Introductions to the Different YubiKey Series

Throughout the YubiKey Technical Manual YubiKey 5 Series, the YubiKey 5 FIPS Series and the YubiKey 5 CSPN Series, are referred to collectively as YubiKey 5 (FIPS/CSPN) Series. This label indicates that a certain specification or feature is available on all three Series. This is possible because they all share the same base hardware and many firmware features.

This topic introduces:

YubiKey 5 Series

About the YubiKey 5 Series

The YubiKey 5 Series security keys offer strong authentication with support for multiple protocols, including FIDO2, which is the new standard that enables the replacement of password-based authentication. The YubiKey strengthens security by replacing passwords with strong hardware-based authentication using public key cryptography.

  • For those who just want to use a YubiKey without programming anything, the most useful part of this guide is Understanding the USB Interfaces. This topic describes how the YubiKey connects and indicates what it can connect to.

    For an overview on setting up two-step verification in a typical case, see Google on using a security key for 2-step verification.

  • The full list of the services that work with YubiKeys is on Yubico’s Works With YubiKey page.

  • Most of the rest of this guide targets systems integrators, IT teams, or developers who expect to integrate support for YubiKeys into their environment.

All the YubiKeys in the YubiKey 5 Series have the basic functionalities and capabilities described in this guide. However, it is the firmware version that determines which of the more specialized functionalities and capabilities are available on your YubiKey.

YubiKey 5 FIPS Series


Federal Information Processing Standards (FIPS) are developed by the United States government for use in computer systems to establish requirements such as ensuring computer security and interoperability. The National Institute of Standards and Technology (NIST) and the Canadian Centre for Cyber Security (CCCS) run the NIST Cryptographic Module Validation Program (CMVP) as a collaborative effort.

FIPS certification demonstrates that a product has gone through a rigorous audit process and adheres to a security standard that can be measured and quantified.

Many government organizations and government contractors are required to use FIPS-approved products, as are highly-regulated industries in general. Other countries also recognize FIPS 140-2. For the U.S. government, the default is that FIPS is required.

Do You Require FIPS Keys?

If you do not have a security auditor, and/or the auditor does not have a compliance requirement, you probably do not need FIPS. The standard line of YubiKeys offers the same security, algorithms, and functionality. The standard line also evolves at a much more rapid pace because it does not need complete an exhaustive validation process, which commonly takes a year or more. Yubico can release standard firmware with new features and enhancements at any time, whereas FIPS-certified products complete the FIPS validation process every time there is a change.

About the YubiKey 5 FIPS Series

The YubiKey 5 FIPS Series is FIPS 140-2 certified. It offers strong authentication with support for multiple protocols - including FIDO2, which is the new standard that enables the replacement of password-based authentication. The YubiKey strengthens security by replacing passwords with strong hardware-based authentication using public key cryptography.

The cryptographic functionality of the YubiKey 5 FIPS Series devices is powered by the FIPS 140-2 certified YubiKey 5 cryptographic module, a single-chip cryptographic processor with a non-extractable key store that handles all of the cryptographic operations. The YubiKey 5 cryptographic module is FIPS 140-2 certified, both Level 1 and Level 2 (Physical Security Level 3).

The YubiKey 5 FIPS Series cryptographic module is a security feature that supports multiple protocols designed to be embedded in USB security tokens. The module can generate, store, and perform cryptographic operations for sensitive data and is accessed through an external touch-button for Test of User Presence in addition to PIN for smart card authentication. The module implements the following major functions, depending on the firmware version on the YubiKey:

Function Firmware Versions
5.4.2 5.4.3
Yubico One Time Password (OTP) yes yes
OATH OTP authentication yes yes
OpenPGP (version 3.4)
PIV-compatible smart card yes yes
FIDO Universal 2nd Factor (U2F) yes yes
FIDO2 WebAuthn yes yes
YubiHSM Auth
SCP03 yes yes

The YubiKey 5 FIPS Series hardware with the 5.4 firmware is certified as an authenticator under both FIPS 140-2 Level 1 and Level 2. It meets the highest authenticator assurance level 3 (AAL3) of NIST SP800-63B guidance. To use security keys from the YubiKey 5 FIPS Series as a Level 2, more stringent initialization is required than for Level 1. Guidance for Level 2 is detailed in the following topics.

FIPS-specific Aspects of the YubiKey 5 FIPS Series

The table below lists the YubiKey 5 FIPS Series with the 5.4 firmware includes configuration changes that are set at programming. These are in addition to the configuration available in the YubiKey 5 FIPS Series.

YubiKey 5 FIPS Series 5.4 Configuration Changes
Configuration Change Description
Enforce power-up self-test (firmware integrity and
algorithm testing)
Minimum PIN length
for FIDO2
6 alphanumeric characters
Unique AAGUIDs for the FIDO Attestation
Attestation (FIDO)
Attestation certificates for FIDO include
Command returns a listing of FIPS, as well as the
FIPS-specific OIDs in the PIV and FIDO attestation
Attestation (PIV)
Attestation certificates for PIV include
the FIPS Form Factor identifier** in the
Form Factor OID (
YubiKey Manager Form factor identifies FIPS Series devices.(2)
  1. The certifications that are supported by a FIDO authenticator can be returned in the certifications member of an authenticatorGetInfo response as set out in paragraph 7.3.1. Authenticator Actions of the Client to Authenticator Protocol (CTAP) Review Draft of March 09, 2021.
  2. Form factor is set during manufacturing and returned as a one-byte value. Currently defined values for this are:
Form Factor
Form Factor

YubiKey Value
Security Key
Value, FW 5.4+
FIPS YubiKey
Value, FW 5.4+
Keychain, USB-A 0x01 0x41 0x81
Nano, USB-A 0x02 N/A 0x82
Keychain, USB-C 0x03 0x43 0x83
Nano, USB-C 0x04 N/A 0x84
Keychain with
Lightning, USB-C
0x05 N/A x85


YubiKeys are programmed in Yubico’s facilities with the latest available firmware and once programmed cannot be updated to another version. The firmware cannot be altered or removed from a YubiKey.

Yubico periodically updates the firmware to take advantage of features and capabilities introduced into the ecosystem.

The firmware version on a YubiKey or an HSM determines whether or not a feature or a capability is available to that device. The quickest and most convenient way to determine your device’s firmware version is to use the YubiKey Manager tool (ykman), a lightweight software package installable on any OS. The YubiKey Manager has both a graphical user interface (GUI) and a command line interface (CLI).

Yubico submitted the firmware for releases 5.4.2 and 5.4.3 to NIST and the organization approved the certification. The certificates can be found here.

Yubico submitted release 5.4.2 to ANSSI for certification and the organization approved the certification. For more information about the YubiKey 5 CSPN Series see YubiKey 5 CSPN Series.

Security Key Series

The Security Key Series differs from a YubiKey 5 Series in that it comes only with the FIDO (FIDO2/FIDO U2F) protocol and does not have a serial number. It is only available in USB-A + NFC and USB-C + NFC form factors.

The Security Key Series - Enterprise Edition is the same as a Security Key Series but includes a serial number to allow for asset tracking. The serial number can be read visually on the back of the key and programmatically through the FIDO HID interface. It is only available in USB-A + NFC and USB-C + NFC form factors.

Get started with Security Key Series (video tutorial)

YubiKey Bio Series

The YubiKey Bio Series offers the familiar YubiKey experience users have come to know and trust, but adds the convenience of a new biometric touch feature.

The series is comprised of two keys:

  • The YubiKey Bio - FIDO Edition (USB-A form factor)
  • The YubiKey C Bio - FIDO Edition (USB-C form factor)

Protocols Supported

Both keys in the YubiKey Bio Series support the FIDO authentication protocols, and work with sites and applications that support the FIDO2 and FIDO U2F protocols (for more information, see YubiKey Bio and FIDO2 and YubiKey Bio and FIDO U2F). FIDO2 (sometimes referred to as WebAuthn) builds upon FIDO U2F, and is the standard that enables the replacement of password-based authentication.

The YubiKey Bio Series provides firmware applications to support two modes of authentication through the FIDO2 and U2F protocols (see YubiKey Bio and FIDO2 and YubiKey Bio and FIDO U2F). Even though the firmware applications are separate from one another, they both share the same PIN and FIDO reset capability. In fact, a FIDO reset resets both applications. To manage these applications, see Tools.

Using the YubiKey Bio

For a quick start to using the YubiKey Bio Series, without a lot of details, see Yubico’s setup page.

This guide, the YubiKey Technical Manual, provides:

Usage Notes

The YubiKey Bio implements biometrics as outlined in the CTAP 2.1 specification. The best user experiences are provided by the YubiKey Bio with client applications and browsers that also implement CTAP 2.1. Applications and browsers that implement CTAP 1 or CTAP 2.0 also work with the YubiKey Bio. However, the UI on client devices is not as intuitive and there might be some limitations.

Interfaces and Applications


Like all YubiKeys, the YubiKey Bio Series are USB 2.0 devices.


Developers: The USB PID and iProduct string are 0x0402 and YubiKey FIDO respectively. See YubiKey USB ID Values.


All keys in the YubiKey Bio Series support WebAuthn sites and applications that support the FIDO2 and FIDO U2F protocols. For more information, see YubiKey Bio and FIDO2 and YubiKey Bio and FIDO U2F. FIDO2 (also known as WebAuthn) is the standard that enables the replacement of password-based authentication.

Each application can be enabled and disabled independently. Up to five fingerprints can be stored on a YubiKey Bio. For management, see Troubleshooting and Tools.

YubiKey 5 CSPN Series


This document describes how to configure and use the YubiKey 5 in compliance with CSPN (“Certificat de Sécurité de Premier Niveau” [RD1]).

For each YubiKey application that requires specific configuration, the documentation provides a short introduction, the required settings to achieve the target, and a technical description of the configuration.


Code Document title Reference
Certification de sécurité
de premier niveau des
technologies de l’information
Certification Report

[RD3] FIDO2: WebAuthn & CTAP
NIST Special Publication
800-73 (PIV)

RFC 4226, An HMAC-Based One-
Time Password Algorithm
T/Key: Second-Factor
Authentication From Secure
Hash Chains
Universal 2nd Factor (U2F)

[RD8] W3C WebAuthn standard
[RD9] YubiKey CSPN security target

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