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They have similar objectives but achieve them differently. Roughly, Private Click Measurement uses very low entropy identifiers to achieve rough of clicks and c

They have similar objectives but achieve them differently. Roughly, Private Click Measurement uses very low entropy identifiers to achieve rough of clicks and conversions. IPA uses multiparty computation instead. Probably the most salient differences are: PCM leaks some information about user behavior, but it has a high degree of uncertainty due to the structure of the reporting. So, you might be able to say that there is an X% chance someone saw this ad. IPA is intended only to reveal aggregate information. The price of this is (1) computational complexity and (2) that you have to have some level of trust in the aggregators (e.g., you trust that they don't collude). PCM doesn't work in cases where the click and the conversion (purchase) happen on different devices (e.g., a phone and a laptop). IPA potentially does. Ben Savage's slides cover this in more detail: https://github.com/patcg/meetings/blob/main/2022/02/09-telecon/IPA%20design%20considerations%20-%20PAT-CG%20preso.pdf https://github.com/patcg/meetings/blob/main/2022/02/09-telec...

olliej 5y ago
The slides imply cross device/browser identification? I can't see how that happens without some kind of shared account mechanism. The slides imply that losing cross device attribution is a regression. It absolutely is not, as such ability does not currently exist. So this While I recognize the advertisers may want attribution, but it still seems like FB+Google both still want to know as much about the user as possible, and both definitely have the resources to achieve the de-anonymising attacks (especially given chrome's ever present attempts to get people to tie their entire browsing session to their google identity).
- ekr____ 5y ago
  You're right that this assumes an account. The way that cross device/browser identification works in IPA is that if you are logged into example.com (though realistically, often Facebook) then it can set a "match key" which is the same on device and browser. You can't read the match key, only write it. This match key is used to link up activities on both. The point of the crypto is to rerandomize the match key that appears in the reports so that it is possible two see that two actions are from the same device but not link that back up to the original match key. Note that in this proposal, the assumption is that anyone would be able to use anyone else's match key (addressed by origin) so that it's not a big advantage to be the site with the account. Re whether this is a regression or not: I am not an expert on how the current attribution mechanism works but I believe that if people are logged into (for instance) Facebook then Facebook can use that to correlate clicks on device A with purchases on device B.
  - olliej 5y ago
    Except in browser's like Brave and Safari that actively work to break that kind of tracking - this feature essentially appears to mandate it.
    - deleted 5y ago
      [deleted]

olliej 5y ago

The slides imply cross device/browser identification? I can't see how that happens without some kind of shared account mechanism. The slides imply that losing cross device attribution is a regression. It absolutely is not, as such ability does not currently exist. So this While I recognize the advertisers may want attribution, but it still seems like FB+Google both still want to know as much about the user as possible, and both definitely have the resources to achieve the de-anonymising attacks (especially given chrome's ever present attempts to get people to tie their entire browsing session to their google identity).

ekr____ 5y ago
You're right that this assumes an account. The way that cross device/browser identification works in IPA is that if you are logged into example.com (though realistically, often Facebook) then it can set a "match key" which is the same on device and browser. You can't read the match key, only write it. This match key is used to link up activities on both. The point of the crypto is to rerandomize the match key that appears in the reports so that it is possible two see that two actions are from the same device but not link that back up to the original match key. Note that in this proposal, the assumption is that anyone would be able to use anyone else's match key (addressed by origin) so that it's not a big advantage to be the site with the account. Re whether this is a regression or not: I am not an expert on how the current attribution mechanism works but I believe that if people are logged into (for instance) Facebook then Facebook can use that to correlate clicks on device A with purchases on device B.
- olliej 5y ago
  Except in browser's like Brave and Safari that actively work to break that kind of tracking - this feature essentially appears to mandate it.
  - deleted 5y ago
    [deleted]