diff --git a/ChangeLog b/ChangeLog
index af1a041..87c6cb9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,24 @@
+2018-09-27  NIIBE Yutaka  <gniibe@fsij.org>
+
+	* src/gnuk.h (LED_WAIT_FOR_BUTTON): New.
+	* src/main.c (main): Blink rapidly when asking ACK.
+	* src/usb-ccid.c (ccid_thread): Use LED_WAIT_FOR_BUTTON.
+
+2018-09-27  NIIBE Yutaka  <gniibe@fsij.org>
+
+	* src/config.h.in: Add @ACKBTN_DEFINE@.
+	* src/configure: Add ACKBTN_SUPPORT.
+	* src/gnuk.h (EV_EXEC_FINISHED_ACK): New.
+	(CCID_STATE_CONFIRM_ACK): New.
+	* src/openpgp.c (process_command_apdu): Change for cmd_pso, and
+	cmd_internal_authenticate.
+	* src/usb-ccid.c (ccid_send_data_block_time_extension): Report
+	time extension differently when waiting ack button.
+	(ccid_handle_data): Support case of CCID_STATE_CONFIRM_ACK.
+	(ccid_handle_timeout): Likewise.
+	(ack_intr) [ACKBTN_SUPPORT]: New.
+	(ccid_thread) [ACKBTN_SUPPORT]: Add ack button handling.
+
 2018-09-26  NIIBE Yutaka  <gniibe@fsij.org>
 
 	* chopstx: Update.
diff --git a/chopstx b/chopstx
index 49b0556..7dc67d2 160000
--- a/chopstx
+++ b/chopstx
@@ -1 +1 @@
-Subproject commit 49b0556a24a9133ee55b06011fd288e264aefc72
+Subproject commit 7dc67d2210fb566bc370f0eea7ce9d9c5744760b
diff --git a/src/gnuk.h b/src/gnuk.h
index 8053cbe..2084026 100644
--- a/src/gnuk.h
+++ b/src/gnuk.h
@@ -445,6 +445,7 @@ extern const uint8_t gnuk_string_serial[];
 #define LED_GNUK_EXEC		 32
 #define LED_START_COMMAND	 64
 #define LED_FINISH_COMMAND	128
+#define LED_WAIT_FOR_BUTTON	256
 #define LED_OFF	 LED_FINISH_COMMAND
 void led_blink (int spec);
 
diff --git a/src/main.c b/src/main.c
index 63f75f2..17feab0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -238,6 +238,7 @@ main (int argc, const char *argv[])
   uintptr_t entry;
 #endif
   chopstx_t ccid_thd;
+  int wait_for_ack = 0;
 
   chopstx_conf_idle (1);
 
@@ -354,7 +355,11 @@ main (int argc, const char *argv[])
     {
       eventmask_t m;
 
-      m = eventflag_wait (&led_event);
+      if (wait_for_ack)
+	m = eventflag_wait_timeout (&led_event, LED_TIMEOUT_INTERVAL);
+      else
+	m = eventflag_wait (&led_event);
+
       switch (m)
 	{
 	case LED_ONESHOT:
@@ -371,12 +376,16 @@ main (int argc, const char *argv[])
 	  display_fatal_code ();
 	  break;
 	case LED_SYNC:
+	  wait_for_ack = 0;
 	  set_led (led_inverted);
 	  break;
 	case LED_GNUK_EXEC:
 	  goto exec;
+	case LED_WAIT_FOR_BUTTON:
+	  wait_for_ack = 1;
+	  /* fall through */
 	default:
-	  emit_led (LED_TIMEOUT_ZERO, LED_TIMEOUT_STOP);
+	  emit_led (LED_TIMEOUT_ONE, LED_TIMEOUT_ZERO);
 	  break;
 	}
     }
diff --git a/src/openpgp.c b/src/openpgp.c
index 15c024c..73cbc05 100644
--- a/src/openpgp.c
+++ b/src/openpgp.c
@@ -1644,8 +1644,7 @@ openpgp_card_thread (void *arg)
 
       led_blink (LED_START_COMMAND);
       r = process_command_apdu ();
-      if (!r)
-	led_blink (LED_FINISH_COMMAND);
+      led_blink (LED_FINISH_COMMAND);
     done:
       eventflag_signal (ccid_comm, r? EV_EXEC_FINISHED_ACK : EV_EXEC_FINISHED);
     }
diff --git a/src/usb-ccid.c b/src/usb-ccid.c
index 6c7a889..941a227 100644
--- a/src/usb-ccid.c
+++ b/src/usb-ccid.c
@@ -29,6 +29,10 @@
 
 #include "config.h"
 
+#ifdef ACKBTN_SUPPORT
+#include <contrib/ackbtn.h>
+#endif
+
 #ifdef DEBUG
 #include "usb-cdc.h"
 #include "debug.h"
@@ -1844,6 +1848,7 @@ ccid_thread (void *arg)
 	if (c->ccid_state == CCID_STATE_EXECUTE)
 	  {
 	    ackbtn_enable ();
+	    led_blink (LED_WAIT_FOR_BUTTON);
 	    c->ccid_state = CCID_STATE_CONFIRM_ACK;
 	  }
 	else