Regression: trusted setup panics

[marmistrz]

This is a regression introduced in #302.
The following code

        let secrets_len = 15;
        let (s1, s2, s3) = generate_trusted_setup(secrets_len, [0; 32]);

panics due to

thread 'commitment::tests::test_prove' panicked at /home/marcin/.cargo/git/checkouts/rust-kzg-f9d605f513aae74b/21670cd/blst/src/utils.rs:34:66:
called `Result::unwrap()` on an `Err` value: "Supplied list is longer than the available max width"```

You likely need to use the ceiling of the log, because the tests succeeds with secrets_len = 16

[ArtiomTr]

Hello @marmistrz! Thank you for your report.

Yep, generate_trusted_setup function no longer supports non-power-of-two secret length. I believe this shouldn't be a breaking change, because this function was a test utility anyway. Adding support for this function to handle arbitrary secret length would not be so easy, as it would require to modify our fft algorithm (it also supports only power-of-two length slices).

Could you please clarify a bit, where this regression happens? Is it our test or some example code? Thank you in advance.

[marmistrz]

Thanks for your reply,

I simply used generate_trusted_setup in the tests for a program using your library, and these tests started failing after updating the library. I think that this would merit at least an assertion in generate_trusted_setup.

Also, is there any way to save a trusted setup that I generated, so that it can later be loaded using load_trusted_setup?

[ArtiomTr]

I simply used generate_trusted_setup in the tests for a program using your library, and these tests started failing after updating the library. I think that this would merit at least an assertion in generate_trusted_setup.

Okay, will add an assertion.

Also, is there any way to save a trusted setup that I generated, so that it can later be loaded using load_trusted_setup?

Nope, currently no possiblity to save generated trusted setup - we just don't really support proper trusted setup generation - this generate_trusted_setup function generates not-so-trusted setup, as it requires for one party to know secret 😄. However, if you want to use it for testing, I believe you can implement this function pretty easily, like so:

writeln!(file, "{}", g1_points.len());
for p in g1_points {
    writeln!(file, "{}", hex::encode(p.to_bytes()));
}
writeln!(file, "{}", g2_points.len());
for p in g2_points {
    writeln!(file, "{}", hex::encode(p.to_bytes()));
}