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Clarify ad URL k-anonymity requirements #362

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Nov 17, 2022
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@@ -128,7 +126,7 @@ The `adComponents` field contains the various ad components (or "products") that
All fields that accept arbitrary metadata objects (`userBiddingSignals` and `metadata` field of ads) must be JSON-serializable.
All fields that specify URLs for loading scripts or JSON (`biddingLogicUrl`, `biddingWasmHelperUrl`, and `trustedBiddingSignalsUrl`) must point to URLs whose responses include the HTTP response header `X-Allow-FLEDGE: true` to ensure they are allowed to be used for loading FLEDGE resources.

The browser will provide protection against microtargeting, by only rendering an ad if the same rendering URL is being shown to a sufficiently large number of people (e.g. at least 100 people would have seen the ad, if it were allowed to show). As discussed in the [Outcome-Based TURTLEDOVE](https://github.com/WICG/turtledove/blob/master/OUTCOME_BASED.md) proposal, this threshold applies only to the rendered creative; all of the metadata associated with ad bidding is not under any such restriction. Since a single interest group can carry multiple possible ads that it might show, the group will have an opportunity to re-bid another one of its ads to act as a "fallback ad" any time its most-preferred choice is below threshold. This means that a small, specialized interest group that is still below the daily-update threshold could still choose to participate in auctions, bidding with a more-generic ad until the group becomes large enough.
The browser will provide protection against microtargeting, by only rendering an ad if the same rendering URL is being shown to a sufficiently large number of people (e.g. at least 100 people would have seen the ad, if it were allowed to show). While in the [Outcome-Based TURTLEDOVE](https://github.com/WICG/turtledove/blob/master/OUTCOME_BASED.md) proposal this threshold applied only to the rendered creative, FLEDGE has the additional requirement that the tuple of the interest group owner, bidding script URL, and rendered creative must be k-anonymous for an ad to be shown (this is necessary to ensure the current event-level reporting for interest group win reporting is sufficiently private). For interest groups that have component ads, all of the component ads must also separately meet this threshold for the ad to be shown. Since a single interest group can carry multiple possible ads that it might show, the group will have an opportunity to re-bid another one of its ads to act as a "fallback ad" any time its most-preferred choice is below threshold. This means that a small, specialized interest group that is still below the daily-update threshold could still choose to participate in auctions, bidding with a more-generic ad until the group becomes large enough.
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While reading the change, I noticed that this preexisting sentence doesn't parse very well: "Since a single interest group can carry multiple possible ads that it might show, the group will have an opportunity to re-bid another one of its ads to act as a "fallback ad" any time its most-preferred choice is below threshold."

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If/when the proposed size changes go through it will be the tuple of the interest group owner, bidding script URL, rendered creative and creative size (however this is expressed)?

By bidding script URL here you mean the biddingLogicUrl?

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@stguav, this PR doesn't modify that sentence. Feel free to propose a PR to reword that sentence.

@dmdabbs, I believe you are correct in both cases.

@JensenPaul JensenPaul merged commit cb62c57 into WICG:main Nov 17, 2022
github-actions bot added a commit that referenced this pull request Nov 17, 2022
SHA: cb62c57
Reason: push, by JensenPaul

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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4 participants