NIST SP 800-63-4: What the new phishing-resistant definition means for federal agencies

The recent drafts from National Institute of Standards and Technology around cybersecurity highlight important updates on where the government is moving on tech...

The recent drafts from National Institute of Standards and Technology around cybersecurity highlight important updates on where the government is moving on technology and the focus on increasing security against cyber threats. This is because NIST’s primary goal is to develop and disseminate the standards that allow technology to work seamlessly and businesses to operate smoothly. In December 2022, NIST provided an update to NIST special publication 800-63-4, which details digital identity guidelines designed to help strengthen digital identity assurance and authentication, recognizing shifts in both risk and emerging authentication models such as phishing-resistant multi-factor authentication and passkeys.

The details of the draft guidelines are important because they affect agency operations at large. 800-63-4 clearly defines what it means to be phishing-resistant, and it comes at a time when many government agencies (especially state and local governments) are besieged by phishing attacks and ransomware demands. However, it’s important to understand what phishing-resistance authentication means for federal, state and local agencies, and what needs to be done to abide by these proposed guidelines.

What does phishing-resistance mean for me and my agency?

As with all federal guidelines and legislation, NIST guidelines will continue to evolve — but federal agencies have been put on notice by 800-63-4 that they should pay close attention to what counts as phishing-resistant technology: “the ability of the authentication protocol to detect and prevent disclosure of authentication secrets and valid authenticator outputs to an impostor relying party without reliance on the vigilance of the subscriber.” At a high level, authentication systems need to prevent phishing attacks even if the attacker can trick a user to try and log into a fake site. Deadlines for compliance — for agencies and the companies that work with them — will be coming up fast, so it’s worth going through 800-63-4 to parse what is most relevant for near-term upgrade plans.

The NIST guidelines are designed to help strengthen digital identity assurance and authentication, recognizing shifts in both risk and emerging authentication models such as passkeys. There are three authentication assurance levels (AALs) identified, with each level building on the previous level’s requirements. AAL3 provides very high confidence that someone logging onto your system can, by proof of possession, prove they are who they are claiming to be. FIPS validated authenticators for federal workers are required for AAL2 (level 1) and AAL3 (level 2).


Single-factor authentication



Two-step or two-factor authentication


Approved cryptographic techniques


Phishing-resistant authenticator encouraged, not required

Hardware-based authenticator


Phishing-resistant authenticator required
(channel or verifier name binding)


The revised NIST guidelines also recognize two methods of phishing-resistant authentication: channel binding and verifier name binding. In plain language, the methods are designed to prevent an imposter from successfully hijacking or intercepting the authentication process.

Channel binding refers to the communication channel between the authenticator (such as a smart card) and the verifier. On traditional networks this communication is protected by the encrypted channel so nobody is able to listen in. This is not the case on the web so standard web communication is not protected enough unless mutual/client authenticated TLS is used, which is the reason verifier name binding method was introduced, which the FIDO2 standard leverages. In verifier name binding, the authentication process will only respond to the previously registered domain name. Both methods are resistant to attempts to compromise or subvert the authentication process.

So when is it all happening? It will be a process, but government agencies, already bound by the FIPS 140 standard, are required by the end of FY2024 to adopt exclusive use of phishing-resistant multi-factor authentication. The minimum standard will be the AAL2 level, but note that certain legacy authentication processes like SMS-based “one-time-passwords” OTP will not meet the new standards for phishing resistance. Some companies may choose to leapfrog AAL2 completely and move to AAL3 to get the highest assurance defense against phishing attacks.

How will this impact what I am using today?

800-630-4 says true phishing resistance is only achieved when all methods of authentication are phishing-resistant. PIV/CAC smart cards support phishing-resistant MFA but in cases where PIV/CAC cannot be used, then those authentication mechanisms must move to a phishing-resistant method like FIDO2.

At the start of 2023, NIST continued a series of updates it has instituted for PIV with its Guidelines for Derived PIV Credentials (SP 800-157r1) and new Guidelines for Personal Identity Verification (PIV) Federation (SP 800-217). The updates are NIST’s way of integrating new methods with established authentication approaches. These guidelines will hopefully provide clarity on how to successfully implement FIDO2 and federation for agencies.

Agencies can implement FIDO2 solutions strategically to cloud and mobile based applications, while continuing to utilize their existing PKI investment on traditional networks. With time they can expand FIDO2’s footprint to include other use cases, such as application login, computer logon, and remote logon.

Don’t swim against the current, let it take you to a safer place

The confluence of President Biden’s new cyber strategy and the draft SP 800-63-4 publication is a good signal for all of us looking to protect what we have — whether that is PII data, agency “crown-jewel” data or communications with third parties.

FIDO2 authentication is an essential part of a larger, flexible, phishing-resistant infrastructure now being developed. FIDO2 and PKI solutions are made to complement each other rather than live in an “either-or” world. Phishing-resistant AAL3 solutions are available today and are being more widely adopted. If federal agencies swim with the current rather than against it, they will strengthen their defenses and curtail phishing attacks dramatically.

Joe Scalone is senior solutions architect at Yubico.

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