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Spec: Pad the payload with null contributions #98

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Sep 26, 2023
Merged

Spec: Pad the payload with null contributions #98

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16 changes: 9 additions & 7 deletions spec.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -794,16 +794,21 @@ 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. If |contributions| [=list/is empty=]:
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
1. Set |contributions| to « |nullContribution| ».
1. [=list/Append=] |nullContribution| to |contributions|.

Issue(56): Replace with more generic padding.
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 |contributionData| be an [=ordered map=] of the following key/value
Expand Down Expand Up @@ -1744,10 +1749,7 @@ count.

The length of the payload could additionally expose some cross-site information,
namely how many contributions are included. To protect against this, the payload
will be padded in the future.

Issue(56): Pad the payload to avoid this risk.

is padded to a fixed number of contributions.
### Temporary debugging mechanism ### {#temporary-debugging-mechanism}

The <code>{{PrivateAggregation/enableDebugMode()}}</code> method allows for many
Expand Down