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Private Aggregation API: increase contribution limit to 100 for Protected Audience callers

Category
Miscellaneous
Type
New or changed feature
Status
In development (Chrome In development)
Intent stage
None

Summary

Enables Protected Audience script runners to make up to 100 contributions per Private Aggregation report, compared to the current limit of 20. Private Aggregation limits the number of histogram contributions that can be embedded in a single aggregatable report, dropping any additional contributions. Shared Storage callers can work around the limit by invoking another Shared Storage operation. However, Protected Audience callers have no persistent storage, so they lose their excess contributions at the end of their auction. Note that this change is privacy neutral as the API's contributions are still limited by the same privacy budget. Due to padding, each Protected Audience report will have a larger payload, even if it did not need the larger contribution limit. We expect that these larger reports will increase the cost of operating the Aggregation Service. Please reach out with any feedback.

Motivation

Private Aggregation imposes a limit on the number of histogram contributions that can be embedded in a single aggregatable report, with any additional contributions being dropped. Shared Storage callers can work around the limit by invoking another Shared Storage operation. However, Protected Audience callers have no persistent storage, so they lose their excess contributions at the end of each auction.

Standards & signals

Explainers: https://github.com/patcg-individual-drafts/private-aggregation-api/pull/138

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