DMOJ 2FA: how to set up an authenticator app

DMOJ (Modern Online Judge) is the competitive programming site where you solve problems, submit code and take part in contests. Two-factor authentication (2FA) on a DMOJ account is optional, and the one method DMOJ's announcements describe is a time-based code from an authenticator app (DMOJ).

Before you turn it on, know the rule that matters most: since January 1, 2022, DMOJ's administrators don't answer any support request about account recovery. If you lose your authenticator and don't have a recovery code, DMOJ says you lose the account for good (DMOJ). This guide uses Authenticator App - Novaz on iPhone, but any authenticator app works the same way.

How we checked this guide: the DMOJ steps come from two announcements on DMOJ's own news page, written by DMOJ's site administrators and linked below. The live site shows a security check to automated visitors, so on October 22, 2026 we read archived copies on web.archive.org, saved on August 2, 2025. DMOJ has no step-by-step help article for 2FA, so the steps below are short. We haven't tested them on a DMOJ account, so a label may differ slightly. The Novaz steps are checked against the app, version 1.0.5.

Turn on 2FA with an authenticator app

DMOJ's 2018 announcement puts the setting on your edit profile page and describes the flow in a few lines (DMOJ). It doesn't name the buttons, so look for the two-factor option on that page.

1. Sign in at dmoj.ca and open your edit profile page.
2. Choose the option to enable two-factor authentication. DMOJ shows a QR code, plus a code you can type in by hand instead.
3. In Novaz, tap +, then Scan QR code, and point the camera at the QR code. If the QR code is on the same iPhone, take a screenshot, tap +, then Choose a photo. See scanning a QR code on the same iPhone.
4. If you'd rather type it, tap +, then Enter key manually in Novaz. Fill in Service (for example, DMOJ), Account if you like, and paste DMOJ's code as the Setup key. See What is a 2FA setup key?
5. Type the 6-digit code from Novaz into DMOJ. DMOJ uses it as a check that the app is set up right, and then finishes turning 2FA on.

After that, Novaz gives you the 6-digit code DMOJ asks for. DMOJ's announcement doesn't say when it asks, beyond using the code for two-factor sign-in.

Save your recovery code right away

DMOJ creates a recovery code when you turn on 2FA (DMOJ). On DMOJ, this code is your only way back in if the authenticator is gone. That makes it more important here than on most sites.

Even if you back up Novaz with iCloud backup or a backup file, keep the recovery code too. Write it down or keep it in a password manager, somewhere you can reach without your phone. If you skipped this step or can't find the code, DMOJ says you can go back to your edit profile page, generate new recovery codes and store them safely (DMOJ). More on keeping them in 2FA backup codes.

If DMOJ rejects your code

DMOJ's one piece of advice is about time: the codes are time-based, so your device's clock has to be correct (DMOJ). On iPhone, open Settings > General > Date & Time and turn on Set Automatically. Novaz also warns you when the clock is 15 seconds or more off. Other causes are in Authenticator code not working?

If you lose your authenticator

Sign in with your recovery code. There is no other route: DMOJ's administrators ignore all account recovery requests, even if you write to them from your email address (DMOJ). DMOJ explains why. Someone who has taken over your email could send the admins the same story about a lost phone, and they have no way to tell the real owner from the attacker. If neither the authenticator nor a recovery code is left, DMOJ's warning is blunt: "access to your account will be lost forever" (DMOJ).

Once you're back in, open edit profile and generate new recovery codes. See also Lost the phone with your authenticator app?

Changing phones

DMOJ's announcements don't explain how to move 2FA to a new phone or how to turn it off. In Novaz, an iCloud backup or a backup file lets you restore your accounts, DMOJ included, on the new iPhone. Keep the old phone working and your recovery code at hand until DMOJ is set up on the new phone, and check your edit profile page for the options you have. See How to transfer your authenticator app to a new iPhone.

Official DMOJ help

• Two Factor Authentication (October 24, 2018)
• On account recovery with two-factor authentication (September 4, 2021)