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<pre class='metadata'>
Title: Private Aggregation API
Shortname: private-aggregation-api
Level: 1
Status: UD
Group: patcg-id
Repository: patcg-individual-drafts/private-aggregation-api
URL: https://patcg-individual-drafts.github.io/private-aggregation-api
Editor: Alexander Turner, Google https://www.google.com, [email protected]
Abstract: A generic API for measuring aggregate, cross-site data in a privacy
preserving manner. The potentially identifying cross-site data is
encapsulated into <em>aggregatable reports</em>. To prevent leakage, this
data is encrypted, ensuring it can only be processed by an <em>aggregation
service</em>. During processing, this service will add noise and impose
limits on how many queries can be performed.
Markup Shorthands: markdown on
Complain About: accidental-2119 on, missing-example-ids on
Assume Explicit For: on
</pre>
<pre class="anchors">
urlPrefix: https://wicg.github.io/turtledove/; type: interface
text: InterestGroupBiddingScriptRunnerGlobalScope
text: InterestGroupScriptRunnerGlobalScope
text: InterestGroupScoringScriptRunnerGlobalScope
text: InterestGroupReportingScriptRunnerGlobalScope
urlPrefix: https://wicg.github.io/shared-storage/; type: interface
text: SharedStorageWorklet
text: SharedStorageWorkletGlobalScope
spec: hr-time; type: dfn; urlPrefix: https://w3c.github.io/hr-time/
text: current wall time; url: #dfn-current-wall-time
text: duration; url: #dfn-duration
text: duration from; url: #dfn-duration-from
text: moment; url: #dfn-moment
text: unix epoch; url: #dfn-unix-epoch
text: wall clock; url: #dfn-wall-clock
spec: html; type: dfn; urlPrefix: https://tc39.es/ecma262/
text: call; url: sec-call
spec: webdriver; urlPrefix: https://w3c.github.io/webdriver/
type: dfn
text: getting a property; url: dfn-getting-properties
text: error code; url: dfn-error-code
</pre>
<pre class=link-defaults>
spec:infra; type:dfn; text:user agent
spec:webidl; type:dfn; text:attribute
</pre>
Introduction {#intro}
=====================
<em>This section is non-normative.</em>
Motivation {#motivation}
------------------------
Browsers are now working to prevent cross-site user tracking, including by
partitioning storage and removing third-party cookies. There are a range of API
proposals to continue supporting legitimate use cases in a way that respects
user privacy. Many of these APIs, including the
<a href="https://wicg.github.io/shared-storage/">Shared Storage API</a> and the
<a href="https://wicg.github.io/turtledove/">Protected Audience API</a>, isolate
potentially identifying cross-site data in special contexts, which ensures that
the data cannot escape the user agent.
Relative to cross-site data from an individual user, aggregate data about groups
of users can be less sensitive and yet would be sufficient for a wide range of
use cases. An aggregation service has been built to allow reporting noisy,
aggregated cross-site data. This service was originally created for use by the
<a href="https://wicg.github.io/attribution-reporting-api/">Attribution
Reporting API</a>, but allowing more general aggregation supports additional use
cases. In particular, the Protected Audience and Shared Storage APIs expect this
functionality to be available.
Overview {#overview}
--------------------
This document oulines a general-purpose API that can be called from isolated
contexts that have access to cross-site data (such as a Shared Storage worklet).
Within these contexts, potentially identifying data can be encapsulated into
"aggregatable reports". To prevent leakage, the cross-site data in these reports
is encrypted to ensure it can only be processed by the aggregation service.
During processing, this service adds noise and imposes limits on how many
queries can be performed.
This API provides functions that allow the origin to construct an aggregatable
report and specify the values to be embedded into its encrypted payload (for
later computation via the aggregation service). These calls result in the
aggregatable report being queued to be sent to the reporting endpoint of the
script's origin after a delay. After the endpoint receives the reports, it will
batch the reports and send them to the aggregation service for processing. The
output of that process is a summary report containing the (approximate) result,
which is dispatched back to the script's origin.
Alternative considered {#alternative-considered}
------------------------------------------------
Instead of the chosen API shape, we considered aligning with a design that is
much closer to {{WindowOrWorkerGlobalScope/fetch()}}. However, there are a few
key differences which make this unfavorable:
- This API is designed to be used in isolated contexts where
{{WindowOrWorkerGlobalScope/fetch()}} is not available.
- It's an anti-goal to give the developer control over when [=aggregatable
reports=] are being sent or knowledge that they were sent (outside of the
isolated context). Note, however, the exception when providing a context ID
from <em>outside</em> the isolated context, see [Protecting against leaks
via the number of
reports](#protecting-against-leaks-via-the-number-of-reports) below.
- The reports cannot be sent to arbitrary reporting endpoints, only a
particular <code>[[RFC8615|.well-known]]</code> path on the script origin.
- The report's input is very specific (an array of {{PAHistogramContribution}}s)
and is not amenable to {{WindowOrWorkerGlobalScope/fetch()}}'s general
purpose contents.
- There is no concept of a response.
So, we chose the more tailored API shape detailed below.
Exposed interface {#exposed-interface}
======================================
<xmp class="idl">
[Exposed=(InterestGroupScriptRunnerGlobalScope,SharedStorageWorklet),
SecureContext]
interface PrivateAggregation {
undefined contributeToHistogram(PAHistogramContribution contribution);
undefined enableDebugMode(optional PADebugModeOptions options = {});
};
dictionary PAHistogramContribution {
required bigint bucket;
required long value;
bigint filteringId = 0;
};
dictionary PADebugModeOptions {
required bigint debugKey;
};
</xmp>
Issue: Per the <a href=https://www.w3.org/TR/design-principles/#numeric-types>
Web Platform Design Principles</a>, we should consider switching `long` to
`[EnforceRange] long long`.
Issue: {{PrivateAggregation/enableDebugMode(options)}}'s argument should not
have a default value of `{}`. Alternatively, {{PADebugModeOptions/debugKey}}
should not be required in {{PADebugModeOptions}}.
Each {{PrivateAggregation}} object has the following fields:
<dl dfn-for="PrivateAggregation">
: <dfn>scoping details</dfn> (default null)
:: A [=scoping details=] or null
: <dfn>allowed to use</dfn> (default false)
:: A [=boolean=]
</dl>
Note: See [Exposing to global scopes](#exposing) below.
<div algorithm>
The <dfn method for="PrivateAggregation">
contributeToHistogram(PAHistogramContribution contribution)</dfn> method steps
are:
</div>
1. If |contribution|["{{PAHistogramContribution/bucket}}"] is not [=set/
contained=] in [=the exclusive range|the range=] 0 to 2<sup>128</sup>,
exclusive, [=exception/throw=] a {{RangeError}}.
1. If |contribution|["{{PAHistogramContribution/value}}"] is negative,
[=exception/throw=] a {{RangeError}}.
1. Let |scopingDetails| be [=this=]'s [=PrivateAggregation/scoping details=].
1. Let |batchingScope| be the result of running |scopingDetails|' [=scoping
details/get batching scope steps=].
1. Let |filteringIdMaxBytes| be the [=default filtering ID max bytes=].
1. If [=pre-specified report parameters map=][|batchingScope|] [=map/exists=]:
1. Set |filteringIdMaxBytes| to [=pre-specified report parameters
map=][|batchingScope|]'s [=pre-specified report parameters/filtering ID
max bytes=].
1. If |contribution|["{{PAHistogramContribution/filteringId}}"] is not [=set/
contained=] in [=the exclusive range|the range=] 0 to
256<sup>|filteringIdMaxBytes|</sup>, exclusive, [=exception/throw=] a
{{RangeError}}.
1. Let |entry| be a new [=contribution cache entry=] with the items:
: [=contribution cache entry/contribution=]
:: |contribution|
: [=contribution cache entry/batching scope=]
:: |batchingScope|
: [=contribution cache entry/debug scope=]
:: The result of running |scopingDetails|' [=scoping details/get debug scope
steps=].
1. [=Append an entry to the contribution cache|Append=] |entry| to the
[=contribution cache=].
Issue: Ensure errors are of an appropriate type, e.g. {{InvalidAccessError}} is
deprecated.
Issue(44): Consider accepting an array of contributions.
<div algorithm>
The <dfn method for="PrivateAggregation">
enableDebugMode(optional PADebugModeOptions options)</dfn> method steps are:
</div>
1. Let |scopingDetails| be [=this=]'s [=PrivateAggregation/scoping details=].
1. Let |debugScope| be the result of running |scopingDetails|' [=scoping
details/get debug scope steps=].
1. If [=debug scope map=][|debugScope|] [=map/exists=], [=exception/throw=] a
"{{DataError}}" {{DOMException}}.
Note: This would occur if `enableDebugMode()` has already been run for this
[=debug scope=].
1. Let |debugKey| be null.
1. If |options| was given:
1. If |options|["{{PADebugModeOptions/debugKey}}"] is not [=set/contained=]
in [=the exclusive range|the range=] 0 to 2<sup>64</sup>, exclusive,
[=exception/throw=] a "{{DataError}}" {{DOMException}}.
1. Set |debugKey| to |options|["{{PADebugModeOptions/debugKey}}"].
1. Let |debugDetails| be a new [=debug details=] with the items:
: [=debug details/enabled=]
:: true
: [=debug details/key=]
:: |debugKey|
1. Optionally, set |debugDetails| to a new [=debug details=].
Note: This allows the user agent to make debug mode unavailable globally or
just for certain callers.
1. [=map/Set=] [=debug scope map=][|debugScope|] to |debugDetails|.
Issue: Ensure errors are of an appropriate type, e.g. {{InvalidAccessError}} is
deprecated.
Exposing to global scopes {#exposing}
=====================================
To expose this API to a global scope, a [=read only=] [=attribute=]
`privateAggregation` of type {{PrivateAggregation}} should be exposed on the
global scope. Its [=getter steps=] should be set to the [=get the
privateAggregation=] steps given [=this=].
Each global scope should set the [=PrivateAggregation/allowed to use=] for the
{{PrivateAggregation}} object it exposes based on whether a relevant
[=document=] is [=allowed to use=] the "<code>[=private-aggregation=]</code>"
[=policy-controlled feature=].
Additionally, each global scope should set the [=PrivateAggregation/scoping
details=] for the {{PrivateAggregation}} object it exposes to a non-null value.
The global scope should wait to set the field until the API is intended to be
available.
<div class="example" id="shared-storage-only-within-operations">
Shared Storage only allows Private Aggregation when an operation is being
invoked, not in the top-level context:
<pre highlight="js">
class ExampleOperation {
async run(data) {
privateAggregation.contributeToHistogram(...) // This is allowed.
}
}
register('example-operation', ExampleOperation);
privateAggregation.contributeToHistogram(...) // This would cause an error.
</pre>
So, Shared Storage sets the [=PrivateAggregation/scoping details=]
immediately after the initial execution of the module script is complete.
</div>
For any [=batching scope=] returned by the [=scoping details/get batching scope
steps=], the [=process contributions for a batching scope=] steps should later
be performed given that same batching scope, the global scope's [=relevant
settings object=]'s [=environment settings object/origin=], some [=context
type=] and a timeout (or null).
Note: This last requirement means that global scopes with different origins
cannot share the same batching scope, see [Same-origin
policy](#same-origin-policy) discussion.
For any [=debug scope=] returned by the [=scoping details/get debug scope
steps=], the [=mark a debug scope complete=] steps should later be performed
given that same [=debug scope=].
Note: A later algorithm [=asserts=] that, for any [=contribution cache entry=]
in the [=contribution cache=], the [=mark a debug scope complete=] steps
were performed given the entry's [=contribution cache entry/debug scope=]
before the [=process contributions for a batching scope=] steps are
performed given the entry's [=contribution cache entry/batching scope=].
Structures {#structures}
========================
<h3 dfn-type=dfn>Batching scope</h3>
A batching scope is a <a spec=HTML>unique internal value</a> that identifies
which {{PAHistogramContribution}}s should be sent in the same [=aggregatable
report=] unless their [=aggregatable report/debug details=] differ.
Issue: Unique internal value is not an exported definition. See
<a href="https://github.com/whatwg/infra/issues/583">infra/583</a>.
<h3 dfn-type=dfn>Debug scope</h3>
A debug scope is a <a spec=HTML>unique internal value</a> that identifies which
{{PAHistogramContribution}}s should have their [=debug details=] affected by the
presence or absence of a call to {{PrivateAggregation/enableDebugMode()}} in the
same period of execution.
<h3 dfn-type=dfn>Scoping details</h3>
A scoping details is a [=struct=] with the following items:
<dl dfn-for="scoping details">
: <dfn>get batching scope steps</dfn>
:: An algorithm returning a [=batching scope=]
: <dfn>get debug scope steps</dfn>
:: An algorithm returning a [=debug scope=]
</dl>
<h3 dfn-type=dfn>Debug details</h3>
A debug details is a [=struct=] with the following items:
<dl dfn-for="debug details">
: <dfn>enabled</dfn> (default false)
:: A [=boolean=]
: <dfn>key</dfn> (default null)
:: An unsigned 64-bit integer or null. The key must be null if [=debug
details/enabled=] is false.
</dl>
<h3 dfn-type=dfn>Contribution cache entry</h3>
A contribution cache entry is a [=struct=] with the following items:
<dl dfn-for="contribution cache entry">
: <dfn>contribution</dfn>
:: A {{PAHistogramContribution}}
: <dfn>batching scope</dfn>
:: A [=batching scope=]
: <dfn>debug scope</dfn>
:: A [=debug scope=]
: <dfn>debug details</dfn> (default null)
:: A [=debug details=] or null
</dl>
<h3 dfn-type=dfn>Aggregatable report</h3>
An aggregatable report is a [=struct=] with the following items:
<dl dfn-for="aggregatable report">
: <dfn>reporting origin</dfn>
:: An [=origin=]
: <dfn>original report time</dfn>
:: A [=moment=]
: <dfn>report time</dfn>
:: A [=moment=]
: <dfn>contributions</dfn>
:: A [=list=] of {{PAHistogramContribution}}s
: <dfn>api</dfn>
:: A [=context type=]
: <dfn>report ID</dfn>
:: A [=string=]
: <dfn>debug details</dfn>
:: A [=debug details=]
: <dfn>aggregation coordinator</dfn>
:: An [=aggregation coordinator=]
: <dfn>context ID</dfn>
:: A [=string=] or null
: <dfn>filtering ID max bytes</dfn>
:: A positive integer
: <dfn>queued</dfn>
:: A [=boolean=]
</dl>
Aggregation coordinator {#aggregation-coordinator-structure}
------------------------------------------------------------
An <dfn>aggregation coordinator</dfn> is an [=origin=] that the [=allowed
aggregation coordinator set=] [=set/contains=].
Issue: Consider switching to the <a spec="attribution-reporting-api">suitable
origin</a> concept used by the Attribution Reporting API here and elsewhere.
Issue: Move other structures to be defined inline instead of via a header.
Consider also removing all the subheadings.
<h3 dfn-type=dfn>Context type</h3>
A context type is a [=string=] indicating what kind of global scope the
{{PrivateAggregation}} object was exposed in. Each API exposing Private
Aggregation should pick a unique string (or multiple) for this.
Pre-specified report parameters {#pre-specified-report-parameters-structure}
----------------------------------------------------------------------------
A <dfn>pre-specified report parameters</dfn> is a [=struct=] with the following
items:
<dl dfn-for="pre-specified report parameters">
: <dfn>context ID</dfn> (default: null)
:: A [=string=] or null
: <dfn>filtering ID max bytes</dfn> (default: [=default filtering ID max bytes=])
:: A positive integer
</dl>
Storage {#storage}
==================
A [=user agent=] holds an <dfn>aggregatable report cache</dfn>, which is a
[=list=] of [=aggregatable reports=].
A [=user agent=] holds an <dfn>aggregation coordinator map</dfn>, which is a
[=map=] from [=batching scopes=] to [=aggregation coordinators=].
A [=user agent=] holds a <dfn>pre-specified report parameters map</dfn>, which
is a [=map=] from [=batching scopes=] to [=pre-specified report parameters=].
A [=user agent=] holds a <dfn>contribution cache</dfn>, which is a [=list=] of
[=contribution cache entries=].
A [=user agent=] holds a <dfn>debug scope map</dfn>, which is a [=map=] from
[=debug scopes=] to [=debug details=].
Issue: Elsewhere, link to definition when using [=user agent=].
Clearing storage {#clearing-storage}
----------------------------------------
The user agent must expose controls that allow the user to delete data from
the [=aggregatable report cache=] as well as any contribution history data
stored for the [=consume budget if permitted=] algorithm.
The user agent may expose controls that allow the user to delete data from the
[=contribution cache=], the [=debug scope map=] and the [=pre-specified report
parameters map=].
Constants {#constants}
======================
<dfn>Default filtering ID max bytes</dfn> is a positive integer controlling the
max bytes used if none is explicitly chosen. Its value is 1.
<dfn>Valid filtering ID max bytes range</dfn> is a [=set=] of positive integers
controlling the allowable values of max bytes. Its value is [=the inclusive
range|the range=] 1 to 8, inclusive.
Issue: Consider adding more constants.
[=Implementation-defined=] values {#implementation-defined-values}
==================================================================
<dfn>Allowed aggregation coordinator set</dfn> is a [=set=] of [=origins=] that
controls which [=origins=] are valid [=aggregation coordinators=]. Every
[=set/item=] in this [=set=] must be a [=potentially trustworthy origin=].
<dfn>Default aggregation coordinator</dfn> is an [=aggregation coordinator=]
that controls which is used for a report if none is explicitly selected.
<dfn>Maximum report contributions</dfn> is a positive integer that controls how
many contributions can be present in a single report.
<dfn>Minimum report delay</dfn> is a non-negative [=duration=] that controls the
minimum delay to deliver an [=aggregatable report=].
<dfn>Randomized report delay</dfn> is a positive [=duration=] that controls the
random delay to deliver an [=aggregatable report=]. This delay is additional to
the [=minimum report delay=].
Permissions Policy integration {#permissions-policy-integration}
================================================================
This specification defines a [=policy-controlled feature=] identified by the
string "<code><dfn>private-aggregation</dfn></code>". Its [=policy-controlled
feature/default allowlist=] is "`*`".
Note: The [=PrivateAggregation/allowed to use=] field is set by other
specifications that integrate with this API according to this
[=policy-controlled feature=].
Algorithms {#algorithms}
====================
To <dfn>serialize an integer</dfn>, represent it as a [=string=] of the shortest
possible decimal number.
Issue: This would ideally be replaced by a more descriptive algorithm in Infra.
See <a href="https://github.com/whatwg/infra/issues/201">infra/201</a>.
Exported algorithms {#exported-algorithms}
------------------------------------------
Note: These algorithms allow other specifications to integrate with this API.
To <dfn algorithm export>get the privateAggregation</dfn> given a
{{PrivateAggregation}} |this|:
1. Let |scopingDetails| be |this|'s [=PrivateAggregation/scoping details=].
1. If |scopingDetails| is null, [=exception/throw=] a "{{NotAllowedError}}"
{{DOMException}}.
Note: This indicates the API is not yet available, for example, because the
initial execution of the script after loading is not complete.
Issue: Consider improving developer ergonomics here (e.g. a way to detect
this case).
1. If |this|'s [=PrivateAggregation/allowed to use=] is false, [=exception/
throw=] an "{{InvalidAccessError}}" {{DOMException}}.
1. Return |this|.
Issue: Ensure errors are of an appropriate type, e.g. {{InvalidAccessError}} is
deprecated.
To <dfn algorithm export>append an entry to the contribution cache</dfn> given a
[=contribution cache entry=] |entry|:
1. [=list/Append=] |entry| to the [=contribution cache=].
To <dfn algorithm export>get a debug details</dfn> given a [=debug scope=]
|debugScope|, perform the following steps. They return a [=debug details=].
1. If [=debug scope map=][|debugScope|] [=map/exists=], return
[=debug scope map=][|debugScope|].
1. Otherwise, return a new [=debug details=].
To <dfn algorithm export>mark a debug scope complete</dfn> given a [=debug
scope=] |debugScope| and an optional [=debug details=] or null
|debugDetailsOverride| (default null):
1. Let |debugDetails| be |debugDetailsOverride|.
1. If [=debug scope map=][|debugScope|] [=map/exists=]:
1. [=Assert=]: |debugDetailsOverride| is null.
Note: The override can be provided if the debug details have not been
set otherwise.
1. Set |debugDetails| to [=debug scope map=][|debugScope|].
1. [=map/Remove=] [=debug scope map=][|debugScope|].
1. If |debugDetails|'s [=debug details/key=] is not null, [=assert=]:
|debugDetails|'s [=debug details/enabled=] is true.
1. If |debugDetails| is null, set |debugDetails| to a new [=debug details=].
1. [=list/iterate|For each=] |entry| of the [=contribution cache=]:
1. If |entry|'s [=contribution cache entry/debug scope=] is |debugScope|,
set |entry|'s [=contribution cache entry/debug details=] to
|debugDetails|.
To <dfn>determine if a report should be sent deterministically</dfn> given a
[=pre-specified report parameters=] |preSpecifiedParams|, perform the following
steps. They return a [=boolean=]:
1. If |preSpecifiedParams|' [=pre-specified report parameters/context ID=] is
not null, return true.
1. If |preSpecifiedParams|' [=pre-specified report parameters/filtering ID max
bytes=] is not the [=default filtering ID max bytes=], return true.
1. Return false.
Note: If a context ID or non-default filtering ID max bytes was specified, a
report is sent, even if there are no contributions or there is insufficent
budget for the requested contributions. See [Protecting against leaks via
the number of reports](#protecting-against-leaks-via-the-number-of-reports).
To <dfn algorithm export>process contributions for a batching scope</dfn> given
a [=batching scope=] |batchingScope|, an [=origin=] |reportingOrigin|, a
[=context type=] |contextType| and a [=moment=] or null |timeout|:
1. Let |batchEntries| be a new [=list=].
1. [=list/iterate|For each=] |entry| of the [=contribution cache=]:
1. If |entry|'s [=contribution cache entry/batching scope=] is
|batchingScope|:
1. [=Assert=]: |entry|'s [=contribution cache entry/debug details=] is
not null.
Note: This asserts that the [=mark a debug scope complete=] steps
were run before the [=process contributions for a batching
scope=] steps.
1. [=list/Append=] |entry| to |batchEntries|.
1. Let |aggregationCoordinator| be the [=default aggregation coordinator=].
1. If [=aggregation coordinator map=][|batchingScope|] [=map/exists=]:
1. Set |aggregationCoordinator| to [=aggregation coordinator
map=][|batchingScope|].
1. [=map/Remove=] [=aggregation coordinator map=][|batchingScope|].
1. Let |preSpecifiedParams| be a new [=pre-specified report parameters=].
1. If [=pre-specified report parameters map=][|batchingScope|] [=map/exists=]:
1. Set |preSpecifiedParams| to [=pre-specified report parameters
map=][|batchingScope|].
1. [=map/Remove=] [=pre-specified report parameters map=][|batchingScope|].
1. Let |isDeterministicReport| be the result of [=determining if a report should
be sent deterministically=] given |preSpecifiedParams|.
1. If |isDeterministicReport| is false, [=assert=]: |timeout| is null.
Note: Timeouts can only be used for deterministic reports.
1. If |batchEntries| [=list/is empty=] and |isDeterministicReport| is false,
return.
1. Let |batchedContributions| be a new [=ordered map=].
1. [=list/iterate|For each=] |entry| of |batchEntries|:
1. [=list/Remove=] |entry| from the [=contribution cache=].
1. Let |debugDetails| be |entry|'s [=contribution cache entry/debug
details=].
1. If |batchedContributions|[|debugDetails|] does not [=map/exist=]:
1. [=map/Set=] |batchedContributions|[|debugDetails|] to a new [=list=].
1. [=list/Append=] |entry|'s [=contribution cache entry/contribution=] to
|batchedContributions|[|debugDetails|].
1. If |batchedContributions| [=map/is empty=]:
1. Let |debugDetails| be a new [=debug details=].
1. Set |batchedContributions|[|debugDetails|] to a new [=list=].
1. [=map/iterate|For each=] |debugDetails| → |contributions| of
|batchedContributions|:
1. Perform the [=report creation and scheduling steps=] with
|reportingOrigin|, |contextType|, |contributions|, |debugDetails|,
|aggregationCoordinator|, |preSpecifiedParams| and |timeout|.
Note: These steps break up the contributions based on their [=debug details=] as
each report can only have one set of metadata.
<div algorithm>
To <dfn export>determine if an origin is an aggregation coordinator</dfn> given
an [=origin=] |origin|, perform the following steps. They return a [=boolean=].
1. Return whether |origin| is an [=aggregation coordinator=].
</div>
<div algorithm>
To <dfn export>set the aggregation coordinator for a batching scope</dfn> given
an [=origin=] |origin| and a [=batching scope=] |batchingScope|:
1. [=Assert=]: |origin| is an [=aggregation coordinator=].
1. [=map/Set=] [=aggregation coordinator map=][|batchingScope|] to |origin|.
</div>
Issue: Elsewhere, surround algorithms in a `<div algorithm>` block to match, and
add styling for all algorithms per
[bikeshed/1472](https://github.com/speced/bikeshed/issues/1472).
To <dfn algorithm export>set the pre-specified report parameters for a batching
scope</dfn> given a [=pre-specified report parameters=] |params| and a
[=batching scope=] |batchingScope|:
1. Let |contextId| be |params|' [=pre-specified report parameters/context ID=].
1. [=Assert=]: |contextId| is null or |contextId|'s [=string/length=] is not
larger than 64.
1. Let |filteringIdMaxBytes| be |params|' [=pre-specified report parameters/
filtering ID max bytes=].
1. [=Assert=]: |filteringIdMaxBytes| is [=set/contained=] in the [=valid
filtering ID max bytes range=]
1. [=map/Set=] [=pre-specified report parameters map=][|batchingScope|] to
|params|.
Scheduling reports {#scheduling-reports}
----------------------------------------
To perform the <dfn algorithm>report creation and scheduling steps</dfn> with an
[=origin=] |reportingOrigin|, a [=context type=] |api|, a [=list=] of
{{PAHistogramContribution}}s |contributions|, a [=debug details=]
|debugDetails|, an [=aggregation coordinator=] |aggregationCoordinator|, a
[=pre-specified report parameters=] |preSpecifiedParams| and a [=moment=] or
null |timeout|:
1. [=Assert=]: |reportingOrigin| is a [=potentially trustworthy origin=].
1. Optionally, return.
Note: This [=implementation-defined=] condition is intended to allow [=user
agents=] to drop reports for a number of reasons, for example user
opt-out or an origin not being
<a href="https://github.com/privacysandbox/attestation">enrolled</a>.
1. Let |truncatedContributions| be a new [=list=].
1. If |contributions| has a [=list/size=] greater than [=maximum report
contributions=]:
1. [=set/For each=] |n| of [=the exclusive range|the range=] 0 to [=maximum
report contributions=], exclusive:
1. [=set/Append=] |contributions|[|n|] to |truncatedContributions|.
1. Otherwise, set |truncatedContributions| to |contributions|.
1. Let |contributionSum| be 0.
1. [=set/iterate|For each=] |contribution| of |truncatedContributions|:
1. [=Assert=]: |contribution|["{{PAHistogramContribution/value}}"] is
non-negative.
1. Add |contribution|["{{PAHistogramContribution/value}}"] to
|contributionSum|.
1. Let |currentWallTime| be the [=current wall time=].
1. Let |sufficientBudget| be the result of [=consuming budget if permitted=]
given |contributionSum|, |reportingOrigin|, |api| and |currentWallTime|.
1. If |sufficientBudget| is false:
1. Let |isDeterministicReport| be the result of [=determining if a report
should be sent deterministically=] given |preSpecifiedParams|.
1. If |isDeterministicReport| is false, return.
1. [=list/Empty=] |truncatedContributions|.
1. Let |report| be the result of [=obtaining an aggregatable report=] given
|reportingOrigin|, |api|, |truncatedContributions|, |debugDetails|,
|aggregationCoordinator|, |preSpecifiedParams|, |timeout| and
|currentWallTime|.
1. [=set/Append=] |report| to the user agent's [=aggregatable report cache=].
To <dfn algorithm>consume budget if permitted</dfn> given a {{long}} |value|, an
[=origin=] <var ignore=''>origin</var>, a [=context type=] |api| and a
[=moment=] |currentTime|, perform [=implementation-defined=] steps. They return
a [=boolean=], which indicates whether there is sufficient 'contribution budget'
left to send the requested contribution |value|. This budget should be bound to
usage over time, e.g. the contribution sum over the last 24 hours. The algorithm
should assume that the contribution will be sent if and only if true is
returned, i.e. it should consume the budget in that case. If |value| is zero,
this algorithm should return true.
To <dfn>obtain an aggregatable report</dfn> given an [=origin=]
|reportingOrigin|, a [=context type=] |api|, a [=list=] of
{{PAHistogramContribution}}s |contributions|, a [=debug details=]
|debugDetails|, an [=aggregation coordinator=] |aggregationCoordinator|, a
[=pre-specified report parameters=] |preSpecifiedParams|, a [=moment] or null
|timeout| and a [=moment=] |currentTime|,
perform the following steps. They return an [=aggregatable report=].
1. [=Assert=]: |reportingOrigin| is a [=potentially trustworthy origin=].
1. Let |reportTime| be the result of running [=obtain a report delivery time=]
given |currentTime| and |timeout|.
1. Let |report| be a new [=aggregatable report=] with the items:
: [=aggregatable report/reporting origin=]
:: |reportingOrigin|
: [=aggregatable report/original report time=]
:: |reportTime|
: [=aggregatable report/report time=]
:: |reportTime|
: [=aggregatable report/contributions=]
:: |contributions|
: [=aggregatable report/api=]
:: |api|
: [=aggregatable report/report ID=]
:: The result of [=generating a random UUID=].
: [=aggregatable report/debug details=]
:: |debugDetails|
: [=aggregatable report/aggregation coordinator=]
:: |aggregationCoordinator|
: [=aggregatable report/context ID=]
:: |preSpecifiedParams|' [=pre-specified report parameters/context ID=]
: [=aggregatable report/filtering ID max bytes=]
:: |preSpecifiedParams|' [=pre-specified report parameters/filtering ID max
bytes=]
: [=aggregatable report/queued=]
:: false
1. Return |report|.
To <dfn algorithm>obtain a report delivery time</dfn> given a [=moment=]
|currentTime| and a [=moment=] or null |timeout|, perform the following steps.
They return a [=moment=].
1. If |timeout| is not null:
1. Return |timeout|.
1. If [=automation local testing mode enabled=] is true, return
|currentTime|.
1. Let |r| be a random double between 0 (inclusive) and 1 (exclusive) with
uniform probability.
1. Return |currentTime| + [=minimum report delay=] + |r| * [=randomized report
delay=].
Sending reports {#sending-reports}
----------------------------------
Note: This section is largely copied from the
<a href="https://wicg.github.io/attribution-reporting-api/">Attribution
Reporting API spec</a>, adapting as necessary.
Issue: Do we have to use the [=queue a task=] algorithm here?
The user agent must periodically [=attempt to queue reports for sending=] given
its [=aggregatable report cache=].
To <dfn>attempt to queue reports for sending</dfn> given a [=list=] of
[=aggregatable reports=] |reports|:
1. [=list/iterate|For each=] |report| of |reports|, run these steps [=in
parallel=]:
1. Run these steps, but [=abort when=] the [=user agent=] shuts down:
1. If |report|'s [=aggregatable report/queued=] value is true, return.
1. Set |report|'s [=aggregatable report/queued=] value to true.
1. Let |currentWallTime| be the [=current wall time=].
1. If |report|'s [=aggregatable report/report time=] is before
|currentWallTime|, set |report|'s [=aggregatable report/report
time=] to |currentWallTime| plus an [=implementation-defined=]
random non-negative [=duration=].
Note: On startup, it is possible the user agent will need to send
many reports whose report times passed while the browser was
closed. Adding random delay prevents temporal joining of
reports.
1. Wait until the [=current wall time=] is equal to or after |report|'s
[=aggregatable report/report time=].
1. Optionally, wait a further [=implementation-defined=] non-negative
[=duration=].
Note: This is intended to allow user agents to optimize device
resource usage and wait for the user agent to be online.
1. Run [=attempt to deliver a report=] with |report|.
1. [=If aborted=], set |report|'s [=aggregatable report/queued=] value to
false.
Note: It might be more practical to perform this step when the [=user
agent=] next starts up.
To <dfn>attempt to deliver a report</dfn> given an [=aggregatable report=]
|report|:
1. Let |url| be the result of [=obtaining a reporting endpoint=] given
|report|'s [=aggregatable report/reporting origin=] and |report|'s
[=aggregatable report/api=].
1. Let |data| be the result of [=serializing an aggregatable report=] given
|report|.
1. If |data| is an error, [=list/remove=] |report| from the [=aggregatable
report cache=].
Issue: Do we need to queue this task?
1. Let |request| be the result of [=creating a report request=] given |url| and
|data|.
1. [=Queue a task=] to [=fetch=] |request| with [=fetch/processResponse=] being
the following steps:
1. Let |shouldRetry| be an [=implementation-defined=] [=boolean=]. The value
should be false if no error occurred.
1. If |shouldRetry| is true:
1. Set |report|'s [=aggregatable report/report time=] to the [=current
wall time=] plus an [=implementation-defined=] non-negative
[=duration=].
1. Set |report|'s [=aggregatable report/queued=] value to false.
1. Otherwise, [=list/remove=] |report| from the [=aggregatable report
cache=].
To <dfn>obtain a reporting endpoint</dfn> given an [=origin=] |reportingOrigin|
and [=context type=] |api|, perform the following steps. They return a [=URL=].
1. [=Assert=]: |reportingOrigin| is a [=potentially trustworthy origin=].
1. Let |path| be the [=string/concatenation=] of
«"<code>[[RFC8615|.well-known]]/private-aggregation/report-</code>", |api|».
Issue(67): Register this well-known directory.
1. Let |base| be the result on running the [=URL parser=] on the [=serialization
of an origin|serialization=] of |reportingOrigin|.
1. [=Assert=]: |base| is not failure.
1. Let |result| be the result of running the [=URL parser=] on |path| with
|base|.
1. [=Assert=]: |result| is not failure.
1. Return |result|.
To <dfn>create a report request</dfn> given a [=URL=] |url| and a [=byte
sequence=] |body|:
1. Let |request| be a new [=request=] with the following properties:
: [=request/method=]
:: "`POST`"
: [=request/URL=]
:: |url|
: [=request/header list=]
:: «("`Content-Type`", "`application/json`")»
: [=request/unsafe-request flag=]
:: set
: [=request/body=]
:: |body|
: [=request/client=]
:: `null`
: [=request/window=]
:: "`no-window`"
: [=request/service-workers mode=]
:: "`none`"
: [=request/initiator=]
:: ""
: [=request/referrer=]
:: "`no-referrer`"
: [=request/mode=]
:: "`cors`"
: [=request/credentials mode=]
:: "`omit`"
: [=request/cache mode=]
:: "`no-store`"
1. Return |request|.
Serializing reports {#serializing-reports}
------------------------------------------
Note: This section is largely copied from the
<a href="https://wicg.github.io/attribution-reporting-api/">Attribution
Reporting API spec</a>, adapting as necessary.
To <dfn>serialize an aggregatable report</dfn> given an [=aggregatable report=]
|report|, perform the following steps. They return a [=byte sequence=] or an
error.
1. Let |aggregationServicePayloads| be the result of [=obtaining the aggregation
service payloads=] given |report|.
1. If |aggregationServicePayloads| is an error, return
|aggregationServicePayloads|.
1. Let |data| be an [=ordered map=] of the following key/value pairs:
: "`aggregation_coordinator_origin`"
:: |report|'s [=aggregatable report/aggregation coordinator=],
[=serialization of an origin|serialized=].
: "`aggregation_service_payloads`"
:: |aggregationServicePayloads|
: "`shared_info`"
:: The result of [=obtaining a report's shared info=] given |report|.
1. Let |debugKey| be |report|'s [=aggregatable report/debug details=]'s [=debug
details/key=].
1. If |debugKey| is not null, [=map/set=] |data|["`debug_key`"] to |debugKey|.
1. Let |contextId| be |report|'s [=aggregatable report/context ID=].
1. If |contextId| is not null, [=map/set=] |data|["`context_id`"] to
|contextId|.
1. Return the [=byte sequence=] resulting from executing [=serialize an infra
value to JSON bytes=] on |data|.
To <dfn>obtain the aggregation service payloads</dfn> given an [=aggregatable
report=] |report|, perform the following steps. They return a [=list=] of
[=maps=] or an error.
1. Let |publicKeyTuple| be the result of [=obtaining the public key for
encryption=] given |report|'s [=aggregatable report/aggregation
coordinator=].
1. If |publicKeyTuple| is an error, return |publicKeyTuple|.
1. Let (|pkR|, |keyId|) be |publicKeyTuple|.
1. Let |plaintextPayload| be the result of [=obtaining the plaintext payload=]
given |report|.
1. Let |sharedInfo| be the result of [=obtaining a report's shared info=] given
|report|.
1. Let |encryptedPayload| be the result of [=encrypting the payload=] given
|plaintextPayload|, |pkR| and |sharedInfo|.
1. If |encryptedPayload| is an error, return |encryptedPayload|.
1. Let |aggregationServicePayloads| be a new [=list=].
1. Let |aggregationServicePayload| be an [=ordered map=] of the following
key/value pairs:
: "`key_id`"
:: |keyId|
: "`payload`"
:: |encryptedPayload|, [=forgiving-base64 encode|base64 encoded=]
1. If |report|'s [=aggregatable report/debug details=]'s [=debug details/
enabled=] field is true:
1. [=map/Set=] |aggregationServicePayload|[`debug_cleartext_payload`] to
|plaintextPayload|, [=forgiving-base64 encode|base64 encoded=].
1. [=list/Append=] |aggregationServicePayload| to |aggregationServicePayloads|.
1. Return |aggregationServicePayloads|.
To <dfn>obtain the public key for encryption</dfn> given an [=aggregation
coordinator=] |aggregationCoordinator|, perform the following steps. They return
a [=tuple=] consisting of a public key and a [=string=], or an error.
1. Let |url| be a new [=URL record=].
1. Set |url|'s [=url/scheme=] to |aggregationCoordinator|'s [=origin/scheme=].
1. Set |url|'s [=url/host=] to |aggregationCoordinator|'s [=origin/host=].
1. Set |url|'s [=url/port=] to |aggregationCoordinator|'s [=origin/port=].
1. Set |url|'s [=url/path=] to «"`.well-known`", "`aggregation-service`",
"`v1`", "`public-keys`"».
1. Return an [=implementation-defined=] [=tuple=] consisting of a public key
from |url| and a [=string=] that should uniquely identify the public key or,
in the event that the user agent failed to obtain the public key from |url|,
an error. This step may be asynchronous.
Issue: Specify this in terms of [=fetch=]. Add details about which encryption
standards to use, length requirements, etc.
Note: The user agent is encouraged to enforce regular key rotation. If there are
multiple keys, the user agent can independently pick a key uniformly at
random for every encryption operation.
To <dfn>obtain the plaintext payload</dfn> given an [=aggregatable report=]
|report|, perform the following steps. They return a [=byte sequence=].
1. Let |payloadData| be a new [=list=].
1. Let |contributions| be |report|'s [=aggregatable report/contributions=].
1. [=Assert=]: |contributions|' [=list/size=] is not greater than [=maximum
report contributions=].
1. [=iteration/While=] |contributions|' [=list/size=] is less than [=maximum
report contributions=]:
1. Let |nullContribution| be a new {{PAHistogramContribution}} with the
items:
: {{PAHistogramContribution/bucket}}
:: 0
: {{PAHistogramContribution/value}}
:: 0
: {{PAHistogramContribution/filteringId}}
:: 0
1. [=list/Append=] |nullContribution| to |contributions|.
Note: This padding protects against the number of contributions being leaked
through the encrypted payload size, see discussion
[below](#protecting-against-leaks-via-payload-size).
1. [=list/iterate|For each=] |contribution| of |report|'s [=aggregatable report/
contributions=]:
1. Let |filteringIdMaxBytes| be |report|'s [=aggregatable report/filtering
id max bytes=].
1. [=Assert=]: |contribution|["{{PAHistogramContribution/filteringId}}"]
is [=set/contained=] in [=the exclusive range|the range=] 0 to
256<sup>|filteringIdMaxBytes|</sup>, exclusive.
1. Let |contributionData| be an [=ordered map=] of the following key/value
pairs:
: "`bucket`"
:: The result of [=encoding an integer for the payload=] given
|contribution|["{{PAHistogramContribution/bucket}}"] and 16.
: "`value`"
:: The result of [=encoding an integer for the payload=] given
|contribution|["{{PAHistogramContribution/value}}"] and 4.
: "`id`"
:: The result of [=encoding an integer for the payload=] given
|contribution|[="{{PAHistogramContribution/filteringId}}"] and
|filteringIdMaxBytes|.
1. [=list/Append=] |contributionData| to |payloadData|.
1. Let |payload| be an [=ordered map=] of the following key/value pairs:
: "`data`"
:: |payloadData|
: "`operation`"
:: "`histogram`"
1. Return the [=byte sequence=] resulting from [[!RFC8949|CBOR encoding]]
|payload|.
To <dfn>encrypt the payload</dfn> given a [=byte sequence=] |plaintextPayload|,
public key |pkR| and a [=string=] |sharedInfo|, perform the following steps.
They return a [=byte sequence=] or an error.
1. Let |info| be the result of [=UTF-8 encoding=] the [=string/concatenation=]
of « "`aggregation_service`", |sharedInfo| ».
1. Let (|kem_id|, |kdf_id|, |aead_id|) be (0x0020, 0x0001, 0x0003).
Note: These indicate the HPKE algorithm identifiers, specifying the KEM
function as DHKEM(X25519, HKDF-SHA256), the KDF function as HKDF-SHA256
and the AEAD function as ChaCha20Poly1305.
1. Let |hpkeContext| be the result of setting up an [[RFC9180|HPKE]]
[[RFC9180#name-encryption-to-a-public-key|sender's context]] with |pkR|,
|info|, |kem_id|, |kdf_id| and |aead_id|.
1. Let |aad| be \`\` (an empty [=byte sequence=]).