Hardware Security Keys: The Strongest Form of Two-Factor Authentication

What Are Hardware Security Keys?

A hardware security key is a small physical device, typically resembling a USB flash drive, that provides cryptographic proof of your identity when logging into online accounts. Unlike passwords, which can be guessed or stolen, and unlike SMS codes, which can be intercepted, a hardware key requires physical possession of the device, making remote attacks virtually impossible.

Hardware security keys represent the gold standard in two-factor authentication. Google reported that after deploying security keys to all 85,000 employees, the company experienced zero successful phishing attacks on employee accounts. This remarkable track record has made hardware keys the recommended authentication method for anyone who faces elevated security risks, including journalists, political figures, executives, and anyone who handles sensitive data.

The technology behind hardware security keys has matured significantly. Modern keys support multiple protocols including FIDO2, WebAuthn, and U2F, and they work with hundreds of services including Google, Microsoft, Apple, GitHub, Facebook, Twitter, and many password managers.

How FIDO2 and WebAuthn Work

The Authentication Process

When you register a hardware security key with a website, the key generates a unique cryptographic key pair for that specific site. The private key stays securely stored on the hardware device and never leaves it. The public key is sent to the website and stored with your account.

When you log in, the website sends a challenge, which is essentially a random number, to your browser. Your browser passes this challenge to the hardware key, which signs it with the private key stored on the device. The signed response is sent back to the website, which verifies it against the stored public key. If the signature matches, you are authenticated.

Why This Defeats Phishing

The critical security advantage lies in how the key identifies the website. During the authentication process, the hardware key checks the domain name of the site requesting authentication. If you are on a phishing site that mimics your bank's login page, the domain will not match the one registered with your key, and the authentication will simply not work. You cannot accidentally authenticate to a fake site because the key will refuse to respond to a request from the wrong domain.

This origin-binding feature is what makes hardware keys fundamentally more secure than SMS codes or authenticator app codes, which can be entered on any site including phishing pages. With a hardware key, the human element of falling for a convincing phishing page is removed from the equation entirely.

Comparing Popular Hardware Security Keys

YubiKey Series

Yubico's YubiKey is the most widely recognized hardware key brand. The YubiKey 5 series supports FIDO2, U2F, smart card, OTP, and OpenPGP protocols. Models are available with USB-A, USB-C, NFC, and Lightning connectors. The YubiKey 5 NFC is particularly versatile, supporting both USB and wireless NFC authentication, making it compatible with both computers and smartphones.

Google Titan Security Key

Google offers its own Titan Security Key in USB-A/NFC and USB-C/NFC variants. The Titan key supports FIDO2 and U2F protocols and is designed to work seamlessly with Google accounts and the Advanced Protection Program. It is a solid, affordable option for users primarily invested in the Google ecosystem.

SoloKeys

For users who prefer open-source hardware, SoloKeys offers FIDO2-compatible security keys with fully open-source firmware and hardware designs. This transparency allows security researchers to audit the entire implementation, providing additional assurance about the key's security properties.

Setting Up a Hardware Security Key

Initial Registration

Setting up a hardware key is straightforward. Navigate to your account's security settings, find the two-factor authentication section, and select the option to add a security key. Insert your key into a USB port or tap it against your phone for NFC, and follow the prompts. The entire process typically takes under a minute.

Start with your most critical accounts: your primary email, password manager, banking, and social media. Use our password generator to ensure each of these accounts also has a strong, unique password as the first authentication factor.

Backup Keys

Always register at least two hardware security keys with each account. Store the backup key in a separate, secure location. If you lose your primary key, the backup ensures you are not locked out of your accounts. Without a backup, losing your only hardware key could mean permanent loss of account access.

Fallback Methods

Most services allow you to configure backup authentication methods alongside your hardware key. These might include backup codes, which you should print and store securely, or a secondary authenticator app. While these fallback methods are less secure than the hardware key, they prevent lockout scenarios.

Who Should Use Hardware Security Keys?

While hardware security keys benefit everyone, they are especially important for certain groups. Journalists and activists working in adversarial environments face targeted phishing campaigns that hardware keys can defeat. System administrators with privileged access to critical infrastructure need the strongest available authentication. Business owners and executives are frequent targets of business email compromise attacks.

However, even everyday users benefit significantly from hardware keys. The cost of a basic security key starts at around $25, which is a trivial price for dramatically improved account security. If you use online banking, store important documents in the cloud, or simply want the peace of mind that comes from knowing your accounts are protected against phishing, a hardware security key is a worthwhile investment.

For accounts that do not yet support hardware keys, use an authenticator app and strong passwords generated with our password generator as interim protection while the ecosystem continues to expand support for this superior authentication method.