Add a method to get session secret for onion packet to KeysInterface

fuzz/fuzz_targets/full_stack_target.rs

@@ -21,7 +21,7 @@ use lightning::ln::channelmanager::{ChannelManager, PaymentFailReason};
 use lightning::ln::peer_handler::{MessageHandler,PeerManager,SocketDescriptor};
 use lightning::ln::router::Router;
 use lightning::util::events::{EventsProvider,Event};
-use lightning::util::reset_rng_state;
+use lightning::util::{reset_rng_state, fill_bytes};
 use lightning::util::logger::Logger;
 use lightning::util::sha2::Sha256;
 use lightning::util::config::UserConfig;
@@ -265,6 +265,12 @@ impl KeysInterface for KeyProvider {
 			}
 		}
 	}
+
+	fn get_session_key(&self) -> SecretKey {
+		let mut session_key = [0; 32];
+		fill_bytes(&mut session_key);
+		SecretKey::from_slice(&Secp256k1::without_caps(), &session_key).unwrap()
+	}
 }
 
 #[inline]

src/chain/keysinterface.rs

@@ -79,6 +79,8 @@ pub trait KeysInterface: Send + Sync {
 	/// Get a new set of ChannelKeys for per-channel secrets. These MUST be unique even if you
 	/// restarted with some stale data!
 	fn get_channel_keys(&self, inbound: bool) -> ChannelKeys;
+	/// Get a secret for construting an onion packet
+	fn get_session_key(&self) -> SecretKey;
 }
 
 /// Set of lightning keys needed to operate a channel as described in BOLT 3
@@ -158,6 +160,8 @@ pub struct KeysManager {
 	shutdown_pubkey: PublicKey,
 	channel_master_key: ExtendedPrivKey,
 	channel_child_index: AtomicUsize,
+	session_master_key: ExtendedPrivKey,
+	session_child_index: AtomicUsize,
 
 	logger: Arc<Logger>,
 }
@@ -184,13 +188,16 @@ impl KeysManager {
 					Err(_) => panic!("Your RNG is busted"),
 				};
 				let channel_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(3)).expect("Your RNG is busted");
+				let session_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(4)).expect("Your RNG is busted");
 				KeysManager {
 					secp_ctx,
 					node_secret,
 					destination_script,
 					shutdown_pubkey,
 					channel_master_key,
 					channel_child_index: AtomicUsize::new(0),
+					session_master_key,
+					session_child_index: AtomicUsize::new(0),
 
 					logger,
 				}
@@ -235,4 +242,19 @@ impl KeysInterface for KeysManager {
 		sha.result(&mut seed);
 		ChannelKeys::new_from_seed(&seed)
 	}
+
+	fn get_session_key(&self) -> SecretKey {
+		let mut sha = Sha256::new();
+		let mut res = [0u8; 32];
+
+		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.session_child_index.fetch_add(1, Ordering::AcqRel);
+		let child_privkey = self.session_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 res);
+		SecretKey::from_slice(&self.secp_ctx, &res).expect("Your RNG is busted")
+	}
 }

src/ln/channel.rs

@@ -3902,6 +3902,7 @@ mod tests {
 		}
 
 		fn get_channel_keys(&self, _inbound: bool) -> ChannelKeys { self.chan_keys.clone() }
+		fn get_session_key(&self) -> SecretKey { panic!(); }
 	}
 
 	#[test]

src/ln/channelmanager.rs

@@ -1199,11 +1199,7 @@ impl ChannelManager {
 			}
 		}
 
-		let session_priv = SecretKey::from_slice(&self.secp_ctx, &{
-			let mut session_key = [0; 32];
-			rng::fill_bytes(&mut session_key);
-			session_key
-		}).expect("RNG is bad!");
+		let session_priv = self.keys_manager.get_session_key();
 
 		let cur_height = self.latest_block_height.load(Ordering::Acquire) as u32 + 1;
 

src/util/mod.rs

@@ -25,7 +25,7 @@ pub mod sha2;
 pub(crate) mod sha2;
 
 #[cfg(feature = "fuzztarget")]
-pub use self::rng::reset_rng_state;
+pub use self::rng::{reset_rng_state, fill_bytes};
 
 #[cfg(test)]
 pub(crate) mod test_utils;