Smash out Borromean

Cargo.lock

@@ -4751,6 +4751,18 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "monero-borromean"
+version = "0.1.0"
+dependencies = [
+ "curve25519-dalek",
+ "monero-generators",
+ "monero-io",
+ "monero-primitives",
+ "std-shims",
+ "zeroize",
+]
+
 [[package]]
 name = "monero-bulletproofs"
 version = "0.1.0"
@@ -4827,7 +4839,9 @@ name = "monero-primitives"
 version = "0.1.0"
 dependencies = [
  "curve25519-dalek",
+ "hex",
  "monero-generators",
+ "monero-io",
  "sha3",
  "std-shims",
  "zeroize",
@@ -4847,6 +4861,7 @@ dependencies = [
  "hex",
  "hex-literal",
  "modular-frost",
+ "monero-borromean",
  "monero-bulletproofs",
  "monero-clsag",
  "monero-generators",

Cargo.toml

@@ -48,6 +48,7 @@ members = [
   "coins/monero/primitives",
   "coins/monero/ringct/mlsag",
   "coins/monero/ringct/clsag",
+  "coins/monero/ringct/borromean",
   "coins/monero/ringct/bulletproofs",
   "coins/monero",
 

coins/monero/Cargo.toml

@@ -49,6 +49,7 @@ monero-generators = { path = "generators", version = "0.4", default-features = f
 monero-primitives = { path = "primitives", version = "0.1", default-features = false }
 monero-mlsag = { path = "ringct/mlsag", version = "0.1", default-features = false }
 monero-clsag = { path = "ringct/clsag", version = "0.1", default-features = false }
+monero-borromean = { path = "ringct/borromean", version = "0.1", default-features = false }
 monero-bulletproofs = { path = "ringct/bulletproofs", version = "0.1", default-features = false }
 
 hex-literal = "0.4"

coins/monero/primitives/Cargo.toml

@@ -25,8 +25,12 @@ sha3 = { version = "0.10", default-features = false }
 curve25519-dalek = { version = "4", default-features = false, features = ["alloc", "zeroize"] }
 
 # Other Monero dependencies
+monero-io = { path = "../io", version = "0.1", default-features = false }
 monero-generators = { path = "../generators", version = "0.4", default-features = false }
 
+[dev-dependencies]
+hex = { version = "0.4", default-features = false, features = ["alloc"] }
+
 [features]
 std = [
   "std-shims/std",

coins/monero/primitives/src/lib.rs

@@ -19,6 +19,12 @@ use curve25519_dalek::{
 
 use monero_generators::H;
 
+mod unreduced_scalar;
+pub use unreduced_scalar::UnreducedScalar;
+
+#[cfg(test)]
+mod tests;
+
 // On std, we cache some variables in statics.
 #[cfg(feature = "std")]
 static INV_EIGHT_CELL: OnceLock<Scalar> = OnceLock::new();

coins/monero/primitives/src/tests.rs

@@ -1,6 +1,6 @@
 use curve25519_dalek::scalar::Scalar;
 
-use crate::unreduced_scalar::*;
+use crate::UnreducedScalar;
 
 #[test]
 fn recover_scalars() {

coins/monero/primitives/src/unreduced_scalar.rs

@@ -1,18 +1,19 @@
 use core::cmp::Ordering;
-
 use std_shims::{
   sync::OnceLock,
   io::{self, *},
 };
 
+use zeroize::Zeroize;
+
 use curve25519_dalek::scalar::Scalar;
 
-use crate::serialize::*;
+use monero_io::*;
 
 static PRECOMPUTED_SCALARS_CELL: OnceLock<[Scalar; 8]> = OnceLock::new();
-/// Precomputed scalars used to recover an incorrectly reduced scalar.
+// Precomputed scalars used to recover an incorrectly reduced scalar.
 #[allow(non_snake_case)]
-pub(crate) fn PRECOMPUTED_SCALARS() -> [Scalar; 8] {
+fn PRECOMPUTED_SCALARS() -> [Scalar; 8] {
   *PRECOMPUTED_SCALARS_CELL.get_or_init(|| {
     let mut precomputed_scalars = [Scalar::ONE; 8];
     for (i, scalar) in precomputed_scalars.iter_mut().enumerate().skip(1) {
@@ -22,14 +23,23 @@ pub(crate) fn PRECOMPUTED_SCALARS() -> [Scalar; 8] {
   })
 }
 
-#[derive(Clone, PartialEq, Eq, Debug)]
+/// An unreduced scalar.
+///
+/// While most of modern Monero enforces scalars be reduced, certain legacy parts of the code did
+/// not. These section can generally simply be read as a scalar/reduced into a scalar when the time
+/// comes, yet a couple have non-standard reductions performed.
+///
+/// This struct delays scalar conversions and offers the non-standard reduction.
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize)]
 pub struct UnreducedScalar(pub [u8; 32]);
 
 impl UnreducedScalar {
+  /// Write an UnreducedScalar.
   pub fn write<W: Write>(&self, w: &mut W) -> io::Result<()> {
     w.write_all(&self.0)
   }
 
+  /// Read an UnreducedScalar.
   pub fn read<R: Read>(r: &mut R) -> io::Result<UnreducedScalar> {
     Ok(UnreducedScalar(read_bytes(r)?))
   }
@@ -43,12 +53,12 @@ impl UnreducedScalar {
     bits
   }
 
-  /// Computes the non-adjacent form of this scalar with width 5.
-  ///
-  /// This matches Monero's `slide` function and intentionally gives incorrect outputs under
-  /// certain conditions in order to match Monero.
-  ///
-  /// This function does not execute in constant time.
+  // Computes the non-adjacent form of this scalar with width 5.
+  //
+  // This matches Monero's `slide` function and intentionally gives incorrect outputs under
+  // certain conditions in order to match Monero.
+  //
+  // This function does not execute in constant time.
   fn non_adjacent_form(&self) -> [i8; 256] {
     let bits = self.as_bits();
     let mut naf = [0i8; 256];
@@ -104,11 +114,11 @@ impl UnreducedScalar {
   /// Recover the scalar that an array of bytes was incorrectly interpreted as by Monero's `slide`
   /// function.
   ///
-  /// In Borromean range proofs Monero was not checking that the scalars used were
-  /// reduced. This lead to the scalar stored being interpreted as a different scalar,
-  /// this function recovers that scalar.
+  /// In Borromean range proofs, Monero was not checking that the scalars used were
+  /// reduced. This lead to the scalar stored being interpreted as a different scalar.
+  /// This function recovers that scalar.
   ///
-  /// See: https://github.com/monero-project/monero/issues/8438
+  /// See https://github.com/monero-project/monero/issues/8438 for more info.
   pub fn recover_monero_slide_scalar(&self) -> Scalar {
     if self.0[31] & 128 == 0 {
       // Computing the w-NAF of a number can only give an output with 1 more bit than

coins/monero/ringct/borromean/Cargo.toml

@@ -0,0 +1,41 @@
+[package]
+name = "monero-borromean"
+version = "0.1.0"
+description = "Borromean ring signatures arranged into a range proof, as done by the Monero protocol"
+license = "MIT"
+repository = "https://github.com/serai-dex/serai/tree/develop/coins/monero/ringct/borromean"
+authors = ["Luke Parker <lukeparker5132@gmail.com>"]
+edition = "2021"
+rust-version = "1.79"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
+[lints]
+workspace = true
+
+[dependencies]
+std-shims = { path = "../../../../common/std-shims", version = "^0.1.1", default-features = false }
+
+zeroize = { version = "^1.5", default-features = false, features = ["zeroize_derive"] }
+
+# Cryptographic dependencies
+curve25519-dalek = { version = "4", default-features = false, features = ["alloc", "zeroize"] }
+
+# Other Monero dependencies
+monero-io = { path = "../../io", version = "0.1", default-features = false }
+monero-generators = { path = "../../generators", version = "0.4", default-features = false }
+monero-primitives = { path = "../../primitives", version = "0.1", default-features = false }
+
+[features]
+std = [
+  "std-shims/std",
+
+  "zeroize/std",
+
+  "monero-io/std",
+  "monero-generators/std",
+  "monero-primitives/std",
+]
+default = ["std"]

coins/monero/ringct/borromean/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2022-2024 Luke Parker
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

coins/monero/ringct/borromean/README.md

@@ -0,0 +1,7 @@
+# Monero Borromean
+
+Borromean ring signatures arranged into a range proof, as done by the Monero
+protocol.
+
+This library is usable under no-std when the `std` feature (on by default) is
+disabled.

coins/monero/ringct/borromean/src/lib.rs

@@ -1,18 +1,26 @@
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![doc = include_str!("../README.md")]
+#![deny(missing_docs)]
+#![cfg_attr(not(feature = "std"), no_std)]
+#![allow(non_snake_case)]
+
 use core::fmt::Debug;
 use std_shims::io::{self, Read, Write};
 
+use zeroize::Zeroize;
+
 use curve25519_dalek::{traits::Identity, Scalar, EdwardsPoint};
 
+use monero_io::*;
 use monero_generators::H_pow_2;
+use monero_primitives::{keccak256_to_scalar, UnreducedScalar};
 
-use crate::{hash_to_scalar, unreduced_scalar::UnreducedScalar, serialize::*};
-
-/// 64 Borromean ring signatures, as needed for a 64-bit range proof.
-///
-/// s0 and s1 are stored as `UnreducedScalar`s due to Monero not requiring they were reduced.
-/// `UnreducedScalar` preserves their original byte encoding and implements a custom reduction
-/// algorithm which was in use.
-#[derive(Clone, PartialEq, Eq, Debug)]
+// 64 Borromean ring signatures, as needed for a 64-bit range proof.
+//
+// s0 and s1 are stored as `UnreducedScalar`s due to Monero not requiring they were reduced.
+// `UnreducedScalar` preserves their original byte encoding and implements a custom reduction
+// algorithm which was in use.
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize)]
 struct BorromeanSignatures {
   s0: [UnreducedScalar; 64],
   s1: [UnreducedScalar; 64],
@@ -20,7 +28,7 @@ struct BorromeanSignatures {
 }
 
 impl BorromeanSignatures {
-  /// Read a set of BorromeanSignatures from a reader.
+  // Read a set of BorromeanSignatures.
   fn read<R: Read>(r: &mut R) -> io::Result<BorromeanSignatures> {
     Ok(BorromeanSignatures {
       s0: read_array(UnreducedScalar::read, r)?,
@@ -29,7 +37,7 @@ impl BorromeanSignatures {
     })
   }
 
-  /// Write the set of BorromeanSignatures to a writer.
+  // Write the set of BorromeanSignatures.
   fn write<W: Write>(&self, w: &mut W) -> io::Result<()> {
     for s0 in &self.s0 {
       s0.write(w)?;
@@ -52,26 +60,26 @@ impl BorromeanSignatures {
       );
       #[allow(non_snake_case)]
       let LV = EdwardsPoint::vartime_double_scalar_mul_basepoint(
-        &hash_to_scalar(LL.compress().as_bytes()),
+        &keccak256_to_scalar(LL.compress().as_bytes()),
         &keys_b[i],
         &self.s1[i].recover_monero_slide_scalar(),
       );
       transcript[(i * 32) .. ((i + 1) * 32)].copy_from_slice(LV.compress().as_bytes());
     }
 
-    hash_to_scalar(&transcript) == self.ee
+    keccak256_to_scalar(transcript) == self.ee
   }
 }
 
 /// A range proof premised on Borromean ring signatures.
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, PartialEq, Eq, Debug, Zeroize)]
 pub struct BorromeanRange {
   sigs: BorromeanSignatures,
   bit_commitments: [EdwardsPoint; 64],
 }
 
 impl BorromeanRange {
-  /// Read a BorromeanRange proof from a reader.
+  /// Read a BorromeanRange proof.
   pub fn read<R: Read>(r: &mut R) -> io::Result<BorromeanRange> {
     Ok(BorromeanRange {
       sigs: BorromeanSignatures::read(r)?,
@@ -79,13 +87,14 @@ impl BorromeanRange {
     })
   }
 
-  /// Write the BorromeanRange proof to a reader.
+  /// Write the BorromeanRange proof.
   pub fn write<W: Write>(&self, w: &mut W) -> io::Result<()> {
     self.sigs.write(w)?;
     write_raw_vec(write_point, &self.bit_commitments, w)
   }
 
   /// Verify the commitment contains a 64-bit value.
+  #[must_use]
   pub fn verify(&self, commitment: &EdwardsPoint) -> bool {
     if &self.bit_commitments.iter().sum::<EdwardsPoint>() != commitment {
       return false;

coins/monero/src/lib.rs

@@ -23,9 +23,6 @@ mod merkle;
 use monero_io as serialize;
 use serialize::{read_byte, read_u16};
 
-/// UnreducedScalar struct with functionality for recovering incorrectly reduced scalars.
-mod unreduced_scalar;
-
 /// Ring Signature structs and functionality.
 pub mod ring_signatures;
 

coins/monero/src/ringct/mod.rs

@@ -16,7 +16,7 @@ pub use monero_mlsag as mlsag;
 /// CLSAG struct, along with signing and verifying functionality.
 pub use monero_clsag as clsag;
 /// BorromeanRange struct, along with verifying functionality.
-pub mod borromean;
+pub use monero_borromean as borromean;
 /// Bulletproofs(+) structs, along with proving and verifying functionality.
 pub use monero_bulletproofs as bulletproofs;
 

coins/monero/src/tests/mod.rs

@@ -1,4 +1,3 @@
-mod unreduced_scalar;
 mod address;
 mod seed;
 mod extra;