Cloudflare researchers outline post quantum credentials for the web

Cloudflare researchers discuss a potential post-quantum path for private web credentials, focusing on how MOLE could extend Privacy Pass beyond today’s classical cryptography. Privacy Pass issues unlinkable tokens to users to curb abuse without compromising privacy, but current implementations rely on RSA/ECDSA-style primitives that quantum computers could undermine.

MOLE introduces endorsements that can be redeemed by a moderator without revealing which anchor issued them, enabling private, anchor-hiding credentials suitable for a range of edge-use cases. An anchor set is agreed in advance, and the client proves issuance by one of the anchors without disclosing which one, allowing servers to treat tokens uniformly while maintaining privacy.

The approach is intended to support diverse credential types, including anonymous rate-limited credentials and anonymous credit tokens, in a way that preserves user privacy even as post‑quantum options are adopted.

The post highlights a breakthrough in multivariate cryptography, notably a blind-signature construction called PoMFRIT based on VOLE-in-the-Head and the MAYO/MQ signature family. PoMFRIT achieves token-size footprints around 6.7KB for the blind signature and only a few hundred bytes for issuance, with a variant using UOV dropping the signature to about 4.3KB at the cost of larger public keys (around 46.6KB).

The paper argues these building blocks can be reconfigured to MOLE’s endorsement and credential schemes, with practical runtimes of a few milliseconds per operation in their implementation. The authors caution that cryptanalysis of multivariate schemes is still maturing, advise security proofs and parameter stabilization, and note that while PQ credentials will be larger than current classical ones, they offer a viable path to post‑quantum private web authentication.