[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, TxIn, 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::recovery::RecoverableSignature;
use bitcoin::secp256k1;

use util::{byte_utils, transaction_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, ClosingTransaction};
use ln::msgs::UnsignedChannelAnnouncement;
use ln::script::ShutdownScript;

use prelude::*;
use core::sync::atomic::{AtomicUsize, Ordering};
use io::{self, Error};
use ln::msgs::{DecodeError, MAX_VALUE_MSAT};

/// Information about a spendable output to a P2WSH script. See
/// SpendableOutputDescriptor::DelayedPaymentOutput for more details on how to spend this.
#[derive(Clone, Debug, PartialEq)]
pub struct DelayedPaymentOutputDescriptor {
        /// The outpoint which is spendable
        pub outpoint: OutPoint,
        /// Per commitment point to derive delayed_payment_key by key holder
        pub per_commitment_point: PublicKey,
        /// The nSequence value which must be set in the spending input to satisfy the OP_CSV in
        /// the witness_script.
        pub to_self_delay: u16,
        /// The output which is referenced by the given outpoint
        pub output: TxOut,
        /// The revocation point specific to the commitment transaction which was broadcast. Used to
        /// derive the witnessScript for this output.
        pub revocation_pubkey: PublicKey,
        /// Arbitrary identification information returned by a call to
        /// `Sign::channel_keys_id()`. This may be useful in re-deriving keys used in
        /// the channel to spend the output.
        pub channel_keys_id: [u8; 32],
        /// The value of the channel which this output originated from, possibly indirectly.
        pub channel_value_satoshis: u64,
}
impl DelayedPaymentOutputDescriptor {
        /// The maximum length a well-formed witness spending one of these should have.
        // Calculated as 1 byte length + 73 byte signature, 1 byte empty vec push, 1 byte length plus
        // redeemscript push length.
        pub const MAX_WITNESS_LENGTH: usize = 1 + 73 + 1 + chan_utils::REVOKEABLE_REDEEMSCRIPT_MAX_LENGTH + 1;
}

impl_writeable_tlv_based!(DelayedPaymentOutputDescriptor, {
        (0, outpoint, required),
        (2, per_commitment_point, required),
        (4, to_self_delay, required),
        (6, output, required),
        (8, revocation_pubkey, required),
        (10, channel_keys_id, required),
        (12, channel_value_satoshis, required),
});

/// Information about a spendable output to our "payment key". See
/// SpendableOutputDescriptor::StaticPaymentOutput for more details on how to spend this.
#[derive(Clone, Debug, PartialEq)]
pub struct StaticPaymentOutputDescriptor {
        /// The outpoint which is spendable
        pub outpoint: OutPoint,
        /// The output which is referenced by the given outpoint
        pub output: TxOut,
        /// Arbitrary identification information returned by a call to
        /// `Sign::channel_keys_id()`. This may be useful in re-deriving keys used in
        /// the channel to spend the output.
        pub channel_keys_id: [u8; 32],
        /// The value of the channel which this transactions spends.
        pub channel_value_satoshis: u64,
}
impl StaticPaymentOutputDescriptor {
        /// The maximum length a well-formed witness spending one of these should have.
        // Calculated as 1 byte legnth + 73 byte signature, 1 byte empty vec push, 1 byte length plus
        // redeemscript push length.
        pub const MAX_WITNESS_LENGTH: usize = 1 + 73 + 34;
}
impl_writeable_tlv_based!(StaticPaymentOutputDescriptor, {
        (0, outpoint, required),
        (2, output, required),
        (4, channel_keys_id, required),
        (6, channel_value_satoshis, required),
});

/// 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 directly, either from
        /// `get_destination_script()` or `get_shutdown_scriptpubkey()`, thus you should already know
        /// how to spend it. No secret keys are provided as rust-lightning was never given any key.
        /// 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
        /// Sign::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
        /// Sign::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 Sign::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.
        DelayedPaymentOutput(DelayedPaymentOutputDescriptor),
        /// An output to a P2WPKH, spendable exclusively by our payment key (ie the private key which
        /// corresponds to the public key in Sign::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.
        StaticPaymentOutput(StaticPaymentOutputDescriptor),
}

impl_writeable_tlv_based_enum!(SpendableOutputDescriptor,
        (0, StaticOutput) => {
                (0, outpoint, required),
                (2, output, required),
        },
;
        (1, DelayedPaymentOutput),
        (2, StaticPaymentOutput),
);

/// A trait to sign lightning channel transactions as described in BOLT 3.
///
/// Signing services could be implemented on a hardware wallet. In this case,
/// the current Sign 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.
// TODO: We should remove Clone by instead requesting a new Sign copy when we create
// ChannelMonitors instead of expecting to clone the one out of the Channel into the monitors.
pub trait BaseSign {
        /// 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(&self, idx: u64, secp_ctx: &Secp256k1<secp256k1::All>) -> 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];
        /// Validate the counterparty's signatures on the holder commitment transaction and HTLCs.
        ///
        /// This is required in order for the signer to make sure that releasing a commitment
        /// secret won't leave us without a broadcastable holder transaction.
        /// Policy checks should be implemented in this function, including checking the amount
        /// sent to us and checking the HTLCs.
        fn validate_holder_commitment(&self, holder_tx: &HolderCommitmentTransaction) -> Result<(), ()>;
        /// Gets the holder's channel public keys and basepoints
        fn pubkeys(&self) -> &ChannelPublicKeys;
        /// Gets an arbitrary identifier describing the set of keys which are provided back to you in
        /// some SpendableOutputDescriptor types. This should be sufficient to identify this
        /// Sign object uniquely and lookup or re-derive its keys.
        fn channel_keys_id(&self) -> [u8; 32];

        /// 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.
        ///
        /// Policy checks should be implemented in this function, including checking the amount
        /// sent to us and checking the HTLCs.
        //
        // TODO: Document the things someone using this interface should enforce before signing.
        fn sign_counterparty_commitment(&self, commitment_tx: &CommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<(Signature, Vec<Signature>), ()>;
        /// Validate the counterparty's revocation.
        ///
        /// This is required in order for the signer to make sure that the state has moved
        /// forward and it is safe to sign the next counterparty commitment.
        fn validate_counterparty_revocation(&self, idx: u64, secret: &SecretKey) -> Result<(), ()>;

        /// 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(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> 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(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<(Signature, Vec<Signature>), ()>;

        /// Create a signature for the given input in a transaction spending an HTLC transaction output
        /// or a commitment transaction `to_local` output when our counterparty broadcasts an old state.
        ///
        /// A justice transaction may claim multiple 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 multiple times 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).
        fn sign_justice_revoked_output(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()>;

        /// Create a signature for the given input in a transaction spending a commitment transaction
        /// HTLC output when our counterparty broadcasts an old state.
        ///
        /// A justice transaction may claim multiple 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 multiple times 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), thus changing the format of the witness script
        /// (which is committed to in the BIP 143 signatures).
        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, ()>;

        /// 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(&self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<secp256k1::All>) -> 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(&self, closing_tx: &ClosingTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> 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(&self, msg: &UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<secp256k1::All>) -> 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 cloneable signer.
///
/// Although we require signers to be cloneable, it may be useful for developers to be able to use
/// signers in an un-sized way, for example as `dyn BaseSign`. Therefore we separate the Clone trait,
/// which implies Sized, into this derived trait.
pub trait Sign: BaseSign + Writeable + Clone {
}

/// 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).
        ///
        /// This method must return the same value each time it is called.
        fn get_node_secret(&self) -> SecretKey;
        /// 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
        /// on-chain funds across channels as controlled to the same user.
        fn get_destination_script(&self) -> Script;
        /// Get a script pubkey which we will send funds to when closing a channel.
        ///
        /// This method should return a different value each time it is called, to avoid linking
        /// on-chain funds across channels as controlled to the same user.
        fn get_shutdown_scriptpubkey(&self) -> ShutdownScript;
        /// Get a new set of Sign for per-channel secrets. These MUST be unique even if you
        /// restarted with some stale data!
        ///
        /// This method must return a different value each time it is called.
        fn get_channel_signer(&self, inbound: bool, channel_value_satoshis: u64) -> Self::Signer;
        /// 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.
        ///
        /// This method must return a different value each time it is called.
        fn get_secure_random_bytes(&self) -> [u8; 32];

        /// Reads a `Signer` for this `KeysInterface` from the given input stream.
        /// This is only called during deserialization of other objects which contain
        /// `Sign`-implementing objects (ie `ChannelMonitor`s and `ChannelManager`s).
        /// The bytes are exactly those which `<Self::Signer 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::Signer, DecodeError>;

        /// Sign an invoice's preimage (note that this is the preimage of the invoice, not the HTLC's
        /// preimage). By parameterizing by the preimage instead of the hash, we allow implementors of
        /// this trait to parse the invoice and make sure they're signing what they expect, rather than
        /// blindly signing the hash.
        fn sign_invoice(&self, invoice_preimage: Vec<u8>) -> Result<RecoverableSignature, ()>;
}

#[derive(Clone)]
/// A simple implementation of Sign 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 InMemorySigner {
        /// 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
        channel_keys_id: [u8; 32],
}

impl InMemorySigner {
        /// Create a new InMemorySigner
        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,
                channel_keys_id: [u8; 32]) -> InMemorySigner {
                let holder_channel_pubkeys =
                        InMemorySigner::make_holder_keys(secp_ctx, &funding_key, &revocation_base_key,
                                                             &payment_key, &delayed_payment_base_key,
                                                             &htlc_base_key);
                InMemorySigner {
                        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,
                        channel_keys_id,
                }
        }

        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()
        }

        /// Sign the single input of spend_tx at index `input_idx` which spends the output
        /// described by descriptor, returning the witness stack for the input.
        ///
        /// Returns an Err if the input at input_idx does not exist, has a non-empty script_sig,
        /// or is not spending the outpoint described by `descriptor.outpoint`.
        pub fn sign_counterparty_payment_input<C: Signing>(&self, spend_tx: &Transaction, input_idx: usize, descriptor: &StaticPaymentOutputDescriptor, secp_ctx: &Secp256k1<C>) -> Result<Vec<Vec<u8>>, ()> {
                // TODO: We really should be taking the SigHashCache as a parameter here instead of
                // spend_tx, but ideally the SigHashCache would expose the transaction's inputs read-only
                // so that we can check them. This requires upstream rust-bitcoin changes (as well as
                // bindings updates to support SigHashCache objects).
                if spend_tx.input.len() <= input_idx { return Err(()); }
                if !spend_tx.input[input_idx].script_sig.is_empty() { return Err(()); }
                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 mut witness = Vec::with_capacity(2);
                witness.push(remotesig.serialize_der().to_vec());
                witness[0].push(SigHashType::All as u8);
                witness.push(remotepubkey.serialize().to_vec());
                Ok(witness)
        }

        /// Sign the single input of spend_tx at index `input_idx` which spends the output
        /// described by descriptor, returning the witness stack for the input.
        ///
        /// Returns an Err if the input at input_idx does not exist, has a non-empty script_sig,
        /// is not spending the outpoint described by `descriptor.outpoint`, or does not have a
        /// sequence set to `descriptor.to_self_delay`.
        pub fn sign_dynamic_p2wsh_input<C: Signing>(&self, spend_tx: &Transaction, input_idx: usize, descriptor: &DelayedPaymentOutputDescriptor, secp_ctx: &Secp256k1<C>) -> Result<Vec<Vec<u8>>, ()> {
                // TODO: We really should be taking the SigHashCache as a parameter here instead of
                // spend_tx, but ideally the SigHashCache would expose the transaction's inputs read-only
                // so that we can check them. This requires upstream rust-bitcoin changes (as well as
                // bindings updates to support SigHashCache objects).
                if spend_tx.input.len() <= input_idx { return Err(()); }
                if !spend_tx.input[input_idx].script_sig.is_empty() { return Err(()); }
                if spend_tx.input[input_idx].previous_output != descriptor.outpoint.into_bitcoin_outpoint() { return Err(()); }
                if spend_tx.input[input_idx].sequence != descriptor.to_self_delay as u32 { return Err(()); }

                let delayed_payment_key = chan_utils::derive_private_key(&secp_ctx, &descriptor.per_commitment_point, &self.delayed_payment_base_key)
                        .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 mut witness = Vec::with_capacity(3);
                witness.push(local_delayedsig.serialize_der().to_vec());
                witness[0].push(SigHashType::All as u8);
                witness.push(vec!()); //MINIMALIF
                witness.push(witness_script.clone().into_bytes());
                Ok(witness)
        }
}

impl BaseSign for InMemorySigner {
        fn get_per_commitment_point(&self, idx: u64, secp_ctx: &Secp256k1<secp256k1::All>) -> 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 validate_holder_commitment(&self, _holder_tx: &HolderCommitmentTransaction) -> Result<(), ()> {
                Ok(())
        }

        fn pubkeys(&self) -> &ChannelPublicKeys { &self.holder_channel_pubkeys }
        fn channel_keys_id(&self) -> [u8; 32] { self.channel_keys_id }

        fn sign_counterparty_commitment(&self, commitment_tx: &CommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> 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 = 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));
                }

                Ok((commitment_sig, htlc_sigs))
        }

        fn validate_counterparty_revocation(&self, _idx: u64, _secret: &SecretKey) -> Result<(), ()> {
                Ok(())
        }

        fn sign_holder_commitment_and_htlcs(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> 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(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> 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_revoked_output(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
                let revocation_key = chan_utils::derive_private_revocation_key(&secp_ctx, &per_commitment_key, &self.revocation_base_key).map_err(|_| ())?;
                let per_commitment_point = PublicKey::from_secret_key(secp_ctx, &per_commitment_key);
                let revocation_pubkey = chan_utils::derive_public_revocation_key(&secp_ctx, &per_commitment_point, &self.pubkeys().revocation_basepoint).map_err(|_| ())?;
                let witness_script = {
                        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))
        }

        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, ()> {
                let revocation_key = chan_utils::derive_private_revocation_key(&secp_ctx, &per_commitment_key, &self.revocation_base_key).map_err(|_| ())?;
                let per_commitment_point = PublicKey::from_secret_key(secp_ctx, &per_commitment_key);
                let revocation_pubkey = chan_utils::derive_public_revocation_key(&secp_ctx, &per_commitment_point, &self.pubkeys().revocation_basepoint).map_err(|_| ())?;
                let witness_script = {
                        let counterparty_htlcpubkey = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().htlc_basepoint).map_err(|_| ())?;
                        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, &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))
        }

        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, ()> {
                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(&self, closing_tx: &ClosingTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
                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);
                Ok(closing_tx.trust().sign(&self.funding_key, &channel_funding_redeemscript, self.channel_value_satoshis, secp_ctx))
        }

        fn sign_channel_announcement(&self, msg: &UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<secp256k1::All>) -> 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());
        }
}

const SERIALIZATION_VERSION: u8 = 1;
const MIN_SERIALIZATION_VERSION: u8 = 1;

impl Sign for InMemorySigner {}

impl Writeable for InMemorySigner {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), Error> {
                write_ver_prefix!(writer, SERIALIZATION_VERSION, MIN_SERIALIZATION_VERSION);

                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.channel_keys_id.write(writer)?;

                write_tlv_fields!(writer, {});

                Ok(())
        }
}

impl Readable for InMemorySigner {
        fn read<R: io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
                let _ver = read_ver_prefix!(reader, SERIALIZATION_VERSION);

                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 =
                        InMemorySigner::make_holder_keys(&secp_ctx, &funding_key, &revocation_base_key,
                                                             &payment_key, &delayed_payment_base_key,
                                                             &htlc_base_key);
                let keys_id = Readable::read(reader)?;

                read_tlv_fields!(reader, {});

                Ok(InMemorySigner {
                        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,
                        channel_keys_id: keys_id,
                })
        }
}

/// 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::All>,
        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,
        rand_bytes_unique_start: Sha256State,

        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], starting_time_secs: u64, starting_time_nanos: u32) -> Self {
                let secp_ctx = Secp256k1::new();
                // 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 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");

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

                                let mut res = 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),
                                        rand_bytes_unique_start,

                                        seed: *seed,
                                        starting_time_secs,
                                        starting_time_nanos,
                                };
                                let secp_seed = res.get_secure_random_bytes();
                                res.secp_ctx.seeded_randomize(&secp_seed);
                                res
                        },
                        Err(_) => panic!("Your rng is busted"),
                }
        }
        /// Derive an old Sign containing per-channel secrets based on a key derivation parameters.
        ///
        /// Key derivation parameters are accessible through a per-channel secrets
        /// Sign::channel_keys_id 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: &[u8; 32]) -> InMemorySigner {
                let chan_id = byte_utils::slice_to_be64(&params[0..8]);
                assert!(chan_id <= core::u32::MAX as u64); // Otherwise the params field wasn't created by us
                let mut unique_start = Sha256::engine();
                unique_start.input(params);
                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 as u32).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);

                InMemorySigner::new(
                        &self.secp_ctx,
                        funding_key,
                        revocation_base_key,
                        payment_key,
                        delayed_payment_base_key,
                        htlc_base_key,
                        commitment_seed,
                        channel_value_satoshis,
                        params.clone()
                )
        }

        /// Creates a Transaction which spends the given descriptors to the given outputs, plus an
        /// output to the given change destination (if sufficient change value remains). The
        /// 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 or
        /// if a descriptor was duplicated.
        ///
        /// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
        ///
        /// May panic if the `SpendableOutputDescriptor`s were not generated by Channels which used
        /// this KeysManager or one of the `InMemorySigner` created by this KeysManager.
        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, ()> {
                let mut input = Vec::new();
                let mut input_value = 0;
                let mut witness_weight = 0;
                let mut output_set = HashSet::with_capacity(descriptors.len());
                for outp in descriptors {
                        match outp {
                                SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
                                        input.push(TxIn {
                                                previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
                                                script_sig: Script::new(),
                                                sequence: 0,
                                                witness: Vec::new(),
                                        });
                                        witness_weight += StaticPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
                                        input_value += descriptor.output.value;
                                        if !output_set.insert(descriptor.outpoint) { return Err(()); }
                                },
                                SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
                                        input.push(TxIn {
                                                previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
                                                script_sig: Script::new(),
                                                sequence: descriptor.to_self_delay as u32,
                                                witness: Vec::new(),
                                        });
                                        witness_weight += DelayedPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
                                        input_value += descriptor.output.value;
                                        if !output_set.insert(descriptor.outpoint) { return Err(()); }
                                },
                                SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output } => {
                                        input.push(TxIn {
                                                previous_output: outpoint.into_bitcoin_outpoint(),
                                                script_sig: Script::new(),
                                                sequence: 0,
                                                witness: Vec::new(),
                                        });
                                        witness_weight += 1 + 73 + 34;
                                        input_value += output.value;
                                        if !output_set.insert(*outpoint) { return Err(()); }
                                }
                        }
                        if input_value > MAX_VALUE_MSAT / 1000 { return Err(()); }
                }
                let mut spend_tx = Transaction {
                        version: 2,
                        lock_time: 0,
                        input,
                        output: outputs,
                };
                transaction_utils::maybe_add_change_output(&mut spend_tx, input_value, witness_weight, feerate_sat_per_1000_weight, change_destination_script)?;

                let mut keys_cache: Option<(InMemorySigner, [u8; 32])> = None;
                let mut input_idx = 0;
                for outp in descriptors {
                        match outp {
                                SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
                                        if keys_cache.is_none() || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id {
                                                keys_cache = Some((
                                                        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).unwrap();
                                },
                                SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
                                        if keys_cache.is_none() || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id {
                                                keys_cache = Some((
                                                        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).unwrap();
                                },
                                SpendableOutputDescriptor::StaticOutput { ref output, .. } => {
                                        let derivation_idx = if output.script_pubkey == self.destination_script {
                                                1
                                        } else {
                                                2
                                        };
                                        let secret = {
                                                // Note that when we aren't serializing the key, network doesn't matter
                                                match ExtendedPrivKey::new_master(Network::Testnet, &self.seed) {
                                                        Ok(master_key) => {
                                                                match master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(derivation_idx).expect("key space exhausted")) {
                                                                        Ok(key) => key,
                                                                        Err(_) => panic!("Your RNG is busted"),
                                                                }
                                                        }
                                                        Err(_) => panic!("Your rng is busted"),
                                                }
                                        };
                                        let pubkey = ExtendedPubKey::from_private(&secp_ctx, &secret).public_key;
                                        if derivation_idx == 2 {
                                                assert_eq!(pubkey.key, self.shutdown_pubkey);
                                        }
                                        let witness_script = bitcoin::Address::p2pkh(&pubkey, Network::Testnet).script_pubkey();
                                        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());
                                },
                        }
                        input_idx += 1;
                }
                Ok(spend_tx)
        }
}

impl KeysInterface for KeysManager {
        type Signer = InMemorySigner;

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

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

        fn get_shutdown_scriptpubkey(&self) -> ShutdownScript {
                ShutdownScript::new_p2wpkh_from_pubkey(self.shutdown_pubkey.clone())
        }

        fn get_channel_signer(&self, _inbound: bool, channel_value_satoshis: u64) -> Self::Signer {
                let child_ix = self.channel_child_index.fetch_add(1, Ordering::AcqRel);
                assert!(child_ix <= core::u32::MAX as usize);
                let mut id = [0; 32];
                id[0..8].copy_from_slice(&byte_utils::be64_to_array(child_ix as u64));
                id[8..16].copy_from_slice(&byte_utils::be64_to_array(self.starting_time_nanos as u64));
                id[16..24].copy_from_slice(&byte_utils::be64_to_array(self.starting_time_secs));
                self.derive_channel_keys(channel_value_satoshis, &id)
        }

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

                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::Signer, DecodeError> {
                InMemorySigner::read(&mut io::Cursor::new(reader))
        }

        fn sign_invoice(&self, invoice_preimage: Vec<u8>) -> Result<RecoverableSignature, ()> {
                Ok(self.secp_ctx.sign_recoverable(&hash_to_message!(&Sha256::hash(&invoice_preimage)), &self.get_node_secret()))
        }
}

// Ensure that BaseSign can have a vtable
#[test]
pub fn dyn_sign() {
        let _signer: Box<dyn BaseSign>;
}