Hardware Security Keys Buyer's Guide: FIDO2 Keys

Hardware security keys are the most straightforward route to phishing-resistant MFA, but buying the wrong model, or deploying keys without attestation and lifecycle controls, leaves gaps an attacker can still use. CISA calls phishing-resistant MFA the gold standard and FIDO/WebAuthn the only widely available form of it, and NIST SP 800-63B-4 requires a non-exportable, hardware-protected key for AAL3. This vendor-neutral buyer's guide covers how to define requirements, which capabilities to compare, what to ask vendors, warning signs and a proof of concept plan for roaming FIDO2 authenticators. It is written for IAM architects, endpoint teams and procurement leads; for rollout and day-to-day operation see the Hardware Security Keys Guide.

Key takeaways

Device-bound is the point. Under NIST SP 800-63B-4, syncable authenticators are inherently exportable and shall not be used at AAL3; keys that never leave the hardware are what security keys add over synced passkeys.
Attestation turns a key into a controllable asset. Enforcing attestation and allow-listing models by AAGUID lets your identity provider accept only the keys you bought; without it, the allow list is guidance, not a control.
Certification has layers. FIDO Certified levels (L1 to L3+) and FIPS 140-3 validation answer different questions, and the FIPS 140-2 sunset on 21 September 2026 moved older certificates to the Historical list.
Protocol support matters for years. Look for current CTAP 2.1 or 2.2 features such as credential management, alwaysUv, minimum PIN length and enterprise attestation.
Plan the lifecycle, not just the purchase. Two keys per user, secure enrolment, loss and revocation processes decide whether the programme survives contact with users.

Define requirements

Assurance target: AAL2 phishing-resistant for most staff, AAL3 for administrators and high-risk roles. AAL3 requires a non-exportable private key in a hardware-protected isolated environment, phishing resistance, and validation to FIPS 140 Level 1 or higher overall (NIST SP 800-63B-4).
User populations: privileged administrators, help desk, finance, executives, shared workstation and frontline staff. CISA advises starting with high-value users such as administrators and help desk. See the Phishing-Resistant MFA Guide.
Synced or device-bound: decide where synced passkeys are acceptable and where only attested hardware keys will do. See the Passwordless and Passkeys Guide.
Platforms and ports: USB-A, USB-C, Lightning, NFC for mobiles, and whether Bluetooth is acceptable in your environment.
Additional functions: PIV smart card for Windows logon or legacy PKI, OpenPGP, or one-time passwords, only if you will use them.
Regulatory drivers: US federal or regulated customers may require FIPS 140-3 validated modules; framework mapping is NIST SP 800-53 Rev. 5 IA-2(1), IA-2(2), IA-2(8) and IA-5(2), and NIST CSF 2.0 PR.AA-03.
Threats: phishing (ATT&CK T1566), adversary-in-the-middle (T1557) and MFA request generation (T1621), as seen in the Uber breach of 2022. See the AiTM Phishing Guide.

Capability areas

Protocol and standards support

FIDO2: WebAuthn (now a W3C Recommendation at Level 3, published 25 August 2026) with CTAP 2.1 or 2.2, plus U2F (CTAP1) for older services, and the option to disable CTAP1 where policy demands.
Discoverable (resident) credentials and the number the key can hold; authenticatorCredentialManagement so users and administrators can list and delete credentials.
credProtect, alwaysUv and setMinPINLength / minPinLength so PIN rules can be enforced on the key and reported to the relying party.

Attestation and model control

A stable AAGUID per model and attestation certificates listed in the FIDO Metadata Service (MDS3), which relying parties use to check certification level and capabilities.
Enterprise attestation (CTAP enterprise attestation parameter): vendor-facilitated mode, where the key returns uniquely identifying attestation only to pre-configured RP IDs, or platform-managed mode, where a managed platform vets the RP ID. This lets you tie a specific serial to a specific user.

Assurance and certification

FIDO Certified level: L1 is a vendor questionnaire evaluated by the FIDO Security Secretariat; L2 and above are tested by a FIDO Accredited Security Laboratory; L3 and L3+ are evaluated by an accredited laboratory against a mapping table, with L3+ tied to a companion programme.
FIPS 140-3 validation of the cryptographic module through the NIST and Canadian Centre for Cyber Security CMVP, with the certificate on the Active list (five years, two for interim validations).

User verification and form factor

PIN, built-in biometric sensor, or both; enrolment of biometrics without a host tool.
Durability, water resistance, keyring or nano form factor for always-inserted laptop use.

Lifecycle and supply

Bulk ordering, pre-registration or enrolment on behalf of users, direct-to-employee shipping, and tamper-evident packaging.
Firmware: whether it can be updated in the field, and how the vendor handles vulnerabilities in non-updatable devices, including replacement programmes.

Evaluation criteria

Criterion	Minimum	Preferred for high assurance	How to verify
Protocol	FIDO2 with CTAP 2.1	CTAP 2.2 with credential management and enterprise attestation	authenticatorGetInfo output; vendor datasheet
FIDO certification	FIDO Certified L1	L2 or higher	FIDO certified products listing and MDS3 entry
FIPS validation	Not required for most commercial use	FIPS 140-3 certificate on CMVP Active list, overall Level 1 or higher (Level 2 or 3 where policy demands)	CMVP certificate number and security policy
Attestation	Batch attestation with published AAGUID	Enterprise attestation for named RP IDs	Registration test with attestation enforced
User verification	PIN	PIN with enforced minimum length, alwaysUv; biometric where usability requires	Policy test in PoC
Credential capacity	Enough discoverable credentials for your passwordless sites	Headroom for growth; manageable via CTAP credential management	Fill test
Additional applets	None needed	PIV for smart card logon if used	Integration test with your PKI
Supply and support	Direct purchase, known lead times	Pre-enrolment, tamper-evident shipping, documented vulnerability response	Contract terms; advisory history

Synced passkeys versus device-bound keys

Property	Synced passkey	Device-bound security key
Key storage	Encrypted and synced through a provider's cloud	Generated and kept on the key; never leaves it
WebAuthn flags	Backup eligible (BE) set: multi-device credential	BE not set: single-device credential
Attestation	Not supported (Microsoft Entra ID documentation)	Supported
NIST 800-63B-4	Up to AAL2; not permitted at AAL3	Eligible for AAL3 with FIPS 140 validation
Recovery	Through the sync provider account	Backup key or reissue; your process

Questions to ask vendors

Which CTAP version does each model implement, and which optional features (credential management, alwaysUv, minPinLength, enterprise attestation) are enabled?
Which FIDO certification level does each model hold, and is it listed in the FIDO Metadata Service with current status?
Which models have a FIPS 140-3 certificate on the CMVP Active list, at what overall level, and which firmware versions does it cover?
Do any keys we would receive still rely on FIPS 140-2 certificates now on the Historical list?
How does enterprise attestation work with our identity provider, and how are our RP IDs provisioned on the keys?
Can firmware be updated? If a vulnerability is found, what is your disclosure and replacement policy?
How do you secure the supply chain from manufacture to employee, and can you pre-enrol or ship directly?
How many discoverable credentials can each model store, and what happens when it is full?

Red flags

"FIDO compatible" or "works with FIDO" without a FIDO Certified listing.
FIPS claims citing "FIPS 140-2 compliant" or "designed to FIPS" with no CMVP certificate number.
No AAGUID or MDS entry, which makes attestation and allow lists impossible.
Devices that support only U2F with no FIDO2 user verification.
No published vulnerability handling for non-updatable firmware.
Low-cost unbranded keys from marketplaces with no supply chain assurance.
Deployment plans with one key per user and no backup, which pushes recovery onto weaker help desk resets. See the MFA Fatigue and Bypass Guide.

Proof of concept

Shortlist two or three models, with at least one in each form factor you need (USB-C plus NFC, nano).
In your identity provider, create a pilot policy with attestation enforced and an AAGUID allow list for the shortlisted models only (Microsoft Entra ID calls these passkey profiles with Enforce attestation and key restrictions).
Register keys for 20 to 50 pilot users, starting with IT administrators and help desk, each with a primary and a backup key.
Test sign-in on Windows, macOS, Linux, iOS and Android, through VPN, VDI and remote desktop, and on your top SaaS apps.
Try to register an unapproved key or a synced passkey under the pilot policy and confirm it is refused.
Set a minimum PIN length on the key and confirm PIN lockout behaviour after repeated failures.
Simulate loss: revoke the key in the IdP, sign in with the backup, and time the replacement process.
Check logs: registration, sign-in and revocation events with AAGUID, sent to your SIEM.
Measure: share of privileged users on phishing-resistant MFA, sign-in failure rate, help desk tickets per 100 users, and mean time to replace a lost key.
Roll back by moving users back to the previous MFA policy group; keep the previous method registered until the pilot exits.

How NHI Mgmt Group can help

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Hardware Security Keys Buyer’s Guide: Evaluating FIDO2 Keys for the Enterprise