ShareUpdate verification method

ferveo/src/lib.rs

@@ -80,6 +80,10 @@ pub enum Error {
     #[error("Invalid share index: {0}")]
     InvalidShareIndex(u32),
 
+    /// Failed to verify a share update
+    #[error("Invalid share update")]
+    InvalidShareUpdate,
+
     /// Failed to produce a precomputed variant decryption share
     #[error("Invalid DKG parameters for precomputed variant: number of shares {0}, threshold {1}")]
     InvalidDkgParametersForPrecomputedVariant(u32, u32),

ferveo/src/pvss.rs

@@ -255,10 +255,12 @@ pub fn do_verify_full<E: Pairing>(
         // We verify that e(G, Y_i) = e(A_i, ek_i) for validator i
         // See #4 in 4.2.3 section of https://eprint.iacr.org/2022/898.pdf
         // e(G,Y) = e(A, ek)
+        // TODO: consider using multipairing
         let is_valid = E::pairing(pvss_params.g, *y_i) == E::pairing(a_i, ek_i);
         if !is_valid {
             return Ok(false);
         }
+        // TODO: Should we return Err()?
     }
 
     Ok(true)

ferveo/src/refresh.rs

@@ -241,6 +241,17 @@ impl<E: Pairing> ShareUpdate<E> {
         )
         // TODO: Cast return elements into ShareRecoveryUpdate
     }
+
+    // TODO: Unit tests
+    pub fn verify(&self, target_validator_public_key: E::G2) -> Result<bool> {
+        let is_valid = E::pairing(E::G1::generator(), self.update)
+            == E::pairing(self.commitment, target_validator_public_key);
+        if is_valid{
+            Ok(true)
+        } else {
+            Err(Error::InvalidShareUpdate)
+        }
+    }
 }
 
 // TODO: working here