implement Zeroize where needed or skip where not needed (#301)

frost-core/src/frost/keys.rs

@@ -261,9 +261,11 @@ pub struct VerifiableSecretSharingCommitment<C: Ciphersuite>(
 #[derive(Clone, Zeroize)]
 pub struct SecretShare<C: Ciphersuite> {
     /// The participant identifier of this [`SecretShare`].
+    #[zeroize(skip)]
     pub identifier: Identifier<C>,
     /// Secret Key.
     pub value: SigningShare<C>,
+    #[zeroize(skip)]
     /// The commitments to be distributed among signers.
     pub commitment: VerifiableSecretSharingCommitment<C>,
 }

frost-core/src/frost/round1.rs

@@ -13,7 +13,7 @@ use crate::{frost, Ciphersuite, Element, Error, Field, Group, Scalar};
 use super::{keys::SigningShare, Identifier};
 
 /// A scalar that is a signing nonce.
-#[derive(Clone, PartialEq, Eq, Zeroize)]
+#[derive(Clone, PartialEq, Eq)]
 pub struct Nonce<C: Ciphersuite>(pub(super) Scalar<C>);
 
 impl<C> Nonce<C>
@@ -71,6 +71,15 @@ where
     }
 }
 
+impl<C> Zeroize for Nonce<C>
+where
+    C: Ciphersuite,
+{
+    fn zeroize(&mut self) {
+        *self = Nonce(<<C::Group as Group>::Field>::zero());
+    }
+}
+
 // impl<C> Drop for Nonce<C>
 // where
 //     C: Ciphersuite,