What is two-factor authentication?

Two-factor authentication (2FA) adds a layer of security by requiring two different types of identification before granting access to an account or system.

Definition of 2FA 

Two-factor authentication (2FA) is a cybersecurity process that adds an additional verification step beyond the basic username and password as a means of identifying a user online. Two distinct forms of identification must be provided by users and verified before they are granted access to an online resource.  

The purpose of 2FA is to prevent unauthorized access by making it more difficult for an imposter to enter systems and applications using stolen credentials to potentially steal personal or sensitive information. This method is part of a broader category known as multi-factor authentication (MFA), which utilizes two or more credentials to verify a user’s identity.

 With two-factor authentication, the first factor is information that the user knows, typically a password or personal identification number (PIN). The second factor is something the user has, which could be a physical token, a smartphone app generating time-based one-time passwords (TOTPs), a text message, or a biometric factor (e.g., fingerprint, retinal scan, or hand print).  

The combination of something a user knows with something they have creates a higher barrier for unauthorized users to overcome when trying to gain illicit access to accounts or systems. 

2FA is widely used to protect against phishing attacks, because an attacker can trick a user into revealing their password but does not have access to the system where the second authentication factor is delivered. 

While it is an effective security measure, 2FA is not without potential weaknesses. For instance, SMS-based 2FA can be vulnerable to SIM swapping attacks, where an attacker convinces a mobile provider to switch the victim’s phone number to a new SIM card, thus receiving the 2FA codes.  

2FA benefits

Commonly cited benefits of 2FA include: 

• Additional identity verification beyond just a username and password 
• Compliance with regulations that require 2FA 
• Mitigation of password vulnerabilities, such as weak passwords, reused passwords across different services, or stolen passwords   
• Protection of sensitive data  
• Protection across multiple services and access points 

2FA authentication methods

Method	Definition
Authenticator apps	Generate time-based one-time passwords (TOTPs) that expire after a short period, usually 30 to 60 seconds; users enter the code from the app to authenticate
Biometric verification	Uses unique biological traits of the user (e.g., fingerprints, facial recognition, or retinal scans) as a second factor
Email-based 2FA	Sends the one-time passcode (OTP) or authentication link to the user’s email address
Hardware tokens	Physical devices that generate an OTP at the push of a button
Push notifications	Authentication requests are sent to a trusted device, often through a mobile app; the user approves or denies the request with a simple tap
SMS and voice calls	An OTP is sent to the user’s mobile phone via SMS or voice call; the user must enter this code to complete the authentication process.
Software tokens	Similar to hardware tokens but implemented in software, software tokens can be used on devices such as smartphones or computers, generating OTPs without the need for physical hardware

2FA implementation

Implementing two-factor authentication is a multi-step process. The following is a high-level overview of the steps for implementing 2FA. 

Choose a 2FA method

Decide on the type of second factor that will be used. Common methods include: 

• sending codes via text  
• email-based codes
• authenticator apps that generate time-based one-time passwords (TOTPs) 
• hardware tokens 
• biometric verification (e.g., fingerprints or facial recognition) The choice of a second authentication factor depends on the level of security required and the resources available. 

The choice of a second authentication factor depends on the level of security required and the resources available. 

Select a 2FA solution

Based on the chosen method for the second authentication factor, select a 2FA solution that fits the organization’s needs. There are various third-party providers and solutions available, some of which can handle multiple types of authentication methods. 

Integrate 2FA into an existing authentication system

This typically involves modifying the authentication flow to include a step for the second factor after the initial password is verified. If a third-party solution is used, their 2FA application programming interface (API) will be integrated into the existing authentication system. When a user attempts to log in, the original system will interact with the 2FA API to initiate the second layer of authentication. 

Provision 2FA tokens or devices

For methods requiring hardware tokens or mobile apps, these will be provisioned to users. For app-based methods, this might involve having users download an authenticator app and linking it to their accounts. 

Prompt for the second factor during login

The login process will be modified to prompt users for the second factor after they successfully enter their password. The exact process will depend on the 2FA method.  

For example, if using short message service (SMS), the 2FA service texts a code to the user’s mobile device. The user then enters this code into the prompt.  

Organizations should ensure the flow is user-friendly and clearly explains the additional steps. 

Verify the second factor

Once the user enters their second factor, the system sends this information back to the 2FA API. If the second factor is correct, the API will confirm, and the system can grant the user access. 

Plan for backup and recovery

Organizations typically have a fallback mechanism for instances where the user cannot use their primary 2FA method. This could be backup codes, administrative reset processes, or alternative verification methods (e.g., secondary phone numbers or email addresses). 

Test and monitor

Before fully rolling out 2FA, organizations conduct thorough testing to ensure the process works seamlessly across different devices and scenarios. This includes testing the fallbacks and any recovery processes.  

After deployment, they monitor the system for any issues and gather user feedback to address any challenges encountered.   

Educate users

Explain to users the importance of 2FA and train them on how to use it. This could involve sending out instructional emails, creating educational articles, or providing in-app instructions during the setup process. 

Enforce 2FA policies

After implementing two-factor authentication, organizations make 2FA mandatory for access to sensitive systems or data. Many also implement policies that require regular updates or changes to the second factor, especially for methods that might become compromised over time. 

Two-factor authentication (2FA) vs multi-factor authentication (MFA)

Two-factor authentication and multi-factor authentication (MFA) are both security processes that restrict access to digital resources until users have provided more than one verified form of identification.  

While 2FA and MFA share a common goal of enhancing security beyond just a username and password, there are differences in their scope and application.

2FA is a subset of MFA and specifically requires only two forms of identification from users—something they know (e.g., password or PIN), something they have (e.g., a smartphone app that generates one-time codes or a security token), or something they are (i.e., biometric verification, such as a fingerprint or facial recognition). MFA, on the other hand, encompasses 2FA but extends the concept by potentially requiring more than two authentication factors. MFA can involve two, three, or more layers of security.  

The choice between 2FA and MFA should be based on specific security needs, risk assessment, and the level of convenience that can be afforded by the users or an organization. Both methods aim to protect against the vulnerabilities inherent in relying solely on passwords for authentication. 

Two-factor authentication considerations

By incorporating an additional verification step that combines something users know with something they possess, 2FA elevates the security threshold, making unauthorized access exponentially more difficult for potential attackers.  

Despite its strengths, it is important to recognize that 2FA is not infallible. If it is used, it should be implemented as part of a larger, more comprehensive, layered approach to security that includes the use of strong password practices, user education, and other security protocols and systems.  

Threats continuously evolve with new attack vectors exploiting vulnerabilities in a changing digital landscape. Cybersecurity must also continuously adapt to stay ahead of creative and highly motivated cybercriminals as they persist in their nefarious work. 

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