What Is Two-Factor Authentication (2FA)

Two-Factor Authentication (2FA) is a protection method that requires confirming your identity using two different factors to log into a system. In other words, a password alone is not enough—you also need a second confirmation element, such as a one-time code from an SMS or app.

Single-Factor vs. Multi-Factor Authentication

Example: An ATM effectively uses two-factor authentication: it requires both a plastic card (physical object) and a PIN code (secret knowledge). Only the correct combination of card and code allows the transaction.

Main Authentication Factors

In multi-factor authentication, different types of factors are usually used—ways for the system to verify that you truly are who you claim to be. These are traditionally described as: "what you know, what you have, who you are." Let’s see what that means in practice.

1. What you know — knowledge factor

This includes anything known only to you: passwords, PIN codes, answers to secret questions, passphrases. For example, when you log into a system by entering a password—you’re using this type of authentication. It’s the most common and also the most vulnerable: passwords are easy to forget, guess, intercept, or steal.

2. What you have — possession factor

This refers to a physical object in your possession.

Includes:

• hardware tokens (e.g., issued by banks),
• smart cards,
• USB dongles,
• your mobile phone.

Examples: one-time code via SMS, push notification from an app, code from a physical token.

The idea is simple: if you have the device, you’re likely the account owner. An attacker doesn’t have access to your phone or token, so they can’t log in.

3. Who you are — biometric factor

This factor is based on unique physical or behavioral traits of a person.

For example:

• fingerprint,
• face,
• voice,
• iris,
• and less obvious traits like gait or typing style.

You’ve probably encountered this type of authentication when unlocking a smartphone—using a fingerprint or facial scan.

Additional Factors

Sometimes additional conditions are added to the system, such as:

• location — for example, access allowed only from the office or a specific IP address;
• time — login allowed only during working hours.

For authentication to truly qualify as two-factor, different types of factors must be used. For example, a password and a PIN code are both "knowledge"—that’s not 2FA. But a password + one-time code from an SMS—that’s a full-fledged two-factor protection.

What is Two-Step Authentication

Two-factor authentication (2FA) involves using two different types of factors—for example, a password (what you know) and a code from a phone app (what you have). Two-step authentication may involve two steps but rely on the same type of factor—for example, first a password, then a code sent to the same email.

In everyday life, the distinction is blurry, and most services call their protection two-step even if it’s truly 2FA. The key is that the protection includes a second element available only to you.

Types of 2FA Methods

Below are the main types of 2FA widely used in practice:

SMS or Email Code

SMS code example

Sending a one-time code via SMS or email is one of the most familiar and understandable 2FA methods. Typically, you enter a password, and the system generates a random confirmation code (one-time password or OTP) and sends it to your phone or email. Sometimes the code arrives via voice call, but the essence is the same—it's an extra check that only you have access to the account.

For example, you receive a six-digit code, enter it on the site—and this proves you have access to the phone or email. This is the "possession factor." Even if an attacker knows your password, they can’t log in without your phone.

This method is widely used—in online banking, email services, and social networks. Its main advantage is simplicity: no need to install anything, and it works even on old phones.

However, SMS codes have downsides. First, delivery depends on mobile service—the message might be delayed or not arrive. The phone may be dead, lost, or disconnected. Second, SMS isn’t the most secure—if someone gains control of your number, they can intercept codes.

In the end, SMS-based 2FA is reliable for most cases, but for especially sensitive services (like online banking), more secure methods are better. Email-based codes work similarly but are even less secure. If your email and main account share a password, an attacker who knows it can get both access and the code. So email 2FA is best as a fallback.

Some services (like Google) offer voice calls as an alternative. This can help if SMS doesn’t arrive, but the method still depends on your phone and service reliability.

Authenticator Apps (Code Generators)

Authenticator apps are special mobile apps that generate one-time codes to log into accounts. Some well-known examples include Google Authenticator, Microsoft Authenticator, Authy, and Duo Mobile.

When setting up 2FA with such an app, the system provides a QR code or key to enter. The app then starts generating a new six-digit code every 30 seconds, to be entered at login. It works via TOTP or HOTP standards—i.e., time-based or counter-based codes.

This method is more secure and convenient than SMS. Its main advantage: the code is generated on your phone and doesn’t depend on internet or mobile service. Even offline, the app still shows a valid code. No need to wait for a message or pay for SMS. From a security standpoint, this is a step up: the codes aren’t transmitted over the network, and the secret key stays with you.

However, there are nuances. You need to install the app and know how to use it—slightly harder than receiving an SMS. If you lose your phone, you could lose account access. So always save backup codes and store them securely.

Hardware Tokens and Security Keys

Example hardware token. Source: tokenguard.com

Hardware tokens are physical devices used as the second login factor. One of the earliest and still-used types is a keyfob with a screen, like RSA SecurID. They display a one-time code synced with the server.

The user reads the code from the device and enters it on the site—it works like an authenticator app, but in a separate device. These tokens are still widely used in banks, enterprises, and other secure environments. Their main advantage: the secret key is embedded in the token and not transmitted over the internet, reducing hacking risks. Downsides: you must carry it, it can be lost, and the battery will eventually die.

Modern alternatives are U2F / FIDO2 security keys, like YubiKey or Google Titan. These small USB-like devices connect to computers via USB, or smartphones via NFC or Bluetooth. Once linked to an account, they confirm identity using built-in cryptography.

Biometric Authentication

Biometrics confirm identity using unique personal traits: fingerprints, face, voice, and other biological or behavioral features. In 2FA, biometrics are usually paired with another factor. For example, to confirm login via smartphone, you unlock it with a fingerprint—confirming the device is really yours.

Biometrics are especially popular for unlocking devices. Nearly all modern smartphones support fingerprint or face recognition—it’s a convenient, password-free way to log in.

But for remote authentication (like website logins), biometrics are used less often. Fingerprints or face scans are sensitive data, and services prefer not to store or transmit them to avoid leaks and protect privacy.

Pros and Cons of Different 2FA Approaches

2FA Security: What It Prevents and What Risks Remain

Two-factor authentication is one of the most effective ways to protect accounts from unauthorized access. It’s especially crucial if your password ends up in an attacker’s hands — for example, via a data leak or phishing site. In such cases, 2FA acts as an extra barrier: even if a criminal knows your password, they can’t log in without the second factor — a code from an SMS, app, or hardware device.

2FA prevents most mass attacks on accounts, including brute force, credential stuffing, and other automated hacks. It also reduces insider threats. For example, if your password is saved in a browser or written down, others still can’t use it without the second factor. Many password-stealing viruses also can’t bypass this added layer — they’d need access to your phone, token, or biometric data, which is much harder to get.

What Threats Still Exist with 2FA

Despite its high effectiveness, two-factor authentication isn’t foolproof. Here are some scenarios where even 2FA can be bypassed:

Phishing the second factor. Even with 2FA enabled, users can fall victim to phishing. An attacker sets up a fake login page that asks for a username, password, and one-time code. Unaware, the user enters all info, which is immediately used to access the real site. This can bypass protections like SMS and TOTP codes from authenticator apps.

Interception or theft of the second factor. Some attacks aim to take control of the second factor:

• SIM-swapping — reissuing the SIM card so the attacker receives SMS codes.

• Malware on the smartphone — can read incoming SMS or codes from apps.

• Physical theft — hardware tokens or keys can be stolen.

• Biometric spoofing — despite high protection, attempts can be made using masks, photos, or other forgeries.

Man-in-the-middle (MITM) attacks. A more complex type of attack where an attacker intercepts communication between the user and the real site in real time. Using a proxy, they can get both the password and 2FA code, pass them to the legit site, and gain access. The user may be shown an error message to avoid suspicion.

Attacks on 2FA reset mechanisms. If the recovery process is poorly protected, an attacker might bypass it. For example, by impersonating the account owner and convincing support to disable 2FA, or by accessing email and disabling it via a recovery link. Thus, the 2FA reset process must be as secure as 2FA itself.

MFA fatigue attack. This social engineering technique abuses push notifications. The attacker sends repeated login confirmation requests, hoping the user gets tired or confused and accidentally presses “Allow.” This method was successfully used in the 2022 Uber breach. Developers have responded with added measures, like requiring users to enter a digit shown in the notification (as in Microsoft Authenticator).

Implementing 2FA in an App or Corporate Infrastructure

Two-factor authentication (2FA) can be implemented in various ways — the choice depends on your goals, users, and technical resources. Below are the main aspects to consider when introducing 2FA in your app or within a company.

1. Choosing the Method and Provider

The first step is deciding which second factor methods to support. Options include:

• SMS codes via an SMS gateway;

• TOTP codes, generated by authenticator apps (RFC 6238 standard);

• Push notifications via third-party services (e.g., Firebase or a custom mobile app);

• Hardware keys (e.g., U2F/FIDO2) supported through WebAuthn.

Each solution requires specific infrastructure. SMS needs a contract with a messaging provider, hardware keys need protocol support on both client and server. It’s best practice to offer users a choice of 2FA methods—this improves convenience and system flexibility.

2. Integration and User Experience (UX)

It’s important not just to implement 2FA, but to make it clear and convenient. Typical scenario: after registration, the user is prompted to enable 2FA—depending on the method, they’re shown a QR code for the app or asked to enter a phone number to receive codes.

Always provide recovery options: backup codes, the ability to disable 2FA via support after verification. Login screens should include hints and instructions—what to do if the code didn’t arrive, phone is lost, etc.

In corporate settings, consider implementing Single Sign-On (SSO) with 2FA support, so users don’t need to re-authenticate in each app.

3. Implementation Security

Follow proven cybersecurity best practices:

• Don’t store 2FA secrets in plain text.

• Use reliable cryptographic libraries.

• Limit code entry attempts.

• Secure code delivery channels — SMS messages should be confidential, push notifications protected from spoofing.

• Ensure all access points require 2FA — including web, mobile, and API interfaces. Don’t forget legacy protocols (e.g., SMTP/IMAP) where app-specific passwords or alternative measures are needed.

4. Administration and Monitoring

For organizational 2FA deployment, consider admin controls:

• Integration with LDAP/AD or other access management systems;

• Policy setup — e.g., mandatory 2FA for admins or users with sensitive access;

• User support: help desk should be ready to assist with access recovery (e.g., via video ID or recovery code).

Track 2FA activity: log successful and failed login attempts, notify users of setting changes, monitor for anomalies (e.g., multiple failed attempts).

5. Testing and Failure Resilience

Thoroughly test the system before launch:

• What happens if an incorrect code is entered?

• How does the system handle expired tokens?

• What if the user doesn’t receive an SMS?

• How are external service failures handled?

Make sure error messages don’t give away too much info (e.g., whether the password or code was incorrect). Also, have fallback plans—for instance, if the SMS gateway fails, allow login via a backup code.

2FA in Altcraft

Altcraft Platform supports two-factor authentication (2FA) to provide additional protection for user accounts. The second factor is an authenticator app—such as Google Authenticator or its alternatives.

Once 2FA is enabled in profile settings, logging in will require not only a username and password but also a six-digit code from the app. This code updates every 30 seconds and can only be used once. This makes account access much more secure—even if someone knows your password, they can’t log in without access to the app.

You can configure 2FA yourself in your user profile. Additionally, an Altcraft account administrator can enforce mandatory 2FA for all users—to comply with company security policies.

During setup, the system generates a QR code to scan in your authenticator app. Backup codes will also be provided—store them securely in case you lose access to the device with the app.

After setup, each login will require an up-to-date code from the app. If the code is incorrect (e.g., due to time mismatch), the platform will send a failed login notification to your email. 2FA can be disabled in profile settings—with access to the second factor or help from an administrator.

The omnichannel Altcraft platform offers a secure yet user-friendly authentication method, provides backup options, and alerts you to suspicious activity. This helps protect accounts from unauthorized access—even if your password is compromised.

How to enable two-factor authentication? Read the simple guide here.

Conclusion

Two-factor authentication is an essential part of modern cybersecurity. It protects accounts by combining two independent elements—such as a password and an SMS code, a hardware key and a fingerprint. This approach makes hacking significantly more difficult and helps counter most mass attacks.

2FA is important for regular users—to protect their email, social media, or crypto wallets—and for organizations where corporate data and client information are at stake.

For IT and cybersecurity professionals, 2FA is no longer a novelty, but a basic standard. Yet the concept is simple enough to be understood by beginner users. The key is to always remember the second key when accessing important data.

When implementing 2FA, it's vital to choose the right method balancing security and convenience, understand each option’s vulnerabilities, and follow best practices. When properly configured, two-factor protection significantly enhances security while barely impacting daily use of services.