Merge pull request #1503 from valentinewallace/2022-05-onion-msgs
[rust-lightning] / lightning / src / chain / keysinterface.rs
index dffe060d91bb71a5f33e8c023de6cac94fb9826d..9a3baea8bb442a3c6928cca83559606a66de95ff 100644 (file)
 //! spendable on-chain outputs which the user owns and is responsible for using just as any other
 //! on-chain output which is theirs.
 
-use bitcoin::blockdata::transaction::{Transaction, TxOut, TxIn, SigHashType};
+use bitcoin::blockdata::transaction::{Transaction, TxOut, TxIn, EcdsaSighashType};
 use bitcoin::blockdata::script::{Script, Builder};
 use bitcoin::blockdata::opcodes;
 use bitcoin::network::constants::Network;
 use bitcoin::util::bip32::{ExtendedPrivKey, ExtendedPubKey, ChildNumber};
-use bitcoin::util::bip143;
+use bitcoin::util::sighash;
 
 use bitcoin::bech32::u5;
 use bitcoin::hashes::{Hash, HashEngine};
@@ -25,12 +25,14 @@ use bitcoin::hashes::sha256::Hash as Sha256;
 use bitcoin::hashes::sha256d::Hash as Sha256dHash;
 use bitcoin::hash_types::WPubkeyHash;
 
-use bitcoin::secp256k1::key::{SecretKey, PublicKey};
-use bitcoin::secp256k1::{Secp256k1, Signature, Signing};
-use bitcoin::secp256k1::recovery::RecoverableSignature;
-use bitcoin::secp256k1;
+use bitcoin::secp256k1::{SecretKey, PublicKey};
+use bitcoin::secp256k1::{Secp256k1, ecdsa::Signature, Signing};
+use bitcoin::secp256k1::ecdh::SharedSecret;
+use bitcoin::secp256k1::ecdsa::RecoverableSignature;
+use bitcoin::{secp256k1, Witness};
 
 use util::{byte_utils, transaction_utils};
+use util::crypto::{hkdf_extract_expand_twice, sign};
 use util::ser::{Writeable, Writer, Readable, ReadableArgs};
 
 use chain::transaction::OutPoint;
@@ -379,15 +381,36 @@ pub trait BaseSign {
 pub trait Sign: BaseSign + Writeable + Clone {
 }
 
+/// Specifies the recipient of an invoice, to indicate to [`KeysInterface::sign_invoice`] what node
+/// secret key should be used to sign the invoice.
+pub enum Recipient {
+       /// The invoice should be signed with the local node secret key.
+       Node,
+       /// The invoice should be signed with the phantom node secret key. This secret key must be the
+       /// same for all nodes participating in the [phantom node payment].
+       ///
+       /// [phantom node payment]: PhantomKeysManager
+       PhantomNode,
+}
+
 /// A trait to describe an object which can get user secrets and key material.
 pub trait KeysInterface {
        /// A type which implements Sign which will be returned by get_channel_signer.
        type Signer : Sign;
 
-       /// Get node secret key (aka node_id or network_key).
+       /// Get node secret key based on the provided [`Recipient`].
        ///
-       /// This method must return the same value each time it is called.
-       fn get_node_secret(&self) -> SecretKey;
+       /// The node_id/network_key is the public key that corresponds to this secret key.
+       ///
+       /// This method must return the same value each time it is called with a given `Recipient`
+       /// parameter.
+       fn get_node_secret(&self, recipient: Recipient) -> Result<SecretKey, ()>;
+       /// Gets the ECDH shared secret of our [`node secret`] and `other_key`, multiplying by `tweak` if
+       /// one is provided. Note that this tweak can be applied to `other_key` instead of our node
+       /// secret, though this is less efficient.
+       ///
+       /// [`node secret`]: Self::get_node_secret
+       fn ecdh(&self, recipient: Recipient, other_key: &PublicKey, tweak: Option<&[u8; 32]>) -> Result<SharedSecret, ()>;
        /// Get a script pubkey which we send funds to when claiming on-chain contestable outputs.
        ///
        /// This method should return a different value each time it is called, to avoid linking
@@ -423,11 +446,22 @@ pub trait KeysInterface {
        /// this trait to parse the invoice and make sure they're signing what they expect, rather than
        /// blindly signing the hash.
        /// The hrp is ascii bytes, while the invoice data is base32.
-       fn sign_invoice(&self, hrp_bytes: &[u8], invoice_data: &[u5]) -> Result<RecoverableSignature, ()>;
+       ///
+       /// The secret key used to sign the invoice is dependent on the [`Recipient`].
+       fn sign_invoice(&self, hrp_bytes: &[u8], invoice_data: &[u5], receipient: Recipient) -> Result<RecoverableSignature, ()>;
 
        /// Get secret key material as bytes for use in encrypting and decrypting inbound payment data.
        ///
+       /// If the implementor of this trait supports [phantom node payments], then every node that is
+       /// intended to be included in the phantom invoice route hints must return the same value from
+       /// this method.
+       //  This is because LDK avoids storing inbound payment data by encrypting payment data in the
+       //  payment hash and/or payment secret, therefore for a payment to be receivable by multiple
+       //  nodes, they must share the key that encrypts this payment data.
+       ///
        /// This method must return the same value each time it is called.
+       ///
+       /// [phantom node payments]: PhantomKeysManager
        fn get_inbound_payment_key_material(&self) -> KeyMaterial;
 }
 
@@ -563,16 +597,16 @@ impl InMemorySigner {
                if spend_tx.input[input_idx].previous_output != descriptor.outpoint.into_bitcoin_outpoint() { return Err(()); }
 
                let remotepubkey = self.pubkeys().payment_point;
-               let witness_script = bitcoin::Address::p2pkh(&::bitcoin::PublicKey{compressed: true, key: remotepubkey}, Network::Testnet).script_pubkey();
-               let sighash = hash_to_message!(&bip143::SigHashCache::new(spend_tx).signature_hash(input_idx, &witness_script, descriptor.output.value, SigHashType::All)[..]);
-               let remotesig = secp_ctx.sign(&sighash, &self.payment_key);
-               let payment_script = bitcoin::Address::p2wpkh(&::bitcoin::PublicKey{compressed: true, key: remotepubkey}, Network::Bitcoin).unwrap().script_pubkey();
+               let witness_script = bitcoin::Address::p2pkh(&::bitcoin::PublicKey{compressed: true, inner: remotepubkey}, Network::Testnet).script_pubkey();
+               let sighash = hash_to_message!(&sighash::SighashCache::new(spend_tx).segwit_signature_hash(input_idx, &witness_script, descriptor.output.value, EcdsaSighashType::All).unwrap()[..]);
+               let remotesig = sign(secp_ctx, &sighash, &self.payment_key);
+               let payment_script = bitcoin::Address::p2wpkh(&::bitcoin::PublicKey{compressed: true, inner: remotepubkey}, Network::Bitcoin).unwrap().script_pubkey();
 
                if payment_script != descriptor.output.script_pubkey  { return Err(()); }
 
                let mut witness = Vec::with_capacity(2);
                witness.push(remotesig.serialize_der().to_vec());
-               witness[0].push(SigHashType::All as u8);
+               witness[0].push(EcdsaSighashType::All as u8);
                witness.push(remotepubkey.serialize().to_vec());
                Ok(witness)
        }
@@ -598,15 +632,15 @@ impl InMemorySigner {
                        .expect("We constructed the payment_base_key, so we can only fail here if the RNG is busted.");
                let delayed_payment_pubkey = PublicKey::from_secret_key(&secp_ctx, &delayed_payment_key);
                let witness_script = chan_utils::get_revokeable_redeemscript(&descriptor.revocation_pubkey, descriptor.to_self_delay, &delayed_payment_pubkey);
-               let sighash = hash_to_message!(&bip143::SigHashCache::new(spend_tx).signature_hash(input_idx, &witness_script, descriptor.output.value, SigHashType::All)[..]);
-               let local_delayedsig = secp_ctx.sign(&sighash, &delayed_payment_key);
+               let sighash = hash_to_message!(&sighash::SighashCache::new(spend_tx).segwit_signature_hash(input_idx, &witness_script, descriptor.output.value, EcdsaSighashType::All).unwrap()[..]);
+               let local_delayedsig = sign(secp_ctx, &sighash, &delayed_payment_key);
                let payment_script = bitcoin::Address::p2wsh(&witness_script, Network::Bitcoin).script_pubkey();
 
                if descriptor.output.script_pubkey != payment_script { return Err(()); }
 
                let mut witness = Vec::with_capacity(3);
                witness.push(local_delayedsig.serialize_der().to_vec());
-               witness[0].push(SigHashType::All as u8);
+               witness[0].push(EcdsaSighashType::All as u8);
                witness.push(vec!()); //MINIMALIF
                witness.push(witness_script.clone().into_bytes());
                Ok(witness)
@@ -645,10 +679,10 @@ impl BaseSign for InMemorySigner {
                for htlc in commitment_tx.htlcs() {
                        let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, commitment_tx.feerate_per_kw(), self.holder_selected_contest_delay(), htlc, self.opt_anchors(), &keys.broadcaster_delayed_payment_key, &keys.revocation_key);
                        let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, self.opt_anchors(), &keys);
-                       let htlc_sighashtype = if self.opt_anchors() { SigHashType::SinglePlusAnyoneCanPay } else { SigHashType::All };
-                       let htlc_sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, htlc_sighashtype)[..]);
+                       let htlc_sighashtype = if self.opt_anchors() { EcdsaSighashType::SinglePlusAnyoneCanPay } else { EcdsaSighashType::All };
+                       let htlc_sighash = hash_to_message!(&sighash::SighashCache::new(&htlc_tx).segwit_signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, htlc_sighashtype).unwrap()[..]);
                        let holder_htlc_key = chan_utils::derive_private_key(&secp_ctx, &keys.per_commitment_point, &self.htlc_base_key).map_err(|_| ())?;
-                       htlc_sigs.push(secp_ctx.sign(&htlc_sighash, &holder_htlc_key));
+                       htlc_sigs.push(sign(secp_ctx, &htlc_sighash, &holder_htlc_key));
                }
 
                Ok((commitment_sig, htlc_sigs))
@@ -687,9 +721,9 @@ impl BaseSign for InMemorySigner {
                        let counterparty_delayedpubkey = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().delayed_payment_basepoint).map_err(|_| ())?;
                        chan_utils::get_revokeable_redeemscript(&revocation_pubkey, self.holder_selected_contest_delay(), &counterparty_delayedpubkey)
                };
-               let mut sighash_parts = bip143::SigHashCache::new(justice_tx);
-               let sighash = hash_to_message!(&sighash_parts.signature_hash(input, &witness_script, amount, SigHashType::All)[..]);
-               return Ok(secp_ctx.sign(&sighash, &revocation_key))
+               let mut sighash_parts = sighash::SighashCache::new(justice_tx);
+               let sighash = hash_to_message!(&sighash_parts.segwit_signature_hash(input, &witness_script, amount, EcdsaSighashType::All).unwrap()[..]);
+               return Ok(sign(secp_ctx, &sighash, &revocation_key))
        }
 
        fn sign_justice_revoked_htlc(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
@@ -701,9 +735,9 @@ impl BaseSign for InMemorySigner {
                        let holder_htlcpubkey = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.pubkeys().htlc_basepoint).map_err(|_| ())?;
                        chan_utils::get_htlc_redeemscript_with_explicit_keys(&htlc, self.opt_anchors(), &counterparty_htlcpubkey, &holder_htlcpubkey, &revocation_pubkey)
                };
-               let mut sighash_parts = bip143::SigHashCache::new(justice_tx);
-               let sighash = hash_to_message!(&sighash_parts.signature_hash(input, &witness_script, amount, SigHashType::All)[..]);
-               return Ok(secp_ctx.sign(&sighash, &revocation_key))
+               let mut sighash_parts = sighash::SighashCache::new(justice_tx);
+               let sighash = hash_to_message!(&sighash_parts.segwit_signature_hash(input, &witness_script, amount, EcdsaSighashType::All).unwrap()[..]);
+               return Ok(sign(secp_ctx, &sighash, &revocation_key))
        }
 
        fn sign_counterparty_htlc_transaction(&self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
@@ -715,9 +749,9 @@ impl BaseSign for InMemorySigner {
                                        } else { return Err(()) }
                                } else { return Err(()) }
                        } else { return Err(()) };
-                       let mut sighash_parts = bip143::SigHashCache::new(htlc_tx);
-                       let sighash = hash_to_message!(&sighash_parts.signature_hash(input, &witness_script, amount, SigHashType::All)[..]);
-                       return Ok(secp_ctx.sign(&sighash, &htlc_key))
+                       let mut sighash_parts = sighash::SighashCache::new(htlc_tx);
+                       let sighash = hash_to_message!(&sighash_parts.segwit_signature_hash(input, &witness_script, amount, EcdsaSighashType::All).unwrap()[..]);
+                       return Ok(sign(secp_ctx, &sighash, &htlc_key))
                }
                Err(())
        }
@@ -731,7 +765,7 @@ impl BaseSign for InMemorySigner {
        fn sign_channel_announcement(&self, msg: &UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<secp256k1::All>)
        -> Result<(Signature, Signature), ()> {
                let msghash = hash_to_message!(&Sha256dHash::hash(&msg.encode()[..])[..]);
-               Ok((secp_ctx.sign(&msghash, &self.node_secret), secp_ctx.sign(&msghash, &self.funding_key)))
+               Ok((sign(secp_ctx, &msghash, &self.node_secret), sign(secp_ctx, &msghash, &self.funding_key)))
        }
 
        fn ready_channel(&mut self, channel_parameters: &ChannelTransactionParameters) {
@@ -810,6 +844,12 @@ impl ReadableArgs<SecretKey> for InMemorySigner {
 /// ChannelMonitor closes may use seed/1'
 /// Cooperative closes may use seed/2'
 /// The two close keys may be needed to claim on-chain funds!
+///
+/// This struct cannot be used for nodes that wish to support receiving phantom payments;
+/// [`PhantomKeysManager`] must be used instead.
+///
+/// Note that switching between this struct and [`PhantomKeysManager`] will invalidate any
+/// previously issued invoices and attempts to pay previous invoices will fail.
 pub struct KeysManager {
        secp_ctx: Secp256k1<secp256k1::All>,
        node_secret: SecretKey,
@@ -853,10 +893,10 @@ impl KeysManager {
                // Note that when we aren't serializing the key, network doesn't matter
                match ExtendedPrivKey::new_master(Network::Testnet, seed) {
                        Ok(master_key) => {
-                               let node_secret = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(0).unwrap()).expect("Your RNG is busted").private_key.key;
+                               let node_secret = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(0).unwrap()).expect("Your RNG is busted").private_key;
                                let destination_script = match master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(1).unwrap()) {
                                        Ok(destination_key) => {
-                                               let wpubkey_hash = WPubkeyHash::hash(&ExtendedPubKey::from_private(&secp_ctx, &destination_key).public_key.to_bytes());
+                                               let wpubkey_hash = WPubkeyHash::hash(&ExtendedPubKey::from_priv(&secp_ctx, &destination_key).to_pub().to_bytes());
                                                Builder::new().push_opcode(opcodes::all::OP_PUSHBYTES_0)
                                                              .push_slice(&wpubkey_hash.into_inner())
                                                              .into_script()
@@ -864,12 +904,12 @@ impl KeysManager {
                                        Err(_) => panic!("Your RNG is busted"),
                                };
                                let shutdown_pubkey = match master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(2).unwrap()) {
-                                       Ok(shutdown_key) => ExtendedPubKey::from_private(&secp_ctx, &shutdown_key).public_key.key,
+                                       Ok(shutdown_key) => ExtendedPubKey::from_priv(&secp_ctx, &shutdown_key).public_key,
                                        Err(_) => panic!("Your RNG is busted"),
                                };
                                let channel_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(3).unwrap()).expect("Your RNG is busted");
                                let rand_bytes_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(4).unwrap()).expect("Your RNG is busted");
-                               let inbound_payment_key: SecretKey = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(5).unwrap()).expect("Your RNG is busted").private_key.key;
+                               let inbound_payment_key: SecretKey = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(5).unwrap()).expect("Your RNG is busted").private_key;
                                let mut inbound_pmt_key_bytes = [0; 32];
                                inbound_pmt_key_bytes.copy_from_slice(&inbound_payment_key[..]);
 
@@ -920,7 +960,7 @@ impl KeysManager {
                // entropy, everything else just ensures uniqueness. We rely on the unique_start (ie
                // starting_time provided in the constructor) to be unique.
                let child_privkey = self.channel_master_key.ckd_priv(&self.secp_ctx, ChildNumber::from_hardened_idx(chan_id as u32).expect("key space exhausted")).expect("Your RNG is busted");
-               unique_start.input(&child_privkey.private_key.key[..]);
+               unique_start.input(&child_privkey.private_key[..]);
 
                let seed = Sha256::from_engine(unique_start).into_inner();
 
@@ -964,7 +1004,7 @@ impl KeysManager {
        /// transaction will have a feerate, at least, of the given value.
        ///
        /// Returns `Err(())` if the output value is greater than the input value minus required fee,
-       /// if a descriptor was duplicated, or if an output descriptor script_pubkey 
+       /// if a descriptor was duplicated, or if an output descriptor `script_pubkey`
        /// does not match the one we can spend.
        ///
        /// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
@@ -983,7 +1023,7 @@ impl KeysManager {
                                                previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
                                                script_sig: Script::new(),
                                                sequence: 0,
-                                               witness: Vec::new(),
+                                               witness: Witness::new(),
                                        });
                                        witness_weight += StaticPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
                                        input_value += descriptor.output.value;
@@ -994,7 +1034,7 @@ impl KeysManager {
                                                previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
                                                script_sig: Script::new(),
                                                sequence: descriptor.to_self_delay as u32,
-                                               witness: Vec::new(),
+                                               witness: Witness::new(),
                                        });
                                        witness_weight += DelayedPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
                                        input_value += descriptor.output.value;
@@ -1005,7 +1045,7 @@ impl KeysManager {
                                                previous_output: outpoint.into_bitcoin_outpoint(),
                                                script_sig: Script::new(),
                                                sequence: 0,
-                                               witness: Vec::new(),
+                                               witness: Witness::new(),
                                        });
                                        witness_weight += 1 + 73 + 34;
                                        input_value += output.value;
@@ -1033,7 +1073,7 @@ impl KeysManager {
                                                        self.derive_channel_keys(descriptor.channel_value_satoshis, &descriptor.channel_keys_id),
                                                        descriptor.channel_keys_id));
                                        }
-                                       spend_tx.input[input_idx].witness = keys_cache.as_ref().unwrap().0.sign_counterparty_payment_input(&spend_tx, input_idx, &descriptor, &secp_ctx)?;
+                                       spend_tx.input[input_idx].witness = Witness::from_vec(keys_cache.as_ref().unwrap().0.sign_counterparty_payment_input(&spend_tx, input_idx, &descriptor, &secp_ctx)?);
                                },
                                SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
                                        if keys_cache.is_none() || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id {
@@ -1041,7 +1081,7 @@ impl KeysManager {
                                                        self.derive_channel_keys(descriptor.channel_value_satoshis, &descriptor.channel_keys_id),
                                                        descriptor.channel_keys_id));
                                        }
-                                       spend_tx.input[input_idx].witness = keys_cache.as_ref().unwrap().0.sign_dynamic_p2wsh_input(&spend_tx, input_idx, &descriptor, &secp_ctx)?;
+                                       spend_tx.input[input_idx].witness = Witness::from_vec(keys_cache.as_ref().unwrap().0.sign_dynamic_p2wsh_input(&spend_tx, input_idx, &descriptor, &secp_ctx)?);
                                },
                                SpendableOutputDescriptor::StaticOutput { ref output, .. } => {
                                        let derivation_idx = if output.script_pubkey == self.destination_script {
@@ -1061,29 +1101,30 @@ impl KeysManager {
                                                        Err(_) => panic!("Your rng is busted"),
                                                }
                                        };
-                                       let pubkey = ExtendedPubKey::from_private(&secp_ctx, &secret).public_key;
+                                       let pubkey = ExtendedPubKey::from_priv(&secp_ctx, &secret).to_pub();
                                        if derivation_idx == 2 {
-                                               assert_eq!(pubkey.key, self.shutdown_pubkey);
+                                               assert_eq!(pubkey.inner, self.shutdown_pubkey);
                                        }
                                        let witness_script = bitcoin::Address::p2pkh(&pubkey, Network::Testnet).script_pubkey();
                                        let payment_script = bitcoin::Address::p2wpkh(&pubkey, Network::Testnet).expect("uncompressed key found").script_pubkey();
 
                                        if payment_script != output.script_pubkey { return Err(()); };
 
-                                       let sighash = hash_to_message!(&bip143::SigHashCache::new(&spend_tx).signature_hash(input_idx, &witness_script, output.value, SigHashType::All)[..]);
-                                       let sig = secp_ctx.sign(&sighash, &secret.private_key.key);
-                                       spend_tx.input[input_idx].witness.push(sig.serialize_der().to_vec());
-                                       spend_tx.input[input_idx].witness[0].push(SigHashType::All as u8);
-                                       spend_tx.input[input_idx].witness.push(pubkey.key.serialize().to_vec());
+                                       let sighash = hash_to_message!(&sighash::SighashCache::new(&spend_tx).segwit_signature_hash(input_idx, &witness_script, output.value, EcdsaSighashType::All).unwrap()[..]);
+                                       let sig = sign(secp_ctx, &sighash, &secret.private_key);
+                                       let mut sig_ser = sig.serialize_der().to_vec();
+                                       sig_ser.push(EcdsaSighashType::All as u8);
+                                       spend_tx.input[input_idx].witness.push(sig_ser);
+                                       spend_tx.input[input_idx].witness.push(pubkey.inner.serialize().to_vec());
                                },
                        }
                        input_idx += 1;
                }
 
-               debug_assert!(expected_max_weight >= spend_tx.get_weight());
+               debug_assert!(expected_max_weight >= spend_tx.weight());
                // Note that witnesses with a signature vary somewhat in size, so allow
                // `expected_max_weight` to overshoot by up to 3 bytes per input.
-               debug_assert!(expected_max_weight <= spend_tx.get_weight() + descriptors.len() * 3);
+               debug_assert!(expected_max_weight <= spend_tx.weight() + descriptors.len() * 3);
 
                Ok(spend_tx)
        }
@@ -1092,8 +1133,19 @@ impl KeysManager {
 impl KeysInterface for KeysManager {
        type Signer = InMemorySigner;
 
-       fn get_node_secret(&self) -> SecretKey {
-               self.node_secret.clone()
+       fn get_node_secret(&self, recipient: Recipient) -> Result<SecretKey, ()> {
+               match recipient {
+                       Recipient::Node => Ok(self.node_secret.clone()),
+                       Recipient::PhantomNode => Err(())
+               }
+       }
+
+       fn ecdh(&self, recipient: Recipient, other_key: &PublicKey, tweak: Option<&[u8; 32]>) -> Result<SharedSecret, ()> {
+               let mut node_secret = self.get_node_secret(recipient)?;
+               if let Some(tweak) = tweak {
+                       node_secret.mul_assign(tweak).map_err(|_| ())?;
+               }
+               Ok(SharedSecret::new(other_key, &node_secret))
        }
 
        fn get_inbound_payment_key_material(&self) -> KeyMaterial {
@@ -1123,19 +1175,131 @@ impl KeysInterface for KeysManager {
 
                let child_ix = self.rand_bytes_child_index.fetch_add(1, Ordering::AcqRel);
                let child_privkey = self.rand_bytes_master_key.ckd_priv(&self.secp_ctx, ChildNumber::from_hardened_idx(child_ix as u32).expect("key space exhausted")).expect("Your RNG is busted");
-               sha.input(&child_privkey.private_key.key[..]);
+               sha.input(&child_privkey.private_key[..]);
 
                sha.input(b"Unique Secure Random Bytes Salt");
                Sha256::from_engine(sha).into_inner()
        }
 
        fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::Signer, DecodeError> {
-               InMemorySigner::read(&mut io::Cursor::new(reader), self.get_node_secret())
+               InMemorySigner::read(&mut io::Cursor::new(reader), self.node_secret.clone())
+       }
+
+       fn sign_invoice(&self, hrp_bytes: &[u8], invoice_data: &[u5], recipient: Recipient) -> Result<RecoverableSignature, ()> {
+               let preimage = construct_invoice_preimage(&hrp_bytes, &invoice_data);
+               let secret = match recipient {
+                       Recipient::Node => self.get_node_secret(Recipient::Node)?,
+                       Recipient::PhantomNode => return Err(()),
+               };
+               Ok(self.secp_ctx.sign_ecdsa_recoverable(&hash_to_message!(&Sha256::hash(&preimage)), &secret))
+       }
+}
+
+/// Similar to [`KeysManager`], but allows the node using this struct to receive phantom node
+/// payments.
+///
+/// A phantom node payment is a payment made to a phantom invoice, which is an invoice that can be
+/// paid to one of multiple nodes. This works because we encode the invoice route hints such that
+/// LDK will recognize an incoming payment as destined for a phantom node, and collect the payment
+/// itself without ever needing to forward to this fake node.
+///
+/// Phantom node payments are useful for load balancing between multiple LDK nodes. They also
+/// provide some fault tolerance, because payers will automatically retry paying other provided
+/// nodes in the case that one node goes down.
+///
+/// Note that multi-path payments are not supported in phantom invoices for security reasons.
+//  In the hypothetical case that we did support MPP phantom payments, there would be no way for
+//  nodes to know when the full payment has been received (and the preimage can be released) without
+//  significantly compromising on our safety guarantees. I.e., if we expose the ability for the user
+//  to tell LDK when the preimage can be released, we open ourselves to attacks where the preimage
+//  is released too early.
+//
+/// Switching between this struct and [`KeysManager`] will invalidate any previously issued
+/// invoices and attempts to pay previous invoices will fail.
+pub struct PhantomKeysManager {
+       inner: KeysManager,
+       inbound_payment_key: KeyMaterial,
+       phantom_secret: SecretKey,
+}
+
+impl KeysInterface for PhantomKeysManager {
+       type Signer = InMemorySigner;
+
+       fn get_node_secret(&self, recipient: Recipient) -> Result<SecretKey, ()> {
+               match recipient {
+                       Recipient::Node => self.inner.get_node_secret(Recipient::Node),
+                       Recipient::PhantomNode => Ok(self.phantom_secret.clone()),
+               }
+       }
+
+       fn ecdh(&self, recipient: Recipient, other_key: &PublicKey, tweak: Option<&[u8; 32]>) -> Result<SharedSecret, ()> {
+               let mut node_secret = self.get_node_secret(recipient)?;
+               if let Some(tweak) = tweak {
+                       node_secret.mul_assign(tweak).map_err(|_| ())?;
+               }
+               Ok(SharedSecret::new(other_key, &node_secret))
+       }
+
+       fn get_inbound_payment_key_material(&self) -> KeyMaterial {
+               self.inbound_payment_key.clone()
+       }
+
+       fn get_destination_script(&self) -> Script {
+               self.inner.get_destination_script()
+       }
+
+       fn get_shutdown_scriptpubkey(&self) -> ShutdownScript {
+               self.inner.get_shutdown_scriptpubkey()
+       }
+
+       fn get_channel_signer(&self, inbound: bool, channel_value_satoshis: u64) -> Self::Signer {
+               self.inner.get_channel_signer(inbound, channel_value_satoshis)
+       }
+
+       fn get_secure_random_bytes(&self) -> [u8; 32] {
+               self.inner.get_secure_random_bytes()
+       }
+
+       fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::Signer, DecodeError> {
+               self.inner.read_chan_signer(reader)
        }
 
-       fn sign_invoice(&self, hrp_bytes: &[u8], invoice_data: &[u5]) -> Result<RecoverableSignature, ()> {
+       fn sign_invoice(&self, hrp_bytes: &[u8], invoice_data: &[u5], recipient: Recipient) -> Result<RecoverableSignature, ()> {
                let preimage = construct_invoice_preimage(&hrp_bytes, &invoice_data);
-               Ok(self.secp_ctx.sign_recoverable(&hash_to_message!(&Sha256::hash(&preimage)), &self.get_node_secret()))
+               let secret = self.get_node_secret(recipient)?;
+               Ok(self.inner.secp_ctx.sign_ecdsa_recoverable(&hash_to_message!(&Sha256::hash(&preimage)), &secret))
+       }
+}
+
+impl PhantomKeysManager {
+       /// Constructs a `PhantomKeysManager` given a 32-byte seed and an additional `cross_node_seed`
+       /// that is shared across all nodes that intend to participate in [phantom node payments] together.
+       ///
+       /// See [`KeysManager::new`] for more information on `seed`, `starting_time_secs`, and
+       /// `starting_time_nanos`.
+       ///
+       /// `cross_node_seed` must be the same across all phantom payment-receiving nodes and also the
+       /// same across restarts, or else inbound payments may fail.
+       ///
+       /// [phantom node payments]: PhantomKeysManager
+       pub fn new(seed: &[u8; 32], starting_time_secs: u64, starting_time_nanos: u32, cross_node_seed: &[u8; 32]) -> Self {
+               let inner = KeysManager::new(seed, starting_time_secs, starting_time_nanos);
+               let (inbound_key, phantom_key) = hkdf_extract_expand_twice(b"LDK Inbound and Phantom Payment Key Expansion", cross_node_seed);
+               Self {
+                       inner,
+                       inbound_payment_key: KeyMaterial(inbound_key),
+                       phantom_secret: SecretKey::from_slice(&phantom_key).unwrap(),
+               }
+       }
+
+       /// See [`KeysManager::spend_spendable_outputs`] for documentation on this method.
+       pub fn spend_spendable_outputs<C: Signing>(&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: Script, feerate_sat_per_1000_weight: u32, secp_ctx: &Secp256k1<C>) -> Result<Transaction, ()> {
+               self.inner.spend_spendable_outputs(descriptors, outputs, change_destination_script, feerate_sat_per_1000_weight, secp_ctx)
+       }
+
+       /// See [`KeysManager::derive_channel_keys`] for documentation on this method.
+       pub fn derive_channel_keys(&self, channel_value_satoshis: u64, params: &[u8; 32]) -> InMemorySigner {
+               self.inner.derive_channel_keys(channel_value_satoshis, params)
        }
 }