Add issuance surjection proof verification

Author: sanket1729

Diff for: src/blind.rs

@@ -883,7 +883,11 @@ impl Transaction {
         // Issuances and reissuances not supported yet
         let mut in_commits = vec![];
         let mut out_commits = vec![];
+        let mut domain = vec![];
         for (i, inp) in self.input.iter().enumerate() {
+            let gen = spent_utxos[i].get_asset_gen(secp)
+                .map_err(|e| VerificationError::SpentTxOutError(i, e))?;
+            domain.push(gen);
             in_commits.push(
                 spent_utxos[i].get_value_commit(secp)
                     .map_err(|e| VerificationError::SpentTxOutError(i, e))?
@@ -899,6 +903,7 @@ impl Transaction {
                         Value::Null => continue,
                         Value::Explicit(v) => {
                             let gen = Generator::new_unblinded(secp, asset.into_tag());
+                            domain.push(gen);
                             let comm = PedersenCommitment::new_unblinded(secp, *v, gen);
                             in_commits.push(comm)
                         },
@@ -908,13 +913,6 @@ impl Transaction {
             }
         }
 
-        let domain = spent_utxos
-            .iter()
-            .enumerate()
-            .map(|(i, out)|
-                out.get_asset_gen(secp).map_err(|e| VerificationError::SpentTxOutError(i, e))
-            )
-            .collect::<Result<Vec<_>, _>>()?;
         for (i, out) in self.output.iter().enumerate() {
 
             // Compute the value commitments and asset generator