audit: bounds check on field elements of input proof

g16ckt/src/gadgets/bn254/fq.rs

@@ -297,14 +297,24 @@ impl Fq {
             &BigUint::from_str(Self::MODULUS_ADD_1_DIV_4).unwrap(),
         )
     }
+
+    /// Return a>b in standard form given inputs in montgomery form
+    pub fn greater_than<C: CircuitContext>(circuit: &mut C, a: &Fq, b: &Fq) -> WireId {
+        // First convert the inputs 'a' and 'b' back to standard form
+        let a = Fq::mul_by_constant_montgomery(circuit, a, &ark_bn254::Fq::ONE);
+        let b = Fq::mul_by_constant_montgomery(circuit, b, &ark_bn254::Fq::ONE);
+        // only now perform comparison
+        bigint::greater_than(circuit, &a, &b)
+    }
 }
 
 #[cfg(test)]
 pub(super) mod tests {
     use std::{array, iter};
 
     use ark_ff::AdditiveGroup;
-    use rand::Rng;
+    use rand::{Rng, SeedableRng};
+    use rand_chacha::ChaCha20Rng;
     use test_log::test;
     use tracing::trace;
 
@@ -680,6 +690,29 @@ pub(super) mod tests {
         assert_eq!(result.output_value.value, expected_c);
     }
 
+    #[test]
+    fn test_fq_sqrt_montgomery_roundtrip() {
+        let mut rng = ChaCha20Rng::seed_from_u64(42);
+        for _ in 0..5 {
+            let aa_v = Fq::random(&mut rng);
+            let sqrt_exists = aa_v.sqrt().is_some();
+
+            let aa_montgomery = Fq::as_montgomery(aa_v);
+            let input = FqInput::new([aa_montgomery]);
+
+            let result =
+                CircuitBuilder::streaming_execute::<_, _, FqOutput>(input, 10_000, |ctx, input| {
+                    let [aa_wire] = input;
+                    let sqrt = Fq::sqrt_montgomery(ctx, aa_wire);
+                    Fq::square_montgomery(ctx, &sqrt)
+                });
+
+            let calc_aa_montgomery = result.output_value.value;
+
+            assert_eq!(sqrt_exists, calc_aa_montgomery == aa_montgomery);
+        }
+    }
+
     #[test]
     fn test_fq_multiplexer() {
         let w = 1;

g16ckt/src/gadgets/bn254/fq2.rs

@@ -15,7 +15,8 @@ use crate::{
     CircuitContext, Gate, WireId,
     circuit::WiresObject,
     gadgets::{
-        bigint::{BigIntWires, select},
+        basic,
+        bigint::{self, BigIntWires, select},
         bn254::{fp254impl::Fp254Impl, fq::Fq},
     },
 };
@@ -444,6 +445,14 @@ impl Fq2 {
 
         Fq2::from_components(c0_final, c1_final)
     }
+
+    /// Return a>b in standard form given inputs in montgomery form
+    pub fn greater_than<C: CircuitContext>(circuit: &mut C, a: &Fq2, b: &Fq2) -> WireId {
+        let c1_equal = bigint::equal(circuit, a.c1(), b.c1());
+        let c1_greater = Fq::greater_than(circuit, a.c1(), b.c1());
+        let c0_greater = Fq::greater_than(circuit, a.c0(), b.c0());
+        basic::selector(circuit, c0_greater, c1_greater, c1_equal)
+    }
 }
 
 #[cfg(test)]