#authenticator #otp #qr #cli


CLI generates 2FA OTP codes from exported QR jpg images from google authenticator

1 stable release

1.0.71 Mar 26, 2023

#868 in Authentication

MIT license

231 lines


CLI generates 2FA OTP codes from exported QR jpg images from google authenticator
version: 1.0.71 date: 2023-03-26 author: bestia.dev repository: Github

Lines in Rust code Lines in Doc comments Lines in Comments Lines in examples Lines in tests

crates.io Documentation crev reviews Lib.rs License Rust

Hashtags: #rust #rustlang #tutorial
My projects on Github are more like a tutorial than a finished product: bestia-dev tutorials.
Generated documentation on github: https://bestia-dev.github.io/cli_google_auth_from_exported_qr_jpg/


After my friend lost his phone on vacation I realized how 2FA can be a gargantuan pain in the ass. I know by heart all of my primary passwords, but it is not enough anymore.
Most of the serious internet services use some kind of 2 factor authentication (2FA) today. My 2FA is mostly linked to my phone and I am screwed if I loose it. First it used to be that the internet services sent me an SMS upon login. This was a terrible idea. If I loose my phone, I can buy a new one in a couple of hours, but to get a SIM from my provider with the same telephone number can be tricky. Especially if I am on the other side of the planet in a foreign country. Not to mention how many times the SMS simply does not work for any reason. Scammers allegedly can get around SMS-based 2FA by using social engineering.

Later all services started to adopt the concept of OTP (one-time password) for 2FA, mostly TOTP (time-based one-time password). Time-based one-time password (TOTP) is a computer algorithm that generates a one-time password (OTP) that uses the current time as a source of uniqueness. TOTP is the cornerstone of Initiative for Open Authentication (OATH), and is used in a number of two-factor authentication (2FA) systems. It has been adopted as an Internet Engineering Task Force (IETF) standard.

I use the Google Authenticator app on my android phone to generate 2FA TOTP for many internet services. It is alright I guess. TOTP is a standard, so I don't expect many differences between apps. But sadly google authenticator works only on android. If I loose my phone I cannot use a Windows or Linux computer to generate my TOTPs. And this is exactly what I want.

There are many TOTP programs for Windows and Linux, but I just need an excuse to make my own. I am a hobbyist programming teacher/tutor after all.

Google authenticator can "transfer" or "export" single TOTP definitions as a QR code. On android I cannot take a screenshot of this QR code, but I can make a photo of it using another phones camera. Silly old school tricks! So now I have a jpg image with all the seed data needed to generator TOTPs on another device. The text inside the QR code is something like:


I want to save this jpg somewhere safe. It is a kind of little silly obfuscation idea to have the data inside a qr jpg and not in a text format. Security is never 100%, it is just a series of steps to make it harder for the hackers to understand what is going on.

In case of need I want a simple one-file CLI program to read this QR inside the jpg and generate my OTP. No secrets are ever typed in the terminal, only the jpg file name.

Because of the tutorial nature of this project, sure everything must be coded in Rust.

Short name

The development project has a very long and expressive name cli_google_auth_from_exported_qr_jpg. For the CLI I want to have a short name like gajpg. To achieve that, I just need to change the name of the directory inside the /src/bin/ directory. I will then call the CLI with a line like this:

gajpg image1.jpg

Test data

I created a TOTP seed just for testing on https://totp-online.tobythe.dev/.


Then I used Google authenticator on Android to create a new auth item. Then I "transferred" or "exported" this item and got a qr code on the screen of my phone. I cannot take a screenshot, because of "security". But I can take a photo of the screen with another camera.

I saved this testing image inside this project as image1.jpg.

First step read the qr from a jpg

To read the qr from the jpg I will use the crate bardecoder. It didn't decode my QR until I edited the image to be clean, black and white with good contrast and around 700x700 pixels. More manual work that I wanted to accept, but it is not impossible and it is done only once.
The qr text inside this jpg image is:


Second step to get secret from migration code

Inside the otpauth-migration google has put the account, the issuer and the secret. I need to extract these. I tried some existing crates, to no avail.


First we need to decode base64. That is not difficult. But then we have a brand new "protobuf" protocol buffer message.


Protocol Buffers are a language-neutral, platform-neutral extensible mechanism for serializing structured data created by google. They claim it is performant and efficient, more than json and xml. Instead of a generic coder/decoder, they prepare optimized code for every specific proto message. They created a code generator for 20 languages, but not for Rust. There is the prost crate that looks it generates rust code from the .proto definition. I created a sub-project called code_generator to generate Rust code from the schema.
The resulting Rust code is copied into gauth_migration_proto_mod.rs.

Third step to generate OTP

When I have the seed secret it is easy to generate the TOTP using the crate totp-rs.

automation helper

I use my crate cargo-auto to code automation tasks like build, release, doc, test,... All is done in Rust code. Fancy. Start with:

cargo auto

And follow the detailed instructions. Then continue with the unambiguous command:

cargo auto build

open-source and free as a beer

My open-source projects are free as a beer (MIT license).

I just love programming.

But I need also to drink. If you find my projects and tutorials helpful,please buy me a beer donating on my paypal.

You know the price of a beer in your local bar ;-) So I can drink a free beer for your health :-)

Na zdravje! Alla salute! Prost! Nazdravlje! 🍻


~218K SLoC