Trusted Key Value Server v2 protocol is available in Chrome

[peiwenhu]

The Key Value Service (TKV) V2 protocol is available in Chrome Stable for on-device Protected Audiences auctions. We recommend testing the V2 protocol for existing developers who've deployed BYOS and expect key-value to be part of their long-term PA design. This is an optional, early-access opportunity for developers.

This enhanced protocol replaces the plaintext HTTPS communication of the existing "Bring Your Own Server" (BYOS) model with encryption, significantly improving user privacy. This is a key step in our journey to transition from BYOS to a privacy-advancing, TEE-based key-value service.

Key benefits of the new protocol:

• Enhanced Privacy: Encryption ensures that sensitive user data remains protected.
• Future-looking: Gives adopters the opportunity to begin migrating to TEE-based key-value services before they're required.

Adtechs are encouraged to evaluate TKV during this phase to:

• Familiarize themselves with the technology: Gain experience with this new solution for providing real time signals for Protected Audience auctions.
• Provide feedback: Contribute to the direction of TKV by offering insights and suggestions.
• Prepare for future changes: Ensure a smooth transition from BYOS.

To start using the feature, follow the steps below:

1. Onboard and deploy a TEE KV server.
2. Users can set up flags and configurations to enable the feature via the command line:

chrome --enable-privacy-sandbox-ads-apis --enable-features=FledgeTrustedSignalsKVv2Support --disable-features=EnforcePrivacySandboxAttestations,FledgeEnforceKAnonymity

3. Once Chrome has started, users can check if the feature is enabled within the context of a web page by running the following code:

navigator.protectedAudience && navigator.protectedAudience.queryFeatureSupport(
    "trustedSignalsKVv2")

4. For buyers to use this feature to fetch real-time bidding signals, set 'trustedBiddingSignalsURL' and trustedBiddingSignalsCoordinator fields when joining interest groups. For example:

const myGroup = {
  'owner': 'https://www.example-dsp.com',
  'name': 'womens-running-shoes'
  ...
  'trustedBiddingSignalsURL': ...,
  'trustedBiddingSignalsCoordinator': 'https://www.publickeyservice.com',
  ...
}

5. For sellers to use this feature to fetch real-time scoring signals, set 'trustedScoringSignalsURL' and trustedScoringSignalsCoordinator fields in auction configuration. For example:

const myAuctionConfig = {
  'seller': 'https://www.example-ssp.com',
  'decisionLogicURL': ...,
  ...
  'trustedScoringSignalsURL': ...,
  'trustedScoringSignalsCoordinator': 'https://www.publickeyservice.com',
  ...
}

6. There are two default coordinator endpoints which can be applied to 'trustedBiddingSignalsCoordinator' and 'trustedScoringSignalsCoordinator':
   1. GCP: https://publickeyservice.pa.gcp.privacysandboxservices.com
   2. AWS: https://publickeyservice.pa.aws.privacysandboxservices.com

Please engage and share feedback by replying to this issue or in other ways you prefer.

[dmdabbs]

Thank you for the update/announcement, @peiwenhu.

Just for grins, I configured a coordinator origin on my testbed that uses cross-origin trusted scoring and bidding signals.

While I did not expect the requests to succeed, I did not expect Chrome to issue CORS preflights in both cases...

(the 403 is endpoint's lack of OPTIONS support)

[MattMenke2]

If the TKVv2 server is cross-origin, CORS preflights are still sent, and the seller JS file must include the header to allow requesting cross-origin signals as well, for cross-origin scoring signals ("Ad-Auction-Allow-Trusted-Scoring-Signals-From" - given the CORS error, it looks like that part is already set up correctly). We do intend to safelist the relevant headers, so the CORS preflight will eventually be replaced by just needing Access-Control response headers instead.

[dmdabbs]

We do intend to safelist the relevant headers, so the CORS preflight will eventually be replaced by just needing Access-Control response headers instead.

Got it. Thanks.