Privacy encoding data

The file ‘privacy_encoding_params’ in this directory is used to calculate parameters to the PrivacyEncoder for each Cobalt 1.1 report with added privacy.

In particular, we use this data to set the prob_bit_flip and num_index_points fields of the ReportDefinition for each Cobalt 1.1 report.

The file contains a lookup table mapping tuples (epsilon, population, sparsity) to precomputed values of prob_bit_flip and num_index_points. This table was generated using a script by pasin@.

The column format is: {epsilon, population, sparsity, prob_bit_flip, num_index_points}

where:

• epsilon is the target epsilon value (in the shuffled model),
• population is the estimated size of the fleet,
• sparsity is the maximum number of buckets with nonzero counts in the histogram contributed by an individual client.
• See the ReportDefinition proto for the meanings of the prob_bit_flip and num_index_points fields.

The file contents are preliminary and may change.