feat(legacy): Display nLockTime in human-readable form.

legacy/firmware/CHANGELOG.md

@@ -12,6 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Changed
 - Allow decreasing the output value in RBF transactions.  [#1491]
 - Support long PIN of up to 50 digits.  [#1167]
+- Display nLockTime in human-readable form.  [#1549]
 
 ### Deprecated
 
@@ -384,3 +385,4 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 [#1415]: https://github.com/trezor/trezor-firmware/pull/1415
 [#1491]: https://github.com/trezor/trezor-firmware/issues/1491
 [#1518]: https://github.com/trezor/trezor-firmware/pull/1518
+[#1549]: https://github.com/trezor/trezor-firmware/issues/1549

legacy/firmware/layout2.c

@@ -22,6 +22,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>
+#include <time.h>
 
 #include "bignum.h"
 #include "bitmaps.h"
@@ -584,10 +585,17 @@ void layoutConfirmNondefaultLockTime(uint32_t lock_time,
                       _("will have no effect."), NULL, _("Continue?"), NULL);
 
   } else {
-    char str_locktime[11] = {0};
-    snprintf(str_locktime, sizeof(str_locktime), "%" PRIu32, lock_time);
-    char *str_type = (lock_time < LOCKTIME_TIMESTAMP_MIN_VALUE) ? "blockheight:"
-                                                                : "timestamp:";
+    char str_locktime[20] = {0};
+    char *str_type = NULL;
+    if (lock_time < LOCKTIME_TIMESTAMP_MIN_VALUE) {
+      str_type = "blockheight:";
+      snprintf(str_locktime, sizeof(str_locktime), "%" PRIu32, lock_time);
+    } else {
+      str_type = "timestamp (UTC):";
+      time_t time = lock_time;
+      const struct tm *tm = gmtime(&time);
+      strftime(str_locktime, sizeof(str_locktime), "%F %T", tm);
+    }
 
     layoutDialogSwipe(&bmp_icon_question, _("Cancel"), _("Confirm"), NULL,
                       _("Locktime for this"), _("transaction is set to"),