Privacy Preserving Measurement
charter-ietf-ppm-01

There are many situations in which it is desirable to take measurements of data
which people consider sensitive. For instance, a browser company might want to
measure web sites that do not render properly without learning which users
visit those sites, or a public health authority might want to measure exposure
to some disease without learning the identities of those exposed. In these
cases, the entity taking the measurement is not interested in people's
individual responses but rather in aggregated data (e.g., how many users had
errors on site X). Conventional methods require collecting individual
measurements in plaintext and then aggregating them, thus representing a threat
to user privacy and rendering many such measurements difficult and impractical.

New cryptographic techniques address this gap through a variety of approaches,
all of which aim to ensure that the server (or multiple, non-colluding servers)
can compute the aggregated value without learning the value of individual
measurements. The Privacy Preserving Measurement (PPM) work will standardize
protocols for deployment of these techniques on the Internet. This will include
mechanisms for:

- Client submission of individual measurements, potentially along with proofs
of validity

- Verification of validity proofs by the server(s), if sent by client

- Computation of aggregate values by the server(s) and reporting of results to
the entity taking the measurement

A successful PPM system assumes that clients and servers are configured with
each other's identities and details of the types of measurements to be
taken. This is assumed to happen out of band and will not be standardized in
this WG.

The WG will deliver one or more protocols which can accommodate multiple PPM
algorithms. The initial deliverables will support the calculation of simple
predefined statistical aggregates such as averages, as well as calculations of
the values that most frequently appear in individual measurements. The PPM
protocols will use cryptographic algorithms and protocols defined by the CFRG
to enable privacy-preserving properties. The protocol will be designed to limit
abuse by both client and server, including exposure of individual user
measurements and denial of service attacks on the measurement system. The
resulting document(s) shall consider deployment contexts, and clearly describe
abuse cases and remaining attacks which are not prevented or mitigated by the
protocol(s).

The starting point for PPM WG discussions shall be draft-gpew-priv-ppm.