Added size check to Bowe-Hopwood gadget evaluate method

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Pending
 
+- [\#120](https://github.com/arkworks-rs/crypto-primitives/pull/120) Add input size check to `bowe_hopwood::CRHGadget::evaluate`.
+
 ### Breaking changes
 
 ### Features

src/crh/bowe_hopwood/constraints.rs

@@ -58,6 +58,16 @@ where
         parameters: &Self::ParametersVar,
         input: &Self::InputVar,
     ) -> Result<Self::OutputVar, SynthesisError> {
+        if (input.len() * 8) > W::WINDOW_SIZE * W::NUM_WINDOWS * CHUNK_SIZE {
+            panic!(
+                "incorrect input bitlength {:?} for window params {:?}x{:?}x{}",
+                input.len() * 8,
+                W::WINDOW_SIZE,
+                W::NUM_WINDOWS,
+                CHUNK_SIZE,
+            );
+        }
+
         // Pad the input if it is not the current length.
         let mut input_in_bits: Vec<Boolean<_>> = input
             .iter()
@@ -267,4 +277,33 @@ mod test {
         assert_eq!(primitive_result, result_var.value().unwrap());
         assert!(cs.is_satisfied().unwrap());
     }
+
+    #[should_panic]
+    #[test]
+    fn test_input_size_check() {
+        // Pick parameters that are far too small for a CRH
+        #[derive(Clone, PartialEq, Eq, Hash)]
+        pub(super) struct TooSmallWindow;
+        impl pedersen::Window for TooSmallWindow {
+            const WINDOW_SIZE: usize = 1;
+            const NUM_WINDOWS: usize = 1;
+        }
+        type TestCRH = bowe_hopwood::CRH<EdwardsConfig, TooSmallWindow>;
+        type TestCRHGadget = bowe_hopwood::constraints::CRHGadget<EdwardsConfig, FqVar>;
+
+        let rng = &mut test_rng();
+        let cs = ConstraintSystem::<Fr>::new_ref();
+
+        let (_, input_var) = generate_u8_input(cs.clone(), 189, rng);
+        println!("number of constraints for input: {}", cs.num_constraints());
+
+        let parameters = TestCRH::setup(rng).unwrap();
+        let parameters_var =
+            <TestCRHGadget as CRHSchemeGadget<TestCRH, Fr>>::ParametersVar::new_witness(
+                ark_relations::ns!(cs, "parameters_var"),
+                || Ok(&parameters),
+            )
+            .unwrap();
+        let _ = TestCRHGadget::evaluate(&parameters_var, &input_var).unwrap();
+    }
 }

src/crh/bowe_hopwood/mod.rs

@@ -118,8 +118,8 @@ impl<P: TECurveConfig, W: pedersen::Window> CRHScheme for CRH<P, W> {
 
         if (input.len() * 8) > W::WINDOW_SIZE * W::NUM_WINDOWS * CHUNK_SIZE {
             panic!(
-                "incorrect input length {:?} for window params {:?}x{:?}x{}",
-                input.len(),
+                "incorrect input bitlength {:?} for window params {:?}x{:?}x{}",
+                input.len() * 8,
                 W::WINDOW_SIZE,
                 W::NUM_WINDOWS,
                 CHUNK_SIZE,