Merge pull request #419 from TheBlueMatt/2019-12-simple-signer-api-step

[rust-lightning] / lightning / src / chain / keysinterface.rs

//! keysinterface provides keys into rust-lightning and defines some useful enums which describe
//! 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, OutPoint, TxOut};
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_hashes::{Hash, HashEngine};
use bitcoin_hashes::sha256::HashEngine as Sha256State;
use bitcoin_hashes::sha256::Hash as Sha256;
use bitcoin_hashes::sha256d::Hash as Sha256dHash;
use bitcoin_hashes::hash160::Hash as Hash160;

use secp256k1::key::{SecretKey, PublicKey};
use secp256k1::{Secp256k1, Signature};
use secp256k1;

use util::byte_utils;
use util::logger::Logger;
use util::ser::Writeable;

use ln::chan_utils;
use ln::chan_utils::{TxCreationKeys, HTLCOutputInCommitment};
use ln::msgs;

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.
pub enum SpendableOutputDescriptor {
        /// Outpoint with an output to a script which was provided via KeysInterface, thus you should
        /// have stored somewhere how to spend script_pubkey!
        /// Outputs from a justice tx, claim tx or preimage tx
        StaticOutput {
                /// The outpoint spendable by user wallet
                outpoint: OutPoint,
                /// The output which is referenced by the given outpoint
                output: TxOut,
        },
        /// Outpoint commits to a P2WSH
        /// P2WSH should be spend by the following witness :
        /// <local_delayedsig> 0 <witnessScript>
        /// With input nSequence set to_self_delay.
        /// Outputs from a HTLC-Success/Timeout tx/commitment tx
        DynamicOutputP2WSH {
                /// Outpoint spendable by user wallet
                outpoint: OutPoint,
                /// local_delayedkey = delayed_payment_basepoint_secret + SHA256(per_commitment_point || delayed_payment_basepoint) OR
                key: SecretKey,
                /// witness redeemScript encumbering output.
                witness_script: Script,
                /// nSequence input must commit to self_delay to satisfy script's OP_CSV
                to_self_delay: u16,
                /// The output which is referenced by the given outpoint
                output: TxOut,
        },
        /// Outpoint commits to a P2WPKH
        /// P2WPKH should be spend by the following witness :
        /// <local_sig> <local_pubkey>
        /// Outputs to_remote from a commitment tx
        DynamicOutputP2WPKH {
                /// Outpoint spendable by user wallet
                outpoint: OutPoint,
                /// localkey = payment_basepoint_secret + SHA256(per_commitment_point || payment_basepoint
                key: SecretKey,
                /// The output which is reference by the given outpoint
                output: TxOut,
        }
}

/// A trait to describe an object which can get user secrets and key material.
pub trait KeysInterface: Send + Sync {
        /// A type which implements ChannelKeys which will be returned by get_channel_keys.
        type ChanKeySigner : ChannelKeys;

        /// Get node secret key (aka node_id or network_key)
        fn get_node_secret(&self) -> SecretKey;
        /// Get destination redeemScript to encumber static protocol exit points.
        fn get_destination_script(&self) -> Script;
        /// Get shutdown_pubkey to use as PublicKey at channel closure
        fn get_shutdown_pubkey(&self) -> PublicKey;
        /// 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) -> Self::ChanKeySigner;
        /// Get a secret and PRNG seed for construting an onion packet
        fn get_onion_rand(&self) -> (SecretKey, [u8; 32]);
        /// Get a unique temporary channel id. Channels will be referred to by this until the funding
        /// transaction is created, at which point they will use the outpoint in the funding
        /// transaction.
        fn get_channel_id(&self) -> [u8; 32];
}

/// Set of lightning keys needed to operate a channel as described in BOLT 3.
///
/// Signing services could be implemented on a hardware wallet. In this case,
/// the current ChannelKeys would be a front-end on top of a communication
/// channel connected to your secure device and lightning key material wouldn't
/// reside on a hot server. Nevertheless, a this deployment would still need
/// to trust the ChannelManager to avoid loss of funds as this latest component
/// could ask to sign commitment transaction with HTLCs paying to attacker pubkeys.
///
/// A more secure iteration would be to use hashlock (or payment points) to pair
/// invoice/incoming HTLCs with outgoing HTLCs to implement a no-trust-ChannelManager
/// at the price of more state and computation on the hardware wallet side. In the future,
/// we are looking forward to design such interface.
///
/// In any case, ChannelMonitor or fallback watchtowers are always going to be trusted
/// to act, as liveness and breach reply correctness are always going to be hard requirements
/// of LN security model, orthogonal of key management issues.
///
/// If you're implementing a custom signer, you almost certainly want to implement
/// Readable/Writable to serialize out a unique reference to this set of keys so
/// that you can serialize the full ChannelManager object.
///
/// (TODO: We shouldn't require that, and should have an API to get them at deser time, due mostly
/// to the possibility of reentrancy issues by calling the user's code during our deserialization
/// routine).
pub trait ChannelKeys : Send {
        /// Gets the private key for the anchor tx
        fn funding_key<'a>(&'a self) -> &'a SecretKey;
        /// Gets the local secret key for blinded revocation pubkey
        fn revocation_base_key<'a>(&'a self) -> &'a SecretKey;
        /// Gets the local secret key used in to_remote output of remote commitment tx
        /// (and also as part of obscured commitment number)
        fn payment_base_key<'a>(&'a self) -> &'a SecretKey;
        /// Gets the local secret key used in HTLC-Success/HTLC-Timeout txn and to_local output
        fn delayed_payment_base_key<'a>(&'a self) -> &'a SecretKey;
        /// Gets the local htlc secret key used in commitment tx htlc outputs
        fn htlc_base_key<'a>(&'a self) -> &'a SecretKey;
        /// Gets the commitment seed
        fn commitment_seed<'a>(&'a self) -> &'a [u8; 32];

        /// Create a signature for a remote commitment transaction and associated HTLC transactions.
        ///
        /// Note that if signing fails or is rejected, the channel will be force-closed.
        ///
        /// TODO: Document the things someone using this interface should enforce before signing.
        /// TODO: Add more input vars to enable better checking (preferably removing commitment_tx and
        /// making the callee generate it via some util function we expose)!
        fn sign_remote_commitment<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, channel_funding_redeemscript: &Script, absolute_fee: u64, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], to_self_delay: u16, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;

        /// Create a signature for a (proposed) closing transaction.
        ///
        /// Note that, due to rounding, there may be one "missing" satoshi, and either party may have
        /// chosen to forgo their output as dust.
        fn sign_closing_transaction<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, channel_funding_redeemscript: &Script, closing_tx: &Transaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;

        /// Signs a channel announcement message with our funding key, proving it comes from one
        /// of the channel participants.
        ///
        /// Note that if this fails or is rejected, the channel will not be publicly announced and
        /// our counterparty may (though likely will not) close the channel on us for violating the
        /// protocol.
        fn sign_channel_announcement<T: secp256k1::Signing>(&self, msg: &msgs::UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
}

#[derive(Clone)]
/// A simple implementation of ChannelKeys that just keeps the private keys in memory.
pub struct InMemoryChannelKeys {
        /// Private key of anchor tx
        pub funding_key: SecretKey,
        /// Local secret key for blinded revocation pubkey
        pub revocation_base_key: SecretKey,
        /// Local secret key used in commitment tx htlc outputs
        pub payment_base_key: SecretKey,
        /// Local secret key used in HTLC tx
        pub delayed_payment_base_key: SecretKey,
        /// Local htlc secret key used in commitment tx htlc outputs
        pub htlc_base_key: SecretKey,
        /// Commitment seed
        pub commitment_seed: [u8; 32],
}

impl ChannelKeys for InMemoryChannelKeys {
        fn funding_key(&self) -> &SecretKey { &self.funding_key }
        fn revocation_base_key(&self) -> &SecretKey { &self.revocation_base_key }
        fn payment_base_key(&self) -> &SecretKey { &self.payment_base_key }
        fn delayed_payment_base_key(&self) -> &SecretKey { &self.delayed_payment_base_key }
        fn htlc_base_key(&self) -> &SecretKey { &self.htlc_base_key }
        fn commitment_seed(&self) -> &[u8; 32] { &self.commitment_seed }

        fn sign_remote_commitment<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, channel_funding_redeemscript: &Script, feerate_per_kw: u64, commitment_tx: &Transaction, keys: &TxCreationKeys, htlcs: &[&HTLCOutputInCommitment], to_self_delay: u16, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
                if commitment_tx.input.len() != 1 { return Err(()); }
                let commitment_sighash = hash_to_message!(&bip143::SighashComponents::new(&commitment_tx).sighash_all(&commitment_tx.input[0], &channel_funding_redeemscript, channel_value_satoshis)[..]);
                let commitment_sig = secp_ctx.sign(&commitment_sighash, &self.funding_key);

                let commitment_txid = commitment_tx.txid();

                let mut htlc_sigs = Vec::with_capacity(htlcs.len());
                for ref htlc in htlcs {
                        if let Some(_) = htlc.transaction_output_index {
                                let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, feerate_per_kw, to_self_delay, htlc, &keys.a_delayed_payment_key, &keys.revocation_key);
                                let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, &keys);
                                let htlc_sighash = hash_to_message!(&bip143::SighashComponents::new(&htlc_tx).sighash_all(&htlc_tx.input[0], &htlc_redeemscript, htlc.amount_msat / 1000)[..]);
                                let our_htlc_key = match chan_utils::derive_private_key(&secp_ctx, &keys.per_commitment_point, &self.htlc_base_key) {
                                        Ok(s) => s,
                                        Err(_) => return Err(()),
                                };
                                htlc_sigs.push(secp_ctx.sign(&htlc_sighash, &our_htlc_key));
                        }
                }

                Ok((commitment_sig, htlc_sigs))
        }

        fn sign_closing_transaction<T: secp256k1::Signing>(&self, channel_value_satoshis: u64, channel_funding_redeemscript: &Script, closing_tx: &Transaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
                if closing_tx.input.len() != 1 { return Err(()); }
                if closing_tx.input[0].witness.len() != 0 { return Err(()); }
                if closing_tx.output.len() > 2 { return Err(()); }

                let sighash = hash_to_message!(&bip143::SighashComponents::new(closing_tx)
                        .sighash_all(&closing_tx.input[0], &channel_funding_redeemscript, channel_value_satoshis)[..]);
                Ok(secp_ctx.sign(&sighash, &self.funding_key))
        }

        fn sign_channel_announcement<T: secp256k1::Signing>(&self, msg: &msgs::UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
                let msghash = hash_to_message!(&Sha256dHash::hash(&msg.encode()[..])[..]);
                Ok(secp_ctx.sign(&msghash, &self.funding_key))
        }
}

impl_writeable!(InMemoryChannelKeys, 0, {
        funding_key,
        revocation_base_key,
        payment_base_key,
        delayed_payment_base_key,
        htlc_base_key,
        commitment_seed
});

/// Simple KeysInterface implementor that takes a 32-byte seed for use as a BIP 32 extended key
/// and derives keys from that.
///
/// Your node_id is seed/0'
/// ChannelMonitor closes may use seed/1'
/// Cooperative closes may use seed/2'
/// The two close keys may be needed to claim on-chain funds!
pub struct KeysManager {
        secp_ctx: Secp256k1<secp256k1::SignOnly>,
        node_secret: SecretKey,
        destination_script: Script,
        shutdown_pubkey: PublicKey,
        channel_master_key: ExtendedPrivKey,
        channel_child_index: AtomicUsize,
        session_master_key: ExtendedPrivKey,
        session_child_index: AtomicUsize,
        channel_id_master_key: ExtendedPrivKey,
        channel_id_child_index: AtomicUsize,

        unique_start: Sha256State,
        logger: Arc<Logger>,
}

impl KeysManager {
        /// Constructs a KeysManager from a 32-byte seed. If the seed is in some way biased (eg your
        /// RNG is busted) this may panic (but more importantly, you will possibly lose funds).
        /// starting_time isn't strictly required to actually be a time, but it must absolutely,
        /// without a doubt, be unique to this instance. ie if you start multiple times with the same
        /// seed, starting_time must be unique to each run. Thus, the easiest way to achieve this is to
        /// simply use the current time (with very high precision).
        ///
        /// The seed MUST be backed up safely prior to use so that the keys can be re-created, however,
        /// obviously, starting_time should be unique every time you reload the library - it is only
        /// used to generate new ephemeral key data (which will be stored by the individual channel if
        /// necessary).
        ///
        /// Note that the seed is required to recover certain on-chain funds independent of
        /// ChannelMonitor data, though a current copy of ChannelMonitor data is also required for any
        /// channel, and some on-chain during-closing funds.
        ///
        /// Note that until the 0.1 release there is no guarantee of backward compatibility between
        /// versions. Once the library is more fully supported, the docs will be updated to include a
        /// detailed description of the guarantee.
        pub fn new(seed: &[u8; 32], network: Network, logger: Arc<Logger>, starting_time_secs: u64, starting_time_nanos: u32) -> KeysManager {
                let secp_ctx = Secp256k1::signing_only();
                match ExtendedPrivKey::new_master(network.clone(), 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 destination_script = match master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(1).unwrap()) {
                                        Ok(destination_key) => {
                                                let pubkey_hash160 = Hash160::hash(&ExtendedPubKey::from_private(&secp_ctx, &destination_key).public_key.key.serialize()[..]);
                                                Builder::new().push_opcode(opcodes::all::OP_PUSHBYTES_0)
                                                              .push_slice(&pubkey_hash160.into_inner())
                                                              .into_script()
                                        },
                                        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,
                                        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 session_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(4).unwrap()).expect("Your RNG is busted");
                                let channel_id_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(5).unwrap()).expect("Your RNG is busted");

                                let mut unique_start = Sha256::engine();
                                unique_start.input(&byte_utils::be64_to_array(starting_time_secs));
                                unique_start.input(&byte_utils::be32_to_array(starting_time_nanos));
                                unique_start.input(seed);

                                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),
                                        channel_id_master_key,
                                        channel_id_child_index: AtomicUsize::new(0),

                                        unique_start,
                                        logger,
                                }
                        },
                        Err(_) => panic!("Your rng is busted"),
                }
        }
}

impl KeysInterface for KeysManager {
        type ChanKeySigner = InMemoryChannelKeys;

        fn get_node_secret(&self) -> SecretKey {
                self.node_secret.clone()
        }

        fn get_destination_script(&self) -> Script {
                self.destination_script.clone()
        }

        fn get_shutdown_pubkey(&self) -> PublicKey {
                self.shutdown_pubkey.clone()
        }

        fn get_channel_keys(&self, _inbound: bool) -> InMemoryChannelKeys {
                // We only seriously intend to rely on the channel_master_key for true secure
                // entropy, everything else just ensures uniqueness. We rely on the unique_start (ie
                // starting_time provided in the constructor) to be unique.
                let mut sha = self.unique_start.clone();

                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("key space exhausted")).expect("Your RNG is busted");
                sha.input(&child_privkey.private_key.key[..]);

                let seed = Sha256::from_engine(sha).into_inner();

                let commitment_seed = {
                        let mut sha = Sha256::engine();
                        sha.input(&seed);
                        sha.input(&b"commitment seed"[..]);
                        Sha256::from_engine(sha).into_inner()
                };
                macro_rules! key_step {
                        ($info: expr, $prev_key: expr) => {{
                                let mut sha = Sha256::engine();
                                sha.input(&seed);
                                sha.input(&$prev_key[..]);
                                sha.input(&$info[..]);
                                SecretKey::from_slice(&Sha256::from_engine(sha).into_inner()).expect("SHA-256 is busted")
                        }}
                }
                let funding_key = key_step!(b"funding key", commitment_seed);
                let revocation_base_key = key_step!(b"revocation base key", funding_key);
                let payment_base_key = key_step!(b"payment base key", revocation_base_key);
                let delayed_payment_base_key = key_step!(b"delayed payment base key", payment_base_key);
                let htlc_base_key = key_step!(b"HTLC base key", delayed_payment_base_key);

                InMemoryChannelKeys {
                        funding_key,
                        revocation_base_key,
                        payment_base_key,
                        delayed_payment_base_key,
                        htlc_base_key,
                        commitment_seed,
                }
        }

        fn get_onion_rand(&self) -> (SecretKey, [u8; 32]) {
                let mut sha = self.unique_start.clone();

                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("key space exhausted")).expect("Your RNG is busted");
                sha.input(&child_privkey.private_key.key[..]);

                let mut rng_seed = sha.clone();
                // Not exactly the most ideal construction, but the second value will get fed into
                // ChaCha so it is another step harder to break.
                rng_seed.input(b"RNG Seed Salt");
                sha.input(b"Session Key Salt");
                (SecretKey::from_slice(&Sha256::from_engine(sha).into_inner()).expect("Your RNG is busted"),
                Sha256::from_engine(rng_seed).into_inner())
        }

        fn get_channel_id(&self) -> [u8; 32] {
                let mut sha = self.unique_start.clone();

                let child_ix = self.channel_id_child_index.fetch_add(1, Ordering::AcqRel);
                let child_privkey = self.channel_id_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[..]);

                (Sha256::from_engine(sha).into_inner())
        }
}