Add a dedicated send/recv CLSAG mask struct

Abstracts the types used internally.

Also moves the tests from monero-serai to monero-clsag.

coins/monero/ringct/clsag/Cargo.toml

@@ -39,6 +39,9 @@ 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 }
 
+[dev-dependencies]
+frost = { package = "modular-frost", path = "../../../../crypto/frost", default-features = false, features = ["ed25519", "tests"] }
+
 [features]
 std = [
   "std-shims/std",

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

@@ -28,7 +28,10 @@ use monero_primitives::{INV_EIGHT, BASEPOINT_PRECOMP, Commitment, Decoys, keccak
 #[cfg(feature = "multisig")]
 mod multisig;
 #[cfg(feature = "multisig")]
-pub use multisig::{ClsagAddendum, ClsagMultisig};
+pub use multisig::{ClsagMultisigMaskSender, ClsagAddendum, ClsagMultisig};
+
+#[cfg(all(feature = "std", test))]
+mod tests;
 
 /// Errors when working with CLSAGs.
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
@@ -219,8 +222,7 @@ fn core(
 pub struct Clsag {
   D: EdwardsPoint,
   s: Vec<Scalar>,
-  // TODO: Remove pub
-  pub c1: Scalar,
+  c1: Scalar,
 }
 
 struct ClsagSignCore {

coins/monero/ringct/clsag/src/multisig.rs

@@ -1,9 +1,9 @@
 use core::{ops::Deref, fmt::Debug};
 use std_shims::{
+  sync::{Arc, Mutex},
   io::{self, Read, Write},
   collections::HashMap,
 };
-use std::sync::{Arc, Mutex};
 
 use rand_core::{RngCore, CryptoRng, SeedableRng};
 use rand_chacha::ChaCha20Rng;
@@ -54,6 +54,35 @@ impl ClsagContext {
   }
 }
 
+/// A channel to send the mask to use for the pseudo-out (rerandomized commitment) with.
+///
+/// A mask must be sent along this channel before any preprocess addendums are handled. Breaking
+/// this rule will cause a panic.
+#[derive(Clone, Debug)]
+pub struct ClsagMultisigMaskSender {
+  buf: Arc<Mutex<Option<Scalar>>>,
+}
+#[derive(Clone, Debug)]
+struct ClsagMultisigMaskReceiver {
+  buf: Arc<Mutex<Option<Scalar>>>,
+}
+impl ClsagMultisigMaskSender {
+  fn new() -> (ClsagMultisigMaskSender, ClsagMultisigMaskReceiver) {
+    let buf = Arc::new(Mutex::new(None));
+    (ClsagMultisigMaskSender { buf: buf.clone() }, ClsagMultisigMaskReceiver { buf })
+  }
+
+  /// Send a mask to a CLSAG multisig instance.
+  pub fn send(self, mask: Scalar) {
+    *self.buf.lock() = Some(mask);
+  }
+}
+impl ClsagMultisigMaskReceiver {
+  fn recv(self) -> Scalar {
+    self.buf.lock().unwrap()
+  }
+}
+
 /// Addendum produced during the signing process.
 #[derive(Clone, PartialEq, Eq, Zeroize, Debug)]
 pub struct ClsagAddendum {
@@ -61,6 +90,7 @@ pub struct ClsagAddendum {
 }
 
 impl ClsagAddendum {
+  /// The key image share within this addendum.
   pub fn key_image_share(&self) -> dfg::EdwardsPoint {
     self.key_image_share
   }
@@ -94,7 +124,7 @@ pub struct ClsagMultisig {
 
   context: ClsagContext,
 
-  mask_mutex: Arc<Mutex<Option<Scalar>>>,
+  mask_recv: Option<ClsagMultisigMaskReceiver>,
   mask: Option<Scalar>,
 
   msg: Option<[u8; 32]>,
@@ -108,23 +138,26 @@ impl ClsagMultisig {
   pub fn new(
     transcript: RecommendedTranscript,
     context: ClsagContext,
-    mask_mutex: Arc<Mutex<Option<Scalar>>>,
-  ) -> ClsagMultisig {
-    ClsagMultisig {
-      transcript,
+  ) -> (ClsagMultisig, ClsagMultisigMaskSender) {
+    let (mask_send, mask_recv) = ClsagMultisigMaskSender::new();
+    (
+      ClsagMultisig {
+        transcript,
 
-      key_image_generator: hash_to_point(context.decoys.signer_ring_members()[0].compress().0),
-      key_image_shares: HashMap::new(),
-      image: None,
+        key_image_generator: hash_to_point(context.decoys.signer_ring_members()[0].compress().0),
+        key_image_shares: HashMap::new(),
+        image: None,
 
-      context,
+        context,
 
-      mask_mutex,
-      mask: None,
+        mask_recv: Some(mask_recv),
+        mask: None,
 
-      msg: None,
-      interim: None,
-    }
+        msg: None,
+        interim: None,
+      },
+      mask_send,
+    )
   }
 
   /// The key image generator used by the signer.
@@ -182,7 +215,7 @@ impl Algorithm<Ed25519> for ClsagMultisig {
       // Fetch the mask from the Mutex
       // We set it to a variable to ensure our view of it is consistent
       // It was this or a mpsc channel... std doesn't have oneshot :/
-      self.mask = Some(self.mask_mutex.lock().unwrap().unwrap());
+      self.mask = Some(self.mask_recv.take().unwrap().recv());
       // Transcript the mask
       self.transcript.append_message(b"mask", self.mask.expect("mask wasn't set").to_bytes());
 

coins/monero/ringct/clsag/src/tests.rs

@@ -1,5 +1,4 @@
 use core::ops::Deref;
-use std::sync::{Arc, Mutex};
 
 use zeroize::Zeroizing;
 use rand_core::{RngCore, OsRng};
@@ -11,16 +10,11 @@ use transcript::{Transcript, RecommendedTranscript};
 #[cfg(feature = "multisig")]
 use frost::curve::Ed25519;
 
-use crate::{
-  Commitment,
-  wallet::Decoys,
-  ringct::{
-    generate_key_image,
-    clsag::{ClsagContext, Clsag},
-  },
-};
+use monero_generators::hash_to_point;
+use monero_primitives::{Commitment, Decoys};
+use crate::{ClsagContext, Clsag};
 #[cfg(feature = "multisig")]
-use crate::ringct::clsag::ClsagMultisig;
+use crate::ClsagMultisig;
 
 #[cfg(feature = "multisig")]
 use frost::{
@@ -72,7 +66,8 @@ fn clsag() {
     .unwrap()
     .swap_remove(0);
 
-    let image = generate_key_image(&secrets.0);
+    let image =
+      hash_to_point((ED25519_BASEPOINT_TABLE * secrets.0.deref()).compress().0) * secrets.0.deref();
     clsag.verify(&ring, &image, &pseudo_out, &msg).unwrap();
 
     // make sure verification fails if we throw a random `c1` at it.
@@ -104,15 +99,15 @@ fn clsag_multisig() {
     ring.push([dest, Commitment::new(mask, amount).calculate()]);
   }
 
-  let algorithm = ClsagMultisig::new(
+  let (algorithm, mask_send) = ClsagMultisig::new(
     RecommendedTranscript::new(b"Monero Serai CLSAG Test"),
     ClsagContext::new(
       Decoys::new((1 ..= RING_LEN).collect(), RING_INDEX, ring.clone()).unwrap(),
       Commitment::new(randomness, AMOUNT),
     )
     .unwrap(),
-    Arc::new(Mutex::new(Some(Scalar::random(&mut OsRng)))),
   );
+  mask_send.send(Scalar::random(&mut OsRng));
 
   sign(
     &mut OsRng,

coins/monero/src/tests/mod.rs

@@ -1,5 +1,4 @@
 mod unreduced_scalar;
-mod clsag;
 mod bulletproofs;
 mod address;
 mod seed;

coins/monero/src/wallet/send/multisig.rs

@@ -3,7 +3,6 @@ use std_shims::{
   io::{self, Read},
   collections::HashMap,
 };
-use std::sync::{Arc, Mutex};
 
 use zeroize::Zeroizing;
 
@@ -27,7 +26,7 @@ use frost::{
 
 use crate::{
   ringct::{
-    clsag::{ClsagContext, ClsagAddendum, ClsagMultisig},
+    clsag::{ClsagContext, ClsagMultisigMaskSender, ClsagAddendum, ClsagMultisig},
     RctPrunable,
   },
   transaction::{Input, Transaction},
@@ -43,7 +42,7 @@ pub struct TransactionMachine {
 
   // Hashed key and scalar offset
   key_images: Vec<(EdwardsPoint, Scalar)>,
-  clsag_mask_mutexes: Vec<Arc<Mutex<Option<Scalar>>>>,
+  clsag_mask_sends: Vec<ClsagMultisigMaskSender>,
   clsags: Vec<AlgorithmMachine<Ed25519, ClsagMultisig>>,
 }
 
@@ -54,7 +53,7 @@ pub struct TransactionSignMachine {
   transcript: RecommendedTranscript,
 
   key_images: Vec<(EdwardsPoint, Scalar)>,
-  clsag_mask_mutexes: Vec<Arc<Mutex<Option<Scalar>>>>,
+  clsag_mask_sends: Vec<ClsagMultisigMaskSender>,
   clsags: Vec<AlgorithmSignMachine<Ed25519, ClsagMultisig>>,
 
   our_preprocess: Vec<Preprocess<Ed25519, ClsagAddendum>>,
@@ -73,11 +72,7 @@ impl SignableTransaction {
     keys: &ThresholdKeys<Ed25519>,
     mut transcript: RecommendedTranscript,
   ) -> Result<TransactionMachine, TransactionError> {
-    let mut clsag_mask_mutexes = vec![];
-    for _ in 0 .. self.inputs.len() {
-      // Doesn't resize as that will use a single Rc for the entire Vec
-      clsag_mask_mutexes.push(Arc::new(Mutex::new(None)));
-    }
+    let mut clsag_mask_sends = vec![];
     let mut clsags = vec![];
 
     // Create a RNG out of the input shared keys, which either requires the view key or being every
@@ -148,7 +143,8 @@ impl SignableTransaction {
 
       let context = ClsagContext::new(decoys.clone(), input.commitment())
         .map_err(TransactionError::ClsagError)?;
-      let clsag = ClsagMultisig::new(transcript.clone(), context, clsag_mask_mutexes[i].clone());
+      let (clsag, clsag_mask_send) = ClsagMultisig::new(transcript.clone(), context);
+      clsag_mask_sends.push(clsag_mask_send);
       key_images.push((
         clsag.key_image_generator(),
         keys.current_offset().unwrap_or(dfg::Scalar::ZERO).0 + self.inputs[i].0.key_offset(),
@@ -161,7 +157,7 @@ impl SignableTransaction {
       i: keys.params().i(),
       transcript,
       key_images,
-      clsag_mask_mutexes,
+      clsag_mask_sends,
       clsags,
     })
   }
@@ -206,7 +202,7 @@ impl PreprocessMachine for TransactionMachine {
         transcript: self.transcript,
 
         key_images: self.key_images,
-        clsag_mask_mutexes: self.clsag_mask_mutexes,
+        clsag_mask_sends: self.clsag_mask_sends,
         clsags,
 
         our_preprocess,
@@ -334,7 +330,7 @@ impl SignMachine<Transaction> for TransactionSignMachine {
       sorted.push((
         images.swap_remove(0),
         self.signable.inputs.swap_remove(0).1,
-        self.clsag_mask_mutexes.swap_remove(0),
+        self.clsag_mask_sends.swap_remove(0),
         self.clsags.swap_remove(0),
         commitments.swap_remove(0),
       ));
@@ -352,7 +348,7 @@ impl SignMachine<Transaction> for TransactionSignMachine {
       } else {
         sum_pseudo_outs += mask;
       }
-      *value.2.lock().unwrap() = Some(mask);
+      value.2.send(mask);
 
       tx.prefix.inputs.push(Input::ToKey {
         amount: None,