Introduce `OutputSpender` trait and implement for `(Phantom)KeysManager`

[rust-lightning] / lightning / src / sign / mod.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.

//! Provides keys to LDK and defines some useful objects describing spendable on-chain outputs.
//!
//! The provided output descriptors follow a custom LDK data format and are currently not fully
//! compatible with Bitcoin Core output descriptors.

use bitcoin::bip32::{ChildNumber, ExtendedPrivKey, ExtendedPubKey};
use bitcoin::blockdata::locktime::absolute::LockTime;
use bitcoin::blockdata::opcodes;
use bitcoin::blockdata::script::{Builder, Script, ScriptBuf};
use bitcoin::blockdata::transaction::{Transaction, TxIn, TxOut};
use bitcoin::ecdsa::Signature as EcdsaSignature;
use bitcoin::network::constants::Network;
use bitcoin::psbt::PartiallySignedTransaction;
use bitcoin::sighash;
use bitcoin::sighash::EcdsaSighashType;

use bitcoin::bech32::u5;
use bitcoin::hash_types::WPubkeyHash;
use bitcoin::hashes::sha256::Hash as Sha256;
use bitcoin::hashes::sha256d::Hash as Sha256dHash;
use bitcoin::hashes::{Hash, HashEngine};

use bitcoin::secp256k1::ecdh::SharedSecret;
use bitcoin::secp256k1::ecdsa::{RecoverableSignature, Signature};
use bitcoin::secp256k1::schnorr;
#[cfg(taproot)]
use bitcoin::secp256k1::All;
use bitcoin::secp256k1::{KeyPair, PublicKey, Scalar, Secp256k1, SecretKey, Signing};
use bitcoin::{secp256k1, Sequence, Txid, Witness};

use crate::chain::transaction::OutPoint;
use crate::crypto::utils::{hkdf_extract_expand_twice, sign, sign_with_aux_rand};
use crate::ln::chan_utils::{
        make_funding_redeemscript, ChannelPublicKeys, ChannelTransactionParameters, ClosingTransaction,
        CommitmentTransaction, HTLCOutputInCommitment, HolderCommitmentTransaction,
};
use crate::ln::channel::ANCHOR_OUTPUT_VALUE_SATOSHI;
use crate::ln::channel_keys::{
        DelayedPaymentBasepoint, DelayedPaymentKey, HtlcBasepoint, HtlcKey, RevocationBasepoint,
        RevocationKey,
};
#[cfg(taproot)]
use crate::ln::msgs::PartialSignatureWithNonce;
use crate::ln::msgs::{UnsignedChannelAnnouncement, UnsignedGossipMessage};
use crate::ln::script::ShutdownScript;
use crate::ln::{chan_utils, PaymentPreimage};
use crate::offers::invoice::UnsignedBolt12Invoice;
use crate::offers::invoice_request::UnsignedInvoiceRequest;
use crate::util::ser::{Readable, ReadableArgs, Writeable, Writer};
use crate::util::transaction_utils;

use crate::crypto::chacha20::ChaCha20;
use crate::io::{self, Error};
use crate::ln::features::ChannelTypeFeatures;
use crate::ln::msgs::{DecodeError, MAX_VALUE_MSAT};
use crate::prelude::*;
use crate::sign::ecdsa::{EcdsaChannelSigner, WriteableEcdsaChannelSigner};
#[cfg(taproot)]
use crate::sign::taproot::TaprootChannelSigner;
use crate::util::atomic_counter::AtomicCounter;
use crate::util::invoice::construct_invoice_preimage;
use core::ops::Deref;
use core::sync::atomic::{AtomicUsize, Ordering};
#[cfg(taproot)]
use musig2::types::{PartialSignature, PublicNonce};

pub(crate) mod type_resolver;

pub mod ecdsa;
#[cfg(taproot)]
pub mod taproot;

/// Used as initial key material, to be expanded into multiple secret keys (but not to be used
/// directly). This is used within LDK to encrypt/decrypt inbound payment data.
///
/// This is not exported to bindings users as we just use `[u8; 32]` directly
#[derive(Hash, Copy, Clone, PartialEq, Eq, Debug)]
pub struct KeyMaterial(pub [u8; 32]);

/// Information about a spendable output to a P2WSH script.
///
/// See [`SpendableOutputDescriptor::DelayedPaymentOutput`] for more details on how to spend this.
#[derive(Clone, Debug, Hash, PartialEq, Eq)]
pub struct DelayedPaymentOutputDescriptor {
        /// The outpoint which is spendable.
        pub outpoint: OutPoint,
        /// Per commitment point to derive the 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: RevocationKey,
        /// Arbitrary identification information returned by a call to [`ChannelSigner::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.
        /// Note: If you have the grind_signatures feature enabled, this will be at least 1 byte
        /// shorter.
        // 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: u64 =
                1 + 73 + 1 + chan_utils::REVOKEABLE_REDEEMSCRIPT_MAX_LENGTH as u64 + 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),
});

pub(crate) const P2WPKH_WITNESS_WEIGHT: u64 = 1 /* num stack items */ +
        1 /* sig length */ +
        73 /* sig including sighash flag */ +
        1 /* pubkey length */ +
        33 /* pubkey */;

/// Information about a spendable output to our "payment key".
///
/// See [`SpendableOutputDescriptor::StaticPaymentOutput`] for more details on how to spend this.
#[derive(Clone, Debug, Hash, PartialEq, Eq)]
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 [`ChannelSigner::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,
        /// The necessary channel parameters that need to be provided to the re-derived signer through
        /// [`ChannelSigner::provide_channel_parameters`].
        ///
        /// Added as optional, but always `Some` if the descriptor was produced in v0.0.117 or later.
        pub channel_transaction_parameters: Option<ChannelTransactionParameters>,
}
impl StaticPaymentOutputDescriptor {
        /// Returns the `witness_script` of the spendable output.
        ///
        /// Note that this will only return `Some` for [`StaticPaymentOutputDescriptor`]s that
        /// originated from an anchor outputs channel, as they take the form of a P2WSH script.
        pub fn witness_script(&self) -> Option<ScriptBuf> {
                self.channel_transaction_parameters.as_ref().and_then(|channel_params| {
                        if channel_params.supports_anchors() {
                                let payment_point = channel_params.holder_pubkeys.payment_point;
                                Some(chan_utils::get_to_countersignatory_with_anchors_redeemscript(&payment_point))
                        } else {
                                None
                        }
                })
        }

        /// The maximum length a well-formed witness spending one of these should have.
        /// Note: If you have the grind_signatures feature enabled, this will be at least 1 byte
        /// shorter.
        pub fn max_witness_length(&self) -> u64 {
                if self.channel_transaction_parameters.as_ref().map_or(false, |p| p.supports_anchors()) {
                        let witness_script_weight = 1 /* pubkey push */ + 33 /* pubkey */ +
                                1 /* OP_CHECKSIGVERIFY */ + 1 /* OP_1 */ + 1 /* OP_CHECKSEQUENCEVERIFY */;
                        1 /* num witness items */ + 1 /* sig push */ + 73 /* sig including sighash flag */ +
                                1 /* witness script push */ + witness_script_weight
                } else {
                        P2WPKH_WITNESS_WEIGHT
                }
        }
}
impl_writeable_tlv_based!(StaticPaymentOutputDescriptor, {
        (0, outpoint, required),
        (2, output, required),
        (4, channel_keys_id, required),
        (6, channel_value_satoshis, required),
        (7, channel_transaction_parameters, option),
});

/// Describes the necessary information to spend a spendable output.
///
/// When on-chain outputs are created by LDK (which our counterparty is not able to claim at any
/// point in the future) a [`SpendableOutputs`] 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.
///
/// [`SpendableOutputs`]: crate::events::Event::SpendableOutputs
#[derive(Clone, Debug, Hash, PartialEq, Eq)]
pub enum SpendableOutputDescriptor {
        /// An output to a script which was provided via [`SignerProvider`] 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 LDK 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.
        ///
        /// [`get_shutdown_scriptpubkey`]: SignerProvider::get_shutdown_scriptpubkey
        /// [`get_destination_script`]: SignerProvider::get_shutdown_scriptpubkey
        StaticOutput {
                /// The outpoint which is spendable.
                outpoint: OutPoint,
                /// The output which is referenced by the given outpoint.
                output: TxOut,
                /// The `channel_keys_id` for the channel which this output came from.
                ///
                /// For channels which were generated on LDK 0.0.119 or later, this is the value which was
                /// passed to the [`SignerProvider::get_destination_script`] call which provided this
                /// output script.
                ///
                /// For channels which were generated prior to LDK 0.0.119, no such argument existed,
                /// however this field may still be filled in if such data is available.
                channel_keys_id: Option<[u8; 32]>,
        },
        /// An output to a P2WSH script which can be spent with a single signature after an `OP_CSV`
        /// delay.
        ///
        /// The witness in the spending input should be:
        /// ```bitcoin
        /// <BIP 143 signature> <empty vector> (MINIMALIF standard rule) <provided witnessScript>
        /// ```
        ///
        /// Note that the `nSequence` field in the spending input must be set to
        /// [`DelayedPaymentOutputDescriptor::to_self_delay`] (which means the transaction is not
        /// broadcastable until at least [`DelayedPaymentOutputDescriptor::to_self_delay`] blocks after
        /// the outpoint confirms, see [BIP
        /// 68](https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki)). Also note that LDK
        /// won't generate a [`SpendableOutputDescriptor`] until the corresponding block height
        /// is reached.
        ///
        /// 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 this input, you must pass the
        /// holder [`InMemorySigner::delayed_payment_base_key`] (i.e., the private key which corresponds to the
        /// [`ChannelPublicKeys::delayed_payment_basepoint`] in [`ChannelSigner::pubkeys`]) and the provided
        /// [`DelayedPaymentOutputDescriptor::per_commitment_point`] to [`chan_utils::derive_private_key`]. The DelayedPaymentKey can be
        /// generated without the secret key using [`DelayedPaymentKey::from_basepoint`] and only the
        /// [`ChannelPublicKeys::delayed_payment_basepoint`] which appears in [`ChannelSigner::pubkeys`].
        ///
        /// To derive the [`DelayedPaymentOutputDescriptor::revocation_pubkey`] provided here (which is
        /// used in the witness script generation), you must pass the counterparty
        /// [`ChannelPublicKeys::revocation_basepoint`] (which appears in the call to
        /// [`ChannelSigner::provide_channel_parameters`]) and the provided
        /// [`DelayedPaymentOutputDescriptor::per_commitment_point`] to
        /// [`RevocationKey`].
        ///
        /// The witness script which is hashed and included in the output `script_pubkey` may be
        /// regenerated by passing the [`DelayedPaymentOutputDescriptor::revocation_pubkey`] (derived
        /// as explained above), our delayed payment pubkey (derived as explained above), and the
        /// [`DelayedPaymentOutputDescriptor::to_self_delay`] contained here to
        /// [`chan_utils::get_revokeable_redeemscript`].
        DelayedPaymentOutput(DelayedPaymentOutputDescriptor),
        /// An output spendable exclusively by our payment key (i.e., the private key that corresponds
        /// to the `payment_point` in [`ChannelSigner::pubkeys`]). The output type depends on the
        /// channel type negotiated.
        ///
        /// On an anchor outputs channel, the witness in the spending input is:
        /// ```bitcoin
        /// <BIP 143 signature> <witness script>
        /// ```
        ///
        /// Otherwise, it is:
        /// ```bitcoin
        /// <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, or after one confirmation
        /// in the case of anchor outputs channels.
        StaticPaymentOutput(StaticPaymentOutputDescriptor),
}

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

impl SpendableOutputDescriptor {
        /// Turns this into a [`bitcoin::psbt::Input`] which can be used to create a
        /// [`PartiallySignedTransaction`] which spends the given descriptor.
        ///
        /// Note that this does not include any signatures, just the information required to
        /// construct the transaction and sign it.
        ///
        /// This is not exported to bindings users as there is no standard serialization for an input.
        /// See [`Self::create_spendable_outputs_psbt`] instead.
        pub fn to_psbt_input(&self) -> bitcoin::psbt::Input {
                match self {
                        SpendableOutputDescriptor::StaticOutput { output, .. } => {
                                // Is a standard P2WPKH, no need for witness script
                                bitcoin::psbt::Input { witness_utxo: Some(output.clone()), ..Default::default() }
                        },
                        SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
                                // TODO we could add the witness script as well
                                bitcoin::psbt::Input {
                                        witness_utxo: Some(descriptor.output.clone()),
                                        ..Default::default()
                                }
                        },
                        SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
                                // TODO we could add the witness script as well
                                bitcoin::psbt::Input {
                                        witness_utxo: Some(descriptor.output.clone()),
                                        ..Default::default()
                                }
                        },
                }
        }

        /// Creates an unsigned [`PartiallySignedTransaction`] which spends the given descriptors to
        /// the given outputs, plus an output to the given change destination (if sufficient
        /// change value remains). The PSBT will have a feerate, at least, of the given value.
        ///
        /// The `locktime` argument is used to set the transaction's locktime. If `None`, the
        /// transaction will have a locktime of 0. It it recommended to set this to the current block
        /// height to avoid fee sniping, unless you have some specific reason to use a different
        /// locktime.
        ///
        /// Returns the PSBT and expected max transaction weight.
        ///
        /// Returns `Err(())` if the output value is greater than the input value minus required fee,
        /// if a descriptor was duplicated, or if an output descriptor `script_pubkey`
        /// does not match the one we can spend.
        ///
        /// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
        pub fn create_spendable_outputs_psbt(
                descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>,
                change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32,
                locktime: Option<LockTime>,
        ) -> Result<(PartiallySignedTransaction, u64), ()> {
                let mut input = Vec::with_capacity(descriptors.len());
                let mut input_value = 0;
                let mut witness_weight = 0;
                let mut output_set = hash_set_with_capacity(descriptors.len());
                for outp in descriptors {
                        match outp {
                                SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
                                        if !output_set.insert(descriptor.outpoint) {
                                                return Err(());
                                        }
                                        let sequence = if descriptor
                                                .channel_transaction_parameters
                                                .as_ref()
                                                .map_or(false, |p| p.supports_anchors())
                                        {
                                                Sequence::from_consensus(1)
                                        } else {
                                                Sequence::ZERO
                                        };
                                        input.push(TxIn {
                                                previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
                                                script_sig: ScriptBuf::new(),
                                                sequence,
                                                witness: Witness::new(),
                                        });
                                        witness_weight += descriptor.max_witness_length();
                                        #[cfg(feature = "grind_signatures")]
                                        {
                                                // Guarantees a low R signature
                                                witness_weight -= 1;
                                        }
                                        input_value += descriptor.output.value;
                                },
                                SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
                                        if !output_set.insert(descriptor.outpoint) {
                                                return Err(());
                                        }
                                        input.push(TxIn {
                                                previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
                                                script_sig: ScriptBuf::new(),
                                                sequence: Sequence(descriptor.to_self_delay as u32),
                                                witness: Witness::new(),
                                        });
                                        witness_weight += DelayedPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
                                        #[cfg(feature = "grind_signatures")]
                                        {
                                                // Guarantees a low R signature
                                                witness_weight -= 1;
                                        }
                                        input_value += descriptor.output.value;
                                },
                                SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output, .. } => {
                                        if !output_set.insert(*outpoint) {
                                                return Err(());
                                        }
                                        input.push(TxIn {
                                                previous_output: outpoint.into_bitcoin_outpoint(),
                                                script_sig: ScriptBuf::new(),
                                                sequence: Sequence::ZERO,
                                                witness: Witness::new(),
                                        });
                                        witness_weight += 1 + 73 + 34;
                                        #[cfg(feature = "grind_signatures")]
                                        {
                                                // Guarantees a low R signature
                                                witness_weight -= 1;
                                        }
                                        input_value += output.value;
                                },
                        }
                        if input_value > MAX_VALUE_MSAT / 1000 {
                                return Err(());
                        }
                }
                let mut tx = Transaction {
                        version: 2,
                        lock_time: locktime.unwrap_or(LockTime::ZERO),
                        input,
                        output: outputs,
                };
                let expected_max_weight = transaction_utils::maybe_add_change_output(
                        &mut tx,
                        input_value,
                        witness_weight,
                        feerate_sat_per_1000_weight,
                        change_destination_script,
                )?;

                let psbt_inputs = descriptors.iter().map(|d| d.to_psbt_input()).collect::<Vec<_>>();
                let psbt = PartiallySignedTransaction {
                        inputs: psbt_inputs,
                        outputs: vec![Default::default(); tx.output.len()],
                        unsigned_tx: tx,
                        xpub: Default::default(),
                        version: 0,
                        proprietary: Default::default(),
                        unknown: Default::default(),
                };
                Ok((psbt, expected_max_weight))
        }
}

/// The parameters required to derive a channel signer via [`SignerProvider`].
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct ChannelDerivationParameters {
        /// The value in satoshis of the channel we're attempting to spend the anchor output of.
        pub value_satoshis: u64,
        /// The unique identifier to re-derive the signer for the associated channel.
        pub keys_id: [u8; 32],
        /// The necessary channel parameters that need to be provided to the re-derived signer through
        /// [`ChannelSigner::provide_channel_parameters`].
        pub transaction_parameters: ChannelTransactionParameters,
}

impl_writeable_tlv_based!(ChannelDerivationParameters, {
        (0, value_satoshis, required),
        (2, keys_id, required),
        (4, transaction_parameters, required),
});

/// A descriptor used to sign for a commitment transaction's HTLC output.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct HTLCDescriptor {
        /// The parameters required to derive the signer for the HTLC input.
        pub channel_derivation_parameters: ChannelDerivationParameters,
        /// The txid of the commitment transaction in which the HTLC output lives.
        pub commitment_txid: Txid,
        /// The number of the commitment transaction in which the HTLC output lives.
        pub per_commitment_number: u64,
        /// The key tweak corresponding to the number of the commitment transaction in which the HTLC
        /// output lives. This tweak is applied to all the basepoints for both parties in the channel to
        /// arrive at unique keys per commitment.
        ///
        /// See <https://github.com/lightning/bolts/blob/master/03-transactions.md#keys> for more info.
        pub per_commitment_point: PublicKey,
        /// The feerate to use on the HTLC claiming transaction. This is always `0` for HTLCs
        /// originating from a channel supporting anchor outputs, otherwise it is the channel's
        /// negotiated feerate at the time the commitment transaction was built.
        pub feerate_per_kw: u32,
        /// The details of the HTLC as it appears in the commitment transaction.
        pub htlc: HTLCOutputInCommitment,
        /// The preimage, if `Some`, to claim the HTLC output with. If `None`, the timeout path must be
        /// taken.
        pub preimage: Option<PaymentPreimage>,
        /// The counterparty's signature required to spend the HTLC output.
        pub counterparty_sig: Signature,
}

impl_writeable_tlv_based!(HTLCDescriptor, {
        (0, channel_derivation_parameters, required),
        (1, feerate_per_kw, (default_value, 0)),
        (2, commitment_txid, required),
        (4, per_commitment_number, required),
        (6, per_commitment_point, required),
        (8, htlc, required),
        (10, preimage, option),
        (12, counterparty_sig, required),
});

impl HTLCDescriptor {
        /// Returns the outpoint of the HTLC output in the commitment transaction. This is the outpoint
        /// being spent by the HTLC input in the HTLC transaction.
        pub fn outpoint(&self) -> bitcoin::OutPoint {
                bitcoin::OutPoint {
                        txid: self.commitment_txid,
                        vout: self.htlc.transaction_output_index.unwrap(),
                }
        }

        /// Returns the UTXO to be spent by the HTLC input, which can be obtained via
        /// [`Self::unsigned_tx_input`].
        pub fn previous_utxo<C: secp256k1::Signing + secp256k1::Verification>(
                &self, secp: &Secp256k1<C>,
        ) -> TxOut {
                TxOut {
                        script_pubkey: self.witness_script(secp).to_v0_p2wsh(),
                        value: self.htlc.amount_msat / 1000,
                }
        }

        /// Returns the unsigned transaction input spending the HTLC output in the commitment
        /// transaction.
        pub fn unsigned_tx_input(&self) -> TxIn {
                chan_utils::build_htlc_input(
                        &self.commitment_txid,
                        &self.htlc,
                        &self.channel_derivation_parameters.transaction_parameters.channel_type_features,
                )
        }

        /// Returns the delayed output created as a result of spending the HTLC output in the commitment
        /// transaction.
        pub fn tx_output<C: secp256k1::Signing + secp256k1::Verification>(
                &self, secp: &Secp256k1<C>,
        ) -> TxOut {
                let channel_params =
                        self.channel_derivation_parameters.transaction_parameters.as_holder_broadcastable();
                let broadcaster_keys = channel_params.broadcaster_pubkeys();
                let counterparty_keys = channel_params.countersignatory_pubkeys();
                let broadcaster_delayed_key = DelayedPaymentKey::from_basepoint(
                        secp,
                        &broadcaster_keys.delayed_payment_basepoint,
                        &self.per_commitment_point,
                );
                let counterparty_revocation_key = &RevocationKey::from_basepoint(
                        &secp,
                        &counterparty_keys.revocation_basepoint,
                        &self.per_commitment_point,
                );
                chan_utils::build_htlc_output(
                        self.feerate_per_kw,
                        channel_params.contest_delay(),
                        &self.htlc,
                        channel_params.channel_type_features(),
                        &broadcaster_delayed_key,
                        &counterparty_revocation_key,
                )
        }

        /// Returns the witness script of the HTLC output in the commitment transaction.
        pub fn witness_script<C: secp256k1::Signing + secp256k1::Verification>(
                &self, secp: &Secp256k1<C>,
        ) -> ScriptBuf {
                let channel_params =
                        self.channel_derivation_parameters.transaction_parameters.as_holder_broadcastable();
                let broadcaster_keys = channel_params.broadcaster_pubkeys();
                let counterparty_keys = channel_params.countersignatory_pubkeys();
                let broadcaster_htlc_key = HtlcKey::from_basepoint(
                        secp,
                        &broadcaster_keys.htlc_basepoint,
                        &self.per_commitment_point,
                );
                let counterparty_htlc_key = HtlcKey::from_basepoint(
                        secp,
                        &counterparty_keys.htlc_basepoint,
                        &self.per_commitment_point,
                );
                let counterparty_revocation_key = &RevocationKey::from_basepoint(
                        &secp,
                        &counterparty_keys.revocation_basepoint,
                        &self.per_commitment_point,
                );
                chan_utils::get_htlc_redeemscript_with_explicit_keys(
                        &self.htlc,
                        channel_params.channel_type_features(),
                        &broadcaster_htlc_key,
                        &counterparty_htlc_key,
                        &counterparty_revocation_key,
                )
        }

        /// Returns the fully signed witness required to spend the HTLC output in the commitment
        /// transaction.
        pub fn tx_input_witness(&self, signature: &Signature, witness_script: &Script) -> Witness {
                chan_utils::build_htlc_input_witness(
                        signature,
                        &self.counterparty_sig,
                        &self.preimage,
                        witness_script,
                        &self.channel_derivation_parameters.transaction_parameters.channel_type_features,
                )
        }

        /// Derives the channel signer required to sign the HTLC input.
        pub fn derive_channel_signer<S: WriteableEcdsaChannelSigner, SP: Deref>(
                &self, signer_provider: &SP,
        ) -> S
        where
                SP::Target: SignerProvider<EcdsaSigner = S>,
        {
                let mut signer = signer_provider.derive_channel_signer(
                        self.channel_derivation_parameters.value_satoshis,
                        self.channel_derivation_parameters.keys_id,
                );
                signer
                        .provide_channel_parameters(&self.channel_derivation_parameters.transaction_parameters);
                signer
        }
}

/// A trait to handle Lightning channel key material without concretizing the channel type or
/// the signature mechanism.
pub trait ChannelSigner {
        /// 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.
        ///
        /// The preimages of outbound HTLCs that were fulfilled since the last commitment are provided.
        /// A validating signer should ensure that an HTLC output is removed only when the matching
        /// preimage is provided, or when the value to holder is restored.
        ///
        /// Note that all the relevant preimages will be provided, but there may also be additional
        /// irrelevant or duplicate preimages.
        fn validate_holder_commitment(
                &self, holder_tx: &HolderCommitmentTransaction,
                outbound_htlc_preimages: Vec<PaymentPreimage>,
        ) -> Result<(), ()>;

        /// 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<(), ()>;

        /// Returns the holder's channel public keys and basepoints.
        fn pubkeys(&self) -> &ChannelPublicKeys;

        /// Returns 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
        /// [`EcdsaChannelSigner`] object uniquely and lookup or re-derive its keys.
        fn channel_keys_id(&self) -> [u8; 32];

        /// Set the counterparty static channel data, including basepoints,
        /// `counterparty_selected`/`holder_selected_contest_delay` and funding outpoint.
        ///
        /// This data is static, and will never change for a channel once set. For a given [`ChannelSigner`]
        /// instance, LDK will call this method exactly once - either immediately after construction
        /// (not including if done via [`SignerProvider::read_chan_signer`]) or when the funding
        /// information has been generated.
        ///
        /// channel_parameters.is_populated() MUST be true.
        fn provide_channel_parameters(&mut self, channel_parameters: &ChannelTransactionParameters);
}

/// Specifies the recipient of an invoice.
///
/// This indicates to [`NodeSigner::sign_invoice`] what node secret key should be used to sign
/// the invoice.
pub enum Recipient {
        /// The invoice should be signed with the local node secret key.
        Node,
        /// The invoice should be signed with the phantom node secret key. This secret key must be the
        /// same for all nodes participating in the [phantom node payment].
        ///
        /// [phantom node payment]: PhantomKeysManager
        PhantomNode,
}

/// A trait that describes a source of entropy.
pub trait EntropySource {
        /// Gets a unique, cryptographically-secure, random 32-byte value. This method must return a
        /// different value each time it is called.
        fn get_secure_random_bytes(&self) -> [u8; 32];
}

/// A trait that can handle cryptographic operations at the scope level of a node.
pub trait NodeSigner {
        /// Get secret key material as bytes for use in encrypting and decrypting inbound payment data.
        ///
        /// If the implementor of this trait supports [phantom node payments], then every node that is
        /// intended to be included in the phantom invoice route hints must return the same value from
        /// this method.
        // This is because LDK avoids storing inbound payment data by encrypting payment data in the
        // payment hash and/or payment secret, therefore for a payment to be receivable by multiple
        // nodes, they must share the key that encrypts this payment data.
        ///
        /// This method must return the same value each time it is called.
        ///
        /// [phantom node payments]: PhantomKeysManager
        fn get_inbound_payment_key_material(&self) -> KeyMaterial;

        /// Get node id based on the provided [`Recipient`].
        ///
        /// This method must return the same value each time it is called with a given [`Recipient`]
        /// parameter.
        ///
        /// Errors if the [`Recipient`] variant is not supported by the implementation.
        fn get_node_id(&self, recipient: Recipient) -> Result<PublicKey, ()>;

        /// Gets the ECDH shared secret of our node secret and `other_key`, multiplying by `tweak` if
        /// one is provided. Note that this tweak can be applied to `other_key` instead of our node
        /// secret, though this is less efficient.
        ///
        /// Note that if this fails while attempting to forward an HTLC, LDK will panic. The error
        /// should be resolved to allow LDK to resume forwarding HTLCs.
        ///
        /// Errors if the [`Recipient`] variant is not supported by the implementation.
        fn ecdh(
                &self, recipient: Recipient, other_key: &PublicKey, tweak: Option<&Scalar>,
        ) -> Result<SharedSecret, ()>;

        /// Sign an invoice.
        ///
        /// By parameterizing by the raw invoice bytes 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.
        ///
        /// The `hrp_bytes` are ASCII bytes, while the `invoice_data` is base32.
        ///
        /// The secret key used to sign the invoice is dependent on the [`Recipient`].
        ///
        /// Errors if the [`Recipient`] variant is not supported by the implementation.
        fn sign_invoice(
                &self, hrp_bytes: &[u8], invoice_data: &[u5], recipient: Recipient,
        ) -> Result<RecoverableSignature, ()>;

        /// Signs the [`TaggedHash`] of a BOLT 12 invoice request.
        ///
        /// May be called by a function passed to [`UnsignedInvoiceRequest::sign`] where
        /// `invoice_request` is the callee.
        ///
        /// Implementors may check that the `invoice_request` is expected rather than blindly signing
        /// the tagged hash. An `Ok` result should sign `invoice_request.tagged_hash().as_digest()` with
        /// the node's signing key or an ephemeral key to preserve privacy, whichever is associated with
        /// [`UnsignedInvoiceRequest::payer_id`].
        ///
        /// [`TaggedHash`]: crate::offers::merkle::TaggedHash
        fn sign_bolt12_invoice_request(
                &self, invoice_request: &UnsignedInvoiceRequest,
        ) -> Result<schnorr::Signature, ()>;

        /// Signs the [`TaggedHash`] of a BOLT 12 invoice.
        ///
        /// May be called by a function passed to [`UnsignedBolt12Invoice::sign`] where `invoice` is the
        /// callee.
        ///
        /// Implementors may check that the `invoice` is expected rather than blindly signing the tagged
        /// hash. An `Ok` result should sign `invoice.tagged_hash().as_digest()` with the node's signing
        /// key or an ephemeral key to preserve privacy, whichever is associated with
        /// [`UnsignedBolt12Invoice::signing_pubkey`].
        ///
        /// [`TaggedHash`]: crate::offers::merkle::TaggedHash
        fn sign_bolt12_invoice(
                &self, invoice: &UnsignedBolt12Invoice,
        ) -> Result<schnorr::Signature, ()>;

        /// Sign a gossip message.
        ///
        /// Note that if this fails, LDK may panic and the message will not be broadcast to the network
        /// or a possible channel counterparty. If LDK panics, the error should be resolved to allow the
        /// message to be broadcast, as otherwise it may prevent one from receiving funds over the
        /// corresponding channel.
        fn sign_gossip_message(&self, msg: UnsignedGossipMessage) -> Result<Signature, ()>;
}

/// A trait that describes a wallet capable of creating a spending [`Transaction`] from a set of
/// [`SpendableOutputDescriptor`]s.
pub trait OutputSpender {
        /// 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.
        ///
        /// The `locktime` argument is used to set the transaction's locktime. If `None`, the
        /// transaction will have a locktime of 0. It it recommended to set this to the current block
        /// height to avoid fee sniping, unless you have some specific reason to use a different
        /// locktime.
        ///
        /// Returns `Err(())` if the output value is greater than the input value minus required fee,
        /// if a descriptor was duplicated, or if an output descriptor `script_pubkey`
        /// does not match the one we can spend.
        fn spend_spendable_outputs<C: Signing>(
                &self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>,
                change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32,
                locktime: Option<LockTime>, secp_ctx: &Secp256k1<C>,
        ) -> Result<Transaction, ()>;
}

// Primarily needed in doctests because of https://github.com/rust-lang/rust/issues/67295
/// A dynamic [`SignerProvider`] temporarily needed for doc tests.
#[cfg(taproot)]
#[doc(hidden)]
#[deprecated(note = "Remove once taproot cfg is removed")]
pub type DynSignerProvider =
        dyn SignerProvider<EcdsaSigner = InMemorySigner, TaprootSigner = InMemorySigner>;

/// A dynamic [`SignerProvider`] temporarily needed for doc tests.
#[cfg(not(taproot))]
#[doc(hidden)]
#[deprecated(note = "Remove once taproot cfg is removed")]
pub type DynSignerProvider = dyn SignerProvider<EcdsaSigner = InMemorySigner>;

/// A trait that can return signer instances for individual channels.
pub trait SignerProvider {
        /// A type which implements [`WriteableEcdsaChannelSigner`] which will be returned by [`Self::derive_channel_signer`].
        type EcdsaSigner: WriteableEcdsaChannelSigner;
        #[cfg(taproot)]
        /// A type which implements [`TaprootChannelSigner`]
        type TaprootSigner: TaprootChannelSigner;

        /// Generates a unique `channel_keys_id` that can be used to obtain a [`Self::EcdsaSigner`] through
        /// [`SignerProvider::derive_channel_signer`]. The `user_channel_id` is provided to allow
        /// implementations of [`SignerProvider`] to maintain a mapping between itself and the generated
        /// `channel_keys_id`.
        ///
        /// This method must return a different value each time it is called.
        fn generate_channel_keys_id(
                &self, inbound: bool, channel_value_satoshis: u64, user_channel_id: u128,
        ) -> [u8; 32];

        /// Derives the private key material backing a `Signer`.
        ///
        /// To derive a new `Signer`, a fresh `channel_keys_id` should be obtained through
        /// [`SignerProvider::generate_channel_keys_id`]. Otherwise, an existing `Signer` can be
        /// re-derived from its `channel_keys_id`, which can be obtained through its trait method
        /// [`ChannelSigner::channel_keys_id`].
        fn derive_channel_signer(
                &self, channel_value_satoshis: u64, channel_keys_id: [u8; 32],
        ) -> Self::EcdsaSigner;

        /// Reads a [`Signer`] for this [`SignerProvider`] from the given input stream.
        /// This is only called during deserialization of other objects which contain
        /// [`WriteableEcdsaChannelSigner`]-implementing objects (i.e., [`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.
        ///
        /// This method is slowly being phased out -- it will only be called when reading objects
        /// written by LDK versions prior to 0.0.113.
        ///
        /// [`Signer`]: Self::EcdsaSigner
        /// [`ChannelMonitor`]: crate::chain::channelmonitor::ChannelMonitor
        /// [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
        fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::EcdsaSigner, DecodeError>;

        /// Get a script pubkey which we send funds to when claiming on-chain contestable outputs.
        ///
        /// If this function returns an error, this will result in a channel failing to open.
        ///
        /// 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. `channel_keys_id` may be
        /// used to derive a unique value for each channel.
        fn get_destination_script(&self, channel_keys_id: [u8; 32]) -> Result<ScriptBuf, ()>;

        /// Get a script pubkey which we will send funds to when closing a channel.
        ///
        /// If this function returns an error, this will result in a channel failing to open or close.
        /// In the event of a failure when the counterparty is initiating a close, this can result in a
        /// channel force close.
        ///
        /// 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) -> Result<ShutdownScript, ()>;
}

/// A simple implementation of [`WriteableEcdsaChannelSigner`] that just keeps the private keys in memory.
///
/// This implementation performs no policy checks and is insufficient by itself as
/// a secure external signer.
#[derive(Debug)]
pub struct InMemorySigner {
        /// Holder secret key in the 2-of-2 multisig script of a channel. This key also backs the
        /// holder's anchor output in a commitment transaction, if one is present.
        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 an HTLC transaction.
        pub delayed_payment_base_key: SecretKey,
        /// Holder HTLC secret key used in commitment transaction 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],
        /// A source of random bytes.
        entropy_source: RandomBytes,
}

impl PartialEq for InMemorySigner {
        fn eq(&self, other: &Self) -> bool {
                self.funding_key == other.funding_key
                        && self.revocation_base_key == other.revocation_base_key
                        && self.payment_key == other.payment_key
                        && self.delayed_payment_base_key == other.delayed_payment_base_key
                        && self.htlc_base_key == other.htlc_base_key
                        && self.commitment_seed == other.commitment_seed
                        && self.holder_channel_pubkeys == other.holder_channel_pubkeys
                        && self.channel_parameters == other.channel_parameters
                        && self.channel_value_satoshis == other.channel_value_satoshis
                        && self.channel_keys_id == other.channel_keys_id
        }
}

impl Clone for InMemorySigner {
        fn clone(&self) -> Self {
                Self {
                        funding_key: self.funding_key.clone(),
                        revocation_base_key: self.revocation_base_key.clone(),
                        payment_key: self.payment_key.clone(),
                        delayed_payment_base_key: self.delayed_payment_base_key.clone(),
                        htlc_base_key: self.htlc_base_key.clone(),
                        commitment_seed: self.commitment_seed.clone(),
                        holder_channel_pubkeys: self.holder_channel_pubkeys.clone(),
                        channel_parameters: self.channel_parameters.clone(),
                        channel_value_satoshis: self.channel_value_satoshis,
                        channel_keys_id: self.channel_keys_id,
                        entropy_source: RandomBytes::new(self.get_secure_random_bytes()),
                }
        }
}

impl InMemorySigner {
        /// Creates 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],
                rand_bytes_unique_start: [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,
                        entropy_source: RandomBytes::new(rand_bytes_unique_start),
                }
        }

        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: RevocationBasepoint::from(from_secret(&revocation_base_key)),
                        payment_point: from_secret(&payment_key),
                        delayed_payment_basepoint: DelayedPaymentBasepoint::from(from_secret(
                                &delayed_payment_base_key,
                        )),
                        htlc_basepoint: HtlcBasepoint::from(from_secret(&htlc_base_key)),
                }
        }

        /// Returns the counterparty's pubkeys.
        ///
        /// Will return `None` if [`ChannelSigner::provide_channel_parameters`] has not been called.
        /// In general, this is safe to `unwrap` only in [`ChannelSigner`] implementation.
        pub fn counterparty_pubkeys(&self) -> Option<&ChannelPublicKeys> {
                self.get_channel_parameters().and_then(|params| {
                        params.counterparty_parameters.as_ref().map(|params| &params.pubkeys)
                })
        }

        /// Returns the `contest_delay` value specified by our counterparty and applied on holder-broadcastable
        /// transactions, i.e., the amount of time that we have to wait to recover our funds if we
        /// broadcast a transaction.
        ///
        /// Will return `None` if [`ChannelSigner::provide_channel_parameters`] has not been called.
        /// In general, this is safe to `unwrap` only in [`ChannelSigner`] implementation.
        pub fn counterparty_selected_contest_delay(&self) -> Option<u16> {
                self.get_channel_parameters().and_then(|params| {
                        params.counterparty_parameters.as_ref().map(|params| params.selected_contest_delay)
                })
        }

        /// Returns the `contest_delay` value specified by us and applied on transactions broadcastable
        /// by our counterparty, i.e., the amount of time that they have to wait to recover their funds
        /// if they broadcast a transaction.
        ///
        /// Will return `None` if [`ChannelSigner::provide_channel_parameters`] has not been called.
        /// In general, this is safe to `unwrap` only in [`ChannelSigner`] implementation.
        pub fn holder_selected_contest_delay(&self) -> Option<u16> {
                self.get_channel_parameters().map(|params| params.holder_selected_contest_delay)
        }

        /// Returns whether the holder is the initiator.
        ///
        /// Will return `None` if [`ChannelSigner::provide_channel_parameters`] has not been called.
        /// In general, this is safe to `unwrap` only in [`ChannelSigner`] implementation.
        pub fn is_outbound(&self) -> Option<bool> {
                self.get_channel_parameters().map(|params| params.is_outbound_from_holder)
        }

        /// Funding outpoint
        ///
        /// Will return `None` if [`ChannelSigner::provide_channel_parameters`] has not been called.
        /// In general, this is safe to `unwrap` only in [`ChannelSigner`] implementation.
        pub fn funding_outpoint(&self) -> Option<&OutPoint> {
                self.get_channel_parameters().map(|params| params.funding_outpoint.as_ref()).flatten()
        }

        /// Returns a [`ChannelTransactionParameters`] for this channel, to be used when verifying or
        /// building transactions.
        ///
        /// Will return `None` if [`ChannelSigner::provide_channel_parameters`] has not been called.
        /// In general, this is safe to `unwrap` only in [`ChannelSigner`] implementation.
        pub fn get_channel_parameters(&self) -> Option<&ChannelTransactionParameters> {
                self.channel_parameters.as_ref()
        }

        /// Returns the channel type features of the channel parameters. Should be helpful for
        /// determining a channel's category, i. e. legacy/anchors/taproot/etc.
        ///
        /// Will return `None` if [`ChannelSigner::provide_channel_parameters`] has not been called.
        /// In general, this is safe to `unwrap` only in [`ChannelSigner`] implementation.
        pub fn channel_type_features(&self) -> Option<&ChannelTypeFeatures> {
                self.get_channel_parameters().map(|params| &params.channel_type_features)
        }

        /// 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 error 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 if an output descriptor `script_pubkey` does not match the one we can spend.
        ///
        /// [`descriptor.outpoint`]: StaticPaymentOutputDescriptor::outpoint
        pub fn sign_counterparty_payment_input<C: Signing>(
                &self, spend_tx: &Transaction, input_idx: usize,
                descriptor: &StaticPaymentOutputDescriptor, secp_ctx: &Secp256k1<C>,
        ) -> Result<Witness, ()> {
                // 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 = bitcoin::PublicKey::new(self.pubkeys().payment_point);
                // We cannot always assume that `channel_parameters` is set, so can't just call
                // `self.channel_parameters()` or anything that relies on it
                let supports_anchors_zero_fee_htlc_tx = self
                        .channel_type_features()
                        .map(|features| features.supports_anchors_zero_fee_htlc_tx())
                        .unwrap_or(false);

                let witness_script = if supports_anchors_zero_fee_htlc_tx {
                        chan_utils::get_to_countersignatory_with_anchors_redeemscript(&remotepubkey.inner)
                } else {
                        ScriptBuf::new_p2pkh(&remotepubkey.pubkey_hash())
                };
                let sighash = hash_to_message!(
                        &sighash::SighashCache::new(spend_tx)
                                .segwit_signature_hash(
                                        input_idx,
                                        &witness_script,
                                        descriptor.output.value,
                                        EcdsaSighashType::All
                                )
                                .unwrap()[..]
                );
                let remotesig = sign_with_aux_rand(secp_ctx, &sighash, &self.payment_key, &self);
                let payment_script = if supports_anchors_zero_fee_htlc_tx {
                        witness_script.to_v0_p2wsh()
                } else {
                        ScriptBuf::new_v0_p2wpkh(&remotepubkey.wpubkey_hash().unwrap())
                };

                if payment_script != descriptor.output.script_pubkey {
                        return Err(());
                }

                let mut witness = Vec::with_capacity(2);
                witness.push(remotesig.serialize_der().to_vec());
                witness[0].push(EcdsaSighashType::All as u8);
                if supports_anchors_zero_fee_htlc_tx {
                        witness.push(witness_script.to_bytes());
                } else {
                        witness.push(remotepubkey.to_bytes());
                }
                Ok(witness.into())
        }

        /// 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 error if the input at `input_idx` does not exist, has a non-empty `script_sig`,
        /// is not spending the outpoint described by [`descriptor.outpoint`], does not have a
        /// sequence set to [`descriptor.to_self_delay`], or if an output descriptor
        /// `script_pubkey` does not match the one we can spend.
        ///
        /// [`descriptor.outpoint`]: DelayedPaymentOutputDescriptor::outpoint
        /// [`descriptor.to_self_delay`]: DelayedPaymentOutputDescriptor::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<Witness, ()> {
                // 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.0 != 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,
                );
                let delayed_payment_pubkey =
                        DelayedPaymentKey::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!(
                        &sighash::SighashCache::new(spend_tx)
                                .segwit_signature_hash(
                                        input_idx,
                                        &witness_script,
                                        descriptor.output.value,
                                        EcdsaSighashType::All
                                )
                                .unwrap()[..]
                );
                let local_delayedsig = EcdsaSignature {
                        sig: sign_with_aux_rand(secp_ctx, &sighash, &delayed_payment_key, &self),
                        hash_ty: EcdsaSighashType::All,
                };
                let payment_script =
                        bitcoin::Address::p2wsh(&witness_script, Network::Bitcoin).script_pubkey();

                if descriptor.output.script_pubkey != payment_script {
                        return Err(());
                }

                Ok(Witness::from_slice(&[
                        &local_delayedsig.serialize()[..],
                        &[], // MINIMALIF
                        witness_script.as_bytes(),
                ]))
        }
}

impl EntropySource for InMemorySigner {
        fn get_secure_random_bytes(&self) -> [u8; 32] {
                self.entropy_source.get_secure_random_bytes()
        }
}

impl ChannelSigner 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,
                _outbound_htlc_preimages: Vec<PaymentPreimage>,
        ) -> Result<(), ()> {
                Ok(())
        }

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

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

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

        fn provide_channel_parameters(&mut self, channel_parameters: &ChannelTransactionParameters) {
                assert!(
                        self.channel_parameters.is_none()
                                || self.channel_parameters.as_ref().unwrap() == channel_parameters
                );
                if self.channel_parameters.is_some() {
                        // The channel parameters were already set and they match, return early.
                        return;
                }
                assert!(channel_parameters.is_populated(), "Channel parameters must be fully populated");
                self.channel_parameters = Some(channel_parameters.clone());
        }
}

const MISSING_PARAMS_ERR: &'static str =
        "ChannelSigner::provide_channel_parameters must be called before signing operations";

impl EcdsaChannelSigner for InMemorySigner {
        fn sign_counterparty_commitment(
                &self, commitment_tx: &CommitmentTransaction,
                _inbound_htlc_preimages: Vec<PaymentPreimage>,
                _outbound_htlc_preimages: Vec<PaymentPreimage>, 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 counterparty_keys = self.counterparty_pubkeys().expect(MISSING_PARAMS_ERR);
                let channel_funding_redeemscript =
                        make_funding_redeemscript(&funding_pubkey, &counterparty_keys.funding_pubkey);

                let built_tx = trusted_tx.built_transaction();
                let commitment_sig = built_tx.sign_counterparty_commitment(
                        &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 channel_parameters = self.get_channel_parameters().expect(MISSING_PARAMS_ERR);
                        let holder_selected_contest_delay =
                                self.holder_selected_contest_delay().expect(MISSING_PARAMS_ERR);
                        let chan_type = &channel_parameters.channel_type_features;
                        let htlc_tx = chan_utils::build_htlc_transaction(
                                &commitment_txid,
                                commitment_tx.feerate_per_kw(),
                                holder_selected_contest_delay,
                                htlc,
                                chan_type,
                                &keys.broadcaster_delayed_payment_key,
                                &keys.revocation_key,
                        );
                        let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, chan_type, &keys);
                        let htlc_sighashtype = if chan_type.supports_anchors_zero_fee_htlc_tx() {
                                EcdsaSighashType::SinglePlusAnyoneCanPay
                        } else {
                                EcdsaSighashType::All
                        };
                        let htlc_sighash = hash_to_message!(
                                &sighash::SighashCache::new(&htlc_tx)
                                        .segwit_signature_hash(
                                                0,
                                                &htlc_redeemscript,
                                                htlc.amount_msat / 1000,
                                                htlc_sighashtype
                                        )
                                        .unwrap()[..]
                        );
                        let holder_htlc_key = chan_utils::derive_private_key(
                                &secp_ctx,
                                &keys.per_commitment_point,
                                &self.htlc_base_key,
                        );
                        htlc_sigs.push(sign(secp_ctx, &htlc_sighash, &holder_htlc_key));
                }

                Ok((commitment_sig, htlc_sigs))
        }

        fn sign_holder_commitment(
                &self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>,
        ) -> Result<Signature, ()> {
                let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
                let counterparty_keys = self.counterparty_pubkeys().expect(MISSING_PARAMS_ERR);
                let funding_redeemscript =
                        make_funding_redeemscript(&funding_pubkey, &counterparty_keys.funding_pubkey);
                let trusted_tx = commitment_tx.trust();
                Ok(trusted_tx.built_transaction().sign_holder_commitment(
                        &self.funding_key,
                        &funding_redeemscript,
                        self.channel_value_satoshis,
                        &self,
                        secp_ctx,
                ))
        }

        #[cfg(any(test, feature = "unsafe_revoked_tx_signing"))]
        fn unsafe_sign_holder_commitment(
                &self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>,
        ) -> Result<Signature, ()> {
                let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
                let counterparty_keys = self.counterparty_pubkeys().expect(MISSING_PARAMS_ERR);
                let funding_redeemscript =
                        make_funding_redeemscript(&funding_pubkey, &counterparty_keys.funding_pubkey);
                let trusted_tx = commitment_tx.trust();
                Ok(trusted_tx.built_transaction().sign_holder_commitment(
                        &self.funding_key,
                        &funding_redeemscript,
                        self.channel_value_satoshis,
                        &self,
                        secp_ctx,
                ))
        }

        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,
                );
                let per_commitment_point = PublicKey::from_secret_key(secp_ctx, &per_commitment_key);
                let revocation_pubkey = RevocationKey::from_basepoint(
                        &secp_ctx,
                        &self.pubkeys().revocation_basepoint,
                        &per_commitment_point,
                );
                let witness_script = {
                        let counterparty_keys = self.counterparty_pubkeys().expect(MISSING_PARAMS_ERR);
                        let holder_selected_contest_delay =
                                self.holder_selected_contest_delay().expect(MISSING_PARAMS_ERR);
                        let counterparty_delayedpubkey = DelayedPaymentKey::from_basepoint(
                                &secp_ctx,
                                &counterparty_keys.delayed_payment_basepoint,
                                &per_commitment_point,
                        );
                        chan_utils::get_revokeable_redeemscript(
                                &revocation_pubkey,
                                holder_selected_contest_delay,
                                &counterparty_delayedpubkey,
                        )
                };
                let mut sighash_parts = sighash::SighashCache::new(justice_tx);
                let sighash = hash_to_message!(
                        &sighash_parts
                                .segwit_signature_hash(input, &witness_script, amount, EcdsaSighashType::All)
                                .unwrap()[..]
                );
                return Ok(sign_with_aux_rand(secp_ctx, &sighash, &revocation_key, &self));
        }

        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,
                );
                let per_commitment_point = PublicKey::from_secret_key(secp_ctx, &per_commitment_key);
                let revocation_pubkey = RevocationKey::from_basepoint(
                        &secp_ctx,
                        &self.pubkeys().revocation_basepoint,
                        &per_commitment_point,
                );
                let witness_script = {
                        let counterparty_keys = self.counterparty_pubkeys().expect(MISSING_PARAMS_ERR);
                        let counterparty_htlcpubkey = HtlcKey::from_basepoint(
                                &secp_ctx,
                                &counterparty_keys.htlc_basepoint,
                                &per_commitment_point,
                        );
                        let holder_htlcpubkey = HtlcKey::from_basepoint(
                                &secp_ctx,
                                &self.pubkeys().htlc_basepoint,
                                &per_commitment_point,
                        );
                        let chan_type = self.channel_type_features().expect(MISSING_PARAMS_ERR);
                        chan_utils::get_htlc_redeemscript_with_explicit_keys(
                                &htlc,
                                chan_type,
                                &counterparty_htlcpubkey,
                                &holder_htlcpubkey,
                                &revocation_pubkey,
                        )
                };
                let mut sighash_parts = sighash::SighashCache::new(justice_tx);
                let sighash = hash_to_message!(
                        &sighash_parts
                                .segwit_signature_hash(input, &witness_script, amount, EcdsaSighashType::All)
                                .unwrap()[..]
                );
                return Ok(sign_with_aux_rand(secp_ctx, &sighash, &revocation_key, &self));
        }

        fn sign_holder_htlc_transaction(
                &self, htlc_tx: &Transaction, input: usize, htlc_descriptor: &HTLCDescriptor,
                secp_ctx: &Secp256k1<secp256k1::All>,
        ) -> Result<Signature, ()> {
                let witness_script = htlc_descriptor.witness_script(secp_ctx);
                let sighash = &sighash::SighashCache::new(&*htlc_tx)
                        .segwit_signature_hash(
                                input,
                                &witness_script,
                                htlc_descriptor.htlc.amount_msat / 1000,
                                EcdsaSighashType::All,
                        )
                        .map_err(|_| ())?;
                let our_htlc_private_key = chan_utils::derive_private_key(
                        &secp_ctx,
                        &htlc_descriptor.per_commitment_point,
                        &self.htlc_base_key,
                );
                let sighash = hash_to_message!(sighash.as_byte_array());
                Ok(sign_with_aux_rand(&secp_ctx, &sighash, &our_htlc_private_key, &self))
        }

        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, ()> {
                let htlc_key =
                        chan_utils::derive_private_key(&secp_ctx, &per_commitment_point, &self.htlc_base_key);
                let revocation_pubkey = RevocationKey::from_basepoint(
                        &secp_ctx,
                        &self.pubkeys().revocation_basepoint,
                        &per_commitment_point,
                );
                let counterparty_keys = self.counterparty_pubkeys().expect(MISSING_PARAMS_ERR);
                let counterparty_htlcpubkey = HtlcKey::from_basepoint(
                        &secp_ctx,
                        &counterparty_keys.htlc_basepoint,
                        &per_commitment_point,
                );
                let htlc_basepoint = self.pubkeys().htlc_basepoint;
                let htlcpubkey = HtlcKey::from_basepoint(&secp_ctx, &htlc_basepoint, &per_commitment_point);
                let chan_type = self.channel_type_features().expect(MISSING_PARAMS_ERR);
                let witness_script = chan_utils::get_htlc_redeemscript_with_explicit_keys(
                        &htlc,
                        chan_type,
                        &counterparty_htlcpubkey,
                        &htlcpubkey,
                        &revocation_pubkey,
                );
                let mut sighash_parts = sighash::SighashCache::new(htlc_tx);
                let sighash = hash_to_message!(
                        &sighash_parts
                                .segwit_signature_hash(input, &witness_script, amount, EcdsaSighashType::All)
                                .unwrap()[..]
                );
                Ok(sign_with_aux_rand(secp_ctx, &sighash, &htlc_key, &self))
        }

        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 counterparty_funding_key =
                        &self.counterparty_pubkeys().expect(MISSING_PARAMS_ERR).funding_pubkey;
                let channel_funding_redeemscript =
                        make_funding_redeemscript(&funding_pubkey, counterparty_funding_key);
                Ok(closing_tx.trust().sign(
                        &self.funding_key,
                        &channel_funding_redeemscript,
                        self.channel_value_satoshis,
                        secp_ctx,
                ))
        }

        fn sign_holder_anchor_input(
                &self, anchor_tx: &Transaction, input: usize, secp_ctx: &Secp256k1<secp256k1::All>,
        ) -> Result<Signature, ()> {
                let witness_script =
                        chan_utils::get_anchor_redeemscript(&self.holder_channel_pubkeys.funding_pubkey);
                let sighash = sighash::SighashCache::new(&*anchor_tx)
                        .segwit_signature_hash(
                                input,
                                &witness_script,
                                ANCHOR_OUTPUT_VALUE_SATOSHI,
                                EcdsaSighashType::All,
                        )
                        .unwrap();
                Ok(sign_with_aux_rand(secp_ctx, &hash_to_message!(&sighash[..]), &self.funding_key, &self))
        }

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

#[cfg(taproot)]
impl TaprootChannelSigner for InMemorySigner {
        fn generate_local_nonce_pair(
                &self, commitment_number: u64, secp_ctx: &Secp256k1<All>,
        ) -> PublicNonce {
                todo!()
        }

        fn partially_sign_counterparty_commitment(
                &self, counterparty_nonce: PublicNonce, commitment_tx: &CommitmentTransaction,
                inbound_htlc_preimages: Vec<PaymentPreimage>,
                outbound_htlc_preimages: Vec<PaymentPreimage>, secp_ctx: &Secp256k1<All>,
        ) -> Result<(PartialSignatureWithNonce, Vec<schnorr::Signature>), ()> {
                todo!()
        }

        fn finalize_holder_commitment(
                &self, commitment_tx: &HolderCommitmentTransaction,
                counterparty_partial_signature: PartialSignatureWithNonce, secp_ctx: &Secp256k1<All>,
        ) -> Result<PartialSignature, ()> {
                todo!()
        }

        fn sign_justice_revoked_output(
                &self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey,
                secp_ctx: &Secp256k1<All>,
        ) -> Result<schnorr::Signature, ()> {
                todo!()
        }

        fn sign_justice_revoked_htlc(
                &self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey,
                htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<All>,
        ) -> Result<schnorr::Signature, ()> {
                todo!()
        }

        fn sign_holder_htlc_transaction(
                &self, htlc_tx: &Transaction, input: usize, htlc_descriptor: &HTLCDescriptor,
                secp_ctx: &Secp256k1<All>,
        ) -> Result<schnorr::Signature, ()> {
                todo!()
        }

        fn sign_counterparty_htlc_transaction(
                &self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey,
                htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<All>,
        ) -> Result<schnorr::Signature, ()> {
                todo!()
        }

        fn partially_sign_closing_transaction(
                &self, closing_tx: &ClosingTransaction, secp_ctx: &Secp256k1<All>,
        ) -> Result<PartialSignature, ()> {
                todo!()
        }

        fn sign_holder_anchor_input(
                &self, anchor_tx: &Transaction, input: usize, secp_ctx: &Secp256k1<All>,
        ) -> Result<schnorr::Signature, ()> {
                todo!()
        }
}

const SERIALIZATION_VERSION: u8 = 1;

const MIN_SERIALIZATION_VERSION: u8 = 1;

impl WriteableEcdsaChannelSigner 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<ES: Deref> ReadableArgs<ES> for InMemorySigner
where
        ES::Target: EntropySource,
{
        fn read<R: io::Read>(reader: &mut R, entropy_source: ES) -> 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,
                        entropy_source: RandomBytes::new(entropy_source.get_secure_random_bytes()),
                })
        }
}

/// Simple implementation of [`EntropySource`], [`NodeSigner`], and [`SignerProvider`] 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'.
/// Unilateral closes may use seed/1'.
/// Cooperative closes may use seed/2'.
/// The two close keys may be needed to claim on-chain funds!
///
/// This struct cannot be used for nodes that wish to support receiving phantom payments;
/// [`PhantomKeysManager`] must be used instead.
///
/// Note that switching between this struct and [`PhantomKeysManager`] will invalidate any
/// previously issued invoices and attempts to pay previous invoices will fail.
pub struct KeysManager {
        secp_ctx: Secp256k1<secp256k1::All>,
        node_secret: SecretKey,
        node_id: PublicKey,
        inbound_payment_key: KeyMaterial,
        destination_script: ScriptBuf,
        shutdown_pubkey: PublicKey,
        channel_master_key: ExtendedPrivKey,
        channel_child_index: AtomicUsize,

        entropy_source: RandomBytes,

        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 (e.g.,
        /// 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.
        ///
        /// [`ChannelMonitor`]: crate::chain::channelmonitor::ChannelMonitor
        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;
                                let node_id = PublicKey::from_secret_key(&secp_ctx, &node_secret);
                                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_priv(&secp_ctx, &destination_key)
                                                                .to_pub()
                                                                .to_bytes(),
                                                );
                                                Builder::new()
                                                        .push_opcode(opcodes::all::OP_PUSHBYTES_0)
                                                        .push_slice(&wpubkey_hash.to_byte_array())
                                                        .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_priv(&secp_ctx, &shutdown_key).public_key
                                        },
                                        Err(_) => panic!("Your RNG is busted"),
                                };
                                let channel_master_key = master_key
                                        .ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(3).unwrap())
                                        .expect("Your RNG is busted");
                                let inbound_payment_key: SecretKey = master_key
                                        .ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(5).unwrap())
                                        .expect("Your RNG is busted")
                                        .private_key;
                                let mut inbound_pmt_key_bytes = [0; 32];
                                inbound_pmt_key_bytes.copy_from_slice(&inbound_payment_key[..]);

                                let mut rand_bytes_engine = Sha256::engine();
                                rand_bytes_engine.input(&starting_time_secs.to_be_bytes());
                                rand_bytes_engine.input(&starting_time_nanos.to_be_bytes());
                                rand_bytes_engine.input(seed);
                                rand_bytes_engine.input(b"LDK PRNG Seed");
                                let rand_bytes_unique_start =
                                        Sha256::from_engine(rand_bytes_engine).to_byte_array();

                                let mut res = KeysManager {
                                        secp_ctx,
                                        node_secret,
                                        node_id,
                                        inbound_payment_key: KeyMaterial(inbound_pmt_key_bytes),

                                        destination_script,
                                        shutdown_pubkey,

                                        channel_master_key,
                                        channel_child_index: AtomicUsize::new(0),

                                        entropy_source: RandomBytes::new(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"),
                }
        }

        /// Gets the "node_id" secret key used to sign gossip announcements, decode onion data, etc.
        pub fn get_node_secret_key(&self) -> SecretKey {
                self.node_secret
        }

        /// Derive an old [`WriteableEcdsaChannelSigner`] containing per-channel secrets based on a key derivation parameters.
        pub fn derive_channel_keys(
                &self, channel_value_satoshis: u64, params: &[u8; 32],
        ) -> InMemorySigner {
                let chan_id = u64::from_be_bytes(params[0..8].try_into().unwrap());
                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) % (1 << 31))
                                        .expect("key space exhausted"),
                        )
                        .expect("Your RNG is busted");
                unique_start.input(&child_privkey.private_key[..]);

                let seed = Sha256::from_engine(unique_start).to_byte_array();

                let commitment_seed = {
                        let mut sha = Sha256::engine();
                        sha.input(&seed);
                        sha.input(&b"commitment seed"[..]);
                        Sha256::from_engine(sha).to_byte_array()
                };
                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).to_byte_array())
                                        .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);
                let prng_seed = self.get_secure_random_bytes();

                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(),
                        prng_seed,
                )
        }

        /// Signs the given [`PartiallySignedTransaction`] which spends the given [`SpendableOutputDescriptor`]s.
        /// The resulting inputs will be finalized and the PSBT will be ready for broadcast if there
        /// are no other inputs that need signing.
        ///
        /// Returns `Err(())` if the PSBT is missing a descriptor or if we fail to sign.
        ///
        /// 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 sign_spendable_outputs_psbt<C: Signing>(
                &self, descriptors: &[&SpendableOutputDescriptor], mut psbt: PartiallySignedTransaction,
                secp_ctx: &Secp256k1<C>,
        ) -> Result<PartiallySignedTransaction, ()> {
                let mut keys_cache: Option<(InMemorySigner, [u8; 32])> = None;
                for outp in descriptors {
                        let get_input_idx = |outpoint: &OutPoint| {
                                psbt.unsigned_tx
                                        .input
                                        .iter()
                                        .position(|i| i.previous_output == outpoint.into_bitcoin_outpoint())
                                        .ok_or(())
                        };
                        match outp {
                                SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
                                        let input_idx = get_input_idx(&descriptor.outpoint)?;
                                        if keys_cache.is_none()
                                                || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id
                                        {
                                                let mut signer = self.derive_channel_keys(
                                                        descriptor.channel_value_satoshis,
                                                        &descriptor.channel_keys_id,
                                                );
                                                if let Some(channel_params) =
                                                        descriptor.channel_transaction_parameters.as_ref()
                                                {
                                                        signer.provide_channel_parameters(channel_params);
                                                }
                                                keys_cache = Some((signer, descriptor.channel_keys_id));
                                        }
                                        let witness = keys_cache.as_ref().unwrap().0.sign_counterparty_payment_input(
                                                &psbt.unsigned_tx,
                                                input_idx,
                                                &descriptor,
                                                &secp_ctx,
                                        )?;
                                        psbt.inputs[input_idx].final_script_witness = Some(witness);
                                },
                                SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
                                        let input_idx = get_input_idx(&descriptor.outpoint)?;
                                        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,
                                                ));
                                        }
                                        let witness = keys_cache.as_ref().unwrap().0.sign_dynamic_p2wsh_input(
                                                &psbt.unsigned_tx,
                                                input_idx,
                                                &descriptor,
                                                &secp_ctx,
                                        )?;
                                        psbt.inputs[input_idx].final_script_witness = Some(witness);
                                },
                                SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output, .. } => {
                                        let input_idx = get_input_idx(outpoint)?;
                                        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_priv(&secp_ctx, &secret).to_pub();
                                        if derivation_idx == 2 {
                                                assert_eq!(pubkey.inner, self.shutdown_pubkey);
                                        }
                                        let witness_script =
                                                bitcoin::Address::p2pkh(&pubkey, Network::Testnet).script_pubkey();
                                        let payment_script = bitcoin::Address::p2wpkh(&pubkey, Network::Testnet)
                                                .expect("uncompressed key found")
                                                .script_pubkey();

                                        if payment_script != output.script_pubkey {
                                                return Err(());
                                        };

                                        let sighash = hash_to_message!(
                                                &sighash::SighashCache::new(&psbt.unsigned_tx)
                                                        .segwit_signature_hash(
                                                                input_idx,
                                                                &witness_script,
                                                                output.value,
                                                                EcdsaSighashType::All
                                                        )
                                                        .unwrap()[..]
                                        );
                                        let sig = sign_with_aux_rand(secp_ctx, &sighash, &secret.private_key, &self);
                                        let mut sig_ser = sig.serialize_der().to_vec();
                                        sig_ser.push(EcdsaSighashType::All as u8);
                                        let witness =
                                                Witness::from_slice(&[&sig_ser, &pubkey.inner.serialize().to_vec()]);
                                        psbt.inputs[input_idx].final_script_witness = Some(witness);
                                },
                        }
                }

                Ok(psbt)
        }
}

impl EntropySource for KeysManager {
        fn get_secure_random_bytes(&self) -> [u8; 32] {
                self.entropy_source.get_secure_random_bytes()
        }
}

impl NodeSigner for KeysManager {
        fn get_node_id(&self, recipient: Recipient) -> Result<PublicKey, ()> {
                match recipient {
                        Recipient::Node => Ok(self.node_id.clone()),
                        Recipient::PhantomNode => Err(()),
                }
        }

        fn ecdh(
                &self, recipient: Recipient, other_key: &PublicKey, tweak: Option<&Scalar>,
        ) -> Result<SharedSecret, ()> {
                let mut node_secret = match recipient {
                        Recipient::Node => Ok(self.node_secret.clone()),
                        Recipient::PhantomNode => Err(()),
                }?;
                if let Some(tweak) = tweak {
                        node_secret = node_secret.mul_tweak(tweak).map_err(|_| ())?;
                }
                Ok(SharedSecret::new(other_key, &node_secret))
        }

        fn get_inbound_payment_key_material(&self) -> KeyMaterial {
                self.inbound_payment_key.clone()
        }

        fn sign_invoice(
                &self, hrp_bytes: &[u8], invoice_data: &[u5], recipient: Recipient,
        ) -> Result<RecoverableSignature, ()> {
                let preimage = construct_invoice_preimage(&hrp_bytes, &invoice_data);
                let secret = match recipient {
                        Recipient::Node => Ok(&self.node_secret),
                        Recipient::PhantomNode => Err(()),
                }?;
                Ok(self.secp_ctx.sign_ecdsa_recoverable(
                        &hash_to_message!(&Sha256::hash(&preimage).to_byte_array()),
                        secret,
                ))
        }

        fn sign_bolt12_invoice_request(
                &self, invoice_request: &UnsignedInvoiceRequest,
        ) -> Result<schnorr::Signature, ()> {
                let message = invoice_request.tagged_hash().as_digest();
                let keys = KeyPair::from_secret_key(&self.secp_ctx, &self.node_secret);
                let aux_rand = self.get_secure_random_bytes();
                Ok(self.secp_ctx.sign_schnorr_with_aux_rand(message, &keys, &aux_rand))
        }

        fn sign_bolt12_invoice(
                &self, invoice: &UnsignedBolt12Invoice,
        ) -> Result<schnorr::Signature, ()> {
                let message = invoice.tagged_hash().as_digest();
                let keys = KeyPair::from_secret_key(&self.secp_ctx, &self.node_secret);
                let aux_rand = self.get_secure_random_bytes();
                Ok(self.secp_ctx.sign_schnorr_with_aux_rand(message, &keys, &aux_rand))
        }

        fn sign_gossip_message(&self, msg: UnsignedGossipMessage) -> Result<Signature, ()> {
                let msg_hash = hash_to_message!(&Sha256dHash::hash(&msg.encode()[..])[..]);
                Ok(self.secp_ctx.sign_ecdsa(&msg_hash, &self.node_secret))
        }
}

impl OutputSpender for KeysManager {
        /// 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).
        ///
        /// See [`OutputSpender::spend_spendable_outputs`] documentation for more information.
        ///
        /// 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`].
        fn spend_spendable_outputs<C: Signing>(
                &self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>,
                change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32,
                locktime: Option<LockTime>, secp_ctx: &Secp256k1<C>,
        ) -> Result<Transaction, ()> {
                let (mut psbt, expected_max_weight) =
                        SpendableOutputDescriptor::create_spendable_outputs_psbt(
                                descriptors,
                                outputs,
                                change_destination_script,
                                feerate_sat_per_1000_weight,
                                locktime,
                        )?;
                psbt = self.sign_spendable_outputs_psbt(descriptors, psbt, secp_ctx)?;

                let spend_tx = psbt.extract_tx();

                debug_assert!(expected_max_weight >= spend_tx.weight().to_wu());
                // Note that witnesses with a signature vary somewhat in size, so allow
                // `expected_max_weight` to overshoot by up to 3 bytes per input.
                debug_assert!(
                        expected_max_weight <= spend_tx.weight().to_wu() + descriptors.len() as u64 * 3
                );

                Ok(spend_tx)
        }
}

impl SignerProvider for KeysManager {
        type EcdsaSigner = InMemorySigner;
        #[cfg(taproot)]
        type TaprootSigner = InMemorySigner;

        fn generate_channel_keys_id(
                &self, _inbound: bool, _channel_value_satoshis: u64, user_channel_id: u128,
        ) -> [u8; 32] {
                let child_idx = self.channel_child_index.fetch_add(1, Ordering::AcqRel);
                // `child_idx` is the only thing guaranteed to make each channel unique without a restart
                // (though `user_channel_id` should help, depending on user behavior). If it manages to
                // roll over, we may generate duplicate keys for two different channels, which could result
                // in loss of funds. Because we only support 32-bit+ systems, assert that our `AtomicUsize`
                // doesn't reach `u32::MAX`.
                assert!(child_idx < core::u32::MAX as usize, "2^32 channels opened without restart");
                let mut id = [0; 32];
                id[0..4].copy_from_slice(&(child_idx as u32).to_be_bytes());
                id[4..8].copy_from_slice(&self.starting_time_nanos.to_be_bytes());
                id[8..16].copy_from_slice(&self.starting_time_secs.to_be_bytes());
                id[16..32].copy_from_slice(&user_channel_id.to_be_bytes());
                id
        }

        fn derive_channel_signer(
                &self, channel_value_satoshis: u64, channel_keys_id: [u8; 32],
        ) -> Self::EcdsaSigner {
                self.derive_channel_keys(channel_value_satoshis, &channel_keys_id)
        }

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

        fn get_destination_script(&self, _channel_keys_id: [u8; 32]) -> Result<ScriptBuf, ()> {
                Ok(self.destination_script.clone())
        }

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

/// Similar to [`KeysManager`], but allows the node using this struct to receive phantom node
/// payments.
///
/// A phantom node payment is a payment made to a phantom invoice, which is an invoice that can be
/// paid to one of multiple nodes. This works because we encode the invoice route hints such that
/// LDK will recognize an incoming payment as destined for a phantom node, and collect the payment
/// itself without ever needing to forward to this fake node.
///
/// Phantom node payments are useful for load balancing between multiple LDK nodes. They also
/// provide some fault tolerance, because payers will automatically retry paying other provided
/// nodes in the case that one node goes down.
///
/// Note that multi-path payments are not supported in phantom invoices for security reasons.
// In the hypothetical case that we did support MPP phantom payments, there would be no way for
// nodes to know when the full payment has been received (and the preimage can be released) without
// significantly compromising on our safety guarantees. I.e., if we expose the ability for the user
// to tell LDK when the preimage can be released, we open ourselves to attacks where the preimage
// is released too early.
//
/// Switching between this struct and [`KeysManager`] will invalidate any previously issued
/// invoices and attempts to pay previous invoices will fail.
pub struct PhantomKeysManager {
        inner: KeysManager,
        inbound_payment_key: KeyMaterial,
        phantom_secret: SecretKey,
        phantom_node_id: PublicKey,
}

impl EntropySource for PhantomKeysManager {
        fn get_secure_random_bytes(&self) -> [u8; 32] {
                self.inner.get_secure_random_bytes()
        }
}

impl NodeSigner for PhantomKeysManager {
        fn get_node_id(&self, recipient: Recipient) -> Result<PublicKey, ()> {
                match recipient {
                        Recipient::Node => self.inner.get_node_id(Recipient::Node),
                        Recipient::PhantomNode => Ok(self.phantom_node_id.clone()),
                }
        }

        fn ecdh(
                &self, recipient: Recipient, other_key: &PublicKey, tweak: Option<&Scalar>,
        ) -> Result<SharedSecret, ()> {
                let mut node_secret = match recipient {
                        Recipient::Node => self.inner.node_secret.clone(),
                        Recipient::PhantomNode => self.phantom_secret.clone(),
                };
                if let Some(tweak) = tweak {
                        node_secret = node_secret.mul_tweak(tweak).map_err(|_| ())?;
                }
                Ok(SharedSecret::new(other_key, &node_secret))
        }

        fn get_inbound_payment_key_material(&self) -> KeyMaterial {
                self.inbound_payment_key.clone()
        }

        fn sign_invoice(
                &self, hrp_bytes: &[u8], invoice_data: &[u5], recipient: Recipient,
        ) -> Result<RecoverableSignature, ()> {
                let preimage = construct_invoice_preimage(&hrp_bytes, &invoice_data);
                let secret = match recipient {
                        Recipient::Node => &self.inner.node_secret,
                        Recipient::PhantomNode => &self.phantom_secret,
                };
                Ok(self.inner.secp_ctx.sign_ecdsa_recoverable(
                        &hash_to_message!(&Sha256::hash(&preimage).to_byte_array()),
                        secret,
                ))
        }

        fn sign_bolt12_invoice_request(
                &self, invoice_request: &UnsignedInvoiceRequest,
        ) -> Result<schnorr::Signature, ()> {
                self.inner.sign_bolt12_invoice_request(invoice_request)
        }

        fn sign_bolt12_invoice(
                &self, invoice: &UnsignedBolt12Invoice,
        ) -> Result<schnorr::Signature, ()> {
                self.inner.sign_bolt12_invoice(invoice)
        }

        fn sign_gossip_message(&self, msg: UnsignedGossipMessage) -> Result<Signature, ()> {
                self.inner.sign_gossip_message(msg)
        }
}

impl OutputSpender for PhantomKeysManager {
        /// See [`OutputSpender::spend_spendable_outputs`] and [`KeysManager::spend_spendable_outputs`]
        /// for documentation on this method.
        fn spend_spendable_outputs<C: Signing>(
                &self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>,
                change_destination_script: ScriptBuf, feerate_sat_per_1000_weight: u32,
                locktime: Option<LockTime>, secp_ctx: &Secp256k1<C>,
        ) -> Result<Transaction, ()> {
                self.inner.spend_spendable_outputs(
                        descriptors,
                        outputs,
                        change_destination_script,
                        feerate_sat_per_1000_weight,
                        locktime,
                        secp_ctx,
                )
        }
}

impl SignerProvider for PhantomKeysManager {
        type EcdsaSigner = InMemorySigner;
        #[cfg(taproot)]
        type TaprootSigner = InMemorySigner;

        fn generate_channel_keys_id(
                &self, inbound: bool, channel_value_satoshis: u64, user_channel_id: u128,
        ) -> [u8; 32] {
                self.inner.generate_channel_keys_id(inbound, channel_value_satoshis, user_channel_id)
        }

        fn derive_channel_signer(
                &self, channel_value_satoshis: u64, channel_keys_id: [u8; 32],
        ) -> Self::EcdsaSigner {
                self.inner.derive_channel_signer(channel_value_satoshis, channel_keys_id)
        }

        fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::EcdsaSigner, DecodeError> {
                self.inner.read_chan_signer(reader)
        }

        fn get_destination_script(&self, channel_keys_id: [u8; 32]) -> Result<ScriptBuf, ()> {
                self.inner.get_destination_script(channel_keys_id)
        }

        fn get_shutdown_scriptpubkey(&self) -> Result<ShutdownScript, ()> {
                self.inner.get_shutdown_scriptpubkey()
        }
}

impl PhantomKeysManager {
        /// Constructs a [`PhantomKeysManager`] given a 32-byte seed and an additional `cross_node_seed`
        /// that is shared across all nodes that intend to participate in [phantom node payments]
        /// together.
        ///
        /// See [`KeysManager::new`] for more information on `seed`, `starting_time_secs`, and
        /// `starting_time_nanos`.
        ///
        /// `cross_node_seed` must be the same across all phantom payment-receiving nodes and also the
        /// same across restarts, or else inbound payments may fail.
        ///
        /// [phantom node payments]: PhantomKeysManager
        pub fn new(
                seed: &[u8; 32], starting_time_secs: u64, starting_time_nanos: u32,
                cross_node_seed: &[u8; 32],
        ) -> Self {
                let inner = KeysManager::new(seed, starting_time_secs, starting_time_nanos);
                let (inbound_key, phantom_key) = hkdf_extract_expand_twice(
                        b"LDK Inbound and Phantom Payment Key Expansion",
                        cross_node_seed,
                );
                let phantom_secret = SecretKey::from_slice(&phantom_key).unwrap();
                let phantom_node_id = PublicKey::from_secret_key(&inner.secp_ctx, &phantom_secret);
                Self {
                        inner,
                        inbound_payment_key: KeyMaterial(inbound_key),
                        phantom_secret,
                        phantom_node_id,
                }
        }

        /// See [`KeysManager::derive_channel_keys`] for documentation on this method.
        pub fn derive_channel_keys(
                &self, channel_value_satoshis: u64, params: &[u8; 32],
        ) -> InMemorySigner {
                self.inner.derive_channel_keys(channel_value_satoshis, params)
        }

        /// Gets the "node_id" secret key used to sign gossip announcements, decode onion data, etc.
        pub fn get_node_secret_key(&self) -> SecretKey {
                self.inner.get_node_secret_key()
        }

        /// Gets the "node_id" secret key of the phantom node used to sign invoices, decode the
        /// last-hop onion data, etc.
        pub fn get_phantom_node_secret_key(&self) -> SecretKey {
                self.phantom_secret
        }
}

/// An implementation of [`EntropySource`] using ChaCha20.
#[derive(Debug)]
pub struct RandomBytes {
        /// Seed from which all randomness produced is derived from.
        seed: [u8; 32],
        /// Tracks the number of times we've produced randomness to ensure we don't return the same
        /// bytes twice.
        index: AtomicCounter,
}

impl RandomBytes {
        /// Creates a new instance using the given seed.
        pub fn new(seed: [u8; 32]) -> Self {
                Self { seed, index: AtomicCounter::new() }
        }
}

impl EntropySource for RandomBytes {
        fn get_secure_random_bytes(&self) -> [u8; 32] {
                let index = self.index.get_increment();
                let mut nonce = [0u8; 16];
                nonce[..8].copy_from_slice(&index.to_be_bytes());
                ChaCha20::get_single_block(&self.seed, &nonce)
        }
}

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

#[cfg(ldk_bench)]
pub mod benches {
        use crate::sign::{EntropySource, KeysManager};
        use bitcoin::blockdata::constants::genesis_block;
        use bitcoin::Network;
        use std::sync::mpsc::TryRecvError;
        use std::sync::{mpsc, Arc};
        use std::thread;
        use std::time::Duration;

        use criterion::Criterion;

        pub fn bench_get_secure_random_bytes(bench: &mut Criterion) {
                let seed = [0u8; 32];
                let now = Duration::from_secs(genesis_block(Network::Testnet).header.time as u64);
                let keys_manager = Arc::new(KeysManager::new(&seed, now.as_secs(), now.subsec_micros()));

                let mut handles = Vec::new();
                let mut stops = Vec::new();
                for _ in 1..5 {
                        let keys_manager_clone = Arc::clone(&keys_manager);
                        let (stop_sender, stop_receiver) = mpsc::channel();
                        let handle = thread::spawn(move || loop {
                                keys_manager_clone.get_secure_random_bytes();
                                match stop_receiver.try_recv() {
                                        Ok(_) | Err(TryRecvError::Disconnected) => {
                                                println!("Terminating.");
                                                break;
                                        },
                                        Err(TryRecvError::Empty) => {},
                                }
                        });
                        handles.push(handle);
                        stops.push(stop_sender);
                }

                bench.bench_function("get_secure_random_bytes", |b| {
                        b.iter(|| keys_manager.get_secure_random_bytes())
                });

                for stop in stops {
                        let _ = stop.send(());
                }
                for handle in handles {
                        handle.join().unwrap();
                }
        }
}