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What Is Two-Factor Authentication (2FA)?
Two-factor authentication (2FA) is a security mechanism that requires someone to provide two different types of authentication credentials before they can be granted access to a digital or physical resource. The purpose of this type of multifactor authentication (MFA) is to verify that someone is who they say they are.
Key Takeaways
- Two-factor authentication adds an additional layer of security to the identity and access control process.
- 2FA requires users to submit two different types of authentication factors before they can be granted access to a protected resource.
- The purpose of 2FA is to verify that someone is actually who they claim to be.
- 2FA is often enabled to make password-based logins more secure.
- Two-factor authentication is an important component of defense in depth.
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Key Components of 2FA
Two-factor authentication requires two distinct types of authentication factors to verify a user’s identity. It also requires access to an authentication server that can verify the user’s information before granting access.
Authentication Factors
The three main types of authentication factors are knowledge, possession, and inherence:
Authentication Servers
An authentication server is software that can verify a user’s identity by processing their login credentials and enforcing a second authentication factor before granting or denying access to a requested resource.
How Two-Factor Authentication Works
When a user attempts to access a resource protected by 2FA, they need to follow these steps:
- Submit their primary authentication factor, which usually consists of a username and password.
- Once that has been validated by the authentication server, they will be prompted for a second authentication factor from a different category.
- As long as the server is able to validate both factors, the user will be granted access to the requested resource.
If adaptable 2FA has been implemented, the server will adjust access requirements based on contextual risk factors. For example, if a user logs into an e-commerce website from a designated trusted device, they may be granted immediate access. If the same user logs into the same site from a new device that doesn’t have anti-virus software installed, however, they will be prompted for a second authentication factor.
2FA vs. MFA
Technically, 2FA is a type of MFA that meets the needs of most use cases. MFA, which requires two or more authentication factors, is primarily used in highly regulated industries and environments that require stricter access controls.
Types of Two-Factor Authentication
Two-factor authentication mechanisms are often categorized by the type of second authentication factor they require:
- SMS 2FA sends a one-time password in a text message to a registered mobile number.
- Email 2FA sends an OTP to the user’s email address.
- Authenticator 2FA requires the user to generate a time-sensitive OTP with an authenticator app.
- Push notification 2FA requires the authentication server to send a push notification to the user’s registered smartphone or tablet through an authentication app. The user then taps “Approve” or “Deny” to confirm or reject the login attempt.
- Hardware 2FA requires a physical security token that can generate authentication codes or plug into a USB port for verification.
- Biometric 2FA uses data captured through fingerprint, facial, or retina scans as a second factor.
- Smart card 2FA requires the user to insert a smart card with embedded authentication credentials into a reader.
- Security questions require the user to verify answers to previously-asked security questions.
Authentication Standards
Authentication standards specify how 2FA should be implemented to ensure security, interoperability, and compliance across different platforms. Examples of authentication standards that are relevant to 2FA include:
2FA Security
While two-factor authentication can significantly improve security, it is not immune to threats. For example, SMS one-time passwords are transmitted in plain text which makes them vulnerable to man-in-the-middle (MITM) and phishing exploits.
Here are some of the other security risks associated with using 2FA:
- SIM-swapping
- Push bombing/fatigue attacks
- Account recovery exploits
- Malware
- Physical device theft
3 Factors to Consider When Implementing 2FA
Before deciding which type of two-factor authentication to implement, it’s important to consider the following factors:
For high-risk environments, stronger 2FA methods like hardware tokens or biometrics are preferred. For general user accounts, authenticator apps or push notifications provide a good balance of security and convenience.
Push notifications and biometrics are easier for non-technical users than using an authenticator app and entering OTP codes manually.
Many regulations require organizations to implement multi-factor authentication (which includes 2FA) to meet data protection, cybersecurity, and identity verification standards.
Two-Factor Authentication Pros & Cons
While 2FA can significantly enhance security, it is not perfect and can introduce challenges depending on the method used:
Pros
- Enhances security by adding a second layer of authentication
- Reduces the risk of unauthorized access, even if passwords are compromised
- Meets compliance requirements for multi-factor authentication
Cons
- Requires an additional step for logging in
- Possession factors can be lost or stolen
- Some types of 2FA are more vulnerable to attack than others
The Bottom Line
Two-factor authentication, by definition, requires users to provide two forms of authentication to access a protected resource. While 2FA can enhance security, it still includes the use of knowledge factors, which can be compromised. This is why many organizations are moving toward passwordless authentication.
FAQs
What is two-factor authentication in simple terms?
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References
- FIDO2?(FIDO Alliance)
- Initiative for Open Authentication (Wiki ArchLinux)
- What Is SAML? Security Assertion Markup Language?(Cisco)
- Password reset poisoning | Web Security Academy (PortSwigger)
