Quantum computers could break web tools that keep you anonymous

Quantum computers could one day defeat a web tool called Privacy Pass, but not in the way the headline might suggest. According to Cloudflare engineers, a future quantum attacker could forge the tokens the tool uses. That attacker still could not tie a token back to you. Your privacy holds up. The sites' defenses are the weak spot.

What Privacy Pass does

Sites need to stop any one visitor from using too many resources. The usual methods cost you something: CAPTCHAs, accounts, or fingerprinting, which means identifying you by your device. Privacy Pass avoids that tradeoff. You get a batch of tokens and hand them over in exchange for access. Each token cannot be linked to the person it was issued to. Cloudflare says it has about 10 years of experience with it, including in iCloud Private Relay and Privacy Gateway.

Where quantum computers come in

Privacy Pass today relies on older math, such as RSA and elliptic curves, that a powerful quantum computer could crack. The authors say such an attacker could make fake tokens at will. That could get around protections like rate limiting. Privacy, though, is described as unconditional. No attacker, quantum or not, can link a token's use to where it was issued. The team says its next-generation tools will keep that promise even after Q-day, the point when such quantum computers arrive.

The size problem

Safer replacements exist, but they are bulky. One post-quantum signature, ML-DSA-44, takes 2,420 bytes. The signature used today, ECDSA-P256, takes 64 bytes. The authors say there is little hope of drop-in replacements soon. Systems will need to be redesigned to carry the extra weight, as with other parts of the move to post-quantum security.

A possible path: MOLE

The post explores one option, called MOLE, short for Moderation Of unLinkable Endorsements. It builds on a recent advance in blind signatures, a way to get something signed without the signer seeing what it signed. In MOLE, a trusted party issues an endorsement. A site redeems it without learning which trusted party issued it. The aim is equal treatment for all kinds of clients, including the automated AI agents Cloudflare wants better tools to manage.

What happens next

The authors say this gives some breathing room, but an alternative will be needed soon. MOLE is presented as one potential future, not a finished product. The material does not say when quantum computers will arrive, or when sites will switch.