implement more secure entropy hedging for offchain RNG

Signed-off-by: Uncle Stretch <uncle.stretch@ghostchain.io>

pallets/exodus/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ghost-exodus"
-version = "0.0.17"
+version = "0.0.18"
 description = "Threshold signature generation with DKG included"
 license.workspace = true
 authors.workspace = true

pallets/exodus/src/benchmarking.rs

@@ -85,8 +85,7 @@ mod benchmarks {
         dkg_state.insert_index(authority_index);
         QualificationDkgState::<T>::insert(&network_curve, dkg_state);
 
-        let mut rng = Pallet::<T>::get_offchain_rng(authority_index);
-
+        let mut rng = ChaCha20Rng::seed_from_u64(694201337);
         let (_, public_package) = network_curve.dkg_part1(
             authority_index,
             max_signers,

pallets/exodus/src/lib.rs

@@ -31,7 +31,7 @@ use sp_io::hashing::blake2_256;
 
 use ghost_helpers::{
     get_byzantium_quorum_threshold, SubstrateBlake2Hasher,
-    hash_chain::sequential_hash,
+    hash_chain::{cumulative_hash, sequential_hash},
     networks::{NetworkData, NetworkCurve, NetworkType},
     bounded_bitmap::{validate_bitmap_sizes, BoundedBitmap},
 };
@@ -3559,12 +3559,10 @@ impl<T: Config> Pallet<T> {
         let authority_index = exodus_storage.authority_index;
         let network_curve = exodus_storage.network_curve;
 
-        #[cfg(not(any(test, feature = "runtime-benchmarks")))]
-        let mut rng = Self::get_offchain_rng();
-
-        #[cfg(any(test, feature = "runtime-benchmarks"))]
-        let mut rng = Self::get_offchain_rng(authority_index);
+        let exodus_storage_encoded = exodus_storage.encode();
+        let rng_context = [exodus_storage_encoded.as_slice(), secret_share];
 
+        let mut rng = Self::get_offchain_rng(&rng_context);
         let (nonce, hiding_commitment, binding_commitment) = network_curve
             .generate_nonce_commitment(secret_share, &mut rng)?;
 
@@ -3776,12 +3774,15 @@ impl<T: Config> Pallet<T> {
             ));
         }
 
-        #[cfg(not(any(test, feature = "runtime-benchmarks")))]
-        let mut rng = Self::get_offchain_rng();
+        let dkg_storage_encoded = dkg_storage.encode();
+        let qualification_state_encoded = qualification_state.encode();
 
-        #[cfg(any(test, feature = "runtime-benchmarks"))]
-        let mut rng = Self::get_offchain_rng(authority_index);
+        let rng_context = [
+            dkg_storage_encoded.as_slice(),
+            qualification_state_encoded.as_slice(),
+        ];
 
+        let mut rng = Self::get_offchain_rng(&rng_context);
         let (secret_package, public_package) = network_curve
             .dkg_part1(authority_index, max_signers, min_signers, &mut rng)?;
 
@@ -4736,11 +4737,17 @@ impl<T: Config> Pallet<T> {
         dkg_index: DkgIndex,
         network_curve: NetworkCurve,
     ) {
-        #[cfg(not(any(test, feature = "runtime-benchmarks")))]
-        let mut rng = Self::get_offchain_rng();
+        let authority_index_bytes = authority_index.to_le_bytes();
+        let dkg_index_bytes = dkg_index.to_le_bytes();
+        let network_curve_bytes = [network_curve as u8];
 
-        #[cfg(any(test, feature = "runtime-benchmarks"))]
-        let mut rng = Self::get_offchain_rng(authority_index);
+        let rng_context = [
+            round1_secret_package,
+            authority_index_bytes.as_slice(),
+            dkg_index_bytes.as_slice(),
+            network_curve_bytes.as_slice(),
+        ];
+        let mut rng = Self::get_offchain_rng(&rng_context);
 
         for (&receiver_index, round2_package) in round2_packages.iter() {
             if receiver_index == authority_index { continue; }
@@ -4811,26 +4818,13 @@ impl<T: Config> Pallet<T> {
         }
     }
 
-    #[cfg(any(test, feature = "runtime-benchmarks"))]
-    fn get_offchain_rng(authority_index: AuthIndex) -> ChaCha20Rng {
-        let mut seed = [0u8; 32];
-
-        let unique_id = (authority_index as u64).saturating_add(1);
-        let index_bytes = unique_id.to_le_bytes();
-
-        for (i, &byte) in index_bytes.iter().enumerate() {
-            if i < seed.len() {
-                seed[i] ^= byte;
-            }
-        }
-
-        rand_chacha::ChaCha20Rng::from_seed(seed)
-    }
-
-    #[cfg(not(any(test, feature = "runtime-benchmarks")))]
-    fn get_offchain_rng() -> ChaCha20Rng {
+    fn get_offchain_rng(context: &[&[u8]]) -> ChaCha20Rng {
         let seed = sp_io::offchain::random_seed();
-        ChaCha20Rng::from_seed(seed)
+        let seeded_context = sp_std::iter::once(&seed[..])
+            .chain(context.iter().copied());
+
+        let hashed_seed = cumulative_hash::<SubstrateBlake2Hasher, _>(seeded_context);
+        ChaCha20Rng::from_seed(hashed_seed.to_fixed_bytes())
     }
 
     fn create_storage_key(first: &[u8], second: &[u8]) -> Vec<u8> {

pallets/exodus/src/types/local_storage.rs

@@ -75,7 +75,7 @@ impl<ExodusInnerType> ExodusStorageWrapper<ExodusInnerType> {
     }
 }
 
-#[derive(Default)]
+#[derive(Default, Encode)]
 pub struct ExodusStorage<BlockNumber, NetworkCurve>
 where
 	BlockNumber: Default,
@@ -365,7 +365,7 @@ where
     }
 }
 
-#[derive(Default, Clone, Copy)]
+#[derive(Default, Encode, Clone, Copy)]
 pub struct DkgStorage<BlockNumber, NetworkCurve>
 where
 	BlockNumber: Copy + Clone,