wow-btc-swap/swap/src/protocol/alice/state.rs

use anyhow::{anyhow, Result};
use ecdsa_fun::{
    adaptor::{Adaptor, EncryptedSignature},
    nonce::Deterministic,
};
use libp2p::request_response::ResponseChannel;
use rand::{CryptoRng, RngCore};
use serde::{Deserialize, Serialize};
use sha2::Sha256;
use std::fmt;
use tracing::info;

use crate::{
    bitcoin,
    bitcoin::{
        current_epoch, timelocks::Timelock, wait_for_cancel_timelock_to_expire, GetBlockHeight,
        TransactionBlockHeight, TxCancel, TxRefund, WatchForRawTransaction,
    },
    monero,
    monero::CreateWalletForOutput,
    network::request_response::AliceToBob,
    protocol::{alice, bob},
    ExpiredTimelocks, SwapAmounts,
};

#[derive(Debug)]
pub enum AliceState {
    Started {
        amounts: SwapAmounts,
        state0: State0,
    },
    Negotiated {
        channel: Option<ResponseChannel<AliceToBob>>,
        amounts: SwapAmounts,
        state3: Box<State3>,
    },
    BtcLocked {
        channel: Option<ResponseChannel<AliceToBob>>,
        amounts: SwapAmounts,
        state3: Box<State3>,
    },
    XmrLocked {
        state3: Box<State3>,
    },
    EncSigLearned {
        encrypted_signature: EncryptedSignature,
        state3: Box<State3>,
    },
    BtcRedeemed,
    BtcCancelled {
        tx_cancel: TxCancel,
        state3: Box<State3>,
    },
    BtcRefunded {
        spend_key: monero::PrivateKey,
        state3: Box<State3>,
    },
    BtcPunishable {
        tx_refund: TxRefund,
        state3: Box<State3>,
    },
    XmrRefunded,
    CancelTimelockExpired {
        state3: Box<State3>,
    },
    BtcPunished,
    SafelyAborted,
}

impl fmt::Display for AliceState {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            AliceState::Started { .. } => write!(f, "started"),
            AliceState::Negotiated { .. } => write!(f, "negotiated"),
            AliceState::BtcLocked { .. } => write!(f, "btc is locked"),
            AliceState::XmrLocked { .. } => write!(f, "xmr is locked"),
            AliceState::EncSigLearned { .. } => write!(f, "encrypted signature is learned"),
            AliceState::BtcRedeemed => write!(f, "btc is redeemed"),
            AliceState::BtcCancelled { .. } => write!(f, "btc is cancelled"),
            AliceState::BtcRefunded { .. } => write!(f, "btc is refunded"),
            AliceState::BtcPunished => write!(f, "btc is punished"),
            AliceState::SafelyAborted => write!(f, "safely aborted"),
            AliceState::BtcPunishable { .. } => write!(f, "btc is punishable"),
            AliceState::XmrRefunded => write!(f, "xmr is refunded"),
            AliceState::CancelTimelockExpired { .. } => write!(f, "cancel timelock is expired"),
        }
    }
}

#[derive(Clone, Debug, Deserialize, Serialize, PartialEq)]
pub struct State0 {
    pub a: bitcoin::SecretKey,
    pub s_a: cross_curve_dleq::Scalar,
    pub v_a: monero::PrivateViewKey,
    #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
    pub btc: bitcoin::Amount,
    pub xmr: monero::Amount,
    pub cancel_timelock: Timelock,
    pub punish_timelock: Timelock,
    pub redeem_address: bitcoin::Address,
    pub punish_address: bitcoin::Address,
}

impl State0 {
    #[allow(clippy::too_many_arguments)]
    pub fn new(
        a: bitcoin::SecretKey,
        s_a: cross_curve_dleq::Scalar,
        v_a: monero::PrivateViewKey,
        btc: bitcoin::Amount,
        xmr: monero::Amount,
        cancel_timelock: Timelock,
        punish_timelock: Timelock,
        redeem_address: bitcoin::Address,
        punish_address: bitcoin::Address,
    ) -> Self {
        Self {
            a,
            s_a,
            v_a,
            redeem_address,
            punish_address,
            btc,
            xmr,
            cancel_timelock,
            punish_timelock,
        }
    }

    pub fn next_message<R: RngCore + CryptoRng>(&self, rng: &mut R) -> alice::Message0 {
        info!("Producing first message");
        let dleq_proof_s_a = cross_curve_dleq::Proof::new(rng, &self.s_a);

        alice::Message0 {
            A: self.a.public(),
            S_a_monero: monero::PublicKey::from_private_key(&monero::PrivateKey {
                scalar: self.s_a.into_ed25519(),
            }),
            S_a_bitcoin: self.s_a.into_secp256k1().into(),
            dleq_proof_s_a,
            v_a: self.v_a,
            redeem_address: self.redeem_address.clone(),
            punish_address: self.punish_address.clone(),
        }
    }

    pub fn receive(self, msg: bob::Message0) -> Result<State1> {
        msg.dleq_proof_s_b.verify(
            msg.S_b_bitcoin.clone().into(),
            msg.S_b_monero
                .point
                .decompress()
                .ok_or_else(|| anyhow!("S_b is not a monero curve point"))?,
        )?;

        let v = self.v_a + msg.v_b;

        Ok(State1 {
            a: self.a,
            B: msg.B,
            s_a: self.s_a,
            S_b_monero: msg.S_b_monero,
            S_b_bitcoin: msg.S_b_bitcoin,
            v,
            btc: self.btc,
            xmr: self.xmr,
            cancel_timelock: self.cancel_timelock,
            punish_timelock: self.punish_timelock,
            refund_address: msg.refund_address,
            redeem_address: self.redeem_address,
            punish_address: self.punish_address,
        })
    }
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct State1 {
    a: bitcoin::SecretKey,
    B: bitcoin::PublicKey,
    s_a: cross_curve_dleq::Scalar,
    S_b_monero: monero::PublicKey,
    S_b_bitcoin: bitcoin::PublicKey,
    v: monero::PrivateViewKey,
    #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
    btc: bitcoin::Amount,
    xmr: monero::Amount,
    cancel_timelock: Timelock,
    punish_timelock: Timelock,
    refund_address: bitcoin::Address,
    redeem_address: bitcoin::Address,
    punish_address: bitcoin::Address,
}

impl State1 {
    pub fn receive(self, msg: bob::Message1) -> State2 {
        State2 {
            a: self.a,
            B: self.B,
            s_a: self.s_a,
            S_b_monero: self.S_b_monero,
            S_b_bitcoin: self.S_b_bitcoin,
            v: self.v,
            btc: self.btc,
            xmr: self.xmr,
            cancel_timelock: self.cancel_timelock,
            punish_timelock: self.punish_timelock,
            refund_address: self.refund_address,
            redeem_address: self.redeem_address,
            punish_address: self.punish_address,
            tx_lock: msg.tx_lock,
        }
    }
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct State2 {
    a: bitcoin::SecretKey,
    B: bitcoin::PublicKey,
    s_a: cross_curve_dleq::Scalar,
    S_b_monero: monero::PublicKey,
    S_b_bitcoin: bitcoin::PublicKey,
    v: monero::PrivateViewKey,
    #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
    btc: bitcoin::Amount,
    xmr: monero::Amount,
    cancel_timelock: Timelock,
    punish_timelock: Timelock,
    refund_address: bitcoin::Address,
    redeem_address: bitcoin::Address,
    punish_address: bitcoin::Address,
    tx_lock: bitcoin::TxLock,
}

impl State2 {
    pub fn next_message(&self) -> alice::Message1 {
        let tx_cancel =
            bitcoin::TxCancel::new(&self.tx_lock, self.cancel_timelock, self.a.public(), self.B);

        let tx_refund = bitcoin::TxRefund::new(&tx_cancel, &self.refund_address);
        // Alice encsigns the refund transaction(bitcoin) digest with Bob's monero
        // pubkey(S_b). The refund transaction spends the output of
        // tx_lock_bitcoin to Bob's refund address.
        // recover(encsign(a, S_b, d), sign(a, d), S_b) = s_b where d is a digest, (a,
        // A) is alice's keypair and (s_b, S_b) is bob's keypair.
        let tx_refund_encsig = self.a.encsign(self.S_b_bitcoin, tx_refund.digest());

        let tx_cancel_sig = self.a.sign(tx_cancel.digest());
        alice::Message1 {
            tx_refund_encsig,
            tx_cancel_sig,
        }
    }

    pub fn receive(self, msg: bob::Message2) -> Result<State3> {
        let tx_cancel =
            bitcoin::TxCancel::new(&self.tx_lock, self.cancel_timelock, self.a.public(), self.B);
        bitcoin::verify_sig(&self.B, &tx_cancel.digest(), &msg.tx_cancel_sig)?;
        let tx_punish =
            bitcoin::TxPunish::new(&tx_cancel, &self.punish_address, self.punish_timelock);
        bitcoin::verify_sig(&self.B, &tx_punish.digest(), &msg.tx_punish_sig)?;

        Ok(State3 {
            a: self.a,
            B: self.B,
            s_a: self.s_a,
            S_b_monero: self.S_b_monero,
            S_b_bitcoin: self.S_b_bitcoin,
            v: self.v,
            // TODO(Franck): Review if these amounts are actually needed
            btc: self.btc,
            xmr: self.xmr,
            cancel_timelock: self.cancel_timelock,
            punish_timelock: self.punish_timelock,
            refund_address: self.refund_address,
            redeem_address: self.redeem_address,
            punish_address: self.punish_address,
            tx_lock: self.tx_lock,
            tx_punish_sig_bob: msg.tx_punish_sig,
            tx_cancel_sig_bob: msg.tx_cancel_sig,
        })
    }
}

#[derive(Clone, Debug, Deserialize, Serialize, PartialEq)]
pub struct State3 {
    pub a: bitcoin::SecretKey,
    pub B: bitcoin::PublicKey,
    pub s_a: cross_curve_dleq::Scalar,
    pub S_b_monero: monero::PublicKey,
    pub S_b_bitcoin: bitcoin::PublicKey,
    pub v: monero::PrivateViewKey,
    #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
    pub btc: bitcoin::Amount,
    pub xmr: monero::Amount,
    pub cancel_timelock: Timelock,
    pub punish_timelock: Timelock,
    pub refund_address: bitcoin::Address,
    pub redeem_address: bitcoin::Address,
    pub punish_address: bitcoin::Address,
    pub tx_lock: bitcoin::TxLock,
    pub tx_punish_sig_bob: bitcoin::Signature,
    pub tx_cancel_sig_bob: bitcoin::Signature,
}

impl State3 {
    pub async fn watch_for_lock_btc<W>(self, bitcoin_wallet: &W) -> Result<State4>
    where
        W: bitcoin::WatchForRawTransaction,
    {
        tracing::info!("watching for lock btc with txid: {}", self.tx_lock.txid());
        let tx = bitcoin_wallet
            .watch_for_raw_transaction(self.tx_lock.txid())
            .await;

        tracing::info!("tx lock seen with txid: {}", tx.txid());

        Ok(State4 {
            a: self.a,
            B: self.B,
            s_a: self.s_a,
            S_b_monero: self.S_b_monero,
            S_b_bitcoin: self.S_b_bitcoin,
            v: self.v,
            btc: self.btc,
            xmr: self.xmr,
            cancel_timelock: self.cancel_timelock,
            punish_timelock: self.punish_timelock,
            refund_address: self.refund_address,
            redeem_address: self.redeem_address,
            punish_address: self.punish_address,
            tx_lock: self.tx_lock,
            tx_punish_sig_bob: self.tx_punish_sig_bob,
            tx_cancel_sig_bob: self.tx_cancel_sig_bob,
        })
    }

    pub async fn wait_for_cancel_timelock_to_expire<W>(&self, bitcoin_wallet: &W) -> Result<()>
    where
        W: WatchForRawTransaction + TransactionBlockHeight + GetBlockHeight,
    {
        wait_for_cancel_timelock_to_expire(
            bitcoin_wallet,
            self.cancel_timelock,
            self.tx_lock.txid(),
        )
        .await
    }

    pub async fn expired_timelocks<W>(&self, bitcoin_wallet: &W) -> Result<ExpiredTimelocks>
    where
        W: WatchForRawTransaction + TransactionBlockHeight + GetBlockHeight,
    {
        current_epoch(
            bitcoin_wallet,
            self.cancel_timelock,
            self.punish_timelock,
            self.tx_lock.txid(),
        )
        .await
    }
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct State4 {
    a: bitcoin::SecretKey,
    B: bitcoin::PublicKey,
    s_a: cross_curve_dleq::Scalar,
    S_b_monero: monero::PublicKey,
    S_b_bitcoin: bitcoin::PublicKey,
    v: monero::PrivateViewKey,
    #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
    btc: bitcoin::Amount,
    xmr: monero::Amount,
    cancel_timelock: Timelock,
    punish_timelock: Timelock,
    refund_address: bitcoin::Address,
    redeem_address: bitcoin::Address,
    punish_address: bitcoin::Address,
    tx_lock: bitcoin::TxLock,
    tx_punish_sig_bob: bitcoin::Signature,
    tx_cancel_sig_bob: bitcoin::Signature,
}

impl State4 {
    pub async fn lock_xmr<W>(self, monero_wallet: &W) -> Result<State5>
    where
        W: monero::Transfer,
    {
        let S_a = monero::PublicKey::from_private_key(&monero::PrivateKey {
            scalar: self.s_a.into_ed25519(),
        });
        let S_b = self.S_b_monero;

        let (tx_lock_proof, fee) = monero_wallet
            .transfer(S_a + S_b, self.v.public(), self.xmr)
            .await?;

        Ok(State5 {
            a: self.a,
            B: self.B,
            s_a: self.s_a,
            S_b_monero: self.S_b_monero,
            S_b_bitcoin: self.S_b_bitcoin,
            v: self.v,
            btc: self.btc,
            xmr: self.xmr,
            cancel_timelock: self.cancel_timelock,
            punish_timelock: self.punish_timelock,
            refund_address: self.refund_address,
            redeem_address: self.redeem_address,
            punish_address: self.punish_address,
            tx_lock: self.tx_lock,
            tx_lock_proof,
            tx_punish_sig_bob: self.tx_punish_sig_bob,
            tx_cancel_sig_bob: self.tx_cancel_sig_bob,
            lock_xmr_fee: fee,
        })
    }

    pub async fn punish<W: bitcoin::BroadcastSignedTransaction>(
        &self,
        bitcoin_wallet: &W,
    ) -> Result<()> {
        let tx_cancel =
            bitcoin::TxCancel::new(&self.tx_lock, self.cancel_timelock, self.a.public(), self.B);
        let tx_punish =
            bitcoin::TxPunish::new(&tx_cancel, &self.punish_address, self.punish_timelock);

        {
            let sig_a = self.a.sign(tx_cancel.digest());
            let sig_b = self.tx_cancel_sig_bob.clone();

            let signed_tx_cancel = tx_cancel.clone().add_signatures(
                &self.tx_lock,
                (self.a.public(), sig_a),
                (self.B, sig_b),
            )?;

            let _ = bitcoin_wallet
                .broadcast_signed_transaction(signed_tx_cancel)
                .await?;
        }

        {
            let sig_a = self.a.sign(tx_punish.digest());
            let sig_b = self.tx_punish_sig_bob.clone();

            let signed_tx_punish =
                tx_punish.add_signatures(&tx_cancel, (self.a.public(), sig_a), (self.B, sig_b))?;

            let _ = bitcoin_wallet
                .broadcast_signed_transaction(signed_tx_punish)
                .await?;
        }

        Ok(())
    }
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct State5 {
    a: bitcoin::SecretKey,
    B: bitcoin::PublicKey,
    s_a: cross_curve_dleq::Scalar,
    S_b_monero: monero::PublicKey,
    S_b_bitcoin: bitcoin::PublicKey,
    v: monero::PrivateViewKey,
    #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
    btc: bitcoin::Amount,
    xmr: monero::Amount,
    cancel_timelock: Timelock,
    punish_timelock: Timelock,
    refund_address: bitcoin::Address,
    redeem_address: bitcoin::Address,
    punish_address: bitcoin::Address,
    tx_lock: bitcoin::TxLock,
    tx_lock_proof: monero::TransferProof,

    tx_punish_sig_bob: bitcoin::Signature,

    tx_cancel_sig_bob: bitcoin::Signature,
    lock_xmr_fee: monero::Amount,
}

impl State5 {
    pub fn next_message(&self) -> alice::Message2 {
        alice::Message2 {
            tx_lock_proof: self.tx_lock_proof.clone(),
        }
    }

    pub fn receive(self, msg: bob::Message3) -> State6 {
        State6 {
            a: self.a,
            B: self.B,
            s_a: self.s_a,
            S_b_monero: self.S_b_monero,
            S_b_bitcoin: self.S_b_bitcoin,
            v: self.v,
            btc: self.btc,
            xmr: self.xmr,
            cancel_timelock: self.cancel_timelock,
            punish_timelock: self.punish_timelock,
            refund_address: self.refund_address,
            redeem_address: self.redeem_address,
            punish_address: self.punish_address,
            tx_lock: self.tx_lock,
            tx_punish_sig_bob: self.tx_punish_sig_bob,
            tx_redeem_encsig: msg.tx_redeem_encsig,
            lock_xmr_fee: self.lock_xmr_fee,
        }
    }

    // watch for refund on btc, recover s_b and refund xmr
    pub async fn refund_xmr<B, M>(self, bitcoin_wallet: &B, monero_wallet: &M) -> Result<()>
    where
        B: WatchForRawTransaction,
        M: CreateWalletForOutput,
    {
        let tx_cancel =
            bitcoin::TxCancel::new(&self.tx_lock, self.cancel_timelock, self.a.public(), self.B);

        let tx_refund = bitcoin::TxRefund::new(&tx_cancel, &self.refund_address);

        let tx_refund_encsig = self.a.encsign(self.S_b_bitcoin, tx_refund.digest());

        let tx_refund_candidate = bitcoin_wallet
            .watch_for_raw_transaction(tx_refund.txid())
            .await;

        let tx_refund_sig =
            tx_refund.extract_signature_by_key(tx_refund_candidate, self.a.public())?;

        let s_b = bitcoin::recover(self.S_b_bitcoin, tx_refund_sig, tx_refund_encsig)?;
        let s_b = monero::private_key_from_secp256k1_scalar(s_b.into());

        let s = s_b.scalar + self.s_a.into_ed25519();

        // NOTE: This actually generates and opens a new wallet, closing the currently
        // open one.
        monero_wallet
            .create_and_load_wallet_for_output(monero::PrivateKey::from_scalar(s), self.v)
            .await?;

        Ok(())
    }
}

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct State6 {
    a: bitcoin::SecretKey,
    B: bitcoin::PublicKey,
    s_a: cross_curve_dleq::Scalar,
    S_b_monero: monero::PublicKey,
    S_b_bitcoin: bitcoin::PublicKey,
    v: monero::PrivateViewKey,
    #[serde(with = "::bitcoin::util::amount::serde::as_sat")]
    btc: bitcoin::Amount,
    xmr: monero::Amount,
    cancel_timelock: Timelock,
    punish_timelock: Timelock,
    refund_address: bitcoin::Address,
    redeem_address: bitcoin::Address,
    punish_address: bitcoin::Address,
    tx_lock: bitcoin::TxLock,

    tx_punish_sig_bob: bitcoin::Signature,
    tx_redeem_encsig: EncryptedSignature,
    lock_xmr_fee: monero::Amount,
}

impl State6 {
    pub async fn redeem_btc<W: bitcoin::BroadcastSignedTransaction>(
        &self,
        bitcoin_wallet: &W,
    ) -> Result<()> {
        let adaptor = Adaptor::<Sha256, Deterministic<Sha256>>::default();

        let tx_redeem = bitcoin::TxRedeem::new(&self.tx_lock, &self.redeem_address);

        let sig_a = self.a.sign(tx_redeem.digest());
        let sig_b =
            adaptor.decrypt_signature(&self.s_a.into_secp256k1(), self.tx_redeem_encsig.clone());

        let sig_tx_redeem =
            tx_redeem.add_signatures(&self.tx_lock, (self.a.public(), sig_a), (self.B, sig_b))?;
        bitcoin_wallet
            .broadcast_signed_transaction(sig_tx_redeem)
            .await?;

        Ok(())
    }

    pub fn lock_xmr_fee(&self) -> monero::Amount {
        self.lock_xmr_fee
    }
}