WebAuthn: Difference between revisions

The combination of username and password has been the standard mechanism for users to prove to a website that they are a specific person since the dawn of web-based services.<ref>{{Cite book |last1=Bonneau|first1=Joseph|last2=Herley|first2=Cormac|last3=Oorschot|first3=Paul C. van|last4=Stajano|first4=Frank|chapter=The Quest to Replace Passwords: A Framework for Comparative Evaluation of Web Authentication Schemes |date=2012|title=2012 IEEE Symposium on Security and Privacy|pages=553–567|doi=10.1109/SP.2012.44 |bibcode=2012sp...conf...46B |isbn=978-1-4673-1244-8 }}</ref> However, password-based authentication has been known to be flawed for many years, even decades, with most issues relating to poor practices on either the user side or the server side. Users routinely reuse passwords across services (which exposes them to [[credential stuffing]]),<ref>{{Cite book |last1=Wang|first1=Chun|last2=Jan|first2=Steve T.K.|last3=Hu|first3=Hang|last4=Bossart|first4=Douglas|last5=Wang|first5=Gang|title=Proceedings of the Eighth ACM Conference on Data and Application Security and Privacy |chapter=The Next Domino to Fall: Empirical Analysis of User Passwords across Online Services |date=2018-03-13 |language=en|publisher=ACM|pages=196–203|doi=10.1145/3176258.3176332|isbn=978-1-4503-5632-9}}</ref> choose weak passwords that can be brute-forced and predicted in a short amount of time<ref>{{Cite book |last1=Mazurek|first1=Michelle L.|last2=Komanduri|first2=Saranga|last3=Vidas|first3=Timothy|last4=Bauer|first4=Lujo|last5=Christin|first5=Nicolas|last6=Cranor|first6=Lorrie Faith|last7=Kelley|first7=Patrick Gage|last8=Shay|first8=Richard|last9=Ur|first9=Blase|title=Proceedings of the 2013 ACM SIGSAC conference on Computer & communications security - CCS '13 |chapter=Measuring password guessability for an entire university |date=2013 |language=en|publisher=ACM Press|pages=173–186|doi=10.1145/2508859.2516726|isbn=978-1-4503-2477-9}}</ref>, and store them in insecure ways that allows for their disclosure (for example writing them down on a piece of paper or a document),<ref>{{Cite conference|publisher=USENIX Association|isbn=978-1-939133-10-6|pages=13–30|last1=Habib|first1=Hana|last2=Naeini|first2=Pardis Emami|last3=Devlin|first3=Summer|last4=Oates|first4=Maggie|last5=Swoopes|first5=Chelse|last6=Bauer|first6=Lujo|last7=Christin|first7=Nicolas|last8=Cranor|first8=Lorrie Faith|title=User behaviors and attitudes under password expiration policies|location=Baltimore, MD|date=2018|conference=Fourteenth Symposium On Usable Privacy and Security (SOUPS 2018)|book-title=}}</ref> with each of those contributing to the likelihood of credentials and account compromise. Likewise, servers often deal with passwords improperly, both while storing them in [[Database|databases]], and while processing them. Flaws include plain-text storage, lack of [[Salt (cryptography)|salted]] [[Hash (cryptography)|hashing]] (or more advanced schemes for at-rest credentials),<ref>{{Cite web |title=Password Storage - OWASP Cheat Sheet Series |url=https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html |access-date=2026-11-01 |website=cheatsheetseries.owasp.org}}</ref> arbitrary restrictions on password length and [[charset]], mandatory ineffective password changes, and deliberate incompatibility with [[Password manager|password managers]] (for instance, by preventing passwords to be pasted).<ref>{{Cite journal |last1=Lee |first1=Kevin |last2=Sjöberg |first2=Sten |last3=Narayanan |first3=Arvind |date=2022 |title=Password policies of most top websites fail to follow best practices |url=https://www.usenix.org/conference/soups2022/presentation/lee |journal=Soups '22 |language=en |pages=561–580 |isbn=978-1-939133-30-4}}</ref>

As a result, in 2012, [[Google]] alongside [[Yubico]] started working on a standard called [[Universal 2nd Factor|Universal 2 Factor]] (U2F)<ref>{{Cite web |title=Yubico Company Timeline|url=https://www.yubico.com/why-yubico/yubico-innovation-history/|access-date=2026-06-04|website=Yubico|language=en-US}}</ref> that would allow websites to programmatically verify a second-factor about the user by verifying the presence of hardware-based tokens (like [[smart card]]s) on the user. This standard was considered an improvement over existing solutions like time-based [[one-time password]] ([[TOTP - Time-based One-time Password Algorithm|TOTP]]) or SMS-based authentication that still left the user vulnerable to sophisticated [[phishing]] campaigns. The standard was later adopted into a larger industry-wide collaboration called the [[FIDO Alliance|FIDO (Fast IDentity Online) Alliance]]. The first draft for this proposed standard was published in 2014.<ref>{{Cite web |date=2014-12-09|title=FIDO Alliance Publishes Final FIDO 1.0 Specifications, First Industry Standards for Universal Strong Authentication|url=https://www.yubico.com/press-releases/fido-alliance-publishes-final-fido-1-0-specifications-first-industry-standards-for-universal-strong-authentication/|access-date=2026-06-04|website=Yubico|language=en-US}}</ref> In 2015, the FIDO Alliance started developing the [[FIDO2 Project|FIDO 2 Project]], releasing a proposed standard where they sought to improve upon the existing U2F standard by addressing many of its weaknesses.<ref>{{Cite web |date=2015-09-04|title=FIDO Complete Spec 2015-09-04|url=https://fidoalliance.org/specs/fido-v2.0-ps-20150904/FIDO-COMPLETE-v2.0-ps-20150904.pdf|access-date=5 June 2026|website=Fido Alliance}}</ref> For example, the U2F standard still required the use of passwords alongside a second factor which still left websites vulnerable to password leaks and other similar attacks that were common against passwords.<ref name=":0">{{Cite book |last1=Ghorbani Lyastani|first1=Sanam|last2=Schilling|first2=Michael|last3=Neumayr|first3=Michaela|last4=Backes|first4=Michael|last5=Bugiel|first5=Sven|title=2020 IEEE Symposium on Security and Privacy (SP) |chapter=Is FIDO2 the Kingslayer of User Authentication? A Comparative Usability Study of FIDO2 Passwordless Authentication |date=May 2020 |publisher=IEEE|pages=268–285|doi=10.1109/SP40000.2020.00047|bibcode=2020sp...conf...24G |isbn=978-1-7281-3497-0}}</ref> Additionally, the U2F specification only verified the second factor device and did not perform any user authentication.<ref name=":0" /> This meant that if the second factor device had been stolen or lost anyone with access to the U2F device would be able to bypass the second factor of authentication for accounts linked to the device.<ref name=":0" />

''Passkey'' is the [[de facto]] [[Technical language|non-technical]] term for a saved sign-in credential, a piece of [[cryptographic]] information that is capable of being used to authenticate a user using the WebAuthn standard.<ref name="docsrs-webauthnrs"/><ref name="imperialviolet-webauthn"/> Most user interfaces that support using WebAuthn refer to it as supporting ''passkeys''.<ref name="arstechnica-not-usable"/>

Due to the open-ended nature of the WebAuthn specification, a passkey can be stored on software or hardware that is capable of authenticating a user. This includes technology like [[Windows Hello]] which works by using facial recognition to authenticate users,<ref>{{Cite web |last=|title=Support for Passkeys in Windows|url=https://learn.microsoft.com/en-us/windows/security/identity-protection/passkeys/|access-date=2026-06-06|website=learn.microsoft.com|language=en-us}}</ref><ref>{{Cite web |title=Configure Windows Hello - Microsoft Support|url=https://support.microsoft.com/en-us/windows/configure-windows-hello-dae28983-8242-bb2a-d3d1-87c9d265a5f0|access-date=2026-06-06|website=support.microsoft.com}}</ref> [[Bitwarden]] which authenticates users through a [[browser extension]]<ref>{{Cite web |title=Log In With Passkeys|url=https://bitwarden.com/help/login-with-passkeys/|access-date=2026-06-06|website=Bitwarden|language=en}}</ref> or [[YubiKey]]s that allow a user to authenticate using a physical hardware token.<ref>{{Cite web |last=|first=|last2=|title=Stop changing weak passwords. Start replacing them with passkeys|url=https://www.pcworld.com/article/2591499/stop-changing-weak-passwords-start-replacing-them-with-passkeys.html|access-date=2026-06-06|website=PCWorld|language=en}}</ref> The cryptographic keys stored by the software are only available to use for the browser once the software or hardware has authenticated the user.<ref name="arstechnica-not-usable"/>

When Apple first prominently introduced passkeys to the public in 2022,<ref>{{cite news |last1=Clemons|first1=Taylor|title=WWDC 2022: Apple announces Passkey feature to eliminate passwords across platforms|url=https://www.zdnet.com/article/wwdc-2022-apple-announces-passkey-feature/|access-date=4 July 2025|publisher=ZD Net|date=6 June 2022|archive-date=6 June 2023|archive-url=https://web.archive.org/web/20230606212207/https://www.zdnet.com/article/wwdc-2022-apple-announces-passkey-feature/|url-status=live}}</ref> they emphasized integrations with their own products. This, combined with the lack of clear communication from other companies, led to speculation that passkeys were proprietary to Apple.<ref>{{cite news |last1=Shakir|first1=Umar|title=Reminder: passkeys are not just from Apple|url=https://www.theverge.com/2022/8/5/23293643/apple-passkeys-fido-alliance-passwordless-google-microsoft|access-date=4 July 2025|publisher=The Verge|date=6 August 2022|archive-date=24 September 2023|archive-url=https://web.archive.org/web/20230924231545/https://www.theverge.com/2022/8/5/23293643/apple-passkeys-fido-alliance-passwordless-google-microsoft|url-status=live}}</ref> As browsers and websites began to implement WebAuthn, the inconsistent feature-sets have often resulted in a variety of understandings of what exactly counted as a passkey.<ref name="arstechnica-not-usable"/>

The WebAuthn standard provides a mechanism for a device or a program, known as the "authenticator") to verify a user's identity to a website through their web browser by confirming that the user possesses the device.<ref name="W3C-WebAuthn-Level-1" /> To do this in a secure manner, the standard defines two events, the registration ceremony and the authentication ceremony. During these events the authenticator communicates with the website through the web browser to register itself as a device the user possesses and proves to the website that the user still possesses the device respectively.<ref name="W3C-WebAuthn-Level-1" />

Authenticator is a multi-factor [[Cryptography|cryptographic]] authenticator that uses [[Cryptography#Public-key cryptography|public-key cryptography]] to sign an authentication assertion targeted at the website. Assuming the authenticator uses either a [[Facial recognition system|facial recognition]], fingerprint or PIN for user verification, the authenticator itself is ''something you have'' while the facial recognition and fingerprint (biometric) are ''something you are'' and the PIN is ''something you know''.

To initiate the authentication flow, the website indicates its intentions to the web browser via [[JavaScript]].<ref name="Web_Authentication_API-1">{{cite web |url=https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API |title=Web Authentication API |at=Section [https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API#Authentication Authentication] |publisher=[[Mozilla]] |access-date=18 March 2019 |archive-date=28 November 2020 |archive-url=https://web.archive.org/web/20201128172824/https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API |url-status=live }}</ref> The web browser communicates with the authenticator using a JavaScript [[API]] implemented in the browser.<ref name="Web_Authentication_API-1" /><ref name="W3C-WebAuthn-Level-1" /> A hardware authenticator in the user's possession  conforms to the FIDO [[Client to Authenticator Protocol]] (CTAP),<ref name="FIDO-CTAP">{{cite web |editor1-last=Brand |editor1-first=Christiaan |editor2-last=Czeskis |editor2-first=Alexei |editor3-last=Ehrensvärd |editor3-first=Jakob |editor4-last=Jones |editor4-first=Michael B. |editor5-last=Kumar |editor5-first=Akshay |editor6-last=Lindemann |editor6-first=Rolf |editor7-last=Powers |editor7-first=Adam |editor8-last=Verrept |editor8-first=Johan |title=Client to Authenticator Protocol (CTAP) |url=https://fidoalliance.org/specs/fido-v2.0-ps-20190130-pub/fido-client-to-authenticator-protocol-v2.0-ps-20190130.html |publisher=FIDO Alliance |access-date=7 March 2019 |date=30 January 2019 |archive-date=8 March 2019 |archive-url=https://web.archive.org/web/20190308081859/https://fidoalliance.org/specs/fido-v2.0-ps-20190130-pub/fido-client-to-authenticator-protocol-v2.0-ps-20190130.html |url-status=dead }}</ref> and connects over [[USB]], [[Bluetooth Low Energy]], or [[near-field communications]] (NFC). WebAuthn however does not strictly require a hardware authenticator. A platform authenticator (i.e., an authenticator implemented directly on the web browser or operating system) can  be used.<ref>{{Cite journal |last1=Vasileios Grammatopoulos |first1=Athanasios |last2=Politis |first2=Ilias |last3=Xenakis |first3=Christos |date=2021-08-17 |title=A web tool for analyzing FIDO2/WebAuthn Requests and Responses |url=https://dl.acm.org/doi/10.1145/3465481.3469209 |journal=Proceedings of the 16th International Conference on Availability, Reliability and Security |language=en |publisher=ACM |pages=1–10 |doi=10.1145/3465481.3469209 |isbn=978-1-4503-9051-4}}</ref> If the user has registered their keys on a different device the WebAuthn 3 specification allows for the web browser to access credentials stored on another device without having to copy over the keys to the current device.  

===Registration===

When the website receives the signed authentication assertion from the browser, the digital signature on the assertion is verified using a trusted public key for the user.

To obtain a public key for the user, the website initiates a WebAuthn registration flow<ref>{{cite web |url=https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API |title=Web Authentication API |at=Section [https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API#Registration Registration] |publisher=[[Mozilla]] |access-date=18 March 2019 |archive-date=28 November 2020 |archive-url=https://web.archive.org/web/20201128172824/https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API |url-status=live }}</ref> that is similar to the authentication flow illustrated above. The primary difference is that the authenticator now signs an attestation statement with its attestation private key. The signed attestation statement contains a copy of the public key that the website ultimately uses to verify a signed authentication assertion. The attestation certificate contains metadata describing the authenticator itself.<ref>{{Cite web |date=2025-05-28 |title=Attestation and Assertion - Web APIs |url=https://developer.mozilla.org/en-US/docs/Web/API/Web_Authentication_API/Attestation_and_Assertion |access-date=2025-09-20 |website=[[MDN Web Docs]] |language=en-US}}</ref>

The digital signature on the attestation statement is verified with the trusted attestation public key for that particular model of authenticator. How the website obtains its store of trusted attestation public keys is unspecified. One option is to use the FIDO metadata service.<ref>{{cite web |title=Metadata Service |date=15 September 2015 |url=https://fidoalliance.org/metadata/ |publisher=[[FIDO Alliance]] |access-date=18 March 2019}}</ref>

The attestation type specified in the JavaScript determines the trust model. For instance, an attestation type called self-attestation may be desired, for which the trust model is essentially [[trust on first use]].

=== Level 3 ===

WebAuthn Level 3 introduces several capabilities beyond authentication alone. The PRF (Pseudo-Random Function) extension allows a passkey to derive encryption keys, enabling it to help protect encrypted data such as backups without a separate password.<ref name="enpass-webauthn3">{{Cite web |title=What Is WebAuthn Level 3 & How Does Enpass Support It? |url=https://www.enpass.io/blog/security/what-is-webauthn-level-3-how-does-enpass-support-it/ |publisher=Enpass |date=23 July 2026 |access-date=20 August 2026}}</ref> Related Origin Requests (ROR) let a single passkey be used across multiple domains belonging to the same organization, reducing the need for duplicate credentials.<ref name="enpass-webauthn3" /> The specification also added a section addressing the privacy implications of using WebAuthn credentials across origins, including risks associated with cross-origin iframes.<ref>{{Cite web |title=[L3 REC] Transition Request Draft |url=https://github.com/w3c/webauthn/issues/2399 |publisher=GitHub |website=w3c/webauthn |access-date=20 August 2026}}</ref>

One of the first FIDO2-compatible [[authenticator]]s was the second-generation [[YubiKey|Security Key]] by Yubico, announced on 10 April 2018.<ref>{{cite press release |url=https://www.yubico.com/press-releases/280530/ |title=Yubico Launches New Developer Program and Security Key for FIDO2 and WebAuthn W3C Specifications |date=2018-04-10 |access-date=2018-05-11 |archive-date=7 May 2018 |archive-url=https://web.archive.org/web/20180507085439/https://www.yubico.com/press-releases/280530/ |url-status=live }}</ref> The first FIDO2-compatible authenticator with a display was Trezor Model T by SatoshiLabs, announced on 6 November 2019.<ref>{{cite web |url=https://medium.com/trezor-security-blog/make-passwords-a-thing-of-the-past-a402745750dc |title=Make Passwords a Thing of the Past, FIDO2 Is Now Available on Trezor Model T |date=2019-11-06 |access-date=2019-11-06}}</ref> Trezor Model T was also the first authenticator that allowed users to select which FIDO2 resident credential should be used directly on a device.