revm_precompile/bls12_381/
g2_mul.rs

1use super::{
2    g2::{encode_g2_point, extract_g2_input, G2_INPUT_ITEM_LENGTH},
3    utils::{extract_scalar_input, NBITS},
4};
5use crate::{u64_to_address, PrecompileWithAddress};
6use blst::{blst_p2, blst_p2_affine, blst_p2_from_affine, blst_p2_mult, blst_p2_to_affine};
7use revm_primitives::{Bytes, Precompile, PrecompileError, PrecompileOutput, PrecompileResult};
8
9/// [EIP-2537](https://eips.ethereum.org/EIPS/eip-2537#specification) BLS12_G2MUL precompile.
10pub const PRECOMPILE: PrecompileWithAddress =
11    PrecompileWithAddress(u64_to_address(ADDRESS), Precompile::Standard(g2_mul));
12/// BLS12_G2MUL precompile address.
13pub const ADDRESS: u64 = 0x0f;
14/// Base gas fee for BLS12-381 g2_mul operation.
15pub(super) const BASE_GAS_FEE: u64 = 45000;
16
17/// Input length of g2_mul operation.
18pub(super) const INPUT_LENGTH: usize = 288;
19
20/// G2 multiplication call expects `288` bytes as an input that is interpreted as
21/// byte concatenation of encoding of G2 point (`256` bytes) and encoding of a
22/// scalar value (`32` bytes).
23/// Output is an encoding of multiplication operation result - single G2 point
24/// (`256` bytes).
25/// See also: <https://eips.ethereum.org/EIPS/eip-2537#abi-for-g2-multiplication>
26pub(super) fn g2_mul(input: &Bytes, gas_limit: u64) -> PrecompileResult {
27    if BASE_GAS_FEE > gas_limit {
28        return Err(PrecompileError::OutOfGas.into());
29    }
30    if input.len() != INPUT_LENGTH {
31        return Err(PrecompileError::Other(format!(
32            "G2MUL input should be {INPUT_LENGTH} bytes, was {}",
33            input.len()
34        ))
35        .into());
36    }
37
38    // NB: Scalar multiplications, MSMs and pairings MUST perform a subgroup check.
39    //
40    // So we set the subgroup_check flag to `true`
41    let p0_aff = &extract_g2_input(&input[..G2_INPUT_ITEM_LENGTH], true)?;
42    let mut p0 = blst_p2::default();
43    // SAFETY: p0 and p0_aff are blst values.
44    unsafe { blst_p2_from_affine(&mut p0, p0_aff) };
45
46    let input_scalar0 = extract_scalar_input(&input[G2_INPUT_ITEM_LENGTH..])?;
47
48    let mut p = blst_p2::default();
49    // SAFETY: input_scalar0.b has fixed size, p and p0 are blst values.
50    unsafe { blst_p2_mult(&mut p, &p0, input_scalar0.b.as_ptr(), NBITS) };
51    let mut p_aff = blst_p2_affine::default();
52    // SAFETY: p_aff and p are blst values.
53    unsafe { blst_p2_to_affine(&mut p_aff, &p) };
54
55    let out = encode_g2_point(&p_aff);
56    Ok(PrecompileOutput::new(BASE_GAS_FEE, out))
57}