Implement Zeroize for SecretKey

CHANGELOG.md

@@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Add `Zeroize` trait implementation for `SecretKey` [#12]
+
+### Removed
+
+- Remove `Copy` trait from `SecretKey` [#12]
+- Remove `From<SecretKey>` for `PublicKey`, use `From<&SecretKey>` instead [#12]
+
 ## [0.2.2] - 2024-03-11
 
 ### Added
@@ -32,6 +41,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add initial commit, this package continues the development of [dusk-schnorr](https://github.com/dusk-network/schnorr/) at version `0.18.0` under the new name: jubjub-schnorr
 
 <!-- ISSUES -->
+[#12]: https://github.com/dusk-network/jubjub-schnorr/issues/12
 [#9]: https://github.com/dusk-network/jubjub-schnorr/issues/9
 [#3]: https://github.com/dusk-network/jubjub-schnorr/issues/3
 [#2]: https://github.com/dusk-network/jubjub-schnorr/issues/2

Cargo.toml

@@ -20,10 +20,11 @@ dusk-bytes = "0.1"
 dusk-poseidon = { version ="0.33", default-features = false }
 dusk-plonk = { version = "0.19", default-features = false }
 dusk-bls12_381 = { version = "0.13", default-features = false }
-dusk-jubjub = { version = "0.14", default-features = false }
+dusk-jubjub = { version = "0.14", default-features = false, features = ["zeroize"] }
+ff = { version = "0.13", default-features = false }
+zeroize = { version = "1", default-features = false, features = ["derive"] }
 rkyv = { version = "0.7", optional = true, default-features = false }
 bytecheck = { version = "0.6", optional = true, default-features = false }
-ff = { version = "0.13", default-features = false }
 
 [dev-dependencies]
 rkyv = { version = "0.7", default-features = false, features = ["size_32"] }

src/keys/public.rs

@@ -272,13 +272,6 @@ impl From<&SecretKey> for PublicKeyDouble {
     }
 }
 
-#[cfg(feature = "double")]
-impl From<SecretKey> for PublicKeyDouble {
-    fn from(sk: SecretKey) -> Self {
-        (&sk).into()
-    }
-}
-
 #[cfg(feature = "double")]
 impl Serializable<64> for PublicKeyDouble {
     type Error = Error;

src/keys/secret.rs

@@ -16,6 +16,7 @@ use dusk_bytes::{Error, Serializable};
 use dusk_jubjub::{JubJubScalar, GENERATOR_EXTENDED};
 use ff::Field;
 use rand_core::{CryptoRng, RngCore};
+use zeroize::Zeroize;
 
 use crate::{PublicKey, Signature};
 
@@ -37,19 +38,30 @@ use rkyv::{Archive, Deserialize, Serialize};
 /// Structure representing a [`SecretKey`], represented as a private scalar
 /// in the JubJub scalar field.
 ///
+/// ## Safety
+///
+/// To ensure that no secret information lingers in memory after the variable
+/// goes out of scope, we advice calling `zeroize` before the variable goes out
+/// of scope.
+///
 /// ## Examples
 ///
 /// Generate a random `SecretKey`:
 /// ```
 /// use jubjub_schnorr::SecretKey;
 /// use rand::rngs::StdRng;
 /// use rand::SeedableRng;
+/// use zeroize::Zeroize;
 ///
 /// let mut rng = StdRng::seed_from_u64(12345);
-/// let sk = SecretKey::random(&mut rng);
+/// let mut sk = SecretKey::random(&mut rng);
+///
+/// // do something with the sk
+///
+/// sk.zeroize();
 /// ```
 #[allow(non_snake_case)]
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Zeroize)]
 #[cfg_attr(
     feature = "rkyv-impl",
     derive(Archive, Serialize, Deserialize),

src/signatures.rs

@@ -173,7 +173,7 @@ pub(crate) fn challenge_hash(
 ///
 /// let sk = SecretKey::random(&mut rng);
 /// let message = BlsScalar::random(&mut rng);
-/// let pk_double: PublicKeyDouble = sk.into();
+/// let pk_double = PublicKeyDouble::from(&sk);
 ///
 /// let signature = sk.sign_double(&mut rng, message);
 ///

tests/keys.rs

@@ -59,6 +59,16 @@ fn partial_eq_pk() {
     assert_ne!(PublicKey::from(left), PublicKey::from(wrong))
 }
 
+#[test]
+fn test_zeroize() {
+    use zeroize::Zeroize;
+
+    let mut sk = SecretKey::from(JubJubScalar::from(42u64));
+    sk.zeroize();
+
+    assert_eq!(sk, SecretKey::from(JubJubScalar::default()));
+}
+
 #[test]
 #[cfg(feature = "double")]
 fn partial_eq_pk_double() {

tests/schnorr_double.rs

@@ -17,7 +17,7 @@ fn sign_verify() {
 
     let sk = SecretKey::random(&mut rng);
     let message = BlsScalar::random(&mut rng);
-    let pk_double: PublicKeyDouble = sk.into();
+    let pk_double = PublicKeyDouble::from(&sk);
 
     let sig = sk.sign_double(&mut rng, message);
 
@@ -35,7 +35,7 @@ fn test_wrong_keys() {
 
     // Derive random public key
     let wrong_sk = SecretKey::random(&mut rng);
-    let pk_double: PublicKeyDouble = wrong_sk.into();
+    let pk_double = PublicKeyDouble::from(&wrong_sk);
 
     assert!(!pk_double.verify(&sig, message));
 }