files changed, 30 insertions, 20 deletions

diff --git a/Net/OpenID/CryptUtil.php b/Net/OpenID/CryptUtil.php
index 379f2d4..9249d5a 100644
--- a/Net/OpenID/CryptUtil.php
+++ b/Net/OpenID/CryptUtil.php
@@ -1,31 +1,41 @@
 <?php
 
-class Net_OpenID_CryptUtil {
-    function _getFourBytes() {
-        $x = mt_rand();
-        
-        $sources = array(
-            time(),
-            getmypid(),
-            getmygid(),
-            getmyuid(),
-            disk_free_space(__FILE__)
-            );
-
-        foreach ($sources as $ent) {
-            $x ^= $ent;
-            mt_srand($x);
-            $x = mt_rand();
-        }
-        return $x;
-    }
+if (!defined(Net_OpenID_RAND_SOURCE)) {
+	/**
+	 * The filename for a source of random bytes. Define this yourself if you
+	 * have a different source of randomness.
+	 */
+	define('Net_OpenID_RAND_SOURCE', '/dev/urandom');
+}
 
+/**
+ * Cryptographic utility functions
+ */
+class Net_OpenID_CryptUtil {
+    /** 
+	 * Get the specified number of random bytes.
+	 *
+	 * Attempts to use a cryptographically secure (not predictable) source of
+	 * randomness if available. If there is no high-entropy randomness source
+	 * available, it will fail. As a last resort, for non-critical systems,
+	 * define <code>Net_OpenID_USE_INSECURE_RAND</code>, and the code will
+	 * fall back on a pseudo-random number generator.
+	 *
+	 * @static
+	 * @param int $num_bytes The length of the return value
+	 * @return string $num_bytes random bytes
+	 */
     function getBytes($num_bytes) {
         $f = @fopen("/dev/urandom", "r");
         if ($f === FALSE) {
+            if (!defined(Net_OpenID_USE_INSECURE_RAND)) {
+                trigger_error('Set Net_OpenID_USE_INSECURE_RAND to ' .
+                              'continue with insecure random.',
+                              E_USER_ERROR);
+            }
             $bytes = '';
             for ($i = 0; $i < $num_bytes; $i += 4) {
-                $bytes .= Net_OpenID_CryptUtil::_getFourBytes();
+                $bytes .= pack('L', mt_rand());
             }
             $bytes = substr($bytes, 0, $num_bytes);
         } else {