feat: support zeroize codegen

Cargo.toml

@@ -23,6 +23,7 @@ subtle = { version = "2.2.1", default-features = false, features = ["i128"] }
 [dev-dependencies]
 blake2b_simd = "1"
 rand = "0.8"
+zeroize = { version = "1", default-features = false }
 
 [features]
 default = ["bits", "std"]
@@ -32,7 +33,8 @@ derive = ["byteorder", "ff_derive"]
 std = ["alloc"]
 # with MSRV 1.60 this could be merged into bits with ff_derive?/bits
 # see PR#72 for more information.
-derive_bits = ["bits", "ff_derive/bits"]
+derive_bits = ["bits", "derive", "ff_derive/bits"]
+test_derive_zeroize = ["derive", "ff_derive/zeroize"]
 
 [[test]]
 name = "derive"

ff_derive/Cargo.toml

@@ -15,6 +15,8 @@ edition = "2021"
 [features]
 # enabled when generating bitvec code utilizing the version of ff's bitvec
 bits = []
+# enabled when generating zeroize bindings
+zeroize = []
 
 [lib]
 proc-macro = true

ff_derive/src/lib.rs

@@ -332,6 +332,14 @@ fn prime_field_repr_impl(
 ) -> proc_macro2::TokenStream {
     let repr_iter_be = endianness.iter_be();
 
+    let prime_field_repr_zeroize_impl = if cfg!(feature = "zeroize") {
+        Some(quote! {
+            impl ::zeroize::DefaultIsZeroes for #repr {}
+        })
+    } else {
+        None
+    };
+
     quote! {
         #[derive(Copy, Clone)]
         pub struct #repr(pub [u8; #bytes]);
@@ -386,6 +394,8 @@ fn prime_field_repr_impl(
                 &mut self.0
             }
         }
+
+        #prime_field_repr_zeroize_impl
     }
 }
 
@@ -942,6 +952,14 @@ fn prime_field_impl(
         }
     };
 
+    let prime_field_zeroize_impl = if cfg!(feature = "zeroize") {
+        Some(quote! {
+            impl ::zeroize::DefaultIsZeroes for #name {}
+        })
+    } else {
+        None
+    };
+
     let top_limb_index = limbs - 1;
 
     quote! {
@@ -1261,6 +1279,7 @@ fn prime_field_impl(
         }
 
         #prime_field_bits_impl
+        #prime_field_zeroize_impl
 
         impl ::ff::Field for #name {
             const ZERO: Self = #name([0; #limbs]);

tests/derive.rs

@@ -135,3 +135,20 @@ fn batch_inversion() {
         }
     }
 }
+
+#[cfg(feature = "test_derive_zeroize")]
+#[test]
+fn zeroize() {
+    use ff::{Field, PrimeField};
+    use rand::rngs::OsRng;
+    use zeroize::Zeroize;
+
+    let mut f = Bls381K12Scalar::random(OsRng);
+    let mut r = f.to_repr();
+
+    f.zeroize();
+    assert_eq!(f, Bls381K12Scalar::ZERO);
+
+    r.zeroize();
+    assert_eq!(r, Default::default());
+}