Clear 'Poly' and 'BivarPoly' coeffs on drop.

poly.rs

@@ -18,6 +18,7 @@
 
 use std::borrow::Borrow;
 use std::hash::{Hash, Hasher};
+use std::ptr::write_volatile;
 use std::{cmp, iter, ops};
 
 use pairing::bls12_381::{Fr, FrRepr, G1, G1Affine};
@@ -123,6 +124,18 @@ impl<B: Borrow<Self>> ops::MulAssign<B> for Poly {
     }
 }
 
+impl Drop for Poly {
+    fn drop(&mut self) {
+        let start = self.coeff.as_mut_ptr();
+        unsafe {
+            for i in 0..self.coeff.len() {
+                let ptr = start.offset(i as isize);
+                write_volatile(ptr, Fr::zero());
+            }
+        }
+    }
+}
+
 impl Poly {
     /// Creates a random polynomial.
     pub fn random<R: Rng>(degree: usize, rng: &mut R) -> Self {
@@ -327,6 +340,18 @@ pub struct BivarPoly {
     coeff: Vec<Fr>,
 }
 
+impl Drop for BivarPoly {
+    fn drop(&mut self) {
+        let start = self.coeff.as_mut_ptr();
+        unsafe {
+            for i in 0..self.coeff.len() {
+                let ptr = start.offset(i as isize);
+                write_volatile(ptr, Fr::zero());
+            }
+        }
+    }
+}
+
 impl BivarPoly {
     /// Creates a random polynomial.
     pub fn random<R: Rng>(degree: usize, rng: &mut R) -> Self {