Added clear-on-drop secret-keys to 'NetworkInfo'.

Cargo.toml

@@ -6,6 +6,7 @@ authors = ["Vladimir Komendantskiy <komendantsky@gmail.com>"]
 [dependencies]
 bincode = "1.0.0"
 byteorder = "1.2.3"
+clear_on_drop = "0.2.3"
 derive_deref = "1.0.1"
 env_logger = "0.5.10"
 error-chain = "0.11.0"

src/crypto/mod.rs

@@ -8,6 +8,7 @@ use std::fmt;
 use std::hash::{Hash, Hasher};
 
 use byteorder::{BigEndian, ByteOrder};
+use clear_on_drop::ClearOnDrop;
 use init_with::InitWith;
 use pairing::{CurveAffine, CurveProjective, Engine, Field, PrimeField};
 use rand::{ChaChaRng, OsRng, Rng, SeedableRng};
@@ -119,6 +120,12 @@ impl<E: Engine> PartialEq for SecretKey<E> {
     }
 }
 
+impl<E: Engine> Default for SecretKey<E> {
+    fn default() -> Self {
+        SecretKey(E::Fr::zero())
+    }
+}
+
 impl<E: Engine> SecretKey<E> {
     /// Creates a new secret key.
     pub fn new<R: Rng>(rng: &mut R) -> Self {
@@ -290,8 +297,13 @@ impl<E: Engine> SecretKeySet<E> {
     }
 
     /// Returns the `i`-th secret key share.
-    pub fn secret_key_share<T: Into<<E::Fr as PrimeField>::Repr>>(&self, i: T) -> SecretKey<E> {
-        SecretKey(self.poly.evaluate(from_repr_plus_1::<E::Fr>(i.into())))
+    pub fn secret_key_share<T>(&self, i: T) -> ClearOnDrop<Box<SecretKey<E>>>
+    where
+        T: Into<<E::Fr as PrimeField>::Repr>
+    {
+        ClearOnDrop::new(Box::new(
+            SecretKey(self.poly.evaluate(from_repr_plus_1::<E::Fr>(i.into())))
+        ))
     }
 
     /// Returns the corresponding public key set. That information can be shared publicly.
@@ -423,9 +435,9 @@ mod tests {
         assert_ne!(pk_set.public_key(), pk_set.public_key_share(2));
 
         // Make sure we don't hand out the main secret key to anyone.
-        assert_ne!(sk_set.secret_key(), sk_set.secret_key_share(0));
-        assert_ne!(sk_set.secret_key(), sk_set.secret_key_share(1));
-        assert_ne!(sk_set.secret_key(), sk_set.secret_key_share(2));
+        assert_ne!(sk_set.secret_key(), *sk_set.secret_key_share(0));
+        assert_ne!(sk_set.secret_key(), *sk_set.secret_key_share(1));
+        assert_ne!(sk_set.secret_key(), *sk_set.secret_key_share(2));
 
         let msg = "Totally real news";
 

src/lib.rs

@@ -95,6 +95,7 @@
 
 extern crate bincode;
 extern crate byteorder;
+extern crate clear_on_drop;
 #[macro_use(Deref, DerefMut)]
 extern crate derive_deref;
 #[macro_use]

src/messaging.rs

@@ -1,6 +1,7 @@
 use std::collections::{BTreeMap, BTreeSet};
 use std::fmt::Debug;
 
+use clear_on_drop::ClearOnDrop;
 use pairing::bls12_381::Bls12;
 
 use crypto::{PublicKeySet, SecretKey};
@@ -130,13 +131,19 @@ impl<'a, D: DistAlgorithm + 'a> Iterator for OutputIter<'a, D> {
 }
 
 /// Common data shared between algorithms.
+///
+/// *NOTE* `NetworkInfo` requires its `secret_key` to be heap allocated and
+/// wrapped by the `ClearOnDrop` type from the `clear_on_drop` crate. We
+/// use this construction to zero out the section of heap memory that is
+/// allocated for `secret_key` when the corresponding instance of
+/// `NetworkInfo` goes out of scope.
 #[derive(Debug)]
 pub struct NetworkInfo<NodeUid> {
     our_uid: NodeUid,
     all_uids: BTreeSet<NodeUid>,
     num_nodes: usize,
     num_faulty: usize,
-    secret_key: SecretKey<Bls12>,
+    secret_key: ClearOnDrop<Box<SecretKey<Bls12>>>,
     public_key_set: PublicKeySet<Bls12>,
     node_indices: BTreeMap<NodeUid, usize>,
 }
@@ -145,7 +152,7 @@ impl<NodeUid: Clone + Ord> NetworkInfo<NodeUid> {
     pub fn new(
         our_uid: NodeUid,
         all_uids: BTreeSet<NodeUid>,
-        secret_key: SecretKey<Bls12>,
+        secret_key: ClearOnDrop<Box<SecretKey<Bls12>>>,
         public_key_set: PublicKeySet<Bls12>,
     ) -> Self {
         if !all_uids.contains(&our_uid) {