to_bytes unimplemented for pasta field types

[srinathsetty]

Fp types in secp256k1 and pasta are implemented similarly using the same macro:

• https://github.com/privacy-scaling-explorations/halo2curves/blob/main/src/pasta/fp.rs
• https://github.com/privacy-scaling-explorations/halo2curves/blob/main/src/secp256k1/fp.rs

However, to_bytes is implemented for secp256k1's Fp but not for pasta's Fp. Is there a reason for this? To illustrate this consider the following example that fails to build.

use halo2curves::{
  pasta::Fp as PallasScalar,
  secp256k1::Fp as SecpScalar,
};

fn main() {
  let pallas_scalar = PallasScalar::from(42);
  let secp_scalar = SecpScalar::from(42);

  println!("pallas scalar: {:?}", pallas_scalar);
  println!("secp scalar: {:?}", secp_scalar);

  println!("pallas scalar: {:?}", pallas_scalar.to_bytes());
  println!("secp scalar: {:?}", secp_scalar.to_bytes());
}

To avoid this discrepancy, a pending PR on Nova uses a hack:

• https://github.com/microsoft/Nova/blob/d1535fbcb440dc63b6a787577149d124fcd4c1af/src/provider/traits.rs#L202 (for bn256 and secp256k1 curves, uses to_bytes method to extract a byte representation)
• https://github.com/microsoft/Nova/blob/d1535fbcb440dc63b6a787577149d124fcd4c1af/src/provider/traits.rs#L224 (for pasta curves, to extract a byte representation).

We would like to avoid this hack and use a uniform implementation. Can you help?

[davidnevadoc]

Removing the pasta re-export and implementing it directly seems to have solved the issue (#180) .

Upgrading the halo2curves dependency to v0.7.1 should be enough to get rid of the hack 👍
Let me know if that works @srinathsetty

[srinathsetty]

Thanks @davidnevadoc for the quick response! I could point my Cargo.toml to the halo2curves github repo and I was able to get rid of the hack.

However, on crates.io and in the halo2curves repo, I only see version 0.7.0. Do you plan to publish 0.7.1 soon?

Also, there's a typo here:

halo2curves/src/pasta/pallas.rs

Line 22 in 94e3692

PastaAffine,

(it should be PallasAffine rather than PastaAffine to keep the naming consistent).

[davidnevadoc]

You're right!
I'll get that fixed and publish the release in crates.io before EOW.