Asynchronous Remote Key Generation and its Applications in W3C WebAuthn and FIDO
Creators: name: Frymann, Nick
Publisher: name: University of Surrey
Year: 2025
Subjects: Authentication
Cybersecurity
Internet or World Wide Web (WWW)

description: WebAuthn, forming part of FIDO2, is a W3C standard for strong authentication,
description: which employs digital signatures to authenticate web users whilst preserving their
description: privacy. Owned by users, WebAuthn authenticators generate attested and unlinkable
description: public-key credentials for each web service to authenticate users. Since the
description: loss of authenticators prevents users from accessing web services, usable recovery
description: solutions preserving the original WebAuthn design choices and security objectives
description: are urgently needed. Additionally, there exist challenges when the account
description: owner wants to delegate certain rights to a proxy user, such as to access their
description: accounts or perform actions on their behalf, as delegation must not undermine the
description: decentralisation, unlinkability, and attestation properties provided by WebAuthn.
description: With recent proposals to provide security in a post-quantum web, it is clear that
description: any solutions should also be future-proofed.
description: To address these issues, we introduce a new primitive, called Asynchronous Remote
description: Key Generation (ARKG), which allows some primary authenticator to generate
description: unlinkable public keys for which the backup authenticator may later recover
description: corresponding private keys. Both processes occur asynchronously without the need for
description: authenticators to export or share secrets, adhering to WebAuthn’s attestation
description: requirements. Our construction satisfies ARKG’s security properties under the discrete
description: logarithm and PRF-ODH assumptions in the random oracle model.
description: We use ARKG to provide a potential solution to account recovery in WebAuthn
description: for hardware authenticators. We then continue by presenting two approaches to
description: tackling delegation, called remote and direct, maintaining the standard’s properties.
description: Both of which also make use of ARKG, with the direct version making use of a new
description: primitive providing a delegation-by-warrant approach called Proxy Signature with
description: Unlinkable Warrants (PSUW)—which we use to extend WebAuthn’s unlinkability
description: property to proxy users and show it can be constructed generically from ARKG.
description: For all three issues and corresponding solutions, we discuss their individual
description: implementation and compatibility with WebAuthn, including extensions required
description: for CTAP, and provide sample instantiations alongside performance metrics and
description: discussion on key management and usability.
description: For post-quantum ARKG, we address challenges associated with the noisiness of
description: lattice hardness assumptions, whilst preserving the security and privacy
description: properties of the former instantiation. Our ARKG construction uses key encapsulation
description: techniques by Brendel et al. [5] (SAC 2020) coined Split KEMs.