Google Authenticator OTP Algorithm in Detail

Google Authenticator is a popular two-factor authentication (2FA) app that uses a time-based one-time password (TOTP) algorithm to generate a six-digit code. This code is used to verify a user's identity.

The TOTP algorithm was developed by the Internet Engineering Task Force (IETF) and is an open standard for generating time-based one-time passwords. It's based on a shared secret key and the current time.

The algorithm uses a hash function to generate a 32-bit code, which is then truncated to 6 digits to create the one-time password. This process happens in real-time, making it virtually impossible to predict or intercept the code.

Here's an interesting read: Google One

Google Authenticator is an implementation of the TOTP algorithm, which generates a unique password for each login attempt using time as a counter.

This makes it a convenient and secure way to access your accounts, as you just need an authenticator app on your phone.

The codes generated by Google Authenticator are based on a fixed interval, usually 30 seconds, making it easy to keep track of your passwords.

Related reading: Azure Authenticator

Unlike traditional passwords, Google Authenticator doesn't require internet access to generate codes, making it both secure and convenient.

This offline generation of codes addresses the issues of forgotten, stolen, or guessed passwords, providing an added layer of security to your online accounts.

The use of an authenticator app on your phone eliminates the need for SMS or email delivery, reducing the risk of new attack vectors.

Google Authenticator uses a Time-Based One-Time Password (TOTP) algorithm to generate unique passwords. This algorithm is based on the current time and a shared secret key.

The TOTP algorithm generates a new password every fixed interval, typically 30 seconds. This is done using a combination of the shared secret key and the current time. The algorithm uses a form of symmetric key cryptography, where the same key is used by both the client and the server to independently generate the OTP.

A TOTP code is generated using a shared secret key and the current time. The shared secret key is a unique, random string of characters generated when TOTP is enabled for an account. This key is stored securely on both the server and the client device.

For another approach, see: Google Password Storage

The TOTP algorithm uses the HMAC (Keyed-Hash Message Authentication Code) algorithm to generate a hash value. This hash value is then used to create the one-time password. The length of the TOTP is typically six to eight digits, making it easy for users to enter manually while still being secure.

Here's a breakdown of the TOTP process:

The client and server clocks must be synchronized for the TOTP algorithm to work correctly. One time passwords remain valid for a period of 30 seconds, and the message #timeRemaining tells you how far along you are in the current period.

One-Time Passwords (OTPs) are a type of authentication code designed for single-use or transactional authentication processes. They enhance security by ensuring their validity is confined to a singular instance or intended transaction.

An OTP method consists of two different components: a seed and a moving factor. The seed is a secret value or key that serves as a starting point for generating these one-time passwords, while the moving factor is the element that changes with each OTP generation.

Check this out: Azure Active Directory Authentication

There are two types of OTP methods: Time-Based OTP (TOTP) and Hash-Based OTP (HOTP). TOTP relies on the current time to generate one-time passwords, while HOTP uses a counter value that increments with each use.

Here's a comparison of TOTP and HOTP:

TOTP is generally considered secure, especially with its time-sensitive nature, reducing the window for potential attacks. HOTP is also secure, but the lack of time sensitivity might expose it to certain vulnerabilities if intercepted passwords are used within the allowable window.

For more insights, see: How to Secure Google Drive

Google Authenticator's OTP algorithm has several benefits that make it a popular choice for online security. It adds an extra layer of security to your online accounts, making it harder for hackers to gain access.

TOTP codes are generated locally on your mobile device, making it extremely convenient as it doesn't need internet or network access. This means you can use it even when traveling internationally or in areas with poor network connectivity.

One of the main advantages of using TOTP is that it's safer than just using passwords. TOTPs are meant for one-time use, which makes them resistant against replay attacks.

Here are the benefits of using TOTP:

However, there are some drawbacks to consider. TOTP uses a secret key in the client and server that makes it susceptible to interception by potential hackers. This can be a concern if you're using a public Wi-Fi network or a network that's not secure.

Security is a top priority when it comes to online accounts, and TOTP adds an extra layer of protection. TOTP codes are generated locally on your device, making them harder to intercept.

TOTP codes are generated locally, so they don't need to be sent over a network, which reduces the risk of interception. This adds an extra layer of security to your online accounts.

Using TOTP is extremely convenient because it doesn't require internet or network access. You can use it anywhere, anytime, without worrying about connectivity issues.

Related reading: Google Super Admin Google Drive Individual Accounts

Here are some key benefits of using TOTP:

TOTP is also safer than just using passwords because it's meant for one-time use, making it resistant against replay attacks. This reduces the risk when user passwords get stolen.

Using Time-Based One-Time Passwords (TOTP) or HMAC-Based One-Time Passwords (HOTP) can be a bit of a gamble. Here are some drawbacks to consider.

Shared secrets are used in TOTP generation, which makes the server a tempting target for attackers. If they steal the secrets, they can generate passcodes to access user accounts fraudulently.

Device dependency is a significant issue with TOTP. If a user's device is stolen, lost, or broken, the TOTP authenticator will no longer work as intended.

Intercept attacks are a concern with TOTP, as it uses a secret key in the client and server that can be intercepted by potential hackers.

Users may experience inconvenience with TOTP due to its time-sensitive nature. If they fail to input the code within the designated time window, they'll need to make multiple requests.

Intriguing read: Google One vs Google Drive

Here are some specific risks associated with TOTP:

HOTP, on the other hand, is not time-sensitive, which might expose it to certain vulnerabilities. For example, if an intercepted password is used within the allowable window, it can be reused.

HOTP has some drawbacks that make it less secure than TOTP. The inclusion of a moving factor, or counter, in HOTP helps mitigate the risk of replay attacks, but it's not time-sensitive.

This lack of time constraints might expose HOTP to certain vulnerabilities, such as if an intercepted password is used within the allowable window. As a result, HOTP is more susceptible to brute force attacks.

Here are some key differences between HOTP and TOTP:

This means that while HOTP is user-friendly and doesn't increment until the user requests a new OTP, it also makes it easier for attackers to try multiple passwords within the allowable window.

To implement Google Authenticator's OTP algorithm, you need to go through the registration process, which involves TOTP (Time-Based One-Time Password) registration. This process is initiated by the user entering their username and presenting the first factor of authentication.

The server generates a shared secret key, known as the seed, and embeds it in a URL or QR code that's then passed on to the client. The server also stores the seed in a database for future retrieval.

The user completes the registration by clicking the URL or scanning the QR code, which securely stores the seed in the client device.

Registration is a crucial step in the implementation of 2FA. The user enters their username and presents the first factor of authentication.

They then choose authenticator apps as their preferred second factor while setting up 2FA. The server generates a shared secret key, known as the seed, which is embedded in a URL or QR code.

The server passes this code to the client, and also stores the seed in a database for future retrieval. To complete the registration, the user clicks the URL or scans the QR code, which triggers TOTP registration.

The TOTP authenticator stores the seed in the client device in a secure manner. A process of TOTP validation occurs to complete the registration.

Some applications require two TOTP validations to complete registration.

The source code for the Google Authenticator is fully documented and can be found on SmalltalkHub in a project called GoogleAuthenticator.

You can load it with the following expression, which makes it easy to access and start working with the code.

The project also contains the source code and tests of Base32Encoder, which is a useful component to have in your toolkit.

This project is a great resource for developers looking to implement the Google Authenticator, as it provides a comprehensive and well-maintained codebase to work from.