serai/coins/monero/src/ringct/bulletproofs.rs

#![allow(non_snake_case)]

use rand_core::{RngCore, CryptoRng};

use curve25519_dalek::{scalar::Scalar, edwards::EdwardsPoint};

use crate::{Commitment, wallet::TransactionError, serialize::*};

pub(crate) const MAX_OUTPUTS: usize = 16;

#[derive(Clone, PartialEq, Debug)]
pub struct Bulletproofs {
  pub A: EdwardsPoint,
  pub S: EdwardsPoint,
  pub T1: EdwardsPoint,
  pub T2: EdwardsPoint,
  pub taux: Scalar,
  pub mu: Scalar,
  pub L: Vec<EdwardsPoint>,
  pub R: Vec<EdwardsPoint>,
  pub a: Scalar,
  pub b: Scalar,
  pub t: Scalar
}

impl Bulletproofs {
  pub(crate) fn fee_weight(outputs: usize) -> usize {
    let proofs = 6 + usize::try_from(usize::BITS - (outputs - 1).leading_zeros()).unwrap();
    let len = (9 + (2 * proofs)) * 32;

    let mut clawback = 0;
    let padded = 1 << (proofs - 6);
    if padded > 2 {
      const BP_BASE: usize = 368;
      clawback = ((BP_BASE * padded) - len) * 4 / 5;
    }

    len + clawback
  }

  pub fn new<R: RngCore + CryptoRng>(rng: &mut R, outputs: &[Commitment]) -> Result<Bulletproofs, TransactionError> {
    if outputs.len() > MAX_OUTPUTS {
      return Err(TransactionError::TooManyOutputs)?;
    }

    let mut seed = [0; 32];
    rng.fill_bytes(&mut seed);

    let masks = outputs.iter().map(|commitment| commitment.mask.to_bytes()).collect::<Vec<_>>();
    let amounts = outputs.iter().map(|commitment| commitment.amount).collect::<Vec<_>>();

    let res;
    unsafe {
      #[link(name = "wrapper")]
      extern "C" {
        fn free(ptr: *const u8);
        fn c_generate_bp(seed: *const u8, len: u8, amounts: *const u64, masks: *const [u8; 32]) -> *const u8;
      }

      let ptr = c_generate_bp(
        seed.as_ptr(),
        u8::try_from(outputs.len()).unwrap(),
        amounts.as_ptr(),
        masks.as_ptr()
      );

      let mut len = 6 * 32;
      len += (2 * (1 + (usize::from(ptr.add(len).read()) * 32))) + (3 * 32);
      res = Bulletproofs::deserialize(
        // Wrap in a cursor to provide a mutable Reader
        &mut std::io::Cursor::new(std::slice::from_raw_parts(ptr, len))
      ).expect("Couldn't deserialize Bulletproofs from Monero");
      free(ptr);
    };

    Ok(res)
  }

  #[must_use]
  pub fn verify<R: RngCore + CryptoRng>(&self, rng: &mut R, commitments: &[EdwardsPoint]) -> bool {
    if commitments.len() > 16 {
      return false;
    }

    let mut seed = [0; 32];
    rng.fill_bytes(&mut seed);

    let mut serialized = Vec::with_capacity((9 + (2 * self.L.len())) * 32);
    self.serialize(&mut serialized).unwrap();
    let commitments: Vec<[u8; 32]> = commitments.iter().map(
      |commitment| (commitment * Scalar::from(8u8).invert()).compress().to_bytes()
    ).collect();

    unsafe {
      #[link(name = "wrapper")]
      extern "C" {
        fn c_verify_bp(
          seed: *const u8,
          serialized_len: usize,
          serialized: *const u8,
          commitments_len: u8,
          commitments: *const [u8; 32]
        ) -> bool;
      }

      c_verify_bp(
        seed.as_ptr(),
        serialized.len(),
        serialized.as_ptr(),
        u8::try_from(commitments.len()).unwrap(),
        commitments.as_ptr()
      )
    }
  }

  fn serialize_core<
    W: std::io::Write,
    F: Fn(&[EdwardsPoint], &mut W) -> std::io::Result<()>
  >(&self, w: &mut W, specific_write_vec: F) -> std::io::Result<()> {
    write_point(&self.A, w)?;
    write_point(&self.S, w)?;
    write_point(&self.T1, w)?;
    write_point(&self.T2, w)?;
    write_scalar(&self.taux, w)?;
    write_scalar(&self.mu, w)?;
    specific_write_vec(&self.L, w)?;
    specific_write_vec(&self.R, w)?;
    write_scalar(&self.a, w)?;
    write_scalar(&self.b, w)?;
    write_scalar(&self.t, w)
  }

  pub fn signature_serialize<W: std::io::Write>(&self, w: &mut W) -> std::io::Result<()> {
    self.serialize_core(w, |points, w| write_raw_vec(write_point, points, w))
  }

  pub fn serialize<W: std::io::Write>(&self, w: &mut W) -> std::io::Result<()> {
    self.serialize_core(w, |points, w| write_vec(write_point, points, w))
  }

  pub fn deserialize<R: std::io::Read>(r: &mut R) -> std::io::Result<Bulletproofs> {
    let bp = Bulletproofs {
      A: read_point(r)?,
      S: read_point(r)?,
      T1: read_point(r)?,
      T2: read_point(r)?,
      taux: read_scalar(r)?,
      mu: read_scalar(r)?,
      L: read_vec(read_point, r)?,
      R: read_vec(read_point, r)?,
      a: read_scalar(r)?,
      b: read_scalar(r)?,
      t: read_scalar(r)?
    };

    if bp.L.len() != bp.R.len() {
      Err(std::io::Error::new(std::io::ErrorKind::Other, "mismatched L/R len"))?;
    }
    Ok(bp)
  }
}