What is two-factor authentication (2FA)?

What is 2FA?

Two-factor authentication in cybersecurity

The digital landscape is evolving, and so are cyberthreats. 2FA plays a critical role in securing digital environments, but it is only part of the solution.

Organizations must adapt by adopting more sophisticated 2FA and multi-factor authentication (MFA) technologies. Implementing centralized user identity and access management (IAM) solutions can enhance security teams' ability to detect and respond to threats effectively.

However, these solutions should be paired with improving user education and awareness. By proactively addressing the challenges and vulnerabilities of 2FA, organizations can stay one step ahead of cybercriminals in the ongoing battle for digital security.

Authentication factors are commonly grouped into three categories — knowledge, possession, and inherence — as described in NIST Special Publication 800-63B-4 (Digital Identity Guidelines: Authentication and Lifecycle Management), the U.S. standard for authentication assurance.

Is 2FA secure?

While 2FA significantly enhances security, it's not foolproof. Vulnerabilities within solutions and misconfigurations can be exploited by attackers. Cybersecurity professionals must continuously evolve their security strategy as cybercriminals find new ways of compromising systems—including 2FA.

Understanding the attack vectors that threaten 2FA is vital. Cybercriminals employ tactics like phishing and push bombing to trick users and evade this protective layer. For example:

• Phishing attacks can trick users into disclosing their 2FA information to attackers, who can then impersonate legitimate users.
• Push bombing overwhelms users with authentication requests, causing them to accidentally approve malicious ones due to MFA fatigue.

Read our free e-book, "Phishing for Dummies", to better understand phishing attacks with a real-world example of push bombing.

Benefits of 2FA

What are the benefits of 2FA?

Reduced risk of fraud: 2FA can help to reduce the risk of fraud, such as unauthorized account access and financial transactions.

Minimized attack surface: 2FA mitigates the risk of attacks from compromised passwords and unauthorized access to better protect all users, and reduce the organization's attack surface.

Improved compliance: Many industries and regulations now require organizations to implement 2FA to protect sensitive data. For instance, 2FA is mandatory for cybersecurity insurance and for financial institutions to meet Federal Trade Commission (FTC) compliance.

Overall, 2FA is a simple and effective way to add an extra layer of security to your online accounts and systems. It is highly recommended that you enable 2FA on all your important accounts, such as your email, bank, and social media accounts.

Why 2FA?

Why use 2FA authentication?

As the number of security breaches continues to rise, 2FA has become an essential web security tool because it mitigates the risk associated with compromised login credentials. If a password is hacked, guessed, or even phished, 2FA prevents an attacker from gaining permission without approval by a second factor.

Passwords are vulnerable

2FA is a crucial security step because passwords alone are not enough to ensure the security of online accounts and systems. Passwords are like house keys; they grant admission but provide no assurance of who's holding them.

A mere password cannot guarantee secure connection to digital resources, underscoring the importance of access security tools like 2FA, MFA, and passwordless authentication.

What is passwordless authentication?

When you hear the term passwordless authentication, it refers to identity verification methods not dependent on passwords. This approach incorporates biometrics, security keys, and specialized mobile apps for secure entry, like Duo Mobile.

Passwordless authentication offers ease of use, strengthens security, and minimizes administrative overhead, creating a frictionless login experience for users across various enterprise scenarios.

What is push-based authentication?

Push-based 2FA typically works through a mobile authenticator app. The app sends a notification on a user's device, requiring their approval to authenticate access to accounts, applications, and resources.

Push-based and passwordless authentication mitigate password-related risks, such as password interception or duplication, common vulnerabilities in Short Message Service (SMS)-based 2FA. To stay ahead of attackers, organizations are transitioning to push-based 2FA and passwordless authentication.

Push-based authentication with number matching asks users to enter a matching number when approving authentication requests, providing additional security against push harassment and fatigue attacks.

Adaptive authentication dynamically considers risk signals at the time of authentication and may step up the authentication method. For example, it may require push with number matching or passwordless authentication to mitigate risk.

Moving away from SMS-based 2FA is recommended in favor of adaptive authentication and passwordless authentication, which are more secure options. They not only protect your accounts but also simplify the user experience to frustrate attackers, not trusted users.

How 2FA Works

How does 2FA work?

Processes vary among the different 2FA methods, but a 2FA transaction generally happens like this:

• The user logs in to the website or service with their username and password.
• The password is validated by an authentication server and, if correct, the user becomes eligible for the second factor.
• The authentication server sends a unique code to the user's second-factor method (such as a smartphone app).
• The user confirms their identity by providing the additional authentication for their second-factor method.

How do I enable 2FA?

To enable 2FA for services and applications, you need to follow a process specific to each platform. For example, follow these steps to enable Duo 2FA:

1. Start the setup prompt "Choose your authentication device type," such as mobile phone, tablet, security key, etc.
2. Enter your phone number "Choose your platform," such as iPhone, Android, Windows.
3. Install Duo Mobile app.
4. Activate Duo Mobile.
5. Configure your device options.

Visit the enrollment guide for a step-by-step tutorial on how to enroll Duo 2FA.

What are the different types of 2FA?

Common 2FA methods compared

What are the limitations of 2FA?

Not all 2FA is equally strong. SMS-based codes can be intercepted through SIM-swapping or phishing, and push notifications can be exploited through "push bombing," where attackers flood a user with prompts hoping one is approved by mistake.

Phishing-resistant methods — such as hardware security keys and biometrics built on WebAuthn and passkeys — close these gaps. Push with number matching and adaptive authentication, which adjusts requirements based on risk signals, further reduce the chance of a successful attack.

2FA vs MFA

Two-factor authentication uses exactly two factors. Multi-factor authentication (MFA) uses two or more, so every instance of 2FA is a form of MFA, but not all MFA is 2FA. Organizations that need stronger assurance may require three or more factors. For a deeper look at MFA, see What is multi-factor authentication?

Authenticator apps

Authenticator apps such as Duo Mobile support 2FA by acting as the second layer of security whenever a user tries to log in. To log in, the user must complete a separate verification step, such as a phone call, an SMS, a one-time passcode, a push notification, biometrics, or something else.

Discover Duo Push

Hardware tokens

Using a hardware token, you can press a button to verify who you are. This device is programmed to generate a passcode that you must type into your two-factor prompt.

Learn how tokens work

SMS passcodes

A unique passcode is sent to your phone by SMS that you must type into your two-factor prompt.

What is Duo's stance on SMS

Mobile passcodes

Similar to SMS, a two-factor authentication app can generate new, unique passcodes for you to type into the two-factor prompt. These are known as a time-based, one-time passcode (TOTP).

Explore passcodes

Biometrics

WebAuthn and Passkeys allow you to use the TouchID fingerprint reader on MacOS laptops as a second factor to authenticate access to your accounts.

Read about biometrics

Which type of 2FA is the most secure?

The most secure 2FA method is to use either hardware tokens or a mobile authenticator app. Biometrics also offer heightened security due to unique biological signatures.

This method requires physical possession to authenticate, minimizing the risk of remote hacking attempts. Unlike SMS passcodes or mobile passcodes, they aren't susceptible to interception or replication, providing a strong layer of protection.

How 2FA works with other authentication tools

Single sign-on (SSO)

Implementation of 2FA along with SSO can help organizations improve security and compliance. Single sign-on is an identification and access system that allows users to access multiple applications and websites with one set of login credentials.

The implementation of SSO within an organization helps reduce repetitive authentication requests during the workday and improves security as workers access applications that are on-premises as well as in the cloud.

See the benefits of SSO

Multi-factor authentication (MFA)

Multi-factor authentication (MFA) is a security tool that requires users to provide two factors to verify their identity before logging in to an account or system. This makes it difficult for attackers to gain access to sensitive data, even if they have compromised a user's password.

MFA is essential for organizations of all sizes, as it can help to protect against a wide range of cyberattacks, including phishing, password breaches, and malware. It is also becoming increasingly important for organizations that are digitizing operations and storing customer data.

Learn how MFA works

Risk-based authentication

Finding the balance between usability and security is now easier than ever. With risk-based authentication, users have the access they need, secured by real-time contextual signals. Organizations can increase security efficacy by dynamically adjusting authentication requirements based on risk levels.

Risk-based authentication now includes Wi-Fi fingerprint, risk-based remembered devices, and Verified Duo Push features, which work together to reduce risk while preserving user experience by only requesting additional verification for suspicious logins or a change in risk.

Explore risk-based authentication

Secure remote access

Secure remote access is essential for businesses to protect their data and devices as more employees work remotely with their own devices. It involves implementing security solutions that help ensure only authorized individuals can access resources, often using secure VPNs, end-to-end encryption, strong authentication tools, and device security measures.

Two-factor authentication (2FA) is one of the crucial solutions that secures remote access. Adding an extra verification step to the authentication process makes it harder for cybercriminals to compromise credentials, safeguarding your workforce's remote connections.

Explore secure remote access

Security training and awareness

Regular cybersecurity training and user awareness can help mitigate risks, especially in situations where prompt bombardment can confuse users into inadvertently granting access to attackers.

Train users to recognize and respond to prompts correctly to mitigate security risks. Communicate with users the importance of best practices for security access, especially during prompt verification that allows access to network systems.

Cybersecurity is an ever-evolving field. Continuous monitoring, regular assessment of 2FA solutions, and keeping abreast of best practices are essential to maintain a robust security posture.

See our security training (PDF)

Common questions about two-factor authentication