One-Time Passwords (OTP) - Example

In this section, we shall provide an example of how to generate and validate One-Time Passwords (OTP) in Python. The Python library of our choice is PyOTP, which implement the RFC 4226 and RFC 6238 standards. If you want to use this library you should follow the requirements in those standards. Installation:

pip install pyotp

Server-Side Setup

We need to create a base32 secret which has to be shared between the authentication server and the client. We will use Google Authenticator OpenSource OTP model which produce a URI for an exchange, the secret and additional client-server details. It includes the shared secret, the client's username, and the issuer's name.

import pyotp

base32secret = pyotp.random_base32()
print('Secret:', base32secret)

totp_uri = pyotp.totp.TOTP(base32secret).provisioning_uri(
    "[e-mail]",
    issuer_name="Secure App")
print(totp_uri)

Run the above code example: https://repl.it/@nakov/OTP-Server-Side-in-Python.

Sample output:

Secret: S3K3TPI5MYA2M67V
otpauth://totp/Secure%20App:alice%40google.com?secret=S3K3TPI5MYA2M67V&issuer=Secure%20App

Client-Side Setup

Once the client stores the secret in a secure way, in a time-interval of a 30 seconds (by default) a new code will be generated.

import pyotp
import time

base32secret = 'S3K3TPI5MYA2M67V'
print('Secret:', base32secret)

totp = pyotp.TOTP(base32secret)
print('OTP code:', totp.now())
time.sleep(30)
print('OTP code:', totp.now())

Run the above code example: https://repl.it/@nakov/OTP-Client-Side-in-Python.

Sample output:

Secret: S3K3TPI5MYA2M67V
OTP code: 339838
OTP code: 284911

Working Example

You can install Google Authenticator from Google Play or App Store and scan the QR code below:

OTP Auth

Example validation check:

import pyotp

base32secret = 'S3K3TPI5MYA2M67V'
print('Secret:', base32secret)

totp = pyotp.TOTP(base32secret)
your_code = '123456'
print(totp.verify('Code Valid:', your_code))

Run the above code example: https://repl.it/@nakov/QR-code-scanner-in-Python.

Output:

Secret: S3K3TPI5MYA2M67V
Code Valid: True