Restore Monero multisig TX code

coins/monero/wallet/src/old_send/builder.rs

@@ -11,7 +11,6 @@ use crate::{
 struct SignableTransactionBuilderInternal {
   protocol: WalletProtocol,
   fee_rate: FeeRate,
-
   r_seed: Option<Zeroizing<[u8; 32]>>,
   inputs: Vec<(SpendableOutput, Decoys)>,
   payments: Vec<(MoneroAddress, u64)>,

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

@@ -1,414 +0,0 @@
-use std_shims::{
-  vec::Vec,
-  io::{self, Read},
-  collections::HashMap,
-};
-
-use zeroize::Zeroizing;
-
-use rand_core::{RngCore, CryptoRng, SeedableRng};
-use rand_chacha::ChaCha20Rng;
-
-use group::ff::Field;
-use curve25519_dalek::{traits::Identity, scalar::Scalar, edwards::EdwardsPoint};
-use dalek_ff_group as dfg;
-
-use transcript::{Transcript, RecommendedTranscript};
-use frost::{
-  curve::Ed25519,
-  Participant, FrostError, ThresholdKeys,
-  dkg::lagrange,
-  sign::{
-    Writable, Preprocess, CachedPreprocess, SignatureShare, PreprocessMachine, SignMachine,
-    SignatureMachine, AlgorithmMachine, AlgorithmSignMachine, AlgorithmSignatureMachine,
-  },
-};
-
-use monero_serai::{
-  ringct::{
-    clsag::{ClsagContext, ClsagMultisigMaskSender, ClsagAddendum, ClsagMultisig},
-    RctPrunable, RctProofs,
-  },
-  transaction::{Input, Transaction},
-};
-use crate::{TransactionError, InternalPayment, SignableTransaction, key_image_sort, uniqueness};
-
-/// FROST signing machine to produce a signed transaction.
-pub struct TransactionMachine {
-  signable: SignableTransaction,
-
-  i: Participant,
-  transcript: RecommendedTranscript,
-
-  // Hashed key and scalar offset
-  key_images: Vec<(EdwardsPoint, Scalar)>,
-  clsag_mask_sends: Vec<ClsagMultisigMaskSender>,
-  clsags: Vec<AlgorithmMachine<Ed25519, ClsagMultisig>>,
-}
-
-pub struct TransactionSignMachine {
-  signable: SignableTransaction,
-
-  i: Participant,
-  transcript: RecommendedTranscript,
-
-  key_images: Vec<(EdwardsPoint, Scalar)>,
-  clsag_mask_sends: Vec<ClsagMultisigMaskSender>,
-  clsags: Vec<AlgorithmSignMachine<Ed25519, ClsagMultisig>>,
-
-  our_preprocess: Vec<Preprocess<Ed25519, ClsagAddendum>>,
-}
-
-pub struct TransactionSignatureMachine {
-  tx: Transaction,
-  clsags: Vec<AlgorithmSignatureMachine<Ed25519, ClsagMultisig>>,
-}
-
-impl SignableTransaction {
-  /// Create a FROST signing machine out of this signable transaction.
-  /// The height is the Monero blockchain height to synchronize around.
-  pub fn multisig(
-    self,
-    keys: &ThresholdKeys<Ed25519>,
-    mut transcript: RecommendedTranscript,
-  ) -> Result<TransactionMachine, TransactionError> {
-    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
-    // sender, and the payments (address and amount), which a passive adversary may be able to know
-    // depending on how these transactions are coordinated
-    // Being every sender would already let you note rings which happen to use your transactions
-    // multiple times, already breaking privacy there
-
-    transcript.domain_separate(b"monero_transaction");
-
-    // Also include the spend_key as below only the key offset is included, so this transcripts the
-    // sum product
-    // Useful as transcripting the sum product effectively transcripts the key image, further
-    // guaranteeing the one time properties noted below
-    transcript.append_message(b"spend_key", keys.group_key().0.compress().to_bytes());
-
-    if let Some(r_seed) = &self.r_seed {
-      transcript.append_message(b"r_seed", r_seed);
-    }
-
-    for (input, decoys) in &self.inputs {
-      // These outputs can only be spent once. Therefore, it forces all RNGs derived from this
-      // transcript (such as the one used to create one time keys) to be unique
-      transcript.append_message(b"input_hash", input.output.absolute.tx);
-      transcript.append_message(b"input_output_index", [input.output.absolute.o]);
-      // Not including this, with a doxxed list of payments, would allow brute forcing the inputs
-      // to determine RNG seeds and therefore the true spends
-      transcript.append_message(b"input_shared_key", input.key_offset().to_bytes());
-
-      // Ensure all signers are signing the same rings
-      transcript.append_message(b"real_spend", [decoys.signer_index()]);
-      for (i, ring_member) in decoys.ring().iter().enumerate() {
-        transcript
-          .append_message(b"ring_member", [u8::try_from(i).expect("ring size exceeded 255")]);
-        transcript.append_message(b"ring_member_offset", decoys.offsets()[i].to_le_bytes());
-        transcript.append_message(b"ring_member_key", ring_member[0].compress().to_bytes());
-        transcript.append_message(b"ring_member_commitment", ring_member[1].compress().to_bytes());
-      }
-    }
-
-    for payment in &self.payments {
-      match payment {
-        InternalPayment::Payment(payment, need_dummy_payment_id) => {
-          transcript.append_message(b"payment_address", payment.0.to_string().as_bytes());
-          transcript.append_message(b"payment_amount", payment.1.to_le_bytes());
-          transcript.append_message(
-            b"need_dummy_payment_id",
-            [if *need_dummy_payment_id { 1u8 } else { 0u8 }],
-          );
-        }
-        InternalPayment::Change(change, change_view) => {
-          transcript.append_message(b"change_address", change.0.to_string().as_bytes());
-          transcript.append_message(b"change_amount", change.1.to_le_bytes());
-          if let Some(view) = change_view.as_ref() {
-            transcript.append_message(b"change_view_key", Zeroizing::new(view.to_bytes()));
-          }
-        }
-      }
-    }
-
-    let mut key_images = vec![];
-    for (i, (input, decoys)) in self.inputs.iter().enumerate() {
-      // Check this the right set of keys
-      let offset = keys.offset(dfg::Scalar(input.key_offset()));
-      if offset.group_key().0 != input.key() {
-        Err(TransactionError::WrongPrivateKey)?;
-      }
-
-      let context = ClsagContext::new(decoys.clone(), input.commitment())
-        .map_err(TransactionError::ClsagError)?;
-      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(),
-      ));
-      clsags.push(AlgorithmMachine::new(clsag, offset));
-    }
-
-    Ok(TransactionMachine {
-      signable: self,
-      i: keys.params().i(),
-      transcript,
-      key_images,
-      clsag_mask_sends,
-      clsags,
-    })
-  }
-}
-
-impl PreprocessMachine for TransactionMachine {
-  type Preprocess = Vec<Preprocess<Ed25519, ClsagAddendum>>;
-  type Signature = Transaction;
-  type SignMachine = TransactionSignMachine;
-
-  fn preprocess<R: RngCore + CryptoRng>(
-    mut self,
-    rng: &mut R,
-  ) -> (TransactionSignMachine, Self::Preprocess) {
-    // Iterate over each CLSAG calling preprocess
-    let mut preprocesses = Vec::with_capacity(self.clsags.len());
-    let clsags = self
-      .clsags
-      .drain(..)
-      .map(|clsag| {
-        let (clsag, preprocess) = clsag.preprocess(rng);
-        preprocesses.push(preprocess);
-        clsag
-      })
-      .collect();
-    let our_preprocess = preprocesses.clone();
-
-    // We could add further entropy here, and previous versions of this library did so
-    // As of right now, the multisig's key, the inputs being spent, and the FROST data itself
-    // will be used for RNG seeds. In order to recreate these RNG seeds, breaking privacy,
-    // counterparties must have knowledge of the multisig, either the view key or access to the
-    // coordination layer, and then access to the actual FROST signing process
-    // If the commitments are sent in plain text, then entropy here also would be, making it not
-    // increase privacy. If they're not sent in plain text, or are otherwise inaccessible, they
-    // already offer sufficient entropy. That's why further entropy is not included
-
-    (
-      TransactionSignMachine {
-        signable: self.signable,
-
-        i: self.i,
-        transcript: self.transcript,
-
-        key_images: self.key_images,
-        clsag_mask_sends: self.clsag_mask_sends,
-        clsags,
-
-        our_preprocess,
-      },
-      preprocesses,
-    )
-  }
-}
-
-impl SignMachine<Transaction> for TransactionSignMachine {
-  type Params = ();
-  type Keys = ThresholdKeys<Ed25519>;
-  type Preprocess = Vec<Preprocess<Ed25519, ClsagAddendum>>;
-  type SignatureShare = Vec<SignatureShare<Ed25519>>;
-  type SignatureMachine = TransactionSignatureMachine;
-
-  fn cache(self) -> CachedPreprocess {
-    unimplemented!(
-      "Monero transactions don't support caching their preprocesses due to {}",
-      "being already bound to a specific transaction"
-    );
-  }
-
-  fn from_cache(
-    (): (),
-    _: ThresholdKeys<Ed25519>,
-    _: CachedPreprocess,
-  ) -> (Self, Self::Preprocess) {
-    unimplemented!(
-      "Monero transactions don't support caching their preprocesses due to {}",
-      "being already bound to a specific transaction"
-    );
-  }
-
-  fn read_preprocess<R: Read>(&self, reader: &mut R) -> io::Result<Self::Preprocess> {
-    self.clsags.iter().map(|clsag| clsag.read_preprocess(reader)).collect()
-  }
-
-  fn sign(
-    mut self,
-    mut commitments: HashMap<Participant, Self::Preprocess>,
-    msg: &[u8],
-  ) -> Result<(TransactionSignatureMachine, Self::SignatureShare), FrostError> {
-    if !msg.is_empty() {
-      panic!("message was passed to the TransactionMachine when it generates its own");
-    }
-
-    // Find out who's included
-    // This may not be a valid set of signers yet the algorithm machine will error if it's not
-    commitments.remove(&self.i); // Remove, if it was included for some reason
-    let mut included = commitments.keys().copied().collect::<Vec<_>>();
-    included.push(self.i);
-    included.sort_unstable();
-
-    // Start calculating the key images, as needed on the TX level
-    let mut images = vec![EdwardsPoint::identity(); self.clsags.len()];
-    for (image, (generator, offset)) in images.iter_mut().zip(&self.key_images) {
-      *image = generator * offset;
-    }
-
-    // Convert the serialized nonces commitments to a parallelized Vec
-    let mut commitments = (0 .. self.clsags.len())
-      .map(|c| {
-        included
-          .iter()
-          .map(|l| {
-            // Add all commitments to the transcript for their entropy
-            // While each CLSAG will do this as they need to for security, they have their own
-            // transcripts cloned from this TX's initial premise's transcript. For our TX
-            // transcript to have the CLSAG data for entropy, it'll have to be added ourselves here
-            self.transcript.append_message(b"participant", (*l).to_bytes());
-
-            let preprocess = if *l == self.i {
-              self.our_preprocess[c].clone()
-            } else {
-              commitments.get_mut(l).ok_or(FrostError::MissingParticipant(*l))?[c].clone()
-            };
-
-            {
-              let mut buf = vec![];
-              preprocess.write(&mut buf).unwrap();
-              self.transcript.append_message(b"preprocess", buf);
-            }
-
-            // While here, calculate the key image
-            // Clsag will parse/calculate/validate this as needed, yet doing so here as well
-            // provides the easiest API overall, as this is where the TX is (which needs the key
-            // images in its message), along with where the outputs are determined (where our
-            // outputs may need these in order to guarantee uniqueness)
-            images[c] +=
-              preprocess.addendum.key_image_share().0 * lagrange::<dfg::Scalar>(*l, &included).0;
-
-            Ok((*l, preprocess))
-          })
-          .collect::<Result<HashMap<_, _>, _>>()
-      })
-      .collect::<Result<Vec<_>, _>>()?;
-
-    // Remove our preprocess which shouldn't be here. It was just the easiest way to implement the
-    // above
-    for map in &mut commitments {
-      map.remove(&self.i);
-    }
-
-    // Create the actual transaction
-    let (mut tx, output_masks) = {
-      let mut sorted_images = images.clone();
-      sorted_images.sort_by(key_image_sort);
-
-      self.signable.prepare_transaction(
-        // Technically, r_seed is used for the transaction keys if it's provided
-        &mut ChaCha20Rng::from_seed(self.transcript.rng_seed(b"transaction_keys_bulletproofs")),
-        uniqueness(
-          &sorted_images
-            .iter()
-            .map(|image| Input::ToKey { amount: None, key_offsets: vec![], key_image: *image })
-            .collect::<Vec<_>>(),
-        ),
-      )
-    };
-
-    // Sort the inputs, as expected
-    let mut sorted = Vec::with_capacity(self.clsags.len());
-    while !self.clsags.is_empty() {
-      sorted.push((
-        images.swap_remove(0),
-        self.signable.inputs.swap_remove(0).1,
-        self.clsag_mask_sends.swap_remove(0),
-        self.clsags.swap_remove(0),
-        commitments.swap_remove(0),
-      ));
-    }
-    sorted.sort_by(|x, y| key_image_sort(&x.0, &y.0));
-
-    let mut rng = ChaCha20Rng::from_seed(self.transcript.rng_seed(b"pseudo_out_masks"));
-    let mut sum_pseudo_outs = Scalar::ZERO;
-    while !sorted.is_empty() {
-      let value = sorted.remove(0);
-
-      let mut mask = Scalar::random(&mut rng);
-      if sorted.is_empty() {
-        mask = output_masks - sum_pseudo_outs;
-      } else {
-        sum_pseudo_outs += mask;
-      }
-      value.2.send(mask);
-
-      tx.prefix_mut().inputs.push(Input::ToKey {
-        amount: None,
-        key_offsets: value.1.offsets().to_vec(),
-        key_image: value.0,
-      });
-
-      self.clsags.push(value.3);
-      commitments.push(value.4);
-    }
-
-    let msg = tx.signature_hash().unwrap();
-
-    // Iterate over each CLSAG calling sign
-    let mut shares = Vec::with_capacity(self.clsags.len());
-    let clsags = self
-      .clsags
-      .drain(..)
-      .map(|clsag| {
-        let (clsag, share) = clsag.sign(commitments.remove(0), &msg)?;
-        shares.push(share);
-        Ok(clsag)
-      })
-      .collect::<Result<_, _>>()?;
-
-    Ok((TransactionSignatureMachine { tx, clsags }, shares))
-  }
-}
-
-impl SignatureMachine<Transaction> for TransactionSignatureMachine {
-  type SignatureShare = Vec<SignatureShare<Ed25519>>;
-
-  fn read_share<R: Read>(&self, reader: &mut R) -> io::Result<Self::SignatureShare> {
-    self.clsags.iter().map(|clsag| clsag.read_share(reader)).collect()
-  }
-
-  fn complete(
-    mut self,
-    shares: HashMap<Participant, Self::SignatureShare>,
-  ) -> Result<Transaction, FrostError> {
-    let mut tx = self.tx;
-    match tx {
-      Transaction::V2 {
-        proofs:
-          Some(RctProofs {
-            prunable: RctPrunable::Clsag { ref mut clsags, ref mut pseudo_outs, .. },
-            ..
-          }),
-        ..
-      } => {
-        for (c, clsag) in self.clsags.drain(..).enumerate() {
-          let (clsag, pseudo_out) = clsag.complete(
-            shares.iter().map(|(l, shares)| (*l, shares[c].clone())).collect::<HashMap<_, _>>(),
-          )?;
-          clsags.push(clsag);
-          pseudo_outs.push(pseudo_out);
-        }
-      }
-      _ => unreachable!("attempted to sign a multisig TX which wasn't CLSAG"),
-    }
-    Ok(tx)
-  }
-}

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

@@ -31,6 +31,13 @@ mod tx;
 mod eventuality;
 pub use eventuality::Eventuality;
 
+#[cfg(feature = "multisig")]
+mod multisig;
+
+pub(crate) fn key_image_sort(x: &EdwardsPoint, y: &EdwardsPoint) -> core::cmp::Ordering {
+  x.compress().to_bytes().cmp(&y.compress().to_bytes()).reverse()
+}
+
 #[derive(Clone, PartialEq, Eq, Zeroize)]
 enum ChangeEnum {
   None,
@@ -406,9 +413,6 @@ impl SignableTransaction {
     debug_assert_eq!(self.inputs.len(), key_images.len());
 
     // Sort the inputs by their key images
-    fn key_image_sort(x: &EdwardsPoint, y: &EdwardsPoint) -> core::cmp::Ordering {
-      x.compress().to_bytes().cmp(&y.compress().to_bytes()).reverse()
-    }
     let mut sorted_inputs = self.inputs.into_iter().zip(key_images).collect::<Vec<_>>();
     sorted_inputs
       .sort_by(|(_, key_image_a), (_, key_image_b)| key_image_sort(key_image_a, key_image_b));
@@ -461,12 +465,7 @@ impl SignableTransaction {
     }
 
     // Get the output commitments' mask sum
-    let mask_sum = tx
+    let mask_sum = tx.intent.sum_output_masks(&tx.key_images);
-      .intent
-      .commitments_and_encrypted_amounts(&tx.key_images)
-      .into_iter()
-      .map(|(commitment, _)| commitment.mask)
-      .sum::<Scalar>();
 
     // Get the actual TX, just needing the CLSAGs
     let mut tx = tx.transaction_without_signatures();

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

@@ -0,0 +1,302 @@
+use std_shims::{
+  vec::Vec,
+  io::{self, Read},
+  collections::HashMap,
+};
+
+use rand_core::{RngCore, CryptoRng};
+
+use group::ff::Field;
+use curve25519_dalek::{traits::Identity, Scalar, EdwardsPoint};
+use dalek_ff_group as dfg;
+
+use transcript::{Transcript, RecommendedTranscript};
+use frost::{
+  curve::Ed25519,
+  Participant, FrostError, ThresholdKeys,
+  dkg::lagrange,
+  sign::{
+    Preprocess, CachedPreprocess, SignatureShare, PreprocessMachine, SignMachine, SignatureMachine,
+    AlgorithmMachine, AlgorithmSignMachine, AlgorithmSignatureMachine,
+  },
+};
+
+use monero_serai::{
+  ringct::{
+    clsag::{ClsagContext, ClsagMultisigMaskSender, ClsagAddendum, ClsagMultisig},
+    RctPrunable, RctProofs,
+  },
+  transaction::Transaction,
+};
+use crate::send::{SendError, SignableTransaction, key_image_sort};
+
+/// FROST signing machine to produce a signed transaction.
+pub struct TransactionMachine {
+  signable: SignableTransaction,
+
+  i: Participant,
+
+  // The key image generator, and the scalar offset from the spend key
+  key_image_generators_and_offsets: Vec<(EdwardsPoint, Scalar)>,
+  clsags: Vec<(ClsagMultisigMaskSender, AlgorithmMachine<Ed25519, ClsagMultisig>)>,
+}
+
+pub struct TransactionSignMachine {
+  signable: SignableTransaction,
+
+  i: Participant,
+
+  key_image_generators_and_offsets: Vec<(EdwardsPoint, Scalar)>,
+  clsags: Vec<(ClsagMultisigMaskSender, AlgorithmSignMachine<Ed25519, ClsagMultisig>)>,
+
+  our_preprocess: Vec<Preprocess<Ed25519, ClsagAddendum>>,
+}
+
+pub struct TransactionSignatureMachine {
+  tx: Transaction,
+  clsags: Vec<AlgorithmSignatureMachine<Ed25519, ClsagMultisig>>,
+}
+
+impl SignableTransaction {
+  /// Create a FROST signing machine out of this signable transaction.
+  pub fn multisig(self, keys: &ThresholdKeys<Ed25519>) -> Result<TransactionMachine, SendError> {
+    let mut clsags = vec![];
+
+    let mut key_image_generators_and_offsets = vec![];
+    for (i, (input, decoys)) in self.inputs.iter().enumerate() {
+      // Check this is the right set of keys
+      let offset = keys.offset(dfg::Scalar(input.key_offset()));
+      if offset.group_key().0 != input.key() {
+        Err(SendError::WrongPrivateKey)?;
+      }
+
+      let context =
+        ClsagContext::new(decoys.clone(), input.commitment()).map_err(SendError::ClsagError)?;
+      let (clsag, clsag_mask_send) = ClsagMultisig::new(
+        RecommendedTranscript::new(b"Monero Multisignature Transaction"),
+        context,
+      );
+      key_image_generators_and_offsets.push((
+        clsag.key_image_generator(),
+        keys.current_offset().unwrap_or(dfg::Scalar::ZERO).0 + self.inputs[i].0.key_offset(),
+      ));
+      clsags.push((clsag_mask_send, AlgorithmMachine::new(clsag, offset)));
+    }
+
+    Ok(TransactionMachine {
+      signable: self,
+      i: keys.params().i(),
+      key_image_generators_and_offsets,
+      clsags,
+    })
+  }
+}
+
+impl PreprocessMachine for TransactionMachine {
+  type Preprocess = Vec<Preprocess<Ed25519, ClsagAddendum>>;
+  type Signature = Transaction;
+  type SignMachine = TransactionSignMachine;
+
+  fn preprocess<R: RngCore + CryptoRng>(
+    mut self,
+    rng: &mut R,
+  ) -> (TransactionSignMachine, Self::Preprocess) {
+    // Iterate over each CLSAG calling preprocess
+    let mut preprocesses = Vec::with_capacity(self.clsags.len());
+    let clsags = self
+      .clsags
+      .drain(..)
+      .map(|(clsag_mask_send, clsag)| {
+        let (clsag, preprocess) = clsag.preprocess(rng);
+        preprocesses.push(preprocess);
+        (clsag_mask_send, clsag)
+      })
+      .collect();
+    let our_preprocess = preprocesses.clone();
+
+    (
+      TransactionSignMachine {
+        signable: self.signable,
+
+        i: self.i,
+
+        key_image_generators_and_offsets: self.key_image_generators_and_offsets,
+        clsags,
+
+        our_preprocess,
+      },
+      preprocesses,
+    )
+  }
+}
+
+impl SignMachine<Transaction> for TransactionSignMachine {
+  type Params = ();
+  type Keys = ThresholdKeys<Ed25519>;
+  type Preprocess = Vec<Preprocess<Ed25519, ClsagAddendum>>;
+  type SignatureShare = Vec<SignatureShare<Ed25519>>;
+  type SignatureMachine = TransactionSignatureMachine;
+
+  fn cache(self) -> CachedPreprocess {
+    unimplemented!(
+      "Monero transactions don't support caching their preprocesses due to {}",
+      "being already bound to a specific transaction"
+    );
+  }
+
+  fn from_cache(
+    (): (),
+    _: ThresholdKeys<Ed25519>,
+    _: CachedPreprocess,
+  ) -> (Self, Self::Preprocess) {
+    unimplemented!(
+      "Monero transactions don't support caching their preprocesses due to {}",
+      "being already bound to a specific transaction"
+    );
+  }
+
+  fn read_preprocess<R: Read>(&self, reader: &mut R) -> io::Result<Self::Preprocess> {
+    self.clsags.iter().map(|clsag| clsag.1.read_preprocess(reader)).collect()
+  }
+
+  fn sign(
+    self,
+    mut commitments: HashMap<Participant, Self::Preprocess>,
+    msg: &[u8],
+  ) -> Result<(TransactionSignatureMachine, Self::SignatureShare), FrostError> {
+    if !msg.is_empty() {
+      panic!("message was passed to the TransactionMachine when it generates its own");
+    }
+
+    // We do not need to be included here, yet this set of signers has yet to be validated
+    // We explicitly remove ourselves to ensure we aren't included twice, if we were redundantly
+    // included
+    commitments.remove(&self.i);
+
+    // Find out who's included
+    let mut included = commitments.keys().copied().collect::<Vec<_>>();
+    // This push won't duplicate due to the above removal
+    included.push(self.i);
+    // unstable sort may reorder elements of equal order
+    // Given our lack of duplicates, we should have no elements of equal order
+    included.sort_unstable();
+
+    // Start calculating the key images, as needed on the TX level
+    let mut key_images = vec![EdwardsPoint::identity(); self.clsags.len()];
+    for (image, (generator, offset)) in
+      key_images.iter_mut().zip(&self.key_image_generators_and_offsets)
+    {
+      *image = generator * offset;
+    }
+
+    // Convert the serialized nonces commitments to a parallelized Vec
+    let mut commitments = (0 .. self.clsags.len())
+      .map(|c| {
+        included
+          .iter()
+          .map(|l| {
+            let preprocess = if *l == self.i {
+              self.our_preprocess[c].clone()
+            } else {
+              commitments.get_mut(l).ok_or(FrostError::MissingParticipant(*l))?[c].clone()
+            };
+
+            // While here, calculate the key image as needed to call sign
+            // The CLSAG algorithm will independently calculate the key image/verify these shares
+            key_images[c] +=
+              preprocess.addendum.key_image_share().0 * lagrange::<dfg::Scalar>(*l, &included).0;
+
+            Ok((*l, preprocess))
+          })
+          .collect::<Result<HashMap<_, _>, _>>()
+      })
+      .collect::<Result<Vec<_>, _>>()?;
+
+    // The above inserted our own preprocess into these maps (which is unnecessary)
+    // Remove it now
+    for map in &mut commitments {
+      map.remove(&self.i);
+    }
+
+    // The actual TX will have sorted its inputs by key image
+    // We apply the same sort now to our CLSAG machines
+    let mut clsags = Vec::with_capacity(self.clsags.len());
+    for ((key_image, clsag), commitments) in key_images.iter().zip(self.clsags).zip(commitments) {
+      clsags.push((key_image, clsag, commitments));
+    }
+    clsags.sort_by(|x, y| key_image_sort(x.0, y.0));
+    let clsags =
+      clsags.into_iter().map(|(_, clsag, commitments)| (clsag, commitments)).collect::<Vec<_>>();
+
+    // Specify the TX's key images
+    let tx = self.signable.with_key_images(key_images);
+
+    // We now need to decide the masks for each CLSAG
+    let clsag_len = clsags.len();
+    let output_masks = tx.intent.sum_output_masks(&tx.key_images);
+    let mut rng = tx.intent.seeded_rng(b"multisig_pseudo_out_masks");
+    let mut sum_pseudo_outs = Scalar::ZERO;
+    let mut to_sign = Vec::with_capacity(clsag_len);
+    for (i, ((clsag_mask_send, clsag), commitments)) in clsags.into_iter().enumerate() {
+      let mut mask = Scalar::random(&mut rng);
+      if i == (clsag_len - 1) {
+        mask = output_masks - sum_pseudo_outs;
+      } else {
+        sum_pseudo_outs += mask;
+      }
+      clsag_mask_send.send(mask);
+      to_sign.push((clsag, commitments));
+    }
+
+    let tx = tx.transaction_without_signatures();
+    let msg = tx.signature_hash().unwrap();
+
+    // Iterate over each CLSAG calling sign
+    let mut shares = Vec::with_capacity(to_sign.len());
+    let clsags = to_sign
+      .drain(..)
+      .map(|(clsag, commitments)| {
+        let (clsag, share) = clsag.sign(commitments, &msg)?;
+        shares.push(share);
+        Ok(clsag)
+      })
+      .collect::<Result<_, _>>()?;
+
+    Ok((TransactionSignatureMachine { tx, clsags }, shares))
+  }
+}
+
+impl SignatureMachine<Transaction> for TransactionSignatureMachine {
+  type SignatureShare = Vec<SignatureShare<Ed25519>>;
+
+  fn read_share<R: Read>(&self, reader: &mut R) -> io::Result<Self::SignatureShare> {
+    self.clsags.iter().map(|clsag| clsag.read_share(reader)).collect()
+  }
+
+  fn complete(
+    mut self,
+    shares: HashMap<Participant, Self::SignatureShare>,
+  ) -> Result<Transaction, FrostError> {
+    let mut tx = self.tx;
+    match tx {
+      Transaction::V2 {
+        proofs:
+          Some(RctProofs {
+            prunable: RctPrunable::Clsag { ref mut clsags, ref mut pseudo_outs, .. },
+            ..
+          }),
+        ..
+      } => {
+        for (c, clsag) in self.clsags.drain(..).enumerate() {
+          let (clsag, pseudo_out) = clsag.complete(
+            shares.iter().map(|(l, shares)| (*l, shares[c].clone())).collect::<HashMap<_, _>>(),
+          )?;
+          clsags.push(clsag);
+          pseudo_outs.push(pseudo_out);
+        }
+      }
+      _ => unreachable!("attempted to sign a multisig TX which wasn't CLSAG"),
+    }
+    Ok(tx)
+  }
+}

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

@@ -228,4 +228,12 @@ impl SignableTransaction {
     }
     res
   }
+
+  pub(crate) fn sum_output_masks(&self, key_images: &[EdwardsPoint]) -> Scalar {
+    self
+      .commitments_and_encrypted_amounts(key_images)
+      .into_iter()
+      .map(|(commitment, _)| commitment.mask)
+      .sum()
+  }
 }