What Is FIDO2 and How Does It Work? FIDO Authentication Explained

You’re probably here because you're tired of passwords.

You’ve likely heard about FIDO authentication and how it’s changing the game for online security. And you need to understand if the FIDO2 is the right tool to protect you or your business.

Well… at Hideez, we've been helping organizations transition to passwordless technologies for many years now, so we know how it works from the inside out.

In this guide, we have collected our best bits of knowledge to explain how FIDO2 works and why it may (or may not) be the right move to increase your personal or business security.

First of all, a few key things to know:

• If you think about passwordless logins for personal accounts, many popular websites already support FIDO2. Most of the time, the only thing you need is your mobile phone.

• With FIDO, the 'secret' that proves your identity is locked inside your device and physically cannot leave it. That means there's no secret to be phished, no password to be guessed, and nothing for a hacker to intercept.

• Not every app or service is ready for FIDO technology yet, especially in the B2B world with its complex web of software. But it's definitely possible to have your old password-based systems and new passwordless methods work together.

What is FIDO2? The new passwordless standard

FIDO stands for Fast Identity Online, and it’s essentially a big consortium of tech companies — PayPal and Lenovo were some of the originals — who got together with a single, ambitious goal: to kill the password. They knew there had to be a safer and easier way for us to prove who we are online.

FIDO2 is the latest and greatest standard from the FIDO Alliance. It's the one that makes modern passkeys possible and basically brings together the best parts of their earlier work:

• U2F: Focused on using physical security keys as a second factor.

• UAF: Was all about using biometrics (like your fingerprint) on your phone.

The mix of U2F, UAF, and FIDO2 can be confusing at first, so here’s a simple table that breaks down the main differences:

At its core, FIDO2 is all about getting rid of the stuff we all hate: passwords that are impossible to remember and multi-factor methods that are just plain annoying. Nobody likes scrambling for an SMS code or having to approve yet another push notification.

Instead of relying on something you know (a password or a one-time code), FIDO authentication uses a combination of something you have (your phone or a security key) and something you are (your fingerprint or face).  These form factors are also commonly referred to as Passkeys.

Although the concept might sound futuristic, you may have already used passkeys to sign in to your Google or Microsoft accounts — often without realizing that it’s FIDO-based authentication. Today, FIDO authentication is supported across all major operating systems, including Windows, Android, iOS, and macOS.

How does the FIDO2 protocol work?

So how does FIDO authentication actually get rid of passwords? It all comes down to a clever system called public-key cryptography.

Instead of a single password that can be stolen, your device creates a matched pair of digital keys. One key is public (which the web service knows about), and the other is private (which is your secret and never, ever leaves your device). By proving you have the secret private key, you prove you're you — without ever sending a password or secret over the internet.

We’ll show the workflow using the example of our own platform:

1. When you go to a website that supports passwordless sign-in, you’ll see an option to use a FIDO authenticator instead of typing your login and password. The button might say "Sign-in options" or something similar.

   

2. Once you select it, a system window pops up asking you to choose your authentication device. This could be the computer you're on, your phone, or a separate hardware security key you plug in.

   

3. The first time you do this, you'll go through a quick, one-time registration. Your device generates that cryptographic key pair — the private key stays locked down on your device, while the public key is sent to the website to keep on file for your account. You’ll usually be asked to scan your fingerprint, use your face ID, or enter your PIN just to confirm it's you.

   

4. For every login after that, the service sends a unique cryptographic challenge to your device. Your device then uses its private key to sign this challenge. This acts as proof that you have the device, but the secret key itself is never revealed.

5. Finally, the server checks that signature using the public key it has on file. If everything matches up, you're in!

So, what are the main FIDO2 advantages?

The secret sauce is that FIDO authentication is designed to protect you from every angle:

1. Strong security. It stops credential-based attacks such as phishing. Unlike a password that you can be tricked into giving away, FIDO's private key is a secret that’s locked inside your physical device and literally cannot be shared or stolen. This also means that your login credentials are safer during data breaches. If hackers break into a server, they’ll only find your public key, which is completely useless for logging in without your device.

2. Better user experience. FIDO authentication removes the hassle of typing in passwords and OTPs, therefore increasing the speed of authentication. Because FIDO authentication is inherently phishing-resistant, all those extra security layers we've grown to tolerate become redundant.

3. Compliance.FIDO authentication is considered the most advanced method of authentication, aligning with standards like GDPR, HIPAA, PSD2, and NIS2 by enforcing strong user verification without relying on shared secrets. It supports phishing-resistant MFA as recommended by NIST SP 800-63 and CISA guidelines. Major enterprises and governments — including the U.S. federal agencies under Executive Order 14028 — are actively adopting FIDO-based solutions as part of their zero trust strategies.

Where can you actually use FIDO & Passkeys?

The best part about this whole passwordless movement is that you can enable passwordless logins on a ton of the apps and websites you already use every day.

Let's break down where you can use them.

For your personal accounts

First up, your personal accounts. The big three — Apple, Google, and Microsoft — are all-in on Passkeys. That means you can log into your iCloud, Google, and Microsoft accounts without even thinking about a password. Beyond them, a huge list of other services, from social media platforms to your bank, have also jumped on board, letting you use passkeys or physical security keys to log in.

Once you've confirmed your service supports FIDO, getting set up takes less than a minute. Just head into your account's security settings and look for the option to add a new passkey.

Here’s our biggest piece of advice: don’t stop at pairing just one device. We strongly recommend adding several passkeys right away — for example, one for your phone and another for your laptop.

Most passkeys sync automatically through your ecosystem, like your Google Account or iCloud. This is a huge deal because it means if you ever lose your phone, you won’t be locked out of your accounts. You can just grab your laptop, sign in with your fingerprint or PIN, and get right back in.

At work (even for apps that don't seem to support it)

This is where it gets really interesting. You might have work apps that don't support FIDO Authentication directly, but you can often still make them passwordless using Single Sign-On (SSO) via the FIDO-certified Identity Provider (IdP) — like Hideez.

Think of it as your digital security office. When you try to open an app, it sends you to that "office" first. You prove who you are with a quick, secure FIDO-based  login, and the security office gives you a verified pass that every other connected work app trusts.

At Hideez, we support a couple of great ways to log in securely.

Our main method is the new standard for passwordless security: passkeys. This means you can use the built-in features on your devices, like Face ID or a fingerprint scan on your phone and laptop. We also fully support physical, FIDO-certified hardware keys for anyone who prefers a separate security device.

As another flexible option, we also offer a mobile authenticator that works with dynamic QR codes. To log in on your computer, you simply open our app on your phone and scan the QR code on the screen. It’s a fast and secure way to prove it's you by using the trusted device you have in your hand.

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What are the main disadvantages of FIDO2 implementation?

Okay, we've covered the benefits of FIDO2, but let's get real about the downsides. Stripping away the marketing fluff, here are the actual challenges you should be aware of before going all-in on passwordless.

1. The "Legacy Tech" Problem

The biggest headache is that not every app is ready for FIDO. You’ll inevitably run into older, legacy systems—think on-premise software, old VPN clients, or specific RDP gateways—that support neither FIDO nor modern SSO. For those systems, you're pretty much stuck in the password era for now, and you'll need a way to manage both login methods.

Our hardware keys are designed for this exact problem. They do double duty: for modern services, they work as a FIDO2 key that resolves cryptographic challenges. But for all your older apps, the very same key functions as an encrypted password manager. It safely stores 1000+ usernames and passwords per device and can autofill them with a click (and optionally a PIN), giving users one secure way to access everything.

2. The Password Doesn't Always Disappear

Here's a frustrating irony with passkeys today: for most services, your old password doesn't actually go away. It often sticks around as a "fallback option" in case you lose your passkey device. 

While that sounds helpful, it means the weakest link—the password—is still active, leaving a door open to the very attacks passkeys were meant to stop. While the trend is moving toward letting you delete the password entirely, for now, that fallback vulnerability is still a reality for most accounts.

3. Not All Passkeys Are Equal (Synced vs. Device-Bound)

This is a critical point for businesses. There are two main types of passkeys, and they offer a trade-off between convenience and control:

• Synced Passkeys: These are the kind you get with your Google or Apple account. They're super convenient for users because they automatically sync across all of their devices via iCloud or Google Password Manager. However, for a business needing tight security, this can be a drawback because you lose control over which specific device is being used.

• Device-Bound Passkeys: These are locked to a single, specific piece of hardware, like a physical security key or a mobile authenticator app that stores the key locally. This approach offers far more control, as the company knows the credential can't be used from an unapproved personal laptop or tablet. For high-security environments, using authenticators that create device-bound keys is often the better choice.

How to Enable FIDO2 Authentication with Hideez?

Feeling a bit overwhelmed about where to even start with passwordless authentication? We get it, and we wanted to make it easy for you to get started.

As certified members of the FIDO Alliance, we built our Hideez Cloud Identity platform with a free tier that lets you set up passwordless Single Sign-On (SSO) for up to 20 users.

It gives your employees a couple of simple ways to log in: they can either use the synced passkeys they already have on their personal devices (from Google or Apple) or use our Hideez Authenticator app, which uses secure QR codes to tie their login to their specific phone for an extra layer of control.

For companies with more complex needs — like dealing with old-school legacy apps, securing RDP sessions, or even managing physical access — we offer our Enterprise Identity service. It's designed to connect everything, bridging the gap between your modern cloud apps and the trickier parts of your IT infrastructure.

The best way to figure out the right approach is to just talk it through. Book a demo call with us, and we'll have a one-on-one consultation to help you find the perfect passwordless formula for your business.

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FAQ

1. What is a FIDO authenticator?

A FIDO2 authenticator is a device or software that supports the FIDO2 standard for passwordless login. Designed to meet the FIDO2 standard, these tools generate and store cryptographic keys, allowing you to access accounts without passwords. They come in various forms, generally falling into these three categories:

• Biometric Authentication: Biometric authentication allows users to log in by scanning their fingerprint or face. It’s a fast, secure, and convenient option, widely supported on mobile phones and many modern laptops.

• Screen Lock: In the absence of biometric sensors, users can authenticate with a device-specific PIN or screen lock to access their account. This option is especially suitable for desktops or older devices lacking built-in biometrics, maintaining a secure yet accessible authentication process. 

• Physical Security Keys: Also known as hardware tokens or FIDO2 keys, physical security keys are external devices that enable passwordless logins by connecting to endpoint devices through USB, NFC, or Bluetooth. Popular examples include YubiKeys, Hideez Keys, and others. Security key owners authenticate by inserting or tapping the key, often in combination with a PIN for added protection. Some keys even incorporate biometric sensors, combining the security of hardware authentication with the convenience of biometrics.

2. Types and examples of FIDO authenticators

Platform authenticators are built into your device and can’t be removed, making them easy and convenient. Essentially, you can complete the entire authentication process on the same device you used to start the login.

Example: Scanning your fingerprint with a built-in fingerprint reader on your laptop. No external device is needed — just a quick touch, and you’re in.

Example of Platform Authentication

Cross-platforms authenticators, also known as roaming authenticators, cross-platform authenticators are external devices designed to work across multiple devices. For instance, you might use your smartphone or a physical security key, like the Hideez Key, to log into a desktop application on your computer.

Example: Physical security keys are always classified as cross-platform, while smartphones can act as both internal (platform) and external (cross-platform) authenticators, depending on how you use them.

3. What platforms and browsers do support FIDO2? 

Finally, just remember that your device and browser need to be on board. As of 2025, pretty much every modern operating system (Windows, macOS, iOS, Android) and browser (Chrome, Safari, Edge, Firefox) is good to go. The experience might look a little different from one device to another, but the powerful security underneath is the same.

The screenshot below gives you an idea of the current support across the board:

4. FIDO2 vs. U2F - What is the difference?

The key distinction between FIDO2 and FIDO U2F lies in their scope. FIDO2 was created to enable passwordless authentication, eliminating the need for passwords entirely. In contrast, FIDO U2F was designed specifically as a second factor to strengthen password-based logins, acting as FIDO 2FA.

With the release of FIDO2, U2F has been integrated into the FIDO2 framework under the name CTAP1 (Client to Authenticator Protocol 1). This ensures that existing U2F devices can still function as a second factor in FIDO2-enabled systems, offering backward compatibility. Websites that support FIDO2 typically allow for passwordless logins, but some may still use U2F for enhanced 2FA scenarios.

Moreover, FIDO2 introduced CTAP2 and WebAuthn as part of its modern standard. CTAP2 enables advanced FIDO authentication capabilities, including passwordless login. Devices with CTAP2 support are considered FIDO2 authenticators, and if they also support CTAP1, they can provide backward compatibility with U2F.

5. FIDO2 vs. WebAuthn

FIDO2 and WebAuthn are closely related but serve different purposes. FIDO2 is the broader standard that encompasses both WebAuthn (developed by the W3C) and CTAP2 (developed by the FIDO Alliance). WebAuthn is the web-based API that enables browsers and servers to communicate with FIDO2 authenticators, allowing passwordless login. It is essentially the protocol that makes FIDO2 usable for online authentication across websites and applications. While WebAuthn handles the communication, CTAP2 defines how authenticators interact with client devices.

6. FIDO2 vs. FIDO

FIDO (Fast Identity Online) is the overarching alliance and framework that encompasses all its standards, including FIDO U2F, FIDO2, and the protocols within them. FIDO2 is an evolution of the original FIDO framework, expanding its capabilities to enable passwordless logins through WebAuthn and CTAP2. In contrast, FIDO U2F, as part of the original framework, focused exclusively on providing a secure second-factor authentication mechanism.

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Written by:

Oleg Naumenko

CEO and founder, Hideez