Responses inline On Tuesday, December 3, 2024 at 9:03:22 PM UTC-5 Vladimir Levin wrote:
On Mon, Nov 25, 2024 at 9:15 AM 'Orr Bernstein' via blink-dev < blink-dev@chromium.org> wrote: Contact emails o...@google.com, pauljen...@chromium.org, carai...@chromium.org Explainer https://github.com/WICG/turtledove/pull/1322 Specification https://github.com/WICG/turtledove/pull/1313 Summary Additional bids are a feature of the Protected Audience auction that provide buyers with a way to include server-constructed contextual bids in the auction, which allows negative targeting of those bids. We've identified a potential privacy risk with the current implementation, as well as a potential solution that addresses that risk. Additional bids come from buyers, but are transported to the auction by the auction's seller. To prevent replay of additional bids, additional bids rely on an auction nonce — a unique number created by and used by the browser to uniquely identify that auction. However, this introduces a privacy risk, in that all buyers see the same auction nonce, and could use that auction nonce as a key to join distinct bid requests for an auction. This proposal allows sellers to introduce an additional nonce that gets combined with the browser-provided one so that buyers see different combined nonces across bid requests, preventing the joining of bid requests. The combined nonce is generated through a one-way hash (SHA-256) to prevent the construction of a combined nonce that matches a previous combined nonce, which could otherwise be used to facilitate the replay of an additional bid. According to the explainer, the auction nonce (generated by the browser, and given to the seller (?)) is combined with a seller generated nonce to generate a bid nonce that Correct - the seller does receive the auction nonce. When constructing the auction config, the seller creates an auction nonce using the existing navigator.createAuctionNonce() function. The seller can then send this auction nonce as part of the request to their contextual server. buyers see. That's to make sure that buyers can't use the auction nonce to figure out other bids that are happening for the same auction, right? Correct - with this change, the auction nonce is no longer given to bidders, so that it can not be used to join bid-requests together server-side. Then the bid nonce is returned back to the seller. I presume this is to identify which auction the bid is for? Right -- we want to avoid replay attacks, where a bid is entered into an auction for which it wasn’t intended. This is why the original auction nonce mechanism was created, and this new design should preserve this replay attack protection. What I don't understand is that the bid nonce is then returned to the browser, but the browser only knows the auction nonce so wouldn't it have no way to match that with an auction because it doesn't know seller generated nonce for this bid? The seller nonce is also returned to the browser, via the Ad-Auction-Additional-Bid response header <https://github.com/WICG/turtledove/blob/main/FLEDGE.md#63-http-response-headers:~:text=The%20structure%20of,signed%20additional%20bid%3E>. The browser can then calculate <https://github.com/WICG/turtledove/blob/main/FLEDGE.md#61-auction-and-bid-nonces:~:text=The%20seller%20must%20combine,as%20a%20base64%20string.> the bid nonce from the auction nonce and the seller nonce in the same way that the seller did to send the bid nonce to the buyer. Another unrelated question, does this have any separate implications for Trusted Execution Environments? Specifically, does this apply to both or only to "local" auctions? Currently, additional bids aren’t supported for auctions conducted on Bidding and Auction (B&A) services, although such support could be added in the future, under a different I2S. Thanks, Vlad Blink component Blink>InterestGroups <https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3EInterestGroups> TAG review For Protected Audience: https://github.com/w3ctag/design-reviews/issues/723 TAG review status Completed for Protected Audience, resolved unsatisfied. Risks Interoperability and Compatibility Optional new functionality that does not break existing use. Gecko & WebKit: For Protected Audiences in general - Negative from Mozilla <https://github.com/mozilla/standards-positions/issues/770#issuecomment-2432124085>. No signal from Webkit <https://github.com/WebKit/standards-positions/issues/158#issuecomment-2432121278> . Edge: Edge is running an Origin Trial of the Ad Selection API <https://github.com/WICG/privacy-preserving-ads/blob/main/README.md> which shares a Web API and services protocol with Protected Audience. Web developers: Requested by ad tech in GitHub issue #1198 <https://github.com/WICG/turtledove/issues/1198>. Debuggability Ad-Auction-Additional-Bid response headers are visible in the DevTools Network tab, and each can be trivially decoded into an auction nonce, a seller nonce, and a base-64 encoded signed additional bid. Errors encountered while decoding and parsing the signed additional bid are presented in the DevTools console. Additional bids are debuggable via DevTools debugging of Protected Audience scoring scripts. Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)? It will be supported on all platforms that support Protected Audience, so all but WebView. Is this feature fully tested by web-platform-tests <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md> ? Yes <https://chromium-review.googlesource.com/c/chromium/src/+/5979020> Flag name on chrome://flags None Finch feature name FledgeSellerNonce Requires code in //chrome? False Estimated milestones Shipping on desktop and Android in M132. Anticipated spec changes None Link to entry on the Chrome Platform Status https://chromestatus.com/feature/5081571282124800 This intent message was generated by Chrome Platform Status <https://chromestatus.com/>. -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+unsubscr...@chromium.org. To view this discussion visit https://groups.google.com/a/ chromium.org/d/msgid/blink-dev/CANHsO6stZ5OtCo3xy127pz_ 9w7V_NJjx2ZvfzP%2BnJowRC8cmzg%40mail.gmail.com <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CANHsO6stZ5OtCo3xy127pz_9w7V_NJjx2ZvfzP%2BnJowRC8cmzg%40mail.gmail.com?utm_medium=email&utm_source=footer> . -- You received this message because you are subscribed to the Google Groups "blink-dev" group. 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