Merge pull request #2511 from ProvableHQ/additional-tx-checks

[Fix] Add additional input/output checks to `Execution` verification

synthesizer/process/src/verify_execution.rs

@@ -91,6 +91,7 @@ impl<N: Network> Process<N> {
 
             // Ensure each output is valid.
             let num_inputs = transition.inputs().len();
+            let num_outputs = transition.outputs().len();
             if transition
                 .outputs()
                 .iter()
@@ -106,6 +107,10 @@ impl<N: Network> Process<N> {
             // Retrieve the function from the stack.
             let function = stack.get_function(transition.function_name())?;
 
+            // Ensure the number of inputs and outputs match the expected number in the function.
+            ensure!(function.inputs().len() == num_inputs, "The number of transition inputs is incorrect");
+            ensure!(function.outputs().len() == num_outputs, "The number of transition outputs is incorrect");
+
             // Retrieve the parent program ID.
             // Note: The last transition in the execution does not have a parent, by definition.
             let parent = reverse_call_graph.get(transition.id()).and_then(|tid| execution.get_program_id(tid));

synthesizer/src/vm/verify.rs

@@ -383,7 +383,7 @@ mod tests {
         account::{Address, ViewKey},
         types::Field,
     };
-    use ledger_block::{Block, Header, Metadata, Transaction};
+    use ledger_block::{Block, Header, Metadata, Transaction, Transition};
 
     type CurrentNetwork = test_helpers::CurrentNetwork;
 
@@ -641,4 +641,73 @@ function compute:
         // Ensure that the program can't be deployed.
         assert!(vm.deploy_raw(&program, rng).is_err());
     }
+
+    #[test]
+    fn test_check_mutated_execution() {
+        let rng = &mut TestRng::default();
+
+        // Initialize the VM.
+        let vm = crate::vm::test_helpers::sample_vm();
+        // Fetch the caller's private key.
+        let caller_private_key = crate::vm::test_helpers::sample_genesis_private_key(rng);
+        // Initialize the genesis block.
+        let genesis = crate::vm::test_helpers::sample_genesis_block(rng);
+        // Update the VM.
+        vm.add_next_block(&genesis).unwrap();
+
+        // Fetch a valid execution transaction with a public fee.
+        let valid_transaction = crate::vm::test_helpers::sample_execution_transaction_with_public_fee(rng);
+        vm.check_transaction(&valid_transaction, None, rng).unwrap();
+
+        // Mutate the execution transaction by inserting a Field::Zero as an output.
+        let execution = valid_transaction.execution().unwrap();
+
+        // Extract the first transition from the execution.
+        let transitions: Vec<_> = execution.transitions().collect();
+        assert_eq!(transitions.len(), 1);
+        let transition = transitions[0].clone();
+
+        // Mutate the transition by adding an additional `Field::zero` output. This is significant because the Varuna
+        // verifier pads the inputs with `Field::zero`s, which means that the same proof is valid for both the
+        // original and the mutated executions.
+        let added_output = Output::ExternalRecord(Field::zero());
+        let mutated_outputs = [transition.outputs(), &[added_output]].concat();
+        let mutated_transition = Transition::new(
+            *transition.program_id(),
+            *transition.function_name(),
+            transition.inputs().to_vec(),
+            mutated_outputs,
+            *transition.tpk(),
+            *transition.tcm(),
+            *transition.scm(),
+        )
+        .unwrap();
+
+        // Construct the mutated execution.
+        let mutated_execution = Execution::from(
+            [mutated_transition].into_iter(),
+            execution.global_state_root(),
+            execution.proof().cloned(),
+        )
+        .unwrap();
+
+        // Authorize the fee.
+        let authorization = vm
+            .authorize_fee_public(
+                &caller_private_key,
+                10_000_000,
+                100,
+                mutated_execution.to_execution_id().unwrap(),
+                rng,
+            )
+            .unwrap();
+        // Compute the fee.
+        let fee = vm.execute_fee_authorization(authorization, None, rng).unwrap();
+
+        // Construct the transaction.
+        let mutated_transaction = Transaction::from_execution(mutated_execution, Some(fee)).unwrap();
+
+        // Ensure that the mutated transaction fails verification due to an extra output.
+        assert!(vm.check_transaction(&mutated_transaction, None, rng).is_err());
+    }
 }