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https://github.com/serai-dex/serai.git
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Move RingCT code to a deciated folder
Should help keep things ordered as more RingCT code is added.
This commit is contained in:
Luke Parker
353
coins/monero/src/ringct/clsag/mod.rs
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353
coins/monero/src/ringct/clsag/mod.rs
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@@ -0,0 +1,353 @@
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#![allow(non_snake_case)]
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use lazy_static::lazy_static;
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use thiserror::Error;
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use rand_core::{RngCore, CryptoRng};
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use curve25519_dalek::{
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constants::ED25519_BASEPOINT_TABLE,
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scalar::Scalar,
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traits::VartimePrecomputedMultiscalarMul,
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edwards::{EdwardsPoint, VartimeEdwardsPrecomputation}
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};
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use crate::{
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Commitment,
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wallet::decoys::Decoys,
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random_scalar, hash_to_scalar, hash_to_point,
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serialize::*
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};
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#[cfg(feature = "multisig")]
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mod multisig;
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#[cfg(feature = "multisig")]
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pub use multisig::{ClsagDetails, ClsagMultisig};
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lazy_static! {
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static ref INV_EIGHT: Scalar = Scalar::from(8 as u8).invert();
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}
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#[derive(Error, Debug)]
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pub enum ClsagError {
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#[error("internal error ({0})")]
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InternalError(String),
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#[error("invalid ring member (member {0}, ring size {1})")]
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InvalidRingMember(u8, u8),
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#[error("invalid commitment")]
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InvalidCommitment,
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#[error("invalid D")]
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InvalidD,
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#[error("invalid s")]
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InvalidS,
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#[error("invalid c1")]
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InvalidC1
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}
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#[derive(Clone, Debug)]
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pub struct ClsagInput {
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// The actual commitment for the true spend
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pub commitment: Commitment,
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// True spend index, offsets, and ring
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pub decoys: Decoys
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}
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impl ClsagInput {
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pub fn new(
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commitment: Commitment,
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decoys: Decoys
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) -> Result<ClsagInput, ClsagError> {
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let n = decoys.len();
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if n > u8::MAX.into() {
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Err(ClsagError::InternalError("max ring size in this library is u8 max".to_string()))?;
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}
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if decoys.i >= (n as u8) {
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Err(ClsagError::InvalidRingMember(decoys.i, n as u8))?;
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}
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// Validate the commitment matches
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if decoys.ring[usize::from(decoys.i)][1] != commitment.calculate() {
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Err(ClsagError::InvalidCommitment)?;
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}
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Ok(ClsagInput { commitment, decoys })
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}
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}
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enum Mode {
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Sign(usize, EdwardsPoint, EdwardsPoint),
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#[cfg(feature = "experimental")]
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Verify(Scalar)
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}
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// Core of the CLSAG algorithm, applicable to both sign and verify with minimal differences
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// Said differences are covered via the above Mode
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fn core(
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ring: &[[EdwardsPoint; 2]],
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I: &EdwardsPoint,
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pseudo_out: &EdwardsPoint,
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msg: &[u8; 32],
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D: &EdwardsPoint,
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s: &[Scalar],
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A_c1: Mode
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) -> ((EdwardsPoint, Scalar, Scalar), Scalar) {
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let n = ring.len();
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let images_precomp = VartimeEdwardsPrecomputation::new([I, D]);
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let D = D * *INV_EIGHT;
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// Generate the transcript
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// Instead of generating multiple, a single transcript is created and then edited as needed
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let mut to_hash = vec![];
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to_hash.reserve_exact(((2 * n) + 5) * 32);
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const PREFIX: &[u8] = "CLSAG_".as_bytes();
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const AGG_0: &[u8] = "CLSAG_agg_0".as_bytes();
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const ROUND: &[u8] = "round".as_bytes();
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to_hash.extend(AGG_0);
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to_hash.extend([0; 32 - AGG_0.len()]);
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let mut P = Vec::with_capacity(n);
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for member in ring {
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P.push(member[0]);
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to_hash.extend(member[0].compress().to_bytes());
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}
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let mut C = Vec::with_capacity(n);
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for member in ring {
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C.push(member[1] - pseudo_out);
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to_hash.extend(member[1].compress().to_bytes());
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}
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to_hash.extend(I.compress().to_bytes());
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to_hash.extend(D.compress().to_bytes());
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to_hash.extend(pseudo_out.compress().to_bytes());
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// mu_P with agg_0
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let mu_P = hash_to_scalar(&to_hash);
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// mu_C with agg_1
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to_hash[AGG_0.len() - 1] = '1' as u8;
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let mu_C = hash_to_scalar(&to_hash);
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// Truncate it for the round transcript, altering the DST as needed
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to_hash.truncate(((2 * n) + 1) * 32);
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for i in 0 .. ROUND.len() {
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to_hash[PREFIX.len() + i] = ROUND[i] as u8;
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}
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// Unfortunately, it's I D pseudo_out instead of pseudo_out I D, meaning this needs to be
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// truncated just to add it back
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to_hash.extend(pseudo_out.compress().to_bytes());
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to_hash.extend(msg);
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// Configure the loop based on if we're signing or verifying
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let start;
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let end;
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let mut c;
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match A_c1 {
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Mode::Sign(r, A, AH) => {
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start = r + 1;
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end = r + n;
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to_hash.extend(A.compress().to_bytes());
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to_hash.extend(AH.compress().to_bytes());
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c = hash_to_scalar(&to_hash);
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},
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#[cfg(feature = "experimental")]
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Mode::Verify(c1) => {
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start = 0;
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end = n;
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c = c1;
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}
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}
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// Perform the core loop
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let mut c1 = None;
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for i in (start .. end).map(|i| i % n) {
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if i == 0 {
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c1 = Some(c);
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}
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let c_p = mu_P * c;
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let c_c = mu_C * c;
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let L = (&s[i] * &ED25519_BASEPOINT_TABLE) + (c_p * P[i]) + (c_c * C[i]);
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let PH = hash_to_point(&P[i]);
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// Shouldn't be an issue as all of the variables in this vartime statement are public
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let R = (s[i] * PH) + images_precomp.vartime_multiscalar_mul(&[c_p, c_c]);
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to_hash.truncate(((2 * n) + 3) * 32);
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to_hash.extend(L.compress().to_bytes());
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to_hash.extend(R.compress().to_bytes());
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c = hash_to_scalar(&to_hash);
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}
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// This first tuple is needed to continue signing, the latter is the c to be tested/worked with
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((D, c * mu_P, c * mu_C), c1.unwrap_or(c))
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}
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#[derive(Clone, Debug)]
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pub struct Clsag {
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pub D: EdwardsPoint,
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pub s: Vec<Scalar>,
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pub c1: Scalar
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}
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impl Clsag {
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// Sign core is the extension of core as needed for signing, yet is shared between single signer
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// and multisig, hence why it's still core
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pub(crate) fn sign_core<R: RngCore + CryptoRng>(
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rng: &mut R,
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I: &EdwardsPoint,
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input: &ClsagInput,
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mask: Scalar,
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msg: &[u8; 32],
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A: EdwardsPoint,
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AH: EdwardsPoint
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) -> (Clsag, EdwardsPoint, Scalar, Scalar) {
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let r: usize = input.decoys.i.into();
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let pseudo_out = Commitment::new(mask, input.commitment.amount).calculate();
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let z = input.commitment.mask - mask;
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let H = hash_to_point(&input.decoys.ring[r][0]);
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let D = H * z;
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let mut s = Vec::with_capacity(input.decoys.ring.len());
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for _ in 0 .. input.decoys.ring.len() {
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s.push(random_scalar(rng));
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}
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let ((D, p, c), c1) = core(&input.decoys.ring, I, &pseudo_out, msg, &D, &s, Mode::Sign(r, A, AH));
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(
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Clsag { D, s, c1 },
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pseudo_out,
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p,
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c * z
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)
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}
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// Single signer CLSAG
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pub fn sign<R: RngCore + CryptoRng>(
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rng: &mut R,
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inputs: &[(Scalar, EdwardsPoint, ClsagInput)],
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sum_outputs: Scalar,
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msg: [u8; 32]
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) -> Vec<(Clsag, EdwardsPoint)> {
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let nonce = random_scalar(rng);
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let mut rand_source = [0; 64];
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rng.fill_bytes(&mut rand_source);
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let mut res = Vec::with_capacity(inputs.len());
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let mut sum_pseudo_outs = Scalar::zero();
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for i in 0 .. inputs.len() {
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let mut mask = random_scalar(rng);
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if i == (inputs.len() - 1) {
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mask = sum_outputs - sum_pseudo_outs;
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} else {
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sum_pseudo_outs += mask;
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}
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let mut rand_source = [0; 64];
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rng.fill_bytes(&mut rand_source);
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let (mut clsag, pseudo_out, p, c) = Clsag::sign_core(
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rng,
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&inputs[i].1,
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&inputs[i].2,
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mask,
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&msg,
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&nonce * &ED25519_BASEPOINT_TABLE,
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nonce * hash_to_point(&inputs[i].2.decoys.ring[usize::from(inputs[i].2.decoys.i)][0])
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);
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clsag.s[inputs[i].2.decoys.i as usize] = nonce - ((p * inputs[i].0) + c);
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res.push((clsag, pseudo_out));
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}
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res
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}
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// Not extensively tested nor guaranteed to have expected parity with Monero
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#[cfg(feature = "experimental")]
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pub fn rust_verify(
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&self,
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ring: &[[EdwardsPoint; 2]],
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I: &EdwardsPoint,
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pseudo_out: &EdwardsPoint,
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msg: &[u8; 32]
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) -> Result<(), ClsagError> {
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let (_, c1) = core(
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ring,
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I,
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pseudo_out,
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msg,
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&self.D.mul_by_cofactor(),
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&self.s,
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Mode::Verify(self.c1)
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);
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if c1 != self.c1 {
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Err(ClsagError::InvalidC1)?;
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}
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Ok(())
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}
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pub fn serialize<W: std::io::Write>(&self, w: &mut W) -> std::io::Result<()> {
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write_raw_vec(write_scalar, &self.s, w)?;
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w.write_all(&self.c1.to_bytes())?;
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write_point(&self.D, w)
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}
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pub fn deserialize<R: std::io::Read>(decoys: usize, r: &mut R) -> std::io::Result<Clsag> {
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Ok(
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Clsag {
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s: read_raw_vec(read_scalar, decoys, r)?,
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c1: read_scalar(r)?,
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D: read_point(r)?
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}
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)
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}
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pub fn verify(
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&self,
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ring: &[[EdwardsPoint; 2]],
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I: &EdwardsPoint,
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pseudo_out: &EdwardsPoint,
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msg: &[u8; 32]
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) -> Result<(), ClsagError> {
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// Serialize it to pass the struct to Monero without extensive FFI
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let mut serialized = Vec::with_capacity(1 + ((self.s.len() + 2) * 32));
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write_varint(&self.s.len().try_into().unwrap(), &mut serialized).unwrap();
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self.serialize(&mut serialized).unwrap();
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let I_bytes = I.compress().to_bytes();
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let mut ring_bytes = vec![];
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for member in ring {
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ring_bytes.extend(&member[0].compress().to_bytes());
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ring_bytes.extend(&member[1].compress().to_bytes());
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}
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let pseudo_out_bytes = pseudo_out.compress().to_bytes();
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unsafe {
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// Uses Monero's C verification function to ensure compatibility with Monero
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#[link(name = "wrapper")]
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extern "C" {
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pub(crate) fn c_verify_clsag(
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serialized_len: usize,
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serialized: *const u8,
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ring_size: u8,
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ring: *const u8,
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I: *const u8,
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pseudo_out: *const u8,
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msg: *const u8
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) -> bool;
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}
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if c_verify_clsag(
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serialized.len(), serialized.as_ptr(),
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ring.len() as u8, ring_bytes.as_ptr(),
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I_bytes.as_ptr(), pseudo_out_bytes.as_ptr(), msg.as_ptr()
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) {
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Ok(())
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} else {
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Err(ClsagError::InvalidC1)
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}
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}
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}
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}
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