cl: test partial transaction balance commitment

cl/src/balance.rs

@@ -0,0 +1,16 @@
+use jubjub::{ExtendedPoint, Scalar};
+use lazy_static::lazy_static;
+
+lazy_static! {
+    static ref PEDERSON_COMMITMENT_BLINDING_POINT: ExtendedPoint =
+        crate::crypto::hash_to_curve(b"NOMOS_CL_PEDERSON_COMMITMENT_BLINDING");
+}
+
+pub fn unit_point(unit: &str) -> ExtendedPoint {
+    crate::crypto::hash_to_curve(unit.as_bytes())
+}
+
+pub fn balance(value: u64, unit: &str, blinding: Scalar) -> ExtendedPoint {
+    let value_scalar = Scalar::from(value);
+    unit_point(unit) * value_scalar + *PEDERSON_COMMITMENT_BLINDING_POINT * blinding
+}

cl/src/main.rs

@@ -1,3 +1,4 @@
+pub mod balance;
 pub mod crypto;
 pub mod error;
 pub mod input;

cl/src/note.rs

@@ -1,17 +1,8 @@
 use blake2::{Blake2s256, Digest};
 use group::GroupEncoding;
 use jubjub::{ExtendedPoint, Scalar};
-use lazy_static::lazy_static;
 
-use crate::{
-    crypto,
-    nullifier::{NullifierCommitment, NullifierNonce},
-};
-
-lazy_static! {
-    static ref PEDERSON_COMMITMENT_BLINDING_POINT: ExtendedPoint =
-        crypto::hash_to_curve(b"NOMOS_CL_PEDERSON_COMMITMENT_BLINDING");
-}
+use crate::nullifier::{NullifierCommitment, NullifierNonce};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct NoteCommitment([u8; 32]);
@@ -37,12 +28,11 @@ impl Note {
     }
 
     pub fn unit_point(&self) -> ExtendedPoint {
-        crypto::hash_to_curve(self.unit.as_bytes())
+        crate::balance::unit_point(&self.unit)
     }
 
     pub fn balance(&self, blinding: Scalar) -> ExtendedPoint {
-        let value_scalar = Scalar::from(self.value);
-        self.unit_point() * value_scalar + *PEDERSON_COMMITMENT_BLINDING_POINT * blinding
+        crate::balance::balance(self.value, &self.unit, blinding)
     }
 
     pub fn commit(&self, nf_pk: NullifierCommitment, nonce: NullifierNonce) -> NoteCommitment {

cl/src/partial_tx.rs

@@ -142,4 +142,31 @@ mod test {
 
         assert!(ptx.verify(&ptx_proof));
     }
+
+    #[test]
+    fn test_partial_tx_balance() {
+        let mut rng = seed_rng(0);
+
+        let nmo_10 = InputWitness::random(Note::new(10, "NMO"), &mut rng);
+        let eth_23 = InputWitness::random(Note::new(23, "ETH"), &mut rng);
+        let crv_4840 = OutputWitness::random(
+            Note::new(4840, "CRV"),
+            NullifierSecret::random(&mut rng).commit(), // transferring to a random owner
+            &mut rng,
+        );
+
+        let ptx_witness = PartialTxWitness {
+            inputs: vec![nmo_10.clone(), eth_23.clone()],
+            outputs: vec![crv_4840.clone()],
+        };
+
+        let ptx = PartialTx::from_witness(ptx_witness.clone());
+
+        assert_eq!(
+            ptx.balance(),
+            crate::balance::balance(10, "NMO", nmo_10.balance_blinding)
+                + crate::balance::balance(23, "ETH", eth_23.balance_blinding)
+                - crate::balance::balance(4840, "CRV", crv_4840.balance_blinding)
+        );
+    }
 }