Universal Second Factor (U2F) keys are hardware devices used for network authentication often called the key to the Internet. They remain secure and phishing-resistant, but as of 2025, they are considered a legacy standard, with FIDO2/WebAuthn and passkeys now the preferred choice for modern authentication.
This guide explains what U2F is, how it works, why it’s still relevant, and how organizations can transition to future-proof authentication without disrupting existing systems.
What Does U2F Stand For?
U2F means Universal Second Factor a two-factor authentication (2FA) method that adds a physical security key as a second component to the traditional password.
This makes account compromise far harder, because an attacker would need:
- Something you know – a password
- Something you have – the U2F key
Why U2F Keys Are Still Trusted
Even in 2025, U2F keys:
- Are immune to phishing because private keys never leave the device
- Protect against session hijacking, man-in-the-middle attacks, and credential theft
- Require no drivers, codes, or extra apps they work instantly once registered
Real-world proof:
Google deployed U2F keys to over 85,000 employees in 2017 and has reported zero successful phishing-based account takeovers since.
U2F vs. FIDO2: 2025 Status
- U2F – Legacy FIDO standard for second-factor authentication. Still supported by major browsers and many services.
- FIDO2/WebAuthn – Modern FIDO standard supporting both passwordless and second-factor authentication.
- Passkeys – Built on FIDO2, allowing users to log in without passwords at all.
Key difference: FIDO2 offers more flexibility, works with device biometrics, and is actively developed by the FIDO Alliance and W3C.
Recommendation: Keep using U2F where it’s deployed, but adopt FIDO2 for new rollouts.
How U2F Keys Work
- Registration – The key generates a unique key pair for the service.
- Login – The user inserts the key into USB or taps via NFC, then confirms with a button press.
- Verification – The service checks the signed challenge with the stored public key.
Advantages of U2F Keys
- Strong, phishing-resistant authentication
- Fast and simple — no code entry or app switching
- Privacy-friendly — unique key pair per service; private key never leaves the device
- Open standard — supports multiple applications and platforms
Where U2F Keys Are Used in 2025
- Securing Google, Microsoft, and Facebook accounts
- Enterprise SSO platforms (Okta, Ping Identity, Azure AD)
- Developer and admin accounts on GitHub, GitLab, AWS, etc.
- VPN and remote access systems
Deploying U2F and FIDO2 Across the Enterprise
Traditionally, enabling hardware-based authentication across all apps required significant development work especially for legacy systems.
Secfense solves this with its User Access Security Broker (UASB):
- Adds U2F, FIDO2, and passkeys to any app without code changes
- Extends phishing-resistant MFA across cloud and legacy systems
- Supports Privileged Access & Microauthorizations for sensitive in-app actions
- Enables policy-based rollout for every user and system
📩 Contact Us to Modernize Your Authentication
What to Expect
- A short conversation to understand your requirements and security goals
- Discussion of commercial terms for relevant Secfense solutions such as Phishing-Resistant MFA, Passwordless IAM, CIAM, Legacy App Protection, or Privileged Access controls
- Agreement on next steps proof of concept, contract details, or rollout plan
Who It’s For
- Prospects ready to scope a project and discuss budgets
- Existing customers expanding Secfense coverage to more systems
- Organizations planning to upgrade from U2F to FIDO2/passkeys without disruption
Antoni Sikora 