Begin crate smashing

coins/monero/primitives/src/lib.rs

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+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use std_shims::{vec, vec::Vec};
+#[cfg(feature = "std")]
+use std_shims::sync::OnceLock;
+
+use zeroize::{Zeroize, ZeroizeOnDrop};
+
+use sha3::{Digest, Keccak256};
+use curve25519_dalek::{
+  constants::ED25519_BASEPOINT_POINT,
+  traits::VartimePrecomputedMultiscalarMul,
+  scalar::Scalar,
+  edwards::{EdwardsPoint, VartimeEdwardsPrecomputation},
+};
+
+use monero_io::varint_len;
+use monero_generators::H;
+
+// TODO: Replace this with a const
+#[cfg(feature = "std")]
+static INV_EIGHT_CELL: OnceLock<Scalar> = OnceLock::new();
+#[cfg(feature = "std")]
+#[allow(non_snake_case)]
+pub fn INV_EIGHT() -> Scalar {
+  *INV_EIGHT_CELL.get_or_init(|| Scalar::from(8u8).invert())
+}
+#[cfg(not(feature = "std"))]
+#[allow(non_snake_case)]
+pub fn INV_EIGHT() -> Scalar {
+  Scalar::from(8u8).invert()
+}
+
+// On std, we cache this in a static
+// In no-std environments, we prefer the reduced memory use and calculate it ad-hoc
+#[cfg(feature = "std")]
+static BASEPOINT_PRECOMP_CELL: OnceLock<VartimeEdwardsPrecomputation> = OnceLock::new();
+#[cfg(feature = "std")]
+#[allow(non_snake_case)]
+pub fn BASEPOINT_PRECOMP() -> &'static VartimeEdwardsPrecomputation {
+  BASEPOINT_PRECOMP_CELL
+    .get_or_init(|| VartimeEdwardsPrecomputation::new([ED25519_BASEPOINT_POINT]))
+}
+#[cfg(not(feature = "std"))]
+#[allow(non_snake_case)]
+pub fn BASEPOINT_PRECOMP() -> VartimeEdwardsPrecomputation {
+  VartimeEdwardsPrecomputation::new([ED25519_BASEPOINT_POINT])
+}
+
+pub fn keccak256(data: impl AsRef<[u8]>) -> [u8; 32] {
+  Keccak256::digest(data.as_ref()).into()
+}
+
+/// Hash the provided data to a scalar via keccak256(data) % l.
+pub fn keccak256_to_scalar(data: impl AsRef<[u8]>) -> Scalar {
+  let scalar = Scalar::from_bytes_mod_order(keccak256(data.as_ref()));
+  // Monero will explicitly error in this case
+  // This library acknowledges its practical impossibility of it occurring, and doesn't bother to
+  // code in logic to handle it. That said, if it ever occurs, something must happen in order to
+  // not generate/verify a proof we believe to be valid when it isn't
+  assert!(scalar != Scalar::ZERO, "ZERO HASH: {:?}", data.as_ref());
+  scalar
+}
+
+/// Transparent structure representing a Pedersen commitment's contents.
+#[allow(non_snake_case)]
+#[derive(Clone, PartialEq, Eq, Zeroize, ZeroizeOnDrop)]
+pub struct Commitment {
+  pub mask: Scalar,
+  pub amount: u64,
+}
+
+impl core::fmt::Debug for Commitment {
+  fn fmt(&self, fmt: &mut core::fmt::Formatter<'_>) -> Result<(), core::fmt::Error> {
+    fmt.debug_struct("Commitment").field("amount", &self.amount).finish_non_exhaustive()
+  }
+}
+
+impl Commitment {
+  /// A commitment to zero, defined with a mask of 1 (as to not be the identity).
+  pub fn zero() -> Commitment {
+    Commitment { mask: Scalar::ONE, amount: 0 }
+  }
+
+  pub fn new(mask: Scalar, amount: u64) -> Commitment {
+    Commitment { mask, amount }
+  }
+
+  /// Calculate a Pedersen commitment, as a point, from the transparent structure.
+  pub fn calculate(&self) -> EdwardsPoint {
+    EdwardsPoint::vartime_double_scalar_mul_basepoint(&Scalar::from(self.amount), &H(), &self.mask)
+  }
+}
+
+/// Decoy data, containing the actual member as well (at index `i`).
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize, ZeroizeOnDrop)]
+pub struct Decoys {
+  pub i: u8,
+  pub offsets: Vec<u64>,
+  pub ring: Vec<[EdwardsPoint; 2]>,
+}
+
+#[allow(clippy::len_without_is_empty)]
+impl Decoys {
+  pub fn fee_weight(offsets: &[u64]) -> usize {
+    varint_len(offsets.len()) + offsets.iter().map(|offset| varint_len(*offset)).sum::<usize>()
+  }
+
+  pub fn len(&self) -> usize {
+    self.offsets.len()
+  }
+
+  pub fn indexes(&self) -> Vec<u64> {
+    let mut res = vec![self.offsets[0]; self.len()];
+    for m in 1 .. res.len() {
+      res[m] = res[m - 1] + self.offsets[m];
+    }
+    res
+  }
+}