Chalamet

An implementation of the Chalamet Private Information Retrieval scheme.

We introduce ChalametPIR: a single-server Private Information Retrieval (PIR) scheme supporting fast, low-bandwidth keyword queries, with a conceptually very simple design. In particular, we develop a generic framework for converting PIR schemes for index queries over flat arrays (based on the Learning With Errors problem) into keyword PIR. This involves representing a key-value map using any probabilistic filter that permits reconstruction of elements from inclusion queries (e.g. Cuckoo filters). In particular, we make use of recently developed Binary Fuse filters to construct ChalametPIR, with minimal efficiency blow-up compared with state-of-the-art index-based schemes (all costs bounded by a factor of ≤ 1.08). Furthermore, we show that ChalametPIR achieves runtimes and financial costs that are factors of between 6×-11× and 3.75×-11.4× more efficient, respectively, than state-of-the-art keyword PIR approaches, for varying database configurations. Bandwidth costs are additionally reduced or remain competitive, depending on the configuration. Finally, we believe that our application of Binary Fuse filters in the cryptography setting may bring immediate independent value towards developing efficient variants of other related primitives that benefit from using such filters.

Warning: This code is a research prototype. Do not use it in production.

Requirements

In order to natively build, run, test and benchmark the library, you will need the following:

  Rust >= 1.61.0
  Cargo
  Make
  Python3 >= 3.9.7

To obtain our performance numbers as reported in our paper, we run our benchmarks in AWS EC2 t2.t2xlarge and c5.9xlarge machines.

Note that we internally use the xorf library, but we modify it as seen here.

Quickstart

Local

Building

To install the latest version of Rust, use the following command (you can also check how to install on the Rust documentation):

  curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

To build the library, run:

  make build

Testing

To run the tests:

  make test

We test:

• A client and server workflow when using Chalamet (internally with FrodoPIR) (10 times).
• A test to check that the library fails if parameters are reused.

If all test build and run correctly, you should see an ok next to them.

Documentation

To view documentation (in a web browser manner):

  make docs

Benchmarking

To run a specific set of benchmarks, run (note the this process is slow. On average, it takes 12 minutes):

  make bench

This command will execute client query benchmarks and Database generation benchmarks (for more details, see the benches/bench.rs file).

To run all benchmarks (note that this process is very slow, it takes around 30 minutes):

  make bench-standard

This command will execute client query benchmarks and Database generation benchmarks for 16, 17, 18, 19 and 20 Number of DB items (log(m)). The results of these benchmarks can be found on Table 2 of our paper.

In order to see the results of the benchmarks, navigate to the benchmarks-x-x.txt file.

You can also run:

  make bench-keyword

to reproduce the results of Table 3 of our paper.

If all benches build and run correctly, you should see an Finished ... benchmarks under them. We use Criterion for benchmarking. If you want to see and have explanations of the benchmarks, you can locally open target/criterion/report/index.html in your browser.

Note: When running the benches, a warning might appear Warning: Unable to complete 10 samples in 100.0s. You may wish to increase target time to 486.6s.. If you want to silence the warning, you can change line 30 of benches/bech.rs file to 500 or more. Note that this will make the running of benches slower.

Tests

We have two big tests that the library executes:

1. client_kv_query_to_server_10_times test which executes the client-to-server functionality: the client asks for an item in the database (by its key) and the server is able to privately return it. The test asserts that the returned item is indeed the correct item in the database. It executes a for loop 10 times.
2. client_query_to_server_attempt_params_reuse test which executes the client-to-server functionality one time. It asserts that once parameters for a query are used, they are marked as so, and cannot be reused.