Add Zeroize trait implementation for Witness

Resolves #818

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Add `zeroize` as an optional dependency [#818]
+- Add `zeroize` feature [#818]
+- Add `Zeroize` trait implementation for `Witness` behind `zeroize` feature [#818]
+
 ## [0.19.1] - 2024-02-28
 
 ### Changed
@@ -573,6 +579,7 @@ is necessary since `rkyv/validation` was required as a bound.
 - Proof system module.
 
 <!-- ISSUES -->
+[#818]: https://github.com/dusk-network/plonk/issues/818
 [#815]: https://github.com/dusk-network/plonk/issues/815
 [#813]: https://github.com/dusk-network/plonk/issues/813
 [#805]: https://github.com/dusk-network/plonk/issues/805

Cargo.toml

@@ -33,6 +33,7 @@ rkyv = {version = "0.7", optional = true, default-features = false}
 bytecheck = {version = "0.6", optional = true, default-features = false}
 backtrace = {version = "0.3", optional = true}
 dusk-cdf = {version = "0.5", optional = true}
+zeroize = { version = "1", optional = true }
 
 [dev-dependencies]
 criterion = "0.5"

src/composer/constraint_system/witness.rs

@@ -52,3 +52,6 @@ impl Witness {
         self.index
     }
 }
+
+#[cfg(feature = "zeroize")]
+impl zeroize::DefaultIsZeroes for Witness {}