Two-Factor Authentication using Google Authenticator in Python

Two Factor Authentication or 2FA is an advanced method of user authentication and a subset of multi-factor authentication mechanisms. 2FA enhances the security of its user accounts by adding another layer of authenticity challenge after traditional passwords are used in single-factor authentication.

This article will show you how to implement Two-Factor Authentication using Google Authenticator App using a general-purpose programming language called  Python.

Modules and Apps required

To implement this we need to use 3 modules - 

• time - Inbuilt python module for time-related operations
• pyotp - to generate OTP
• QRcode - To generate QRcode

Run the following to install the required modules:

pip install pyotp qrcode

Users also need to Download and install the Google Authenticator app from the Playstore / Appstore onto their phones.

Importing required modules

Here we are going to import the required module.

import time
import pyotp
import qrcode

Generating the Key

k = pyotp.random_base32()

Using the random_base32() method of the pyotp module, random alphanumeric keys can be generated. Every time the code generates a new key making it impossible to recover in case it gets lost.

secret_key = "GeeksforGeeksIsBestForEverything"

We can also define a specific secret key like the above, we just have to pass this in the TOTP method in later steps, this will never change and will be easier to maintain.

Creating a Time-based OTP (TOTP)

In the following snippet, we are passing the secret_key into the TOTP and provisioning a URI (Uniform Resource Identifier) with the name of the user and the issuer_name, this way the issuer can generate multiple keys for different users, making it easier to identify them. 

totp_auth = pyotp.totp.TOTP(
  secret_key).provisioning_uri(
  name='Dwaipayan_Bandyopadhyay',
  issuer_name='GeeksforGeeks')

print(totp_auth)

Output:

otpauth://totp/GeeksforGeeks:Dwaipayan_Bandyopadhyay?secret=GeeksforGeeksIsBestForEverything&issuer=GeeksforGeeks

The above output is the link that gets generated, but as Google Authenticator supports QR code scanning we would convert this into a QR code which we will scan through our Google Authenticator.

Generating a QR Code 

qrcode.make(totp_auth).save("qr_auth.png")
totp_qr = pyotp.TOTP(secret_key)

Here the QR codes get saved with the name qr_auth and we can scan it and get some new code every time which we can enter in our python script to verify.

Steps to Setup Google Authenticator - 

1. Download the App from Playstore/AppStore.
2. Follow the initial setup procedure till a blank screen is reached.
3. Tap on the + sign at the lower right corner and select the Scan a QR Code Option.
4. Scan the generated QR code.
5. Now, a new account in the following format will be added with a TOTP which is valid for 30 seconds.

IssuerName (UserName)
<Unique Code that lasts for 30 seconds>

Verify the code using Python - 

We can also verify the code generated using Python.

totp = pyotp.TOTP(secret_key)

while True:
    print(totp.verify(input(("Enter the Code : "))))

Output:

The first code was the real one, second was to see what if we give a longer and different code result it returns, we can see that the first code after a while gives us the result False as it has expired, the code at the last line has taken its place for next 30 seconds.

Complete Implementation

import time
import pyotp
import qrcode

key = "GeeksforGeeksIsBestForEverything"

uri = pyotp.totp.TOTP(key).provisioning_uri(
    name='Dwaipayan_Bandyopadhyay',
    issuer_name='GeeksforGeeks')

print(uri)


# Qr code generation step
qrcode.make(uri).save("qr.png")

"""Verifying stage starts"""

totp = pyotp.TOTP(key)

# verifying the code
while True:
  print(totp.verify(input(("Enter the Code : "))))

Note: Make sure to comment out the QR code generation step after the first execution or it will keep on generating a QR code every time the code is executed.

dwaipayan_bandyopadhyay

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Article Tags :

• Technical Scripter
• Python
• Technical Scripter 2022

Practice Tags :

• python