OTP Code Generator

Table of Contents

How It Works

The tool operates entirely in your browser, ensuring your secret key is never sent over the internet. You input your secret key, and the tool uses the current time to generate a new, unique code every 30 seconds.

The Algorithm

The generator uses the standard TOTP algorithm, which combines your secret key with the current time (the “epoch”) to produce a code. This is a common and secure method for 2FA used by many online services. The process involves several steps, which are displayed on the screen for full transparency:

• Secret in hexadecimal: Your secret key is first converted into its hexadecimal representation.
• Epoch: This is the number of seconds that have passed since January 1, 1970. The TOTP algorithm uses this value, divided into 30-second intervals, to ensure the code is time-sensitive.
• Count: The epoch is divided by the time-step (30 seconds) to create a counter. This ensures that everyone using the same secret key generates the same code at the same time.
• Padded hex: The count is converted to a hexadecimal number and padded with leading zeros to meet the algorithm’s requirements.

These values are then combined to produce the final, six-digit TOTP code.

Use Cases

• Testing 2FA setups: Before linking a secret key to a new service, you can use this tool to confirm that it’s generating codes correctly.
• Educational purposes: The tool provides a step-by-step breakdown of how a TOTP is generated, making it a great resource for learning about the underlying cryptographic processes.
• Offline code generation: Since the tool runs in the browser, you can save the webpage and use it to generate codes even without an internet connection (as long as your device’s clock is accurate).
• Backup authenticator: In a pinch, if you lose access to your primary authenticator app, you can use this tool with your secret key to get a valid code.

Input and Output

Input

• Secret: The secret key provided by an online service for 2FA. This is often a string of letters and numbers, like FUWK3M6VWQG2QFCL.

Output

• Time-Based OTP: The large, six-digit number is the final one-time password.
• Previous / Next: These numbers show the codes from the previous and next time intervals, so you know what to expect if you need to wait a moment.
• Timer: A visual timer shows you how much time is left before the current code expires and a new one is generated.
• Intermediate Values: The tool also shows the secret in hexadecimal, the current epoch, the count, and the padded hex value to show how the final OTP is derived.