Bug fix using same seed sequence for channel key geneartion

Author: yuntai

src/chain/keysinterface.rs

@@ -14,11 +14,16 @@ use secp256k1::Secp256k1;
 use secp256k1;
 
 use crypto::hkdf::{hkdf_extract,hkdf_expand};
+use crypto::digest::Digest;
 
 use util::sha2::Sha256;
 use util::logger::Logger;
+use util::rng;
+use util::byte_utils;
 
+use std::time::{SystemTime, UNIX_EPOCH};
 use std::sync::Arc;
+use std::sync::atomic::{AtomicUsize, Ordering};
 
 /// When on-chain outputs are created by rust-lightning an event is generated which informs the
 /// user thereof. This enum describes the format of the output and provides the OutPoint.
@@ -39,7 +44,7 @@ pub enum SpendableOutputDescriptor {
 	DynamicOutput {
 		/// Outpoint spendable by user wallet
 		outpoint: OutPoint,
-		/// local_delayedkey = delayed_payment_basepoint_secret + SHA256(per_commitment_point || delayed_payment_basepoint
+		/// local_delayedkey = delayed_payment_basepoint_secret + SHA256(per_commitment_point || delayed_payment_basepoint)
 		local_delayedkey: SecretKey,
 		/// witness redeemScript encumbering output
 		witness_script: Script,
@@ -137,6 +142,7 @@ pub struct KeysManager {
 	destination_script: Script,
 	shutdown_pubkey: PublicKey,
 	channel_master_key: ExtendedPrivKey,
+	channel_child_index: AtomicUsize,
 
 	logger: Arc<Logger>,
 }
@@ -169,6 +175,7 @@ impl KeysManager {
 					destination_script,
 					shutdown_pubkey,
 					channel_master_key,
+					channel_child_index: AtomicUsize::new(0),
 
 					logger,
 				}
@@ -192,11 +199,25 @@ impl KeysInterface for KeysManager {
 	}
 
 	fn get_channel_keys(&self, _inbound: bool) -> ChannelKeys {
-		let channel_pubkey = ExtendedPubKey::from_private(&self.secp_ctx, &self. channel_master_key);
-		let mut seed = [0; 32];
-		for (arr, slice) in seed.iter_mut().zip((&channel_pubkey.public_key.serialize()[0..32]).iter()) {
-			*arr = *slice;
-		}
+		// We only seriously intend to rely on the channel_master_key for true secure
+		// entropy, everything else just ensures uniqueness. We generally don't expect
+		// all clients to have non-broken RNGs here, so we also include the current
+		// time as a fallback to get uniqueness.
+		let mut sha = Sha256::new();
+
+		let mut seed = [0u8; 32];
+		rng::fill_bytes(&mut seed[..]);
+		sha.input(&seed);
+
+		let now = SystemTime::now().duration_since(UNIX_EPOCH).expect("Time went backwards");
+		sha.input(&byte_utils::be32_to_array(now.subsec_nanos()));
+		sha.input(&byte_utils::be64_to_array(now.as_secs()));
+
+		let child_ix = self.channel_child_index.fetch_add(1, Ordering::AcqRel);
+		let child_privkey = self.channel_master_key.ckd_priv(&self.secp_ctx, ChildNumber::from_hardened_idx(child_ix as u32)).expect("Your RNG is busted");
+		sha.input(&child_privkey.secret_key[..]);
+
+		sha.result(&mut seed);
 		ChannelKeys::new_from_seed(&seed)
 	}
 }