From 6db40dce2a99a500f1d54c511f0e5e9607a25afc Mon Sep 17 00:00:00 2001
From: Lucas Soriano del Pino <l.soriano.del.pino@gmail.com>
Date: Thu, 5 Nov 2020 15:48:31 +1100
Subject: [PATCH] Implement swap recover function for Bob

---
 swap/Cargo.toml     |   1 +
 swap/src/recover.rs | 117 +++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 105 insertions(+), 13 deletions(-)

diff --git a/swap/Cargo.toml b/swap/Cargo.toml
index e8ab1323..e1371f91 100644
--- a/swap/Cargo.toml
+++ b/swap/Cargo.toml
@@ -29,6 +29,7 @@ serde = { version = "1", features = ["derive"] }
 serde_cbor = "0.11"
 serde_derive = "1.0"
 serde_json = "1"
+sha2 = "0.9"
 sled = "0.34"
 structopt = "0.3"
 tempfile = "3"
diff --git a/swap/src/recover.rs b/swap/src/recover.rs
index 87cb11ee..f3addbf0 100644
--- a/swap/src/recover.rs
+++ b/swap/src/recover.rs
@@ -3,13 +3,15 @@ use crate::{
     state::{Alice, Bob, Swap},
 };
 use anyhow::Result;
+use ecdsa_fun::{adaptor::Adaptor, nonce::Deterministic};
 use futures::{
     future::{select, Either},
     pin_mut,
 };
+use sha2::Sha256;
 use xmr_btc::bitcoin::{
     poll_until_block_height_is_gte, BroadcastSignedTransaction, TransactionBlockHeight, TxCancel,
-    TxPunish, TxRefund, WatchForRawTransaction,
+    TxPunish, TxRedeem, TxRefund, WatchForRawTransaction,
 };
 
 pub async fn recover(
@@ -29,7 +31,7 @@ pub async fn alice_recover(
     state: Alice,
 ) -> Result<()> {
     match state {
-        Alice::Handshaken(_) | Alice::BtcLocked(_) | Alice::SwapComplete => Ok(()),
+        Alice::Handshaken(_) | Alice::BtcLocked(_) | Alice::SwapComplete => {}
         Alice::XmrLocked(state) => {
             let tx_cancel = TxCancel::new(
                 &state.tx_lock,
@@ -131,14 +133,11 @@ pub async fn alice_recover(
                         .await?;
                 }
             };
-
-            Ok(())
         }
         Alice::BtcRedeemable { redeem_tx, .. } => {
             bitcoin_wallet
                 .broadcast_signed_transaction(redeem_tx)
                 .await?;
-            Ok(())
         }
         Alice::BtcPunishable(state) => {
             let tx_cancel = TxCancel::new(
@@ -162,8 +161,6 @@ pub async fn alice_recover(
             bitcoin_wallet
                 .broadcast_signed_transaction(sig_tx_punish)
                 .await?;
-
-            Ok(())
         }
         Alice::BtcRefunded {
             view_key,
@@ -173,15 +170,109 @@ pub async fn alice_recover(
             monero_wallet
                 .create_and_load_wallet_for_output(spend_key, view_key)
                 .await?;
-            Ok(())
         }
-    }
+    };
+
+    Ok(())
 }
 
 pub async fn bob_recover(
-    _bitcoin_wallet: crate::bitcoin::Wallet,
-    _monero_wallet: crate::monero::Wallet,
-    _state: Bob,
+    bitcoin_wallet: crate::bitcoin::Wallet,
+    monero_wallet: crate::monero::Wallet,
+    state: Bob,
 ) -> Result<()> {
-    todo!()
+    match state {
+        Bob::Handshaken(_) | Bob::SwapComplete => {}
+        Bob::BtcLocked(state) | Bob::XmrLocked(state) | Bob::BtcRefundable(state) => {
+            let tx_cancel = TxCancel::new(
+                &state.tx_lock,
+                state.refund_timelock,
+                state.A.clone(),
+                state.b.public(),
+            );
+
+            // Ensure that TxCancel is on the blockchain
+            if bitcoin_wallet
+                .0
+                .get_raw_transaction(tx_cancel.txid())
+                .await
+                .is_err()
+            {
+                let tx_lock_height = bitcoin_wallet
+                    .transaction_block_height(state.tx_lock.txid())
+                    .await;
+                poll_until_block_height_is_gte(
+                    &bitcoin_wallet,
+                    tx_lock_height + state.refund_timelock,
+                )
+                .await;
+
+                let sig_a = state.tx_cancel_sig_a.clone();
+                let sig_b = state.b.sign(tx_cancel.digest());
+
+                let tx_cancel = tx_cancel
+                    .clone()
+                    .add_signatures(
+                        &state.tx_lock,
+                        (state.A.clone(), sig_a),
+                        (state.b.public(), sig_b),
+                    )
+                    .expect("sig_{a,b} to be valid signatures for tx_cancel");
+
+                // TODO: We should not fail if the transaction is already on the blockchain
+                bitcoin_wallet
+                    .broadcast_signed_transaction(tx_cancel)
+                    .await?;
+            }
+
+            let tx_refund = TxRefund::new(&tx_cancel, &state.refund_address);
+            let signed_tx_refund = {
+                let adaptor = Adaptor::<Sha256, Deterministic<Sha256>>::default();
+                let sig_a = adaptor
+                    .decrypt_signature(&state.s_b.into_secp256k1(), state.tx_refund_encsig.clone());
+                let sig_b = state.b.sign(tx_refund.digest());
+
+                tx_refund
+                    .add_signatures(
+                        &tx_cancel,
+                        (state.A.clone(), sig_a),
+                        (state.b.public(), sig_b),
+                    )
+                    .expect("sig_{a,b} to be valid signatures for tx_refund")
+            };
+
+            bitcoin_wallet
+                .broadcast_signed_transaction(signed_tx_refund)
+                .await?;
+        }
+        Bob::BtcRedeemed(state) => {
+            let tx_redeem = TxRedeem::new(&state.tx_lock, &state.redeem_address);
+            let tx_redeem_published = bitcoin_wallet
+                .0
+                .get_raw_transaction(tx_redeem.txid())
+                .await?;
+
+            let tx_redeem_encsig = state
+                .b
+                .encsign(state.S_a_bitcoin.clone(), tx_redeem.digest());
+            let tx_redeem_sig =
+                tx_redeem.extract_signature_by_key(tx_redeem_published, state.b.public())?;
+
+            let s_a =
+                xmr_btc::bitcoin::recover(state.S_a_bitcoin, tx_redeem_sig, tx_redeem_encsig)?;
+            let s_a = monero::PrivateKey::from_scalar(
+                xmr_btc::monero::Scalar::from_bytes_mod_order(s_a.to_bytes()),
+            );
+
+            let s_b = monero::PrivateKey {
+                scalar: state.s_b.into_ed25519(),
+            };
+
+            monero_wallet
+                .create_and_load_wallet_for_output(s_a + s_b, state.v)
+                .await?;
+        }
+    };
+
+    Ok(())
 }