--- pam_google_authenticator.c.orig	2014-01-30 15:17:38.000000000 +0000

+++ pam_google_authenticator.c	2014-11-03 20:49:34.748324056 +0000

@@ -503,10 +503,6 @@

 }

 #endif

-static int get_timestamp(void) {

-  return get_time()/30;

-}

-

 static int comparator(const void *a, const void *b) {

   return *(unsigned int *)a - *(unsigned int *)b;

 }

@@ -538,6 +534,41 @@

   return NULL;

 }

+#if !defined(STEPSIZE)

+static int get_timestamp(void) {

+  return get_time()/30;

+}

+#else

+static int get_timestamp(pam_handle_t *pamh, const char *secret_filename,

+                       const char *buf) {

+  const char *value = get_cfg_value(pamh, "STEP_SIZE", buf);

+  if (!value) {

+    // Default step size is 30.

+    free((void *)value);

+    return 30;

+  } else if (value == &oom) {

+    // Out of memory. This is a fatal error.

+    return 0;

+  }

+

+  char *endptr;

+  errno = 0;

+  int step = (int)strtoul(value, &endptr, 10);

+  if (errno || !*value || value == endptr ||

+      (*endptr && *endptr != ' ' && *endptr != '\t' &&

+       *endptr != '\n' && *endptr != '\r') ||

+      step < 1 || step > 60) {

+    free((void *)value);

+    log_message(LOG_ERR, pamh, "Invalid STEP_SIZE option in \"%s\"",

+                secret_filename);

+    return 0;

+  }

+  free((void *)value);

+

+  return get_time()/step;

+}

+#endif

+

 static int set_cfg_value(pam_handle_t *pamh, const char *key, const char *val,

                          char **buf) {

   size_t key_len = strlen(key);

@@ -1162,7 +1193,11 @@

   }

   // Compute verification codes and compare them with user input

+#if !defined(STEPSIZE)

   const int tm = get_timestamp();

+#else

+  const int tm = get_timestamp(pamh, secret_filename, *buf);

+#endif

   const char *skew_str = get_cfg_value(pamh, "TIME_SKEW", *buf);

   if (skew_str == &oom) {

     // Out of memory. This is a fatal error