Internet-Draft | Bulk DAP Submission | October 2024 |
Thomson & Koshelev | Expires 21 April 2025 | [Page] |
A bulk report submission endpoint and format are described for the Distributed Aggregation Protocol (DAP). This provides modest, but meaningful, efficiency benefits over the core protocol for cases where an intermediary is able to collect large numbers of reports.¶
This note is to be removed before publishing as an RFC.¶
The latest revision of this draft can be found at https://martinthomson.github.io/dap-bulk/draft-thomson-ppm-dap-bulk.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-thomson-ppm-dap-bulk/.¶
Discussion of this document takes place on the Privacy Preserving Measurement Working Group mailing list (mailto:ppm@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/ppm/. Subscribe at https://www.ietf.org/mailman/listinfo/ppm/.¶
Source for this draft and an issue tracker can be found at https://github.com/martinthomson/dap-bulk.¶
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The Distributed Aggregation Protocol (DAP) [DAP] accepts reports from many clients and aggregates them in a manner that protects individual contributions. The core protocol requires that each report be submitted to the DAP leader.¶
The assumption implicit in this design is that reports are submitted directly by clients. This is not necessary for security reasons due to the encryption used (this encryption is necessary for the portion of reports that is intended for DAP helpers). Clients could instead pass their reports to an intermediary for forwarding.¶
Use of an intermediary reduces the availability requirements of aggregators and might remove the need for anonymizing proxy to protect client identity from the server (such as the use of Oblivious HTTP [RFC9458] as described in Section 7.4 of [DAP]). It also creates an opportunity to amortize the overheads involved in report submission.¶
This document defines a bulk submissions endpoint for DAP and defines a report submission format for use with that endpoint.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
DAP defines the {leader}/tasks/{task-id}/reports
resource
for report submission for a task.
This document extends DAP
to define the {leader}/tasks/{task-id}/reports/bulk
resource
for bulk report submission for a task.¶
Clients can send a HTTP POST request to this resource with a payload in the bulk submission format (Section 4). A bulk request is equivalent to multiple separate submissions.¶
A DAP leader MAY accept bulk submissions at the regular "reports" resource.¶
The "application/dap-bulk-report" format contains a header that encodes extensions that are common to all reports. The header is followed by any number of reports, from which those shared fields are removed.¶
The common_extensions
field contains
common extensions that are added
to the set of public report extensions
in each report that follows.
Reports that include values for any common extension
override the value in the common extension.¶
The header is followed by any number of reports,
which are encoded exactly as described in [DAP],
except as noted in Section 4.1.
The use of REPORT_COUNT
in Figure 1
is a small abuse of the TLS syntax to signify
that any number of reports are included.
This "value" could be any positive integer.
Unlike a variable-length field,
as denoted with <
and >
,
this format does not require that the size of all included reports
be known before constructing a request.¶
DAP currently encodes report extensions in the plaintext of shares. For extensions that contain public information this is inefficient for a couple of reasons:¶
This document recommends
the addition of a new public report extensions field
to the ReportMetadata
structure.
This would be modified to include extensions that are public,
as shown in Figure 2.¶
This would be sufficient for many extensions, such as those that are defined in [DAP-DP-EXT]. As with the current design (Section 4.5.3 of [DAP]), unknown extensions would result in the report being rejected. The primary difference being that the leader can determine this before initiating the preparation phase.¶
The existing report extensions could also potentially be removed, as shown in Figure 3.¶
These private extensions currently have no defined purpose and add two bytes per aggregator to every report. The risk of removing them is that a purpose for a generic extension is discovered at some point in the future. Though specific VDAF instantiations might define their own extension container, this decision might limit the availability of extensions that apply to any VDAF.¶
Report metadata, which would include the extensions if the recommendations in Section 4.1 are adopted, are included in the additional associated data for every report. Bulk submission is therefore strictly a performance optimization as far as the operation of DAP is concerned.¶
The potential for a single client to generate large amounts of work for a DAP service is a serious threat to service availability. Any DAP leader SHOULD implement measures to defend against resource exhaustion attacks through this interface. This might include strong authentication of the requester. The logical entity to make this request is a collector, which is likely to be known to the leader.¶
The addition of public extensions exposes more information to the leader. This might be used by a malicious leader to selectively remove reports. A leader is already able to do this without helper awareness, but the added information might allow this to be more selective.¶
IANA is requested to register at time of publication the "application/dap-bulk-report" media type in the "Media Types" registry at <https://iana.org/assignments/media-types>, following the procedures of [RFC6838]. That registration includes the following:¶
application¶
dap-bulk-report¶
N/A¶
N/A¶
"binary"¶
N/A¶
this document¶
This type identifies a bulk report submission for the Distributed Aggregation Protocol.¶
N/A¶
See Authors' Addresses section¶
COMMON¶
N/A¶
See Authors' Addresses section¶
IETF¶
TODO acknowledge.¶