Merge pull request #764 from lightning-signer/revoke-enforcement

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

// This file is Copyright its original authors, visible in version control
// history.
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

//! 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, TxOut, SigHashType};
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::hash_types::WPubkeyHash;

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

use util::byte_utils;
use util::ser::{Writeable, Writer, Readable};

use chain::transaction::OutPoint;
use ln::chan_utils;
use ln::chan_utils::{HTLCOutputInCommitment, make_funding_redeemscript, ChannelPublicKeys, HolderCommitmentTransaction, ChannelTransactionParameters, CommitmentTransaction};
use ln::msgs::UnsignedChannelAnnouncement;

use std::sync::atomic::{AtomicUsize, Ordering};
use std::io::Error;
use ln::msgs::DecodeError;

/// When on-chain outputs are created by rust-lightning (which our counterparty is not able to
/// claim at any point in the future) an event is generated which you must track and be able to
/// spend on-chain. The information needed to do this is provided in this enum, including the
/// outpoint describing which txid and output index is available, the full output which exists at
/// that txid/index, and any keys or other information required to sign.
#[derive(Clone, Debug, PartialEq)]
pub enum SpendableOutputDescriptor {
        /// An output to a script which was provided via KeysInterface, thus you should already know
        /// how to spend it. No keys are provided as rust-lightning was never given any keys - only the
        /// script_pubkey as it appears in the output.
        /// These may include outputs from a transaction punishing our counterparty or claiming an HTLC
        /// on-chain using the payment preimage or after it has timed out.
        StaticOutput {
                /// The outpoint which is spendable
                outpoint: OutPoint,
                /// The output which is referenced by the given outpoint.
                output: TxOut,
        },
        /// An output to a P2WSH script which can be spent with a single signature after a CSV delay.
        ///
        /// The witness in the spending input should be:
        /// <BIP 143 signature> <empty vector> (MINIMALIF standard rule) <provided witnessScript>
        ///
        /// Note that the nSequence field in the spending input must be set to to_self_delay
        /// (which means the transaction is not broadcastable until at least to_self_delay
        /// blocks after the outpoint confirms).
        ///
        /// These are generally the result of a "revocable" output to us, spendable only by us unless
        /// it is an output from an old state which we broadcast (which should never happen).
        ///
        /// To derive the delayed_payment key which is used to sign for this input, you must pass the
        /// holder delayed_payment_base_key (ie the private key which corresponds to the pubkey in
        /// ChannelKeys::pubkeys().delayed_payment_basepoint) and the provided per_commitment_point to
        /// chan_utils::derive_private_key. The public key can be generated without the secret key
        /// using chan_utils::derive_public_key and only the delayed_payment_basepoint which appears in
        /// ChannelKeys::pubkeys().
        ///
        /// To derive the revocation_pubkey provided here (which is used in the witness
        /// script generation), you must pass the counterparty revocation_basepoint (which appears in the
        /// call to ChannelKeys::ready_channel) and the provided per_commitment point
        /// to chan_utils::derive_public_revocation_key.
        ///
        /// The witness script which is hashed and included in the output script_pubkey may be
        /// regenerated by passing the revocation_pubkey (derived as above), our delayed_payment pubkey
        /// (derived as above), and the to_self_delay contained here to
        /// chan_utils::get_revokeable_redeemscript.
        //
        // TODO: we need to expose utility methods in KeyManager to do all the relevant derivation.
        DynamicOutputP2WSH {
                /// The outpoint which is spendable
                outpoint: OutPoint,
                /// Per commitment point to derive delayed_payment_key by key holder
                per_commitment_point: PublicKey,
                /// The nSequence value which must be set in the spending input to satisfy the OP_CSV in
                /// the witness_script.
                to_self_delay: u16,
                /// The output which is referenced by the given outpoint
                output: TxOut,
                /// The channel keys state used to proceed to derivation of signing key. Must
                /// be pass to KeysInterface::derive_channel_keys.
                key_derivation_params: (u64, u64),
                /// The revocation_pubkey used to derive witnessScript
                revocation_pubkey: PublicKey
        },
        /// An output to a P2WPKH, spendable exclusively by our payment key (ie the private key which
        /// corresponds to the public key in ChannelKeys::pubkeys().payment_point).
        /// The witness in the spending input, is, thus, simply:
        /// <BIP 143 signature> <payment key>
        ///
        /// These are generally the result of our counterparty having broadcast the current state,
        /// allowing us to claim the non-HTLC-encumbered outputs immediately.
        StaticOutputCounterpartyPayment {
                /// The outpoint which is spendable
                outpoint: OutPoint,
                /// The output which is reference by the given outpoint
                output: TxOut,
                /// The channel keys state used to proceed to derivation of signing key. Must
                /// be pass to KeysInterface::derive_channel_keys.
                key_derivation_params: (u64, u64),
        }
}

impl Writeable for SpendableOutputDescriptor {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
                match self {
                        &SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output } => {
                                0u8.write(writer)?;
                                outpoint.write(writer)?;
                                output.write(writer)?;
                        },
                        &SpendableOutputDescriptor::DynamicOutputP2WSH { ref outpoint, ref per_commitment_point, ref to_self_delay, ref output, ref key_derivation_params, ref revocation_pubkey } => {
                                1u8.write(writer)?;
                                outpoint.write(writer)?;
                                per_commitment_point.write(writer)?;
                                to_self_delay.write(writer)?;
                                output.write(writer)?;
                                key_derivation_params.0.write(writer)?;
                                key_derivation_params.1.write(writer)?;
                                revocation_pubkey.write(writer)?;
                        },
                        &SpendableOutputDescriptor::StaticOutputCounterpartyPayment { ref outpoint, ref output, ref key_derivation_params } => {
                                2u8.write(writer)?;
                                outpoint.write(writer)?;
                                output.write(writer)?;
                                key_derivation_params.0.write(writer)?;
                                key_derivation_params.1.write(writer)?;
                        },
                }
                Ok(())
        }
}

impl Readable for SpendableOutputDescriptor {
        fn read<R: ::std::io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
                match Readable::read(reader)? {
                        0u8 => Ok(SpendableOutputDescriptor::StaticOutput {
                                outpoint: Readable::read(reader)?,
                                output: Readable::read(reader)?,
                        }),
                        1u8 => Ok(SpendableOutputDescriptor::DynamicOutputP2WSH {
                                outpoint: Readable::read(reader)?,
                                per_commitment_point: Readable::read(reader)?,
                                to_self_delay: Readable::read(reader)?,
                                output: Readable::read(reader)?,
                                key_derivation_params: (Readable::read(reader)?, Readable::read(reader)?),
                                revocation_pubkey: Readable::read(reader)?,
                        }),
                        2u8 => Ok(SpendableOutputDescriptor::StaticOutputCounterpartyPayment {
                                outpoint: Readable::read(reader)?,
                                output: Readable::read(reader)?,
                                key_derivation_params: (Readable::read(reader)?, Readable::read(reader)?),
                        }),
                        _ => Err(DecodeError::InvalidValue),
                }
        }
}

/// 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).
// TODO: We should remove Clone by instead requesting a new ChannelKeys copy when we create
// ChannelMonitors instead of expecting to clone the one out of the Channel into the monitors.
pub trait ChannelKeys : Send+Clone + Writeable {
        /// Gets the per-commitment point for a specific commitment number
        ///
        /// Note that the commitment number starts at (1 << 48) - 1 and counts backwards.
        fn get_per_commitment_point<T: secp256k1::Signing + secp256k1::Verification>(&self, idx: u64, secp_ctx: &Secp256k1<T>) -> PublicKey;
        /// Gets the commitment secret for a specific commitment number as part of the revocation process
        ///
        /// An external signer implementation should error here if the commitment was already signed
        /// and should refuse to sign it in the future.
        ///
        /// May be called more than once for the same index.
        ///
        /// Note that the commitment number starts at (1 << 48) - 1 and counts backwards.
        /// TODO: return a Result so we can signal a validation error
        fn release_commitment_secret(&self, idx: u64) -> [u8; 32];
        /// Gets the holder's channel public keys and basepoints
        fn pubkeys(&self) -> &ChannelPublicKeys;
        /// Gets arbitrary identifiers describing the set of keys which are provided back to you in
        /// some SpendableOutputDescriptor types. These should be sufficient to identify this
        /// ChannelKeys object uniquely and lookup or re-derive its keys.
        fn key_derivation_params(&self) -> (u64, u64);

        /// Create a signature for a counterparty's 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.
        fn sign_counterparty_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &CommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;

        /// Create a signatures for a holder's commitment transaction and its claiming HTLC transactions.
        /// This will only ever be called with a non-revoked commitment_tx.  This will be called with the
        /// latest commitment_tx when we initiate a force-close.
        /// This will be called with the previous latest, just to get claiming HTLC signatures, if we are
        /// reacting to a ChannelMonitor replica that decided to broadcast before it had been updated to
        /// the latest.
        /// This may be called multiple times for the same transaction.
        ///
        /// An external signer implementation should check that the commitment has not been revoked.
        ///
        /// May return Err if key derivation fails.  Callers, such as ChannelMonitor, will panic in such a case.
        //
        // TODO: Document the things someone using this interface should enforce before signing.
        // TODO: Key derivation failure should panic rather than Err
        fn sign_holder_commitment_and_htlcs<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;

        /// Same as sign_holder_commitment, but exists only for tests to get access to holder commitment
        /// transactions which will be broadcasted later, after the channel has moved on to a newer
        /// state. Thus, needs its own method as sign_holder_commitment may enforce that we only ever
        /// get called once.
        #[cfg(any(test,feature = "unsafe_revoked_tx_signing"))]
        fn unsafe_sign_holder_commitment_and_htlcs<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;

        /// Create a signature for the given input in a transaction spending an HTLC or commitment
        /// transaction output when our counterparty broadcasts an old state.
        ///
        /// A justice transaction may claim multiples outputs at the same time if timelocks are
        /// similar, but only a signature for the input at index `input` should be signed for here.
        /// It may be called multiples time for same output(s) if a fee-bump is needed with regards
        /// to an upcoming timelock expiration.
        ///
        /// Amount is value of the output spent by this input, committed to in the BIP 143 signature.
        ///
        /// per_commitment_key is revocation secret which was provided by our counterparty when they
        /// revoked the state which they eventually broadcast. It's not a _holder_ secret key and does
        /// not allow the spending of any funds by itself (you need our holder revocation_secret to do
        /// so).
        ///
        /// htlc holds HTLC elements (hash, timelock) if the output being spent is a HTLC output, thus
        /// changing the format of the witness script (which is committed to in the BIP 143
        /// signatures).
        fn sign_justice_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &Option<HTLCOutputInCommitment>, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;

        /// Create a signature for a claiming transaction for a HTLC output on a counterparty's commitment
        /// transaction, either offered or received.
        ///
        /// Such a transaction may claim multiples offered outputs at same time if we know the
        /// preimage for each when we create it, but only the input at index `input` should be
        /// signed for here. It may be called multiple times for same output(s) if a fee-bump is
        /// needed with regards to an upcoming timelock expiration.
        ///
        /// Witness_script is either a offered or received script as defined in BOLT3 for HTLC
        /// outputs.
        ///
        /// Amount is value of the output spent by this input, committed to in the BIP 143 signature.
        ///
        /// Per_commitment_point is the dynamic point corresponding to the channel state
        /// detected onchain. It has been generated by our counterparty and is used to derive
        /// channel state keys, which are then included in the witness script and committed to in the
        /// BIP 143 signature.
        fn sign_counterparty_htlc_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<T>) -> Result<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, 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: &UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;

        /// Set the counterparty static channel data, including basepoints,
        /// counterparty_selected/holder_selected_contest_delay and funding outpoint.
        /// This is done as soon as the funding outpoint is known.  Since these are static channel data,
        /// they MUST NOT be allowed to change to different values once set.
        ///
        /// channel_parameters.is_populated() MUST be true.
        ///
        /// We bind holder_selected_contest_delay late here for API convenience.
        ///
        /// Will be called before any signatures are applied.
        fn ready_channel(&mut self, channel_parameters: &ChannelTransactionParameters);
}

/// 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, channel_value_satoshis: u64) -> Self::ChanKeySigner;
        /// Gets a unique, cryptographically-secure, random 32 byte value. This is used for encrypting
        /// onion packets and for temporary channel IDs. There is no requirement that these be
        /// persisted anywhere, though they must be unique across restarts.
        fn get_secure_random_bytes(&self) -> [u8; 32];

        /// Reads a `ChanKeySigner` for this `KeysInterface` from the given input stream.
        /// This is only called during deserialization of other objects which contain
        /// `ChannelKeys`-implementing objects (ie `ChannelMonitor`s and `ChannelManager`s).
        /// The bytes are exactly those which `<Self::ChanKeySigner as Writeable>::write()` writes, and
        /// contain no versioning scheme. You may wish to include your own version prefix and ensure
        /// you've read all of the provided bytes to ensure no corruption occurred.
        fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::ChanKeySigner, DecodeError>;
}

#[derive(Clone)]
/// A simple implementation of ChannelKeys that just keeps the private keys in memory.
///
/// This implementation performs no policy checks and is insufficient by itself as
/// a secure external signer.
pub struct InMemoryChannelKeys {
        /// Private key of anchor tx
        pub funding_key: SecretKey,
        /// Holder secret key for blinded revocation pubkey
        pub revocation_base_key: SecretKey,
        /// Holder secret key used for our balance in counterparty-broadcasted commitment transactions
        pub payment_key: SecretKey,
        /// Holder secret key used in HTLC tx
        pub delayed_payment_base_key: SecretKey,
        /// Holder htlc secret key used in commitment tx htlc outputs
        pub htlc_base_key: SecretKey,
        /// Commitment seed
        pub commitment_seed: [u8; 32],
        /// Holder public keys and basepoints
        pub(crate) holder_channel_pubkeys: ChannelPublicKeys,
        /// Counterparty public keys and counterparty/holder selected_contest_delay, populated on channel acceptance
        channel_parameters: Option<ChannelTransactionParameters>,
        /// The total value of this channel
        channel_value_satoshis: u64,
        /// Key derivation parameters
        key_derivation_params: (u64, u64),
}

impl InMemoryChannelKeys {
        /// Create a new InMemoryChannelKeys
        pub fn new<C: Signing>(
                secp_ctx: &Secp256k1<C>,
                funding_key: SecretKey,
                revocation_base_key: SecretKey,
                payment_key: SecretKey,
                delayed_payment_base_key: SecretKey,
                htlc_base_key: SecretKey,
                commitment_seed: [u8; 32],
                channel_value_satoshis: u64,
                key_derivation_params: (u64, u64)) -> InMemoryChannelKeys {
                let holder_channel_pubkeys =
                        InMemoryChannelKeys::make_holder_keys(secp_ctx, &funding_key, &revocation_base_key,
                                                             &payment_key, &delayed_payment_base_key,
                                                             &htlc_base_key);
                InMemoryChannelKeys {
                        funding_key,
                        revocation_base_key,
                        payment_key,
                        delayed_payment_base_key,
                        htlc_base_key,
                        commitment_seed,
                        channel_value_satoshis,
                        holder_channel_pubkeys,
                        channel_parameters: None,
                        key_derivation_params,
                }
        }

        fn make_holder_keys<C: Signing>(secp_ctx: &Secp256k1<C>,
                                       funding_key: &SecretKey,
                                       revocation_base_key: &SecretKey,
                                       payment_key: &SecretKey,
                                       delayed_payment_base_key: &SecretKey,
                                       htlc_base_key: &SecretKey) -> ChannelPublicKeys {
                let from_secret = |s: &SecretKey| PublicKey::from_secret_key(secp_ctx, s);
                ChannelPublicKeys {
                        funding_pubkey: from_secret(&funding_key),
                        revocation_basepoint: from_secret(&revocation_base_key),
                        payment_point: from_secret(&payment_key),
                        delayed_payment_basepoint: from_secret(&delayed_payment_base_key),
                        htlc_basepoint: from_secret(&htlc_base_key),
                }
        }

        /// Counterparty pubkeys.
        /// Will panic if ready_channel wasn't called.
        pub fn counterparty_pubkeys(&self) -> &ChannelPublicKeys { &self.get_channel_parameters().counterparty_parameters.as_ref().unwrap().pubkeys }

        /// The contest_delay value specified by our counterparty and applied on holder-broadcastable
        /// transactions, ie the amount of time that we have to wait to recover our funds if we
        /// broadcast a transaction.
        /// Will panic if ready_channel wasn't called.
        pub fn counterparty_selected_contest_delay(&self) -> u16 { self.get_channel_parameters().counterparty_parameters.as_ref().unwrap().selected_contest_delay }

        /// The contest_delay value specified by us and applied on transactions broadcastable
        /// by our counterparty, ie the amount of time that they have to wait to recover their funds
        /// if they broadcast a transaction.
        /// Will panic if ready_channel wasn't called.
        pub fn holder_selected_contest_delay(&self) -> u16 { self.get_channel_parameters().holder_selected_contest_delay }

        /// Whether the holder is the initiator
        /// Will panic if ready_channel wasn't called.
        pub fn is_outbound(&self) -> bool { self.get_channel_parameters().is_outbound_from_holder }

        /// Funding outpoint
        /// Will panic if ready_channel wasn't called.
        pub fn funding_outpoint(&self) -> &OutPoint { self.get_channel_parameters().funding_outpoint.as_ref().unwrap() }

        /// Obtain a ChannelTransactionParameters for this channel, to be used when verifying or
        /// building transactions.
        ///
        /// Will panic if ready_channel wasn't called.
        pub fn get_channel_parameters(&self) -> &ChannelTransactionParameters {
                self.channel_parameters.as_ref().unwrap()
        }
}

impl ChannelKeys for InMemoryChannelKeys {
        fn get_per_commitment_point<T: secp256k1::Signing + secp256k1::Verification>(&self, idx: u64, secp_ctx: &Secp256k1<T>) -> PublicKey {
                let commitment_secret = SecretKey::from_slice(&chan_utils::build_commitment_secret(&self.commitment_seed, idx)).unwrap();
                PublicKey::from_secret_key(secp_ctx, &commitment_secret)
        }

        fn release_commitment_secret(&self, idx: u64) -> [u8; 32] {
                chan_utils::build_commitment_secret(&self.commitment_seed, idx)
        }

        fn pubkeys(&self) -> &ChannelPublicKeys { &self.holder_channel_pubkeys }
        fn key_derivation_params(&self) -> (u64, u64) { self.key_derivation_params }

        fn sign_counterparty_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &CommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
                let trusted_tx = commitment_tx.trust();
                let keys = trusted_tx.keys();

                let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
                let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &self.counterparty_pubkeys().funding_pubkey);

                let built_tx = trusted_tx.built_transaction();
                let commitment_sig = built_tx.sign(&self.funding_key, &channel_funding_redeemscript, self.channel_value_satoshis, secp_ctx);
                let commitment_txid = built_tx.txid;

                let mut htlc_sigs = Vec::with_capacity(commitment_tx.htlcs().len());
                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, &keys.broadcaster_delayed_payment_key, &keys.revocation_key);
                        let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, &keys);
                        let htlc_sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, SigHashType::All)[..]);
                        let holder_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, &holder_htlc_key));
                }

                Ok((commitment_sig, htlc_sigs))
        }

        fn sign_holder_commitment_and_htlcs<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
                let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
                let funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &self.counterparty_pubkeys().funding_pubkey);
                let trusted_tx = commitment_tx.trust();
                let sig = trusted_tx.built_transaction().sign(&self.funding_key, &funding_redeemscript, self.channel_value_satoshis, secp_ctx);
                let channel_parameters = self.get_channel_parameters();
                let htlc_sigs = trusted_tx.get_htlc_sigs(&self.htlc_base_key, &channel_parameters.as_holder_broadcastable(), secp_ctx)?;
                Ok((sig, htlc_sigs))
        }

        #[cfg(any(test,feature = "unsafe_revoked_tx_signing"))]
        fn unsafe_sign_holder_commitment_and_htlcs<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
                let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
                let funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &self.counterparty_pubkeys().funding_pubkey);
                let trusted_tx = commitment_tx.trust();
                let sig = trusted_tx.built_transaction().sign(&self.funding_key, &funding_redeemscript, self.channel_value_satoshis, secp_ctx);
                let channel_parameters = self.get_channel_parameters();
                let htlc_sigs = trusted_tx.get_htlc_sigs(&self.htlc_base_key, &channel_parameters.as_holder_broadcastable(), secp_ctx)?;
                Ok((sig, htlc_sigs))
        }

        fn sign_justice_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &Option<HTLCOutputInCommitment>, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
                let revocation_key = match chan_utils::derive_private_revocation_key(&secp_ctx, &per_commitment_key, &self.revocation_base_key) {
                        Ok(revocation_key) => revocation_key,
                        Err(_) => return Err(())
                };
                let per_commitment_point = PublicKey::from_secret_key(secp_ctx, &per_commitment_key);
                let revocation_pubkey = match chan_utils::derive_public_revocation_key(&secp_ctx, &per_commitment_point, &self.pubkeys().revocation_basepoint) {
                        Ok(revocation_pubkey) => revocation_pubkey,
                        Err(_) => return Err(())
                };
                let witness_script = if let &Some(ref htlc) = htlc {
                        let counterparty_htlcpubkey = match chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().htlc_basepoint) {
                                Ok(counterparty_htlcpubkey) => counterparty_htlcpubkey,
                                Err(_) => return Err(())
                        };
                        let holder_htlcpubkey = match chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.pubkeys().htlc_basepoint) {
                                Ok(holder_htlcpubkey) => holder_htlcpubkey,
                                Err(_) => return Err(())
                        };
                        chan_utils::get_htlc_redeemscript_with_explicit_keys(&htlc, &counterparty_htlcpubkey, &holder_htlcpubkey, &revocation_pubkey)
                } else {
                        let counterparty_delayedpubkey = match chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().delayed_payment_basepoint) {
                                Ok(counterparty_delayedpubkey) => counterparty_delayedpubkey,
                                Err(_) => return 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))
        }

        fn sign_counterparty_htlc_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
                if let Ok(htlc_key) = chan_utils::derive_private_key(&secp_ctx, &per_commitment_point, &self.htlc_base_key) {
                        let witness_script = if let Ok(revocation_pubkey) = chan_utils::derive_public_revocation_key(&secp_ctx, &per_commitment_point, &self.pubkeys().revocation_basepoint) {
                                if let Ok(counterparty_htlcpubkey) = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().htlc_basepoint) {
                                        if let Ok(htlcpubkey) = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.pubkeys().htlc_basepoint) {
                                                chan_utils::get_htlc_redeemscript_with_explicit_keys(&htlc, &counterparty_htlcpubkey, &htlcpubkey, &revocation_pubkey)
                                        } 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))
                }
                Err(())
        }

        fn sign_closing_transaction<T: secp256k1::Signing>(&self, 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 funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
                let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &self.counterparty_pubkeys().funding_pubkey);

                let sighash = hash_to_message!(&bip143::SigHashCache::new(closing_tx)
                        .signature_hash(0, &channel_funding_redeemscript, self.channel_value_satoshis, SigHashType::All)[..]);
                Ok(secp_ctx.sign(&sighash, &self.funding_key))
        }

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

        fn ready_channel(&mut self, channel_parameters: &ChannelTransactionParameters) {
                assert!(self.channel_parameters.is_none(), "Acceptance already noted");
                assert!(channel_parameters.is_populated(), "Channel parameters must be fully populated");
                self.channel_parameters = Some(channel_parameters.clone());
        }
}

impl Writeable for InMemoryChannelKeys {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), Error> {
                self.funding_key.write(writer)?;
                self.revocation_base_key.write(writer)?;
                self.payment_key.write(writer)?;
                self.delayed_payment_base_key.write(writer)?;
                self.htlc_base_key.write(writer)?;
                self.commitment_seed.write(writer)?;
                self.channel_parameters.write(writer)?;
                self.channel_value_satoshis.write(writer)?;
                self.key_derivation_params.0.write(writer)?;
                self.key_derivation_params.1.write(writer)?;

                Ok(())
        }
}

impl Readable for InMemoryChannelKeys {
        fn read<R: ::std::io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
                let funding_key = Readable::read(reader)?;
                let revocation_base_key = Readable::read(reader)?;
                let payment_key = Readable::read(reader)?;
                let delayed_payment_base_key = Readable::read(reader)?;
                let htlc_base_key = Readable::read(reader)?;
                let commitment_seed = Readable::read(reader)?;
                let counterparty_channel_data = Readable::read(reader)?;
                let channel_value_satoshis = Readable::read(reader)?;
                let secp_ctx = Secp256k1::signing_only();
                let holder_channel_pubkeys =
                        InMemoryChannelKeys::make_holder_keys(&secp_ctx, &funding_key, &revocation_base_key,
                                                             &payment_key, &delayed_payment_base_key,
                                                             &htlc_base_key);
                let params_1 = Readable::read(reader)?;
                let params_2 = Readable::read(reader)?;

                Ok(InMemoryChannelKeys {
                        funding_key,
                        revocation_base_key,
                        payment_key,
                        delayed_payment_base_key,
                        htlc_base_key,
                        commitment_seed,
                        channel_value_satoshis,
                        holder_channel_pubkeys,
                        channel_parameters: counterparty_channel_data,
                        key_derivation_params: (params_1, params_2),
                })
        }
}

/// 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,
        rand_bytes_master_key: ExtendedPrivKey,
        rand_bytes_child_index: AtomicUsize,

        seed: [u8; 32],
        starting_time_secs: u64,
        starting_time_nanos: u32,
}

impl KeysManager {
        /// Constructs a KeysManager from a 32-byte seed. If the seed is in some way biased (eg your
        /// CSRNG 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, starting_time_secs: u64, starting_time_nanos: u32) -> Self {
                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 wpubkey_hash = WPubkeyHash::hash(&ExtendedPubKey::from_private(&secp_ctx, &destination_key).public_key.to_bytes());
                                                Builder::new().push_opcode(opcodes::all::OP_PUSHBYTES_0)
                                                              .push_slice(&wpubkey_hash.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 rand_bytes_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(4).unwrap()).expect("Your RNG is busted");

                                KeysManager {
                                        secp_ctx,
                                        node_secret,
                                        destination_script,
                                        shutdown_pubkey,
                                        channel_master_key,
                                        channel_child_index: AtomicUsize::new(0),
                                        rand_bytes_master_key,
                                        rand_bytes_child_index: AtomicUsize::new(0),

                                        seed: *seed,
                                        starting_time_secs,
                                        starting_time_nanos,
                                }
                        },
                        Err(_) => panic!("Your rng is busted"),
                }
        }
        fn derive_unique_start(&self) -> Sha256State {
                let mut unique_start = Sha256::engine();
                unique_start.input(&byte_utils::be64_to_array(self.starting_time_secs));
                unique_start.input(&byte_utils::be32_to_array(self.starting_time_nanos));
                unique_start.input(&self.seed);
                unique_start
        }
        /// Derive an old set of ChannelKeys for per-channel secrets based on a key derivation
        /// parameters.
        /// Key derivation parameters are accessible through a per-channel secrets
        /// ChannelKeys::key_derivation_params and is provided inside DynamicOuputP2WSH in case of
        /// onchain output detection for which a corresponding delayed_payment_key must be derived.
        pub fn derive_channel_keys(&self, channel_value_satoshis: u64, params_1: u64, params_2: u64) -> InMemoryChannelKeys {
                let chan_id = ((params_1 & 0xFFFF_FFFF_0000_0000) >> 32) as u32;
                let mut unique_start = Sha256::engine();
                unique_start.input(&byte_utils::be64_to_array(params_2));
                unique_start.input(&byte_utils::be32_to_array(params_1 as u32));
                unique_start.input(&self.seed);

                // 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 child_privkey = self.channel_master_key.ckd_priv(&self.secp_ctx, ChildNumber::from_hardened_idx(chan_id).expect("key space exhausted")).expect("Your RNG is busted");
                unique_start.input(&child_privkey.private_key.key[..]);

                let seed = Sha256::from_engine(unique_start).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_key = key_step!(b"payment key", revocation_base_key);
                let delayed_payment_base_key = key_step!(b"delayed payment base key", payment_key);
                let htlc_base_key = key_step!(b"HTLC base key", delayed_payment_base_key);

                InMemoryChannelKeys::new(
                        &self.secp_ctx,
                        funding_key,
                        revocation_base_key,
                        payment_key,
                        delayed_payment_base_key,
                        htlc_base_key,
                        commitment_seed,
                        channel_value_satoshis,
                        (params_1, params_2),
                )
        }
}

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, channel_value_satoshis: u64) -> Self::ChanKeySigner {
                let child_ix = self.channel_child_index.fetch_add(1, Ordering::AcqRel);
                let ix_and_nanos: u64 = (child_ix as u64) << 32 | (self.starting_time_nanos as u64);
                self.derive_channel_keys(channel_value_satoshis, ix_and_nanos, self.starting_time_secs)
        }

        fn get_secure_random_bytes(&self) -> [u8; 32] {
                let mut sha = self.derive_unique_start();

                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(b"Unique Secure Random Bytes Salt");
                Sha256::from_engine(sha).into_inner()
        }

        fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::ChanKeySigner, DecodeError> {
                InMemoryChannelKeys::read(&mut std::io::Cursor::new(reader))
        }
}