use const-time op
diff --git a/lib/picotls.c b/lib/picotls.c
index a7ed1b7..03b6884 100644
--- a/lib/picotls.c
+++ b/lib/picotls.c
@@ -2572,7 +2572,7 @@
ptls__key_schedule_update_hash(tls->key_schedule, message.base, message.len, 0);
if ((ret = ech_calc_confirmation(tls->key_schedule, confirm_hash_expected, tls->client_random.inner, label)) != 0)
goto Exit;
- if (memcmp(confirm_hash_delivered, confirm_hash_expected, sizeof(confirm_hash_delivered)) == 0)
+ if (ptls_mem_equal(confirm_hash_delivered, confirm_hash_expected, sizeof(confirm_hash_delivered)))
goto Exit;
memcpy(message.base + confirm_hash_off, confirm_hash_delivered, sizeof(confirm_hash_delivered));
}