Actual no_std support
[rust-lightning] / lightning / src / chain / keysinterface.rs
index 4a3a937a5c4586824ce0b875525b737ca39bdd67..7356dad8e40d64c353a80efa77b89e01c2fed7b8 100644 (file)
@@ -11,7 +11,7 @@
 //! spendable on-chain outputs which the user owns and is responsible for using just as any other
 //! on-chain output which is theirs.
 
-use bitcoin::blockdata::transaction::{Transaction, TxOut, SigHashType};
+use bitcoin::blockdata::transaction::{Transaction, TxOut, TxIn, SigHashType};
 use bitcoin::blockdata::script::{Script, Builder};
 use bitcoin::blockdata::opcodes;
 use bitcoin::network::constants::Network;
@@ -26,9 +26,10 @@ use bitcoin::hash_types::WPubkeyHash;
 
 use bitcoin::secp256k1::key::{SecretKey, PublicKey};
 use bitcoin::secp256k1::{Secp256k1, Signature, Signing};
+use bitcoin::secp256k1::recovery::RecoverableSignature;
 use bitcoin::secp256k1;
 
-use util::byte_utils;
+use util::{byte_utils, transaction_utils};
 use util::ser::{Writeable, Writer, Readable};
 
 use chain::transaction::OutPoint;
@@ -36,9 +37,78 @@ use ln::chan_utils;
 use ln::chan_utils::{HTLCOutputInCommitment, make_funding_redeemscript, ChannelPublicKeys, HolderCommitmentTransaction, ChannelTransactionParameters, CommitmentTransaction};
 use ln::msgs::UnsignedChannelAnnouncement;
 
-use std::sync::atomic::{AtomicUsize, Ordering};
-use std::io::Error;
-use ln::msgs::DecodeError;
+use prelude::*;
+use core::sync::atomic::{AtomicUsize, Ordering};
+use io::{self, Error};
+use ln::msgs::{DecodeError, MAX_VALUE_MSAT};
+
+/// Information about a spendable output to a P2WSH script. See
+/// SpendableOutputDescriptor::DelayedPaymentOutput for more details on how to spend this.
+#[derive(Clone, Debug, PartialEq)]
+pub struct DelayedPaymentOutputDescriptor {
+       /// The outpoint which is spendable
+       pub outpoint: OutPoint,
+       /// Per commitment point to derive delayed_payment_key by key holder
+       pub per_commitment_point: PublicKey,
+       /// The nSequence value which must be set in the spending input to satisfy the OP_CSV in
+       /// the witness_script.
+       pub to_self_delay: u16,
+       /// The output which is referenced by the given outpoint
+       pub output: TxOut,
+       /// The revocation point specific to the commitment transaction which was broadcast. Used to
+       /// derive the witnessScript for this output.
+       pub revocation_pubkey: PublicKey,
+       /// Arbitrary identification information returned by a call to
+       /// `Sign::channel_keys_id()`. This may be useful in re-deriving keys used in
+       /// the channel to spend the output.
+       pub channel_keys_id: [u8; 32],
+       /// The value of the channel which this output originated from, possibly indirectly.
+       pub channel_value_satoshis: u64,
+}
+impl DelayedPaymentOutputDescriptor {
+       /// The maximum length a well-formed witness spending one of these should have.
+       // Calculated as 1 byte length + 73 byte signature, 1 byte empty vec push, 1 byte length plus
+       // redeemscript push length.
+       pub const MAX_WITNESS_LENGTH: usize = 1 + 73 + 1 + chan_utils::REVOKEABLE_REDEEMSCRIPT_MAX_LENGTH + 1;
+}
+
+impl_writeable_tlv_based!(DelayedPaymentOutputDescriptor, {
+       (0, outpoint, required),
+       (2, per_commitment_point, required),
+       (4, to_self_delay, required),
+       (6, output, required),
+       (8, revocation_pubkey, required),
+       (10, channel_keys_id, required),
+       (12, channel_value_satoshis, required),
+});
+
+/// Information about a spendable output to our "payment key". See
+/// SpendableOutputDescriptor::StaticPaymentOutput for more details on how to spend this.
+#[derive(Clone, Debug, PartialEq)]
+pub struct StaticPaymentOutputDescriptor {
+       /// The outpoint which is spendable
+       pub outpoint: OutPoint,
+       /// The output which is referenced by the given outpoint
+       pub output: TxOut,
+       /// Arbitrary identification information returned by a call to
+       /// `Sign::channel_keys_id()`. This may be useful in re-deriving keys used in
+       /// the channel to spend the output.
+       pub channel_keys_id: [u8; 32],
+       /// The value of the channel which this transactions spends.
+       pub channel_value_satoshis: u64,
+}
+impl StaticPaymentOutputDescriptor {
+       /// The maximum length a well-formed witness spending one of these should have.
+       // Calculated as 1 byte legnth + 73 byte signature, 1 byte empty vec push, 1 byte length plus
+       // redeemscript push length.
+       pub const MAX_WITNESS_LENGTH: usize = 1 + 73 + 34;
+}
+impl_writeable_tlv_based!(StaticPaymentOutputDescriptor, {
+       (0, outpoint, required),
+       (2, output, required),
+       (4, channel_keys_id, required),
+       (6, channel_value_satoshis, required),
+});
 
 /// When on-chain outputs are created by rust-lightning (which our counterparty is not able to
 /// claim at any point in the future) an event is generated which you must track and be able to
@@ -47,9 +117,9 @@ use ln::msgs::DecodeError;
 /// that txid/index, and any keys or other information required to sign.
 #[derive(Clone, Debug, PartialEq)]
 pub enum SpendableOutputDescriptor {
-       /// An output to a script which was provided via KeysInterface, thus you should already know
-       /// how to spend it. No keys are provided as rust-lightning was never given any keys - only the
-       /// script_pubkey as it appears in the output.
+       /// An output to a script which was provided via KeysInterface directly, either from
+       /// `get_destination_script()` or `get_shutdown_pubkey()`, thus you should already know how to
+       /// spend it. No secret keys are provided as rust-lightning was never given any key.
        /// These may include outputs from a transaction punishing our counterparty or claiming an HTLC
        /// on-chain using the payment preimage or after it has timed out.
        StaticOutput {
@@ -72,115 +142,45 @@ pub enum SpendableOutputDescriptor {
        ///
        /// To derive the delayed_payment key which is used to sign for this input, you must pass the
        /// holder delayed_payment_base_key (ie the private key which corresponds to the pubkey in
-       /// ChannelKeys::pubkeys().delayed_payment_basepoint) and the provided per_commitment_point to
+       /// Sign::pubkeys().delayed_payment_basepoint) and the provided per_commitment_point to
        /// chan_utils::derive_private_key. The public key can be generated without the secret key
        /// using chan_utils::derive_public_key and only the delayed_payment_basepoint which appears in
-       /// ChannelKeys::pubkeys().
+       /// Sign::pubkeys().
        ///
        /// To derive the revocation_pubkey provided here (which is used in the witness
        /// script generation), you must pass the counterparty revocation_basepoint (which appears in the
-       /// call to ChannelKeys::ready_channel) and the provided per_commitment point
+       /// call to Sign::ready_channel) and the provided per_commitment point
        /// to chan_utils::derive_public_revocation_key.
        ///
        /// The witness script which is hashed and included in the output script_pubkey may be
        /// regenerated by passing the revocation_pubkey (derived as above), our delayed_payment pubkey
        /// (derived as above), and the to_self_delay contained here to
        /// chan_utils::get_revokeable_redeemscript.
-       //
-       // TODO: we need to expose utility methods in KeyManager to do all the relevant derivation.
-       DynamicOutputP2WSH {
-               /// The outpoint which is spendable
-               outpoint: OutPoint,
-               /// Per commitment point to derive delayed_payment_key by key holder
-               per_commitment_point: PublicKey,
-               /// The nSequence value which must be set in the spending input to satisfy the OP_CSV in
-               /// the witness_script.
-               to_self_delay: u16,
-               /// The output which is referenced by the given outpoint
-               output: TxOut,
-               /// The channel keys state used to proceed to derivation of signing key. Must
-               /// be pass to KeysInterface::derive_channel_keys.
-               key_derivation_params: (u64, u64),
-               /// The revocation_pubkey used to derive witnessScript
-               revocation_pubkey: PublicKey
-       },
+       DelayedPaymentOutput(DelayedPaymentOutputDescriptor),
        /// An output to a P2WPKH, spendable exclusively by our payment key (ie the private key which
-       /// corresponds to the public key in ChannelKeys::pubkeys().payment_point).
+       /// corresponds to the public key in Sign::pubkeys().payment_point).
        /// The witness in the spending input, is, thus, simply:
        /// <BIP 143 signature> <payment key>
        ///
        /// These are generally the result of our counterparty having broadcast the current state,
        /// allowing us to claim the non-HTLC-encumbered outputs immediately.
-       StaticOutputCounterpartyPayment {
-               /// The outpoint which is spendable
-               outpoint: OutPoint,
-               /// The output which is reference by the given outpoint
-               output: TxOut,
-               /// The channel keys state used to proceed to derivation of signing key. Must
-               /// be pass to KeysInterface::derive_channel_keys.
-               key_derivation_params: (u64, u64),
-       }
+       StaticPaymentOutput(StaticPaymentOutputDescriptor),
 }
 
-impl Writeable for SpendableOutputDescriptor {
-       fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
-               match self {
-                       &SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output } => {
-                               0u8.write(writer)?;
-                               outpoint.write(writer)?;
-                               output.write(writer)?;
-                       },
-                       &SpendableOutputDescriptor::DynamicOutputP2WSH { ref outpoint, ref per_commitment_point, ref to_self_delay, ref output, ref key_derivation_params, ref revocation_pubkey } => {
-                               1u8.write(writer)?;
-                               outpoint.write(writer)?;
-                               per_commitment_point.write(writer)?;
-                               to_self_delay.write(writer)?;
-                               output.write(writer)?;
-                               key_derivation_params.0.write(writer)?;
-                               key_derivation_params.1.write(writer)?;
-                               revocation_pubkey.write(writer)?;
-                       },
-                       &SpendableOutputDescriptor::StaticOutputCounterpartyPayment { ref outpoint, ref output, ref key_derivation_params } => {
-                               2u8.write(writer)?;
-                               outpoint.write(writer)?;
-                               output.write(writer)?;
-                               key_derivation_params.0.write(writer)?;
-                               key_derivation_params.1.write(writer)?;
-                       },
-               }
-               Ok(())
-       }
-}
-
-impl Readable for SpendableOutputDescriptor {
-       fn read<R: ::std::io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
-               match Readable::read(reader)? {
-                       0u8 => Ok(SpendableOutputDescriptor::StaticOutput {
-                               outpoint: Readable::read(reader)?,
-                               output: Readable::read(reader)?,
-                       }),
-                       1u8 => Ok(SpendableOutputDescriptor::DynamicOutputP2WSH {
-                               outpoint: Readable::read(reader)?,
-                               per_commitment_point: Readable::read(reader)?,
-                               to_self_delay: Readable::read(reader)?,
-                               output: Readable::read(reader)?,
-                               key_derivation_params: (Readable::read(reader)?, Readable::read(reader)?),
-                               revocation_pubkey: Readable::read(reader)?,
-                       }),
-                       2u8 => Ok(SpendableOutputDescriptor::StaticOutputCounterpartyPayment {
-                               outpoint: Readable::read(reader)?,
-                               output: Readable::read(reader)?,
-                               key_derivation_params: (Readable::read(reader)?, Readable::read(reader)?),
-                       }),
-                       _ => Err(DecodeError::InvalidValue),
-               }
-       }
-}
+impl_writeable_tlv_based_enum!(SpendableOutputDescriptor,
+       (0, StaticOutput) => {
+               (0, outpoint, required),
+               (2, output, required),
+       },
+;
+       (1, DelayedPaymentOutput),
+       (2, StaticPaymentOutput),
+);
 
-/// Set of lightning keys needed to operate a channel as described in BOLT 3.
+/// A trait to sign lightning channel transactions as described in BOLT 3.
 ///
 /// Signing services could be implemented on a hardware wallet. In this case,
-/// the current ChannelKeys would be a front-end on top of a communication
+/// the current Sign would be a front-end on top of a communication
 /// channel connected to your secure device and lightning key material wouldn't
 /// reside on a hot server. Nevertheless, a this deployment would still need
 /// to trust the ChannelManager to avoid loss of funds as this latest component
@@ -194,21 +194,13 @@ impl Readable for SpendableOutputDescriptor {
 /// In any case, ChannelMonitor or fallback watchtowers are always going to be trusted
 /// to act, as liveness and breach reply correctness are always going to be hard requirements
 /// of LN security model, orthogonal of key management issues.
-///
-/// If you're implementing a custom signer, you almost certainly want to implement
-/// Readable/Writable to serialize out a unique reference to this set of keys so
-/// that you can serialize the full ChannelManager object.
-///
-// (TODO: We shouldn't require that, and should have an API to get them at deser time, due mostly
-// to the possibility of reentrancy issues by calling the user's code during our deserialization
-// routine).
-// TODO: We should remove Clone by instead requesting a new ChannelKeys copy when we create
+// TODO: We should remove Clone by instead requesting a new Sign copy when we create
 // ChannelMonitors instead of expecting to clone the one out of the Channel into the monitors.
-pub trait ChannelKeys : Send+Clone + Writeable {
+pub trait BaseSign {
        /// Gets the per-commitment point for a specific commitment number
        ///
        /// Note that the commitment number starts at (1 << 48) - 1 and counts backwards.
-       fn get_per_commitment_point<T: secp256k1::Signing + secp256k1::Verification>(&self, idx: u64, secp_ctx: &Secp256k1<T>) -> PublicKey;
+       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
@@ -217,55 +209,67 @@ pub trait ChannelKeys : Send+Clone + Writeable {
        /// 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
+       // TODO: return a Result so we can signal a validation error
        fn release_commitment_secret(&self, idx: u64) -> [u8; 32];
        /// Gets the holder's channel public keys and basepoints
        fn pubkeys(&self) -> &ChannelPublicKeys;
-       /// Gets arbitrary identifiers describing the set of keys which are provided back to you in
-       /// some SpendableOutputDescriptor types. These should be sufficient to identify this
-       /// ChannelKeys object uniquely and lookup or re-derive its keys.
-       fn key_derivation_params(&self) -> (u64, u64);
+       /// Gets an arbitrary identifier describing the set of keys which are provided back to you in
+       /// some SpendableOutputDescriptor types. This should be sufficient to identify this
+       /// Sign object uniquely and lookup or re-derive its keys.
+       fn channel_keys_id(&self) -> [u8; 32];
 
        /// Create a signature for a counterparty's commitment transaction and associated HTLC transactions.
        ///
        /// Note that if signing fails or is rejected, the channel will be force-closed.
        //
        // TODO: Document the things someone using this interface should enforce before signing.
-       fn sign_counterparty_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &CommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()>;
-
-       /// Create a signature for a holder's commitment transaction. This will only ever be called with
-       /// the same commitment_tx (or a copy thereof), though there are currently no guarantees
-       /// that it will not be called multiple times.
+       fn sign_counterparty_commitment(&self, commitment_tx: &CommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<(Signature, Vec<Signature>), ()>;
+
+       /// Create a signatures for a holder's commitment transaction and its claiming HTLC transactions.
+       /// This will only ever be called with a non-revoked commitment_tx.  This will be called with the
+       /// latest commitment_tx when we initiate a force-close.
+       /// This will be called with the previous latest, just to get claiming HTLC signatures, if we are
+       /// reacting to a ChannelMonitor replica that decided to broadcast before it had been updated to
+       /// the latest.
+       /// This may be called multiple times for the same transaction.
+       ///
        /// An external signer implementation should check that the commitment has not been revoked.
+       ///
+       /// May return Err if key derivation fails.  Callers, such as ChannelMonitor, will panic in such a case.
        //
        // TODO: Document the things someone using this interface should enforce before signing.
-       fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
+       // TODO: Key derivation failure should panic rather than Err
+       fn sign_holder_commitment_and_htlcs(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<(Signature, Vec<Signature>), ()>;
 
        /// Same as sign_holder_commitment, but exists only for tests to get access to holder commitment
        /// transactions which will be broadcasted later, after the channel has moved on to a newer
        /// state. Thus, needs its own method as sign_holder_commitment may enforce that we only ever
        /// get called once.
        #[cfg(any(test,feature = "unsafe_revoked_tx_signing"))]
-       fn unsafe_sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
+       fn unsafe_sign_holder_commitment_and_htlcs(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<(Signature, Vec<Signature>), ()>;
 
-       /// Create a signature for each HTLC transaction spending a holder's commitment transaction.
+       /// Create a signature for the given input in a transaction spending an HTLC transaction output
+       /// or a commitment transaction `to_local` output when our counterparty broadcasts an old state.
        ///
-       /// Unlike sign_holder_commitment, this may be called multiple times with *different*
-       /// commitment_tx values. While this will never be called with a revoked
-       /// commitment_tx, it is possible that it is called with the second-latest
-       /// commitment_tx (only if we haven't yet revoked it) if some watchtower/secondary
-       /// ChannelMonitor decided to broadcast before it had been updated to the latest.
+       /// A justice transaction may claim multiple outputs at the same time if timelocks are
+       /// similar, but only a signature for the input at index `input` should be signed for here.
+       /// It may be called multiple times for same output(s) if a fee-bump is needed with regards
+       /// to an upcoming timelock expiration.
+       ///
+       /// Amount is value of the output spent by this input, committed to in the BIP 143 signature.
        ///
-       /// Either an Err should be returned, or a Vec with one entry for each HTLC which exists in
-       /// commitment_tx.
-       fn sign_holder_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Vec<Signature>, ()>;
+       /// per_commitment_key is revocation secret which was provided by our counterparty when they
+       /// revoked the state which they eventually broadcast. It's not a _holder_ secret key and does
+       /// not allow the spending of any funds by itself (you need our holder revocation_secret to do
+       /// so).
+       fn sign_justice_revoked_output(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()>;
 
-       /// Create a signature for the given input in a transaction spending an HTLC or commitment
-       /// transaction output when our counterparty broadcasts an old state.
+       /// Create a signature for the given input in a transaction spending a commitment transaction
+       /// HTLC output when our counterparty broadcasts an old state.
        ///
-       /// A justice transaction may claim multiples outputs at the same time if timelocks are
+       /// A justice transaction may claim multiple outputs at the same time if timelocks are
        /// similar, but only a signature for the input at index `input` should be signed for here.
-       /// It may be called multiples time for same output(s) if a fee-bump is needed with regards
+       /// It may be called multiple times for same output(s) if a fee-bump is needed with regards
        /// to an upcoming timelock expiration.
        ///
        /// Amount is value of the output spent by this input, committed to in the BIP 143 signature.
@@ -275,10 +279,9 @@ pub trait ChannelKeys : Send+Clone + Writeable {
        /// not allow the spending of any funds by itself (you need our holder revocation_secret to do
        /// so).
        ///
-       /// htlc holds HTLC elements (hash, timelock) if the output being spent is a HTLC output, thus
-       /// changing the format of the witness script (which is committed to in the BIP 143
-       /// signatures).
-       fn sign_justice_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &Option<HTLCOutputInCommitment>, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
+       /// htlc holds HTLC elements (hash, timelock), thus changing the format of the witness script
+       /// (which is committed to in the BIP 143 signatures).
+       fn sign_justice_revoked_htlc(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()>;
 
        /// Create a signature for a claiming transaction for a HTLC output on a counterparty's commitment
        /// transaction, either offered or received.
@@ -297,13 +300,13 @@ pub trait ChannelKeys : Send+Clone + Writeable {
        /// detected onchain. It has been generated by our counterparty and is used to derive
        /// channel state keys, which are then included in the witness script and committed to in the
        /// BIP 143 signature.
-       fn sign_counterparty_htlc_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
+       fn sign_counterparty_htlc_transaction(&self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()>;
 
        /// Create a signature for a (proposed) closing transaction.
        ///
        /// Note that, due to rounding, there may be one "missing" satoshi, and either party may have
        /// chosen to forgo their output as dust.
-       fn sign_closing_transaction<T: secp256k1::Signing>(&self, closing_tx: &Transaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
+       fn sign_closing_transaction(&self, closing_tx: &Transaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()>;
 
        /// Signs a channel announcement message with our funding key, proving it comes from one
        /// of the channel participants.
@@ -311,7 +314,7 @@ pub trait ChannelKeys : Send+Clone + Writeable {
        /// Note that if this fails or is rejected, the channel will not be publicly announced and
        /// our counterparty may (though likely will not) close the channel on us for violating the
        /// protocol.
-       fn sign_channel_announcement<T: secp256k1::Signing>(&self, msg: &UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()>;
+       fn sign_channel_announcement(&self, msg: &UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()>;
 
        /// Set the counterparty static channel data, including basepoints,
        /// counterparty_selected/holder_selected_contest_delay and funding outpoint.
@@ -326,40 +329,67 @@ pub trait ChannelKeys : Send+Clone + Writeable {
        fn ready_channel(&mut self, channel_parameters: &ChannelTransactionParameters);
 }
 
+/// A cloneable signer.
+///
+/// Although we require signers to be cloneable, it may be useful for developers to be able to use
+/// signers in an un-sized way, for example as `dyn BaseSign`. Therefore we separate the Clone trait,
+/// which implies Sized, into this derived trait.
+pub trait Sign: BaseSign + Writeable + Clone {
+}
+
 /// A trait to describe an object which can get user secrets and key material.
-pub trait KeysInterface: Send + Sync {
-       /// A type which implements ChannelKeys which will be returned by get_channel_keys.
-       type ChanKeySigner : ChannelKeys;
+pub trait KeysInterface {
+       /// A type which implements Sign which will be returned by get_channel_signer.
+       type Signer : Sign;
 
-       /// Get node secret key (aka node_id or network_key)
+       /// Get node secret key (aka node_id or network_key).
+       ///
+       /// This method must return the same value each time it is called.
        fn get_node_secret(&self) -> SecretKey;
-       /// Get destination redeemScript to encumber static protocol exit points.
+       /// Get a script pubkey which we send funds to when claiming on-chain contestable outputs.
+       ///
+       /// This method should return a different value each time it is called, to avoid linking
+       /// on-chain funds across channels as controlled to the same user.
        fn get_destination_script(&self) -> Script;
-       /// Get shutdown_pubkey to use as PublicKey at channel closure
+       /// Get a public key which we will send funds to (in the form of a P2WPKH output) when closing
+       /// a channel.
+       ///
+       /// This method should return a different value each time it is called, to avoid linking
+       /// on-chain funds across channels as controlled to the same user.
        fn get_shutdown_pubkey(&self) -> PublicKey;
-       /// Get a new set of ChannelKeys for per-channel secrets. These MUST be unique even if you
+       /// Get a new set of Sign for per-channel secrets. These MUST be unique even if you
        /// restarted with some stale data!
-       fn get_channel_keys(&self, inbound: bool, channel_value_satoshis: u64) -> Self::ChanKeySigner;
+       ///
+       /// This method must return a different value each time it is called.
+       fn get_channel_signer(&self, inbound: bool, channel_value_satoshis: u64) -> Self::Signer;
        /// Gets a unique, cryptographically-secure, random 32 byte value. This is used for encrypting
        /// onion packets and for temporary channel IDs. There is no requirement that these be
        /// persisted anywhere, though they must be unique across restarts.
+       ///
+       /// This method must return a different value each time it is called.
        fn get_secure_random_bytes(&self) -> [u8; 32];
 
-       /// Reads a `ChanKeySigner` for this `KeysInterface` from the given input stream.
+       /// Reads a `Signer` for this `KeysInterface` from the given input stream.
        /// This is only called during deserialization of other objects which contain
-       /// `ChannelKeys`-implementing objects (ie `ChannelMonitor`s and `ChannelManager`s).
-       /// The bytes are exactly those which `<Self::ChanKeySigner as Writeable>::write()` writes, and
+       /// `Sign`-implementing objects (ie `ChannelMonitor`s and `ChannelManager`s).
+       /// The bytes are exactly those which `<Self::Signer as Writeable>::write()` writes, and
        /// contain no versioning scheme. You may wish to include your own version prefix and ensure
        /// you've read all of the provided bytes to ensure no corruption occurred.
-       fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::ChanKeySigner, DecodeError>;
+       fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::Signer, DecodeError>;
+
+       /// Sign an invoice's preimage (note that this is the preimage of the invoice, not the HTLC's
+       /// preimage). By parameterizing by the preimage instead of the hash, we allow implementors of
+       /// this trait to parse the invoice and make sure they're signing what they expect, rather than
+       /// blindly signing the hash.
+       fn sign_invoice(&self, invoice_preimage: Vec<u8>) -> Result<RecoverableSignature, ()>;
 }
 
 #[derive(Clone)]
-/// A simple implementation of ChannelKeys that just keeps the private keys in memory.
+/// A simple implementation of Sign that just keeps the private keys in memory.
 ///
 /// This implementation performs no policy checks and is insufficient by itself as
 /// a secure external signer.
-pub struct InMemoryChannelKeys {
+pub struct InMemorySigner {
        /// Private key of anchor tx
        pub funding_key: SecretKey,
        /// Holder secret key for blinded revocation pubkey
@@ -379,11 +409,11 @@ pub struct InMemoryChannelKeys {
        /// The total value of this channel
        channel_value_satoshis: u64,
        /// Key derivation parameters
-       key_derivation_params: (u64, u64),
+       channel_keys_id: [u8; 32],
 }
 
-impl InMemoryChannelKeys {
-       /// Create a new InMemoryChannelKeys
+impl InMemorySigner {
+       /// Create a new InMemorySigner
        pub fn new<C: Signing>(
                secp_ctx: &Secp256k1<C>,
                funding_key: SecretKey,
@@ -393,12 +423,12 @@ impl InMemoryChannelKeys {
                htlc_base_key: SecretKey,
                commitment_seed: [u8; 32],
                channel_value_satoshis: u64,
-               key_derivation_params: (u64, u64)) -> InMemoryChannelKeys {
+               channel_keys_id: [u8; 32]) -> InMemorySigner {
                let holder_channel_pubkeys =
-                       InMemoryChannelKeys::make_holder_keys(secp_ctx, &funding_key, &revocation_base_key,
+                       InMemorySigner::make_holder_keys(secp_ctx, &funding_key, &revocation_base_key,
                                                             &payment_key, &delayed_payment_base_key,
                                                             &htlc_base_key);
-               InMemoryChannelKeys {
+               InMemorySigner {
                        funding_key,
                        revocation_base_key,
                        payment_key,
@@ -408,7 +438,7 @@ impl InMemoryChannelKeys {
                        channel_value_satoshis,
                        holder_channel_pubkeys,
                        channel_parameters: None,
-                       key_derivation_params,
+                       channel_keys_id,
                }
        }
 
@@ -459,10 +489,67 @@ impl InMemoryChannelKeys {
        pub fn get_channel_parameters(&self) -> &ChannelTransactionParameters {
                self.channel_parameters.as_ref().unwrap()
        }
+
+       /// Sign the single input of spend_tx at index `input_idx` which spends the output
+       /// described by descriptor, returning the witness stack for the input.
+       ///
+       /// Returns an Err if the input at input_idx does not exist, has a non-empty script_sig,
+       /// or is not spending the outpoint described by `descriptor.outpoint`.
+       pub fn sign_counterparty_payment_input<C: Signing>(&self, spend_tx: &Transaction, input_idx: usize, descriptor: &StaticPaymentOutputDescriptor, secp_ctx: &Secp256k1<C>) -> Result<Vec<Vec<u8>>, ()> {
+               // TODO: We really should be taking the SigHashCache as a parameter here instead of
+               // spend_tx, but ideally the SigHashCache would expose the transaction's inputs read-only
+               // so that we can check them. This requires upstream rust-bitcoin changes (as well as
+               // bindings updates to support SigHashCache objects).
+               if spend_tx.input.len() <= input_idx { return Err(()); }
+               if !spend_tx.input[input_idx].script_sig.is_empty() { return Err(()); }
+               if spend_tx.input[input_idx].previous_output != descriptor.outpoint.into_bitcoin_outpoint() { return Err(()); }
+
+               let remotepubkey = self.pubkeys().payment_point;
+               let witness_script = bitcoin::Address::p2pkh(&::bitcoin::PublicKey{compressed: true, key: remotepubkey}, Network::Testnet).script_pubkey();
+               let sighash = hash_to_message!(&bip143::SigHashCache::new(spend_tx).signature_hash(input_idx, &witness_script, descriptor.output.value, SigHashType::All)[..]);
+               let remotesig = secp_ctx.sign(&sighash, &self.payment_key);
+
+               let mut witness = Vec::with_capacity(2);
+               witness.push(remotesig.serialize_der().to_vec());
+               witness[0].push(SigHashType::All as u8);
+               witness.push(remotepubkey.serialize().to_vec());
+               Ok(witness)
+       }
+
+       /// Sign the single input of spend_tx at index `input_idx` which spends the output
+       /// described by descriptor, returning the witness stack for the input.
+       ///
+       /// Returns an Err if the input at input_idx does not exist, has a non-empty script_sig,
+       /// is not spending the outpoint described by `descriptor.outpoint`, or does not have a
+       /// sequence set to `descriptor.to_self_delay`.
+       pub fn sign_dynamic_p2wsh_input<C: Signing>(&self, spend_tx: &Transaction, input_idx: usize, descriptor: &DelayedPaymentOutputDescriptor, secp_ctx: &Secp256k1<C>) -> Result<Vec<Vec<u8>>, ()> {
+               // TODO: We really should be taking the SigHashCache as a parameter here instead of
+               // spend_tx, but ideally the SigHashCache would expose the transaction's inputs read-only
+               // so that we can check them. This requires upstream rust-bitcoin changes (as well as
+               // bindings updates to support SigHashCache objects).
+               if spend_tx.input.len() <= input_idx { return Err(()); }
+               if !spend_tx.input[input_idx].script_sig.is_empty() { return Err(()); }
+               if spend_tx.input[input_idx].previous_output != descriptor.outpoint.into_bitcoin_outpoint() { return Err(()); }
+               if spend_tx.input[input_idx].sequence != descriptor.to_self_delay as u32 { return Err(()); }
+
+               let delayed_payment_key = chan_utils::derive_private_key(&secp_ctx, &descriptor.per_commitment_point, &self.delayed_payment_base_key)
+                       .expect("We constructed the payment_base_key, so we can only fail here if the RNG is busted.");
+               let delayed_payment_pubkey = PublicKey::from_secret_key(&secp_ctx, &delayed_payment_key);
+               let witness_script = chan_utils::get_revokeable_redeemscript(&descriptor.revocation_pubkey, descriptor.to_self_delay, &delayed_payment_pubkey);
+               let sighash = hash_to_message!(&bip143::SigHashCache::new(spend_tx).signature_hash(input_idx, &witness_script, descriptor.output.value, SigHashType::All)[..]);
+               let local_delayedsig = secp_ctx.sign(&sighash, &delayed_payment_key);
+
+               let mut witness = Vec::with_capacity(3);
+               witness.push(local_delayedsig.serialize_der().to_vec());
+               witness[0].push(SigHashType::All as u8);
+               witness.push(vec!()); //MINIMALIF
+               witness.push(witness_script.clone().into_bytes());
+               Ok(witness)
+       }
 }
 
-impl ChannelKeys for InMemoryChannelKeys {
-       fn get_per_commitment_point<T: secp256k1::Signing + secp256k1::Verification>(&self, idx: u64, secp_ctx: &Secp256k1<T>) -> PublicKey {
+impl BaseSign for InMemorySigner {
+       fn get_per_commitment_point(&self, idx: u64, secp_ctx: &Secp256k1<secp256k1::All>) -> PublicKey {
                let commitment_secret = SecretKey::from_slice(&chan_utils::build_commitment_secret(&self.commitment_seed, idx)).unwrap();
                PublicKey::from_secret_key(secp_ctx, &commitment_secret)
        }
@@ -472,9 +559,9 @@ impl ChannelKeys for InMemoryChannelKeys {
        }
 
        fn pubkeys(&self) -> &ChannelPublicKeys { &self.holder_channel_pubkeys }
-       fn key_derivation_params(&self) -> (u64, u64) { self.key_derivation_params }
+       fn channel_keys_id(&self) -> [u8; 32] { self.channel_keys_id }
 
-       fn sign_counterparty_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &CommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Vec<Signature>), ()> {
+       fn sign_counterparty_commitment(&self, commitment_tx: &CommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<(Signature, Vec<Signature>), ()> {
                let trusted_tx = commitment_tx.trust();
                let keys = trusted_tx.keys();
 
@@ -490,69 +577,62 @@ impl ChannelKeys for InMemoryChannelKeys {
                        let htlc_tx = chan_utils::build_htlc_transaction(&commitment_txid, commitment_tx.feerate_per_kw(), self.holder_selected_contest_delay(), htlc, &keys.broadcaster_delayed_payment_key, &keys.revocation_key);
                        let htlc_redeemscript = chan_utils::get_htlc_redeemscript(&htlc, &keys);
                        let htlc_sighash = hash_to_message!(&bip143::SigHashCache::new(&htlc_tx).signature_hash(0, &htlc_redeemscript, htlc.amount_msat / 1000, SigHashType::All)[..]);
-                       let holder_htlc_key = match chan_utils::derive_private_key(&secp_ctx, &keys.per_commitment_point, &self.htlc_base_key) {
-                               Ok(s) => s,
-                               Err(_) => return Err(()),
-                       };
+                       let holder_htlc_key = chan_utils::derive_private_key(&secp_ctx, &keys.per_commitment_point, &self.htlc_base_key).map_err(|_| ())?;
                        htlc_sigs.push(secp_ctx.sign(&htlc_sighash, &holder_htlc_key));
                }
 
                Ok((commitment_sig, htlc_sigs))
        }
 
-       fn sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
+       fn sign_holder_commitment_and_htlcs(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<(Signature, Vec<Signature>), ()> {
                let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
                let funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &self.counterparty_pubkeys().funding_pubkey);
-               let sig = commitment_tx.trust().built_transaction().sign(&self.funding_key, &funding_redeemscript, self.channel_value_satoshis, secp_ctx);
-               Ok(sig)
+               let trusted_tx = commitment_tx.trust();
+               let sig = trusted_tx.built_transaction().sign(&self.funding_key, &funding_redeemscript, self.channel_value_satoshis, secp_ctx);
+               let channel_parameters = self.get_channel_parameters();
+               let htlc_sigs = trusted_tx.get_htlc_sigs(&self.htlc_base_key, &channel_parameters.as_holder_broadcastable(), secp_ctx)?;
+               Ok((sig, htlc_sigs))
        }
 
        #[cfg(any(test,feature = "unsafe_revoked_tx_signing"))]
-       fn unsafe_sign_holder_commitment<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
+       fn unsafe_sign_holder_commitment_and_htlcs(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<(Signature, Vec<Signature>), ()> {
                let funding_pubkey = PublicKey::from_secret_key(secp_ctx, &self.funding_key);
-               let channel_funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &self.counterparty_pubkeys().funding_pubkey);
-               Ok(commitment_tx.trust().built_transaction().sign(&self.funding_key, &channel_funding_redeemscript, self.channel_value_satoshis, secp_ctx))
-       }
-
-       fn sign_holder_commitment_htlc_transactions<T: secp256k1::Signing + secp256k1::Verification>(&self, commitment_tx: &HolderCommitmentTransaction, secp_ctx: &Secp256k1<T>) -> Result<Vec<Signature>, ()> {
-               let channel_parameters = self.get_channel_parameters();
+               let funding_redeemscript = make_funding_redeemscript(&funding_pubkey, &self.counterparty_pubkeys().funding_pubkey);
                let trusted_tx = commitment_tx.trust();
-               trusted_tx.get_htlc_sigs(&self.htlc_base_key, &channel_parameters.as_holder_broadcastable(), secp_ctx)
+               let sig = trusted_tx.built_transaction().sign(&self.funding_key, &funding_redeemscript, self.channel_value_satoshis, secp_ctx);
+               let channel_parameters = self.get_channel_parameters();
+               let htlc_sigs = trusted_tx.get_htlc_sigs(&self.htlc_base_key, &channel_parameters.as_holder_broadcastable(), secp_ctx)?;
+               Ok((sig, htlc_sigs))
        }
 
-       fn sign_justice_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &Option<HTLCOutputInCommitment>, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
-               let revocation_key = match chan_utils::derive_private_revocation_key(&secp_ctx, &per_commitment_key, &self.revocation_base_key) {
-                       Ok(revocation_key) => revocation_key,
-                       Err(_) => return Err(())
-               };
+       fn sign_justice_revoked_output(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
+               let revocation_key = chan_utils::derive_private_revocation_key(&secp_ctx, &per_commitment_key, &self.revocation_base_key).map_err(|_| ())?;
                let per_commitment_point = PublicKey::from_secret_key(secp_ctx, &per_commitment_key);
-               let revocation_pubkey = match chan_utils::derive_public_revocation_key(&secp_ctx, &per_commitment_point, &self.pubkeys().revocation_basepoint) {
-                       Ok(revocation_pubkey) => revocation_pubkey,
-                       Err(_) => return Err(())
+               let revocation_pubkey = chan_utils::derive_public_revocation_key(&secp_ctx, &per_commitment_point, &self.pubkeys().revocation_basepoint).map_err(|_| ())?;
+               let witness_script = {
+                       let counterparty_delayedpubkey = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().delayed_payment_basepoint).map_err(|_| ())?;
+                       chan_utils::get_revokeable_redeemscript(&revocation_pubkey, self.holder_selected_contest_delay(), &counterparty_delayedpubkey)
                };
-               let witness_script = if let &Some(ref htlc) = htlc {
-                       let counterparty_htlcpubkey = match chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().htlc_basepoint) {
-                               Ok(counterparty_htlcpubkey) => counterparty_htlcpubkey,
-                               Err(_) => return Err(())
-                       };
-                       let holder_htlcpubkey = match chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.pubkeys().htlc_basepoint) {
-                               Ok(holder_htlcpubkey) => holder_htlcpubkey,
-                               Err(_) => return Err(())
-                       };
+               let mut sighash_parts = bip143::SigHashCache::new(justice_tx);
+               let sighash = hash_to_message!(&sighash_parts.signature_hash(input, &witness_script, amount, SigHashType::All)[..]);
+               return Ok(secp_ctx.sign(&sighash, &revocation_key))
+       }
+
+       fn sign_justice_revoked_htlc(&self, justice_tx: &Transaction, input: usize, amount: u64, per_commitment_key: &SecretKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
+               let revocation_key = chan_utils::derive_private_revocation_key(&secp_ctx, &per_commitment_key, &self.revocation_base_key).map_err(|_| ())?;
+               let per_commitment_point = PublicKey::from_secret_key(secp_ctx, &per_commitment_key);
+               let revocation_pubkey = chan_utils::derive_public_revocation_key(&secp_ctx, &per_commitment_point, &self.pubkeys().revocation_basepoint).map_err(|_| ())?;
+               let witness_script = {
+                       let counterparty_htlcpubkey = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().htlc_basepoint).map_err(|_| ())?;
+                       let holder_htlcpubkey = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.pubkeys().htlc_basepoint).map_err(|_| ())?;
                        chan_utils::get_htlc_redeemscript_with_explicit_keys(&htlc, &counterparty_htlcpubkey, &holder_htlcpubkey, &revocation_pubkey)
-               } else {
-                       let counterparty_delayedpubkey = match chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().delayed_payment_basepoint) {
-                               Ok(counterparty_delayedpubkey) => counterparty_delayedpubkey,
-                               Err(_) => return Err(())
-                       };
-                       chan_utils::get_revokeable_redeemscript(&revocation_pubkey, self.holder_selected_contest_delay(), &counterparty_delayedpubkey)
                };
                let mut sighash_parts = bip143::SigHashCache::new(justice_tx);
                let sighash = hash_to_message!(&sighash_parts.signature_hash(input, &witness_script, amount, SigHashType::All)[..]);
                return Ok(secp_ctx.sign(&sighash, &revocation_key))
        }
 
-       fn sign_counterparty_htlc_transaction<T: secp256k1::Signing + secp256k1::Verification>(&self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
+       fn sign_counterparty_htlc_transaction(&self, htlc_tx: &Transaction, input: usize, amount: u64, per_commitment_point: &PublicKey, htlc: &HTLCOutputInCommitment, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
                if let Ok(htlc_key) = chan_utils::derive_private_key(&secp_ctx, &per_commitment_point, &self.htlc_base_key) {
                        let witness_script = if let Ok(revocation_pubkey) = chan_utils::derive_public_revocation_key(&secp_ctx, &per_commitment_point, &self.pubkeys().revocation_basepoint) {
                                if let Ok(counterparty_htlcpubkey) = chan_utils::derive_public_key(&secp_ctx, &per_commitment_point, &self.counterparty_pubkeys().htlc_basepoint) {
@@ -568,7 +648,7 @@ impl ChannelKeys for InMemoryChannelKeys {
                Err(())
        }
 
-       fn sign_closing_transaction<T: secp256k1::Signing>(&self, closing_tx: &Transaction, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
+       fn sign_closing_transaction(&self, closing_tx: &Transaction, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
                if closing_tx.input.len() != 1 { return Err(()); }
                if closing_tx.input[0].witness.len() != 0 { return Err(()); }
                if closing_tx.output.len() > 2 { return Err(()); }
@@ -581,7 +661,7 @@ impl ChannelKeys for InMemoryChannelKeys {
                Ok(secp_ctx.sign(&sighash, &self.funding_key))
        }
 
-       fn sign_channel_announcement<T: secp256k1::Signing>(&self, msg: &UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<T>) -> Result<Signature, ()> {
+       fn sign_channel_announcement(&self, msg: &UnsignedChannelAnnouncement, secp_ctx: &Secp256k1<secp256k1::All>) -> Result<Signature, ()> {
                let msghash = hash_to_message!(&Sha256dHash::hash(&msg.encode()[..])[..]);
                Ok(secp_ctx.sign(&msghash, &self.funding_key))
        }
@@ -593,8 +673,15 @@ impl ChannelKeys for InMemoryChannelKeys {
        }
 }
 
-impl Writeable for InMemoryChannelKeys {
+const SERIALIZATION_VERSION: u8 = 1;
+const MIN_SERIALIZATION_VERSION: u8 = 1;
+
+impl Sign for InMemorySigner {}
+
+impl Writeable for InMemorySigner {
        fn write<W: Writer>(&self, writer: &mut W) -> Result<(), Error> {
+               write_ver_prefix!(writer, SERIALIZATION_VERSION, MIN_SERIALIZATION_VERSION);
+
                self.funding_key.write(writer)?;
                self.revocation_base_key.write(writer)?;
                self.payment_key.write(writer)?;
@@ -603,15 +690,18 @@ impl Writeable for InMemoryChannelKeys {
                self.commitment_seed.write(writer)?;
                self.channel_parameters.write(writer)?;
                self.channel_value_satoshis.write(writer)?;
-               self.key_derivation_params.0.write(writer)?;
-               self.key_derivation_params.1.write(writer)?;
+               self.channel_keys_id.write(writer)?;
+
+               write_tlv_fields!(writer, {});
 
                Ok(())
        }
 }
 
-impl Readable for InMemoryChannelKeys {
-       fn read<R: ::std::io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
+impl Readable for InMemorySigner {
+       fn read<R: io::Read>(reader: &mut R) -> Result<Self, DecodeError> {
+               let _ver = read_ver_prefix!(reader, SERIALIZATION_VERSION);
+
                let funding_key = Readable::read(reader)?;
                let revocation_base_key = Readable::read(reader)?;
                let payment_key = Readable::read(reader)?;
@@ -622,13 +712,14 @@ impl Readable for InMemoryChannelKeys {
                let channel_value_satoshis = Readable::read(reader)?;
                let secp_ctx = Secp256k1::signing_only();
                let holder_channel_pubkeys =
-                       InMemoryChannelKeys::make_holder_keys(&secp_ctx, &funding_key, &revocation_base_key,
+                       InMemorySigner::make_holder_keys(&secp_ctx, &funding_key, &revocation_base_key,
                                                             &payment_key, &delayed_payment_base_key,
                                                             &htlc_base_key);
-               let params_1 = Readable::read(reader)?;
-               let params_2 = Readable::read(reader)?;
+               let keys_id = Readable::read(reader)?;
 
-               Ok(InMemoryChannelKeys {
+               read_tlv_fields!(reader, {});
+
+               Ok(InMemorySigner {
                        funding_key,
                        revocation_base_key,
                        payment_key,
@@ -638,7 +729,7 @@ impl Readable for InMemoryChannelKeys {
                        channel_value_satoshis,
                        holder_channel_pubkeys,
                        channel_parameters: counterparty_channel_data,
-                       key_derivation_params: (params_1, params_2),
+                       channel_keys_id: keys_id,
                })
        }
 }
@@ -651,14 +742,16 @@ impl Readable for InMemoryChannelKeys {
 /// Cooperative closes may use seed/2'
 /// The two close keys may be needed to claim on-chain funds!
 pub struct KeysManager {
-       secp_ctx: Secp256k1<secp256k1::SignOnly>,
+       secp_ctx: Secp256k1<secp256k1::All>,
        node_secret: SecretKey,
        destination_script: Script,
        shutdown_pubkey: PublicKey,
        channel_master_key: ExtendedPrivKey,
        channel_child_index: AtomicUsize,
+
        rand_bytes_master_key: ExtendedPrivKey,
        rand_bytes_child_index: AtomicUsize,
+       rand_bytes_unique_start: Sha256State,
 
        seed: [u8; 32],
        starting_time_secs: u64,
@@ -685,9 +778,10 @@ impl KeysManager {
        /// Note that until the 0.1 release there is no guarantee of backward compatibility between
        /// versions. Once the library is more fully supported, the docs will be updated to include a
        /// detailed description of the guarantee.
-       pub fn new(seed: &[u8; 32], network: Network, starting_time_secs: u64, starting_time_nanos: u32) -> Self {
-               let secp_ctx = Secp256k1::signing_only();
-               match ExtendedPrivKey::new_master(network.clone(), seed) {
+       pub fn new(seed: &[u8; 32], starting_time_secs: u64, starting_time_nanos: u32) -> Self {
+               let secp_ctx = Secp256k1::new();
+               // Note that when we aren't serializing the key, network doesn't matter
+               match ExtendedPrivKey::new_master(Network::Testnet, seed) {
                        Ok(master_key) => {
                                let node_secret = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(0).unwrap()).expect("Your RNG is busted").private_key.key;
                                let destination_script = match master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(1).unwrap()) {
@@ -706,47 +800,52 @@ impl KeysManager {
                                let channel_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(3).unwrap()).expect("Your RNG is busted");
                                let rand_bytes_master_key = master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(4).unwrap()).expect("Your RNG is busted");
 
-                               KeysManager {
+                               let mut rand_bytes_unique_start = Sha256::engine();
+                               rand_bytes_unique_start.input(&byte_utils::be64_to_array(starting_time_secs));
+                               rand_bytes_unique_start.input(&byte_utils::be32_to_array(starting_time_nanos));
+                               rand_bytes_unique_start.input(seed);
+
+                               let mut res = KeysManager {
                                        secp_ctx,
                                        node_secret,
+
                                        destination_script,
                                        shutdown_pubkey,
+
                                        channel_master_key,
                                        channel_child_index: AtomicUsize::new(0),
+
                                        rand_bytes_master_key,
                                        rand_bytes_child_index: AtomicUsize::new(0),
+                                       rand_bytes_unique_start,
 
                                        seed: *seed,
                                        starting_time_secs,
                                        starting_time_nanos,
-                               }
+                               };
+                               let secp_seed = res.get_secure_random_bytes();
+                               res.secp_ctx.seeded_randomize(&secp_seed);
+                               res
                        },
                        Err(_) => panic!("Your rng is busted"),
                }
        }
-       fn derive_unique_start(&self) -> Sha256State {
-               let mut unique_start = Sha256::engine();
-               unique_start.input(&byte_utils::be64_to_array(self.starting_time_secs));
-               unique_start.input(&byte_utils::be32_to_array(self.starting_time_nanos));
-               unique_start.input(&self.seed);
-               unique_start
-       }
-       /// Derive an old set of ChannelKeys for per-channel secrets based on a key derivation
-       /// parameters.
+       /// Derive an old Sign containing per-channel secrets based on a key derivation parameters.
+       ///
        /// Key derivation parameters are accessible through a per-channel secrets
-       /// ChannelKeys::key_derivation_params and is provided inside DynamicOuputP2WSH in case of
+       /// Sign::channel_keys_id and is provided inside DynamicOuputP2WSH in case of
        /// onchain output detection for which a corresponding delayed_payment_key must be derived.
-       pub fn derive_channel_keys(&self, channel_value_satoshis: u64, params_1: u64, params_2: u64) -> InMemoryChannelKeys {
-               let chan_id = ((params_1 & 0xFFFF_FFFF_0000_0000) >> 32) as u32;
+       pub fn derive_channel_keys(&self, channel_value_satoshis: u64, params: &[u8; 32]) -> InMemorySigner {
+               let chan_id = byte_utils::slice_to_be64(&params[0..8]);
+               assert!(chan_id <= core::u32::MAX as u64); // Otherwise the params field wasn't created by us
                let mut unique_start = Sha256::engine();
-               unique_start.input(&byte_utils::be64_to_array(params_2));
-               unique_start.input(&byte_utils::be32_to_array(params_1 as u32));
+               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).expect("key space exhausted")).expect("Your RNG is busted");
+               let child_privkey = self.channel_master_key.ckd_priv(&self.secp_ctx, ChildNumber::from_hardened_idx(chan_id as u32).expect("key space exhausted")).expect("Your RNG is busted");
                unique_start.input(&child_privkey.private_key.key[..]);
 
                let seed = Sha256::from_engine(unique_start).into_inner();
@@ -772,7 +871,7 @@ impl KeysManager {
                let delayed_payment_base_key = key_step!(b"delayed payment base key", payment_key);
                let htlc_base_key = key_step!(b"HTLC base key", delayed_payment_base_key);
 
-               InMemoryChannelKeys::new(
+               InMemorySigner::new(
                        &self.secp_ctx,
                        funding_key,
                        revocation_base_key,
@@ -781,13 +880,130 @@ impl KeysManager {
                        htlc_base_key,
                        commitment_seed,
                        channel_value_satoshis,
-                       (params_1, params_2),
+                       params.clone()
                )
        }
+
+       /// Creates a Transaction which spends the given descriptors to the given outputs, plus an
+       /// output to the given change destination (if sufficient change value remains). The
+       /// transaction will have a feerate, at least, of the given value.
+       ///
+       /// Returns `Err(())` if the output value is greater than the input value minus required fee or
+       /// if a descriptor was duplicated.
+       ///
+       /// We do not enforce that outputs meet the dust limit or that any output scripts are standard.
+       ///
+       /// May panic if the `SpendableOutputDescriptor`s were not generated by Channels which used
+       /// this KeysManager or one of the `InMemorySigner` created by this KeysManager.
+       pub fn spend_spendable_outputs<C: Signing>(&self, descriptors: &[&SpendableOutputDescriptor], outputs: Vec<TxOut>, change_destination_script: Script, feerate_sat_per_1000_weight: u32, secp_ctx: &Secp256k1<C>) -> Result<Transaction, ()> {
+               let mut input = Vec::new();
+               let mut input_value = 0;
+               let mut witness_weight = 0;
+               let mut output_set = HashSet::with_capacity(descriptors.len());
+               for outp in descriptors {
+                       match outp {
+                               SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
+                                       input.push(TxIn {
+                                               previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
+                                               script_sig: Script::new(),
+                                               sequence: 0,
+                                               witness: Vec::new(),
+                                       });
+                                       witness_weight += StaticPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
+                                       input_value += descriptor.output.value;
+                                       if !output_set.insert(descriptor.outpoint) { return Err(()); }
+                               },
+                               SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
+                                       input.push(TxIn {
+                                               previous_output: descriptor.outpoint.into_bitcoin_outpoint(),
+                                               script_sig: Script::new(),
+                                               sequence: descriptor.to_self_delay as u32,
+                                               witness: Vec::new(),
+                                       });
+                                       witness_weight += DelayedPaymentOutputDescriptor::MAX_WITNESS_LENGTH;
+                                       input_value += descriptor.output.value;
+                                       if !output_set.insert(descriptor.outpoint) { return Err(()); }
+                               },
+                               SpendableOutputDescriptor::StaticOutput { ref outpoint, ref output } => {
+                                       input.push(TxIn {
+                                               previous_output: outpoint.into_bitcoin_outpoint(),
+                                               script_sig: Script::new(),
+                                               sequence: 0,
+                                               witness: Vec::new(),
+                                       });
+                                       witness_weight += 1 + 73 + 34;
+                                       input_value += output.value;
+                                       if !output_set.insert(*outpoint) { return Err(()); }
+                               }
+                       }
+                       if input_value > MAX_VALUE_MSAT / 1000 { return Err(()); }
+               }
+               let mut spend_tx = Transaction {
+                       version: 2,
+                       lock_time: 0,
+                       input,
+                       output: outputs,
+               };
+               transaction_utils::maybe_add_change_output(&mut spend_tx, input_value, witness_weight, feerate_sat_per_1000_weight, change_destination_script)?;
+
+               let mut keys_cache: Option<(InMemorySigner, [u8; 32])> = None;
+               let mut input_idx = 0;
+               for outp in descriptors {
+                       match outp {
+                               SpendableOutputDescriptor::StaticPaymentOutput(descriptor) => {
+                                       if keys_cache.is_none() || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id {
+                                               keys_cache = Some((
+                                                       self.derive_channel_keys(descriptor.channel_value_satoshis, &descriptor.channel_keys_id),
+                                                       descriptor.channel_keys_id));
+                                       }
+                                       spend_tx.input[input_idx].witness = keys_cache.as_ref().unwrap().0.sign_counterparty_payment_input(&spend_tx, input_idx, &descriptor, &secp_ctx).unwrap();
+                               },
+                               SpendableOutputDescriptor::DelayedPaymentOutput(descriptor) => {
+                                       if keys_cache.is_none() || keys_cache.as_ref().unwrap().1 != descriptor.channel_keys_id {
+                                               keys_cache = Some((
+                                                       self.derive_channel_keys(descriptor.channel_value_satoshis, &descriptor.channel_keys_id),
+                                                       descriptor.channel_keys_id));
+                                       }
+                                       spend_tx.input[input_idx].witness = keys_cache.as_ref().unwrap().0.sign_dynamic_p2wsh_input(&spend_tx, input_idx, &descriptor, &secp_ctx).unwrap();
+                               },
+                               SpendableOutputDescriptor::StaticOutput { ref output, .. } => {
+                                       let derivation_idx = if output.script_pubkey == self.destination_script {
+                                               1
+                                       } else {
+                                               2
+                                       };
+                                       let secret = {
+                                               // Note that when we aren't serializing the key, network doesn't matter
+                                               match ExtendedPrivKey::new_master(Network::Testnet, &self.seed) {
+                                                       Ok(master_key) => {
+                                                               match master_key.ckd_priv(&secp_ctx, ChildNumber::from_hardened_idx(derivation_idx).expect("key space exhausted")) {
+                                                                       Ok(key) => key,
+                                                                       Err(_) => panic!("Your RNG is busted"),
+                                                               }
+                                                       }
+                                                       Err(_) => panic!("Your rng is busted"),
+                                               }
+                                       };
+                                       let pubkey = ExtendedPubKey::from_private(&secp_ctx, &secret).public_key;
+                                       if derivation_idx == 2 {
+                                               assert_eq!(pubkey.key, self.shutdown_pubkey);
+                                       }
+                                       let witness_script = bitcoin::Address::p2pkh(&pubkey, Network::Testnet).script_pubkey();
+                                       let sighash = hash_to_message!(&bip143::SigHashCache::new(&spend_tx).signature_hash(input_idx, &witness_script, output.value, SigHashType::All)[..]);
+                                       let sig = secp_ctx.sign(&sighash, &secret.private_key.key);
+                                       spend_tx.input[input_idx].witness.push(sig.serialize_der().to_vec());
+                                       spend_tx.input[input_idx].witness[0].push(SigHashType::All as u8);
+                                       spend_tx.input[input_idx].witness.push(pubkey.key.serialize().to_vec());
+                               },
+                       }
+                       input_idx += 1;
+               }
+               Ok(spend_tx)
+       }
 }
 
 impl KeysInterface for KeysManager {
-       type ChanKeySigner = InMemoryChannelKeys;
+       type Signer = InMemorySigner;
 
        fn get_node_secret(&self) -> SecretKey {
                self.node_secret.clone()
@@ -801,14 +1017,18 @@ impl KeysInterface for KeysManager {
                self.shutdown_pubkey.clone()
        }
 
-       fn get_channel_keys(&self, _inbound: bool, channel_value_satoshis: u64) -> Self::ChanKeySigner {
+       fn get_channel_signer(&self, _inbound: bool, channel_value_satoshis: u64) -> Self::Signer {
                let child_ix = self.channel_child_index.fetch_add(1, Ordering::AcqRel);
-               let ix_and_nanos: u64 = (child_ix as u64) << 32 | (self.starting_time_nanos as u64);
-               self.derive_channel_keys(channel_value_satoshis, ix_and_nanos, self.starting_time_secs)
+               assert!(child_ix <= core::u32::MAX as usize);
+               let mut id = [0; 32];
+               id[0..8].copy_from_slice(&byte_utils::be64_to_array(child_ix as u64));
+               id[8..16].copy_from_slice(&byte_utils::be64_to_array(self.starting_time_nanos as u64));
+               id[16..24].copy_from_slice(&byte_utils::be64_to_array(self.starting_time_secs));
+               self.derive_channel_keys(channel_value_satoshis, &id)
        }
 
        fn get_secure_random_bytes(&self) -> [u8; 32] {
-               let mut sha = self.derive_unique_start();
+               let mut sha = self.rand_bytes_unique_start.clone();
 
                let child_ix = self.rand_bytes_child_index.fetch_add(1, Ordering::AcqRel);
                let child_privkey = self.rand_bytes_master_key.ckd_priv(&self.secp_ctx, ChildNumber::from_hardened_idx(child_ix as u32).expect("key space exhausted")).expect("Your RNG is busted");
@@ -818,7 +1038,17 @@ impl KeysInterface for KeysManager {
                Sha256::from_engine(sha).into_inner()
        }
 
-       fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::ChanKeySigner, DecodeError> {
-               InMemoryChannelKeys::read(&mut std::io::Cursor::new(reader))
+       fn read_chan_signer(&self, reader: &[u8]) -> Result<Self::Signer, DecodeError> {
+               InMemorySigner::read(&mut io::Cursor::new(reader))
+       }
+
+       fn sign_invoice(&self, invoice_preimage: Vec<u8>) -> Result<RecoverableSignature, ()> {
+               Ok(self.secp_ctx.sign_recoverable(&hash_to_message!(&Sha256::hash(&invoice_preimage)), &self.get_node_secret()))
        }
 }
+
+// Ensure that BaseSign can have a vtable
+#[test]
+pub fn dyn_sign() {
+       let _signer: Box<dyn BaseSign>;
+}