VPN by Google One security assessment
The actual pentest findings here are pretty boring, but the architecture details are quite interesting, as are the identified risk models for the attempt at "anonymity."The fundamental anonymity model Google have employed is that the VPN tunnel is authenticated using "blind tokens" which are signed by an authorization service "Zinc." The Zinc service validates OAuth credentials passed in from the client app to verify a user's subscription, then signs the blind token created by the client app to authorize the user's session with the actual VPN backend "Copper." Ostensibly, this will separate the user's Google identity from the VPN identity since the VPN service only knows that it got a valid, signed user token, not what user that token belongs to.Ultimately, as pointed out in the report, this is IMHO not that useful. Google could still trivially re-correlate traffic inside of the VPN service by using packet inspection combined with a crafted (or accidental!) plaintext sidechannel from an authenticated Google client application (unencrypted DNS requests to a special subdomain, port/IP knocking style requests to a specific list of IPs in a specific order, etc.).Also, if there's timestamped logging in both the Zinc and Copper services, the attempt at blinding between the two sides of the system is also quite meaningless since the flow to Zinc and the flow to Copper could just be back-correlated back into a user identity using timing by a Google employee with access to logs.