STAR Randomness Server

This repository implements the randomness server that's proposed in the paper STAR: Distributed Secret Sharing for Private Threshold Aggregation Reporting. The actual oblivious pseudorandom function implementation can be found in the sta-rs repository. This repository implements webservice wrapper to make evaluation available over the network.

It also includes a reproducible container build that can be run inside an AWS Nitro Enclave, providing remote attestation of the implementation and additional security for the private key.

Installation

To test, lint, and build the randomness server, simply run:

make

To execute just the randomness webapp with logging, run:

RUST_LOG=tower_http=trace,star_randsrv=debug cargo run

To build a reproducible container image of the randomness server, run:

make image

Input

The randomness server exposes an HTTP POST request handler at /randomness. The handler expects a JSON-formatted request body. Below is an example of a valid request body.

{
  "points": [
    "uqUmPbpGjpqaQcVnbn39PZGtL4DjfY+h9R+XqlKLuVc=",
    "CCBnmLsPR8hFzuxhRz0a05TAh+p0jFhebMCDgOcfdWk=",
    "bNQSygww5ykQpfsDMJXTiaX/MmpWW4qnfmuRpdR/1yY="
  ]
}

The JSON array points contains a list of one or more Base64-encoded Ristretto points.

Output

The randomness server's response contains a similar JSON structure but its points are punctured based on the client-provided input and the server's secret key. Refer to the STAR paper for details. Below is an example of the server's response:

{
  "epoch": 0,
  "points": [
    "qC3vaUizBSrNZCCkzD3jBhHqMEWZIuNj5IdNk57GGHY=",
    "rh7Tcr1LqwVQVtCEEIZqwUCPDvBOMM5bJPA8EfShnzI=",
    "Bq8LJ0KpfwQHgh1tkr8OP+ogmxPQz7lWHfAPuyVxXU0="
  ]
}

Note that the array's ordering matters. The point at index n of the server's response corresponds to the point at index n of the client's request.