Move completing of Bitcoin redeem tx onto RedeemTx

This allows us to have access to RedeemTx from within the scope
of the state transition which we are going to need for more
efficient watching of what happens to this TX on the blockchain.

swap/src/bitcoin/redeem.rs

@@ -1,12 +1,16 @@
 use crate::bitcoin::{
-    verify_sig, Address, EmptyWitnessStack, NoInputs, NotThreeWitnesses, PublicKey, TooManyInputs,
-    Transaction, TxLock,
+    verify_encsig, verify_sig, Address, EmptyWitnessStack, EncryptedSignature, NoInputs,
+    NotThreeWitnesses, PublicKey, SecretKey, TooManyInputs, Transaction, TxLock,
 };
 use ::bitcoin::util::bip143::SigHashCache;
 use ::bitcoin::{SigHash, SigHashType, Txid};
 use anyhow::{bail, Context, Result};
+use ecdsa_fun::adaptor::{Adaptor, HashTranscript};
+use ecdsa_fun::fun::Scalar;
+use ecdsa_fun::nonce::Deterministic;
 use ecdsa_fun::Signature;
 use miniscript::{Descriptor, DescriptorTrait};
+use sha2::Sha256;
 use std::collections::HashMap;
 
 #[derive(Debug, Clone)]
@@ -44,17 +48,31 @@ impl TxRedeem {
         self.digest
     }
 
-    pub fn add_signatures(
-        self,
-        (A, sig_a): (PublicKey, Signature),
-        (B, sig_b): (PublicKey, Signature),
+    pub fn complete(
+        mut self,
+        encrypted_signature: EncryptedSignature,
+        a: SecretKey,
+        s_a: Scalar,
+        B: PublicKey,
     ) -> Result<Transaction> {
+        verify_encsig(
+            B,
+            PublicKey::from(s_a.clone()),
+            &self.digest(),
+            &encrypted_signature,
+        )
+        .context("Invalid encrypted signature received")?;
+
+        let sig_a = a.sign(self.digest());
+        let adaptor = Adaptor::<HashTranscript<Sha256>, Deterministic<Sha256>>::default();
+        let sig_b = adaptor.decrypt_signature(&s_a, encrypted_signature);
+
         let satisfier = {
             let mut satisfier = HashMap::with_capacity(2);
 
             let A = ::bitcoin::PublicKey {
                 compressed: true,
-                key: A.0.into(),
+                key: a.public.into(),
             };
             let B = ::bitcoin::PublicKey {
                 compressed: true,
@@ -68,11 +86,11 @@ impl TxRedeem {
             satisfier
         };
 
-        let mut tx_redeem = self.inner;
         self.lock_output_descriptor
-            .satisfy(&mut tx_redeem.input[0], satisfier)?;
+            .satisfy(&mut self.inner.input[0], satisfier)
+            .context("Failed to sign Bitcoin redeem transaction")?;
 
-        Ok(tx_redeem)
+        Ok(self.inner)
     }
 
     pub fn extract_signature_by_key(