Introduction to the Different YubiKey Series — YubiKey Technical Manual documentation (2024)

  • Introduction to the Different YubiKey Series
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Where applicable, throughout this guide, the YubiKey 5 Series, the YubiKey Bio Series, the YubiKey 5 FIPS Series and the YubiKey 5 CSPN Series are referred to collectively as the YubiKey 5 (FIPS/CSPN) Series. This label indicates that a certain specification or feature is available on all these Series. This is possible because they all share the same base hardware and many firmware features.

This topic introduces:

  • YubiKey 5 Series
  • YubiKey 5 FIPS Series
  • YubiKey Bio Series
  • YubiKey 5 CSPN Series
  • Firmware
  • Security Key Series

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, with the Protocols and Applications chapter listing these by protocol:

  • FIDO2
  • Smart Card (PIV Compatible)
  • OATH
  • OpenPGP
  • OTP
  • YubiHSM Auth.

However, it is the firmware version that determines which of the more specialized functionalities and capabilities are available on your YubiKey. See Firmware.

YubiKey 5 FIPS Series

Why FIPS?

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 (the non-FIPS series) offers the same security, algorithms, and functionality. The standard line also evolves at a much more rapid pace because it does not need to 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 must go through the FIPS validation process every time there is a firmware 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 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. It 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.

YubiKey 5 FIPS Series Cryptographic Module Major Functions
FunctionFirmware Versions
5.4.25.4.3
Yubico One Time Password (OTP)yesyes
OATH OTP authenticationyesyes
OpenPGP (version 3.4)
yes
PIV-compatible smart cardyesyes
FIDO Universal 2nd Factor (U2F)yesyes
FIDO2 WebAuthnyesyes
YubiHSM Auth
yes
SCP03yesyes

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 Deploying the YubiKey 5 FIPS Series.

FIPS-specific Aspects of the YubiKey 5 FIPS Series

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

YubiKey 5 FIPS Series 5.4 Firmware Configuration Changes
Configuration ChangeDescription
Functional

Enforce power-up self-test (firmware integrity and

algorithm testing)

Minimum PIN length

for FIDO2

6 alphanumeric characters

Identification

(FIDO)

Unique AAGUIDs for the FIDO Attestation

(see AAGUID Values in FIDO2)

Attestation (FIDO)

Attestation certificates for FIDO include

a FIPS OID (1.3.6.1.4.1.41482.12)

FIDO GETINFO

Command returns a listing of FIPS, as well as the

FIPS-specific OIDs in the PIV and FIDO attestation

certificates (see Footnote 1).

Attestation (PIV)

Attestation certificates for PIV include

the FIPS Form Factor identifier** in the

Form Factor OID (1.3.6.1.4.1.41482.3.9)

YubiKey Manager

Form factor identifies FIPS Series devices (see

Footnote 2).

Footnote 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.

Footnote 2 Form factor is set during manufacturing and returned as a one-byte value. Currently defined values for this are set out in the Form Factor table below:

Form Factor

Form Factor

Standard

YubiKey Value

Security Key

Value, FW 5.4+

FIPS YubiKey

Value, FW 5.4+

UNDEFINED0x00N/AN/A
Keychain, USB-A0x010x410x81
Nano, USB-A0x02N/A0x82
Keychain, USB-C0x030x430x83
Nano, USB-C0x04N/A0x84

Keychain with

Lightning, USB-C

0x05N/Ax85

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 four keys:

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

Protocols Supported

All keys in the YubiKey Bio Series support the FIDO authentication protocols, and all 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, which is to say that a FIDO reset resets both applications. To manage these applications, see Tools.

The YubiKey Bio Multi-protocol Edition also supports the PIV protocol, and works with sites and applications that support PIV/SmartCard interfaces. In order to use the biometric feature on the YubiKey Bio Multi-protocol Edition, the YubiKey Smart Card Minidriver (Windows) is required (the Minidriver download is the third item on this page).

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:

  • An explanation of the way the YubiKey Bio works (see How the YubiKey Bio Works) and descriptions of the different user experiences with the various protocols (see User Experiences).
  • Full instructions for enrolling fingerprints using platform support:
    • Using Chrome to Enroll Fingerprints and
    • Using Windows to Enroll Fingerprints
  • Brief descriptions of the protocols supported, in:
    • YubiKey Bio and FIDO2 and
    • YubiKey Bio and FIDO U2F
  • A brief explanation of the role the Yubico Authenticator plays in managing the YubiKey Bio.

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

Interfaces

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

Note

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

Applications

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

Instructions on how to configure and use the YubiKey 5 in compliance with CSPN (“Certificat de Sécurité de Premier Niveau” [RD1]) are given in YubiKey 5 CSPN Series Specifics.

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

References

CodeDocument titleReference (Link)
[RD1]

Certification de sécurité

de premier niveau des

technologies de l’information

https://cyber.gouv.fr/produits-certifies/yubikey-5-series-version-firmware-542
[RD2]

Certification Report

BSI-DSZ-CC-0879-V4-2020

https://www.bsi.bund.de/SharedDocs/Zertifikate_CC/CC/SmartCards_IC_Cryptolib/0879_0879V2_0879V3_0879V4_0879V5.html
[RD3]FIDO2: WebAuthn & CTAPhttps://fidoalliance.org/fido2/
[RD4]

NIST Special Publication

800-73 (PIV)

https://csrc.nist.gov/publications/detail/sp/800-73/4/final
[RD5]

RFC 4226, An HMAC-Based One-

Time Password Algorithm

https://tools.ietf.org/html/rfc4226
[RD6]

T/Key: Second-Factor

Authentication From Secure

Hash Chains

https://arxiv.org/pdf/1708.08424.pdf
[RD7]

Universal 2nd Factor (U2F)

Overview

https://fidoalliance.org/specs/fido-u2f-v1.2-ps-20170411/fido-u2f-overview-v1.2-ps-20170411.html
[RD8]W3C WebAuthn standardhttps://www.w3.org/TR/webauthn-2/
[RD9]YubiKey CSPN security targethttps://cyber.gouv.fr/produits-certifies/yubikey-5-series-version-firmware-542

Firmware

For a summary overview of the firmware features, see Firmware Overview, which includes the capability matrices, listing the features and form factors available per firmware version for each of the products in the YubiKey 5 Series and the Security Key Series.

For more in-depth information about:

  • the most recent firmware release, see 5.7 Firmware Specifics.
  • the firmware prior to the current release, see Firmware Specifics Prior to 5.6.x

Note

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

The firmware version on a YubiKey or a Security Key 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 either the Yubico Authenticator or the YubiKey Manager tool (ykman), a lightweight software package installable on many OS. The YubiKey Manager has both a graphical user interface (GUI) and a command line interface (CLI). For more information, see the .

NIST: FIPS

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. For more information about the YubiKey 5 FIPS Series, see YubiKey 5 FIPS Series Specifics.

ANSI: CSPN

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

Form Factor

Capability

Security Key Series

5.0.x-5.4.x

Security Key Series

- Enterprise Edition

5.4.x

Security Key Series

5.7.x

Security Key Series

- Enterprise Edition

5.7.x

Serial NumberNoYesNoYes

Serial Number

over CCID

NoNoNoYes

PIN Complexity

NoNoNoYes

Serial Number over CCID

The serial number of the Yubico Security Key is retrievable without Windows elevated privileges since the YubiKey Management Application is exposed over CCID. This change was introduced in 5.7.0.

Video Tutorial

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