Time-based One-Time Passwords (TOTP) are a secure authentication method that generates temporary, time-sensitive codes for verifying user identity.
What Does TOTP Mean?
A time-based one-time password (TOTP) is a type of dynamic passcode used in authentication systems to enhance security by generating a temporary, unique code that expires after a short, predefined period.
Based on the HMAC-based One-Time Password (HOTP) algorithm, TOTP combines a shared secret key with the current time, typically using UNIX time intervals as a reference. The result is a one-time password that is both user-specific and time-sensitive. Since the code changes at regular intervals, usually every 30 or 60 seconds, it significantly reduces the risk of replay attacks, as expired codes cannot be reused.
TOTPs are commonly employed in two-factor authentication (2FA) systems, where they serve as an additional layer of verification alongside traditional login credentials, ensuring a higher level of protection against unauthorized access.
What Is the Difference Between 2FA and TOTP?
Two-factor authentication (2FA) is a security method that requires users to verify their identity using two distinct factors, such as something they know (password) and something they have (security token or code). TOTP, or Time-based One-Time Password, is a specific technology often used as the second factor in 2FA systems.
While 2FA refers to the overall security approach, TOTP is a mechanism for generating time-sensitive, unique codes that serve as one part of the 2FA process. Essentially, 2FA is the broader concept of multi-layered authentication, and TOTP is one of the tools used to implement it.
How Does TOTP Work?
TOTP works by generating a unique, time-sensitive code based on a shared secret key and the current time. When setting up TOTP, the service provider and the user exchange a shared secret key, typically encoded in a QR code or alphanumeric string. This key is stored securely in the user's TOTP app, such as Google Authenticator or Authy.
When a TOTP code is required, the app combines the shared secret with the current timestamp, usually using UNIX time divided into intervals (e.g., 30 seconds). A cryptographic hash function (HMAC) is applied to this combination to generate a unique numerical code. The service provider independently calculates the expected TOTP using the same shared secret and time interval. For authentication, the user enters the TOTP code, and the service validates it by comparing it to the expected value. Because the code is tied to a specific time interval, it automatically expires after a short period, ensuring enhanced security.
What Is a TOTP Example?
A common example of TOTP is its use in two-factor authentication (2FA) for online accounts. Suppose a user wants to log in to their email account. After entering their username and password, the system prompts them for a six-digit TOTP code. The user opens a TOTP app, such as Google Authenticator, which displays a code that changes every 30 seconds.
For instance, the app might show the code 438917. The user enters this code into the login prompt, and the system verifies it by calculating its own version of the code using the shared secret and current time. If the codes match, the user is granted access. This process ensures that even if the password is compromised, an attacker cannot log in without the unique TOTP code, which is valid only for a limited time.
How Do I Get TOTP?
To get TOTP, you need a TOTP-compatible app and a service that supports it for authentication. Here's how you can set it up:
- Enable TOTP on the service. Log in to your account on the service you want to secure (e.g., email, cloud storage, banking). Navigate to the security settings and enable two-factor authentication (2FA) using a TOTP app.
- Scan or enter the secret key. The service will provide a QR code or a manual key. Use your TOTP app (like Google Authenticator, Authy, or Microsoft Authenticator) to scan the QR code or manually enter the key.
- Generate TOTP codes. Once set up, the app will generate time-sensitive codes that refresh every 30 or 60 seconds. These codes are tied to the service you registered and are used as the second factor during login.
- Backup the key. Most services provide backup options for the secret key in case you lose access to your device. Save this backup securely for future use.
What Are the Benefits of TOTP?
TOTP provides several key benefits that enhance security and usability in authentication systems. Here are the advantages of this technology:
- Enhanced security. TOTP adds a second layer of protection beyond passwords, significantly reducing the risk of unauthorized access, even if a password is compromised.
- Time-sensitive codes. The short validity period of TOTP codes ensures they expire quickly, mitigating risks such as replay attacks or interception.
- Convenience and accessibility. TOTP is widely supported, with many free and user-friendly apps available for generating codes, making it easy to use across different services.
- Offline functionality. TOTP operates without requiring an internet connection to generate codes, making it reliable in scenarios where connectivity is unavailable.
- Open standards. Based on open standards, TOTP ensures compatibility across numerous platforms and services, avoiding vendor lock-in and providing flexibility.
What Are the Disadvantages of TOTP?
While TOTP enhances security, it has some downsides:
- Reliance on shared secret. TOTP depends on a shared secret key stored on the userโs device, which can be lost, stolen, or compromised.
- Time synchronization issues. If the system time on the userโs device or the service providerโs server is not synchronized, authentication failures may occur.
- Complex setup for some users. The setup process can be challenging for less tech-savvy users, potentially leading to errors or improper backup practices.
- Recovery challenges. Without a backup of the secret key, recovering access to accounts can be difficult if the user loses access to their TOTP app.
- Device dependency. TOTP relies on a physical device, such as a smartphone, introducing risks like damage, theft, or unavailability during critical situations.
Does TOTP Work Online?
Yes, TOTP works online in the context of verifying user access to online services, but the TOTP generation itself operates offline. A TOTP code is generated on your device (via an app like Google Authenticator) using a shared secret key and the current time, without requiring an internet connection. When you input the TOTP code into an online service for authentication, the service verifies it by independently calculating the expected code based on the same secret key and time. This means the process of generating the TOTP is offline, but its verification typically occurs during an online interaction with the service.
How Safe Is TOTP?
TOTP is considered a highly secure method of authentication when implemented correctly, but its safety depends on how well the shared secret key and the user's device are protected. The unique, time-sensitive codes generated by TOTP are difficult to guess due to their reliance on cryptographic algorithms and short validity periods, making it highly resistant to replay attacks and phishing attempts.
However, its security can be compromised if the shared secret key is exposed, such as through device theft, malware, or inadequate backup practices. Additionally, if the device used to generate TOTPs is compromised, an attacker could potentially access the codes. To maintain safety, users should store the shared secret securely, use strong security practices on their devices, and enable backups for account recovery. When combined with a strong primary password, TOTP provides robust protection against unauthorized access.
