Introductions to the Different YubiKey Series
Throughout the YubiKey Technical Manual different YubiKeys will be referred to as e.g. “YubiKey 5 (FIPS/CSPN) Series”, indicating that a certain specification or feature is available on the YubiKey 5 Series, the YubiKey 5 FIPS Series and the YubiKey 5 CSPN Series, due to the fact that they share the same base hardware and many firmware features.
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 will be Understanding the USB Interfaces, which 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 to 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 US 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 to go through an exhaustive validation process, which commonly takes a year or more. Yubico can release standard firmware with new features, enhancements, etc. at any time, whereas FIPS-certified products must go through 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 secure element 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 can be utilized via 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 you have:
|Yubico One Time Password (OTP)||yes||yes|
|OATH OTP authentication||yes||yes|
|OpenPGP (version 3.4)||yes|
|PIV-compatible smart card||yes||yes|
|FIDO Universal 2nd Factor (U2F)||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 set out in detail in the following.
FIPS-specific Aspects of the YubiKey 5 FIPS Series
Distinguishing the YubiKey 5 FIPS Series from the YubiKey 5 Series with the 5.4 firmware are the following configuration changes, set at programming:
Enforce power-up self-test (firmware integrity and
Minimum PIN length
|6 alphanumeric characters|
Unique AAGUIDs for the FIDO Attestation
(see AAGUID Values)
Attestation certificates for FIDO include
a FIPS OID (18.104.22.168.4.1.41482.12)
Command returns a listing of FIPS, as well as the
FIPS-specific OIDs in the PIV and FIDO attestation
Attestation certificates for PIV include
the FIPS Form Factor identifier** in the
Form Factor OID (22.214.171.124.4.1.41482.3.9)
|YubiKey Manager||Form factor identifies FIPS Series devices.**|
* 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.
** Form factor is set during manufacturing and returned as a one-byte value. Currently defined values for this are:
|Form Factor||Standard YubiKey Value||Security Key Value (FW 5.4+)||FIPS YubiKey Value (FW 5.4+)|
|Keychain with USB-A||0x01||0x41||0x81|
|Nano with USB-A||0x02||N/A||0x82|
|Keychain with USB-C||0x03||0x43||0x83|
|Nano with USB-C||0x04||N/A||0x84|
|Keychain with Lightning and USB-C||0x05||N/A||0x85|
The YubiKey firmware is separate from the YubiKey itself in the sense that it is put onto each YubiKey in a process separate from the manufacture of the physical key. Nonetheless, it can be neither removed nor altered. Yubico periodically updates the YubiKey firmware to take advantage of features and capabilities introduced into operating systems such as Windows, MacOS, and Ubuntu, etc., as well as to enable new YubiKey features.
The firmware version on a YubiKey or an HSM therefore 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).
- Download the YubiKey Manager tool: https://www.yubico.com/products/services-software/download/yubikey-manager/
- YubiKey Manager (ykman) CLI & GUI Guide
Yubico has submitted the same firmware - releases 5.4.2 and 5.4.3 - to NIST and it has submitted release 5.4.2 to ANSSI for certification. Both organizations have approved certification.
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.
However, the Security Key Series - Enterprise Edition is the same as a Security Key Series but with a serial number to allow for asset tracking. The serial number can be read visually on the back of the key and programatically 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)
Both keys in the YubiKey Bio Series support the FIDO authentication protocols, and will 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 which enables the replacement of password-based authentication.
The YubiKey Bio Series provides firmware applications to support two modes of authentication via 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 will reset both applications (to manage these applications, see Troubleshooting and Tools).
Using the YubiKey Bio
To just start using the keys in the YubiKey Bio Series without going into any details, refer to Yubico’s setup page, which functions as a quick start guide.
The current guide, however, gives:
- An explanation of the way the YubiKey Bio works and descriptions of the different user experiences with the various protocols
- Full instructions for enrolling fingerprints using platform support:
- 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 for Desktop plays in managing the YubiKey Bio, plus links for downloading it and to its documentation.
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 will also work with the YubiKey Bio; however, the UI on client devices will not be as intuitive, and there may be some limitations.
Interfaces and Applications
Like all other YubiKeys, the YubiKey Bio Series are USB 2.0 devices.
Developers: The USB PID and iProduct string are
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 sometimes referred to as WebAuthn) is also 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 Tools.
YubiKey 5 CSPN Series
The aim of this document is to describe how to configure and use the YubiKey 5 in a mode such that it is compliant with CSPN (“Certificat de Sécurité de Premier Niveau” [RD1]).
For each YubiKey application which will require specific configuration, there will be a short introduction, followed by the required settings to achieve the target, and finally, a technical description of the configuration itself.
|AES||Advanced Encryption Standard|
|BSI||Bundesamt für Sicherheit in der Informationstechnik|
|CCID||Chip Card Interface Device|
|CSPN||Certificat de Sécurité de Premier Niveau|
|CTAP2||Client to Authenticator Protocol v2|
|DES||Data Encryption Standard|
|FIDO||Fast Identity Online|
|HMAC||Hash-Based Message Authentication Code|
|HOTP||HMAC-Based One Time Password|
|NIST||National Institute of Standards and Technology|
|OTP||One Time Password|
|PIV||Personal Identity Verification|
|PBKDF2||Password Based Key Derivation Function|
|PIN||Personal Identification Number|
|PIV||Personal Identity Verification|
|PUK||PIN Unblocking Key|
|SHA||Secure Hash Algorithm|
|TOTP||Time-Based One Time Password|
|U2F||Universal Second Factor|
|RFC||Request For Comments|
|W3C||World Wide Web Consortium|
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