From 56e7bcbfb6ac8c7fa04326b4fb79254eca6e5246 Mon Sep 17 00:00:00 2001
From: Michael Vandeberg <mvandeberg@users.noreply.github.com>
Date: Mon, 27 Jan 2025 16:10:29 -0700
Subject: [PATCH] Implement signing of a transaction id

---
 internal/cli/commands.go        | 61 ++++++++++++++++++++++++---------
 internal/cliutil/transaction.go | 13 +++++++
 2 files changed, 58 insertions(+), 16 deletions(-)

diff --git a/internal/cli/commands.go b/internal/cli/commands.go
index 1f905d4..e494a41 100644
--- a/internal/cli/commands.go
+++ b/internal/cli/commands.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/base64"
+	"encoding/hex"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -1418,13 +1419,8 @@ func NewSignTransactionCommand(inv *CommandParseResult) Command {
 	}
 }
 
-// Execute signs a transaction
-func (c *SignTransactionCommand) Execute(ctx context.Context, ee *ExecutionEnvironment) (*ExecutionResult, error) {
-	if !ee.IsWalletOpen() {
-		return nil, fmt.Errorf("%w: cannot sign transaction", cliutil.ErrWalletClosed)
-	}
-
-	trxBytes, err := base64.URLEncoding.DecodeString(c.Transaction)
+func parseTransaction(transaction string) (*protocol.Transaction, error) {
+	trxBytes, err := base64.URLEncoding.DecodeString(transaction)
 	if err != nil {
 		return nil, err
 	}
@@ -1435,25 +1431,58 @@ func (c *SignTransactionCommand) Execute(ctx context.Context, ee *ExecutionEnvir
 		return nil, err
 	}
 
-	err = util.SignTransaction(ee.Key.PrivateBytes(), trx)
-	if err != nil {
-		return nil, err
+	return trx, nil
+}
+
+func parseTransactionId(tid string) ([]byte, error) {
+	return hex.DecodeString(tid[2:])
+}
+
+// Execute signs a transaction
+func (c *SignTransactionCommand) Execute(ctx context.Context, ee *ExecutionEnvironment) (*ExecutionResult, error) {
+	if !ee.IsWalletOpen() {
+		return nil, fmt.Errorf("%w: cannot sign transaction", cliutil.ErrWalletClosed)
 	}
 
-	trxBytes, err = proto.Marshal(trx)
+	trx, err := parseTransaction(c.Transaction)
+	if err == nil {
+		err = util.SignTransaction(ee.Key.PrivateBytes(), trx)
+		if err != nil {
+			return nil, err
+		}
+
+		trxBytes, err := proto.Marshal(trx)
+		if err != nil {
+			return nil, err
+		}
+
+		jsonTrx, err := json.MarshalIndent(trx, "", "  ")
+		if err != nil {
+			return nil, err
+		}
+
+		encodedTrx := base64.URLEncoding.EncodeToString(trxBytes)
+
+		result := NewExecutionResult()
+		result.AddMessage(fmt.Sprintf("Signed Transaction:\nJSON:\n%v\nBase64:\n%v", string(jsonTrx), encodedTrx))
+
+		return result, nil
+	}
+
+	trxErr := err
+
+	tid, err := parseTransactionId(c.Transaction)
 	if err != nil {
-		return nil, err
+		return nil, trxErr
 	}
 
-	jsonTrx, err := json.MarshalIndent(trx, "", "  ")
+	signature, err := cliutil.SignTransactionId(ee.Key.PrivateBytes(), tid)
 	if err != nil {
 		return nil, err
 	}
 
-	encodedTrx := base64.URLEncoding.EncodeToString(trxBytes)
-
 	result := NewExecutionResult()
-	result.AddMessage(fmt.Sprintf("Signed Transaction:\nJSON:\n%v\nBase64:\n%v", string(jsonTrx), encodedTrx))
+	result.AddMessage(fmt.Sprintf("Transaction Signature: %v", base64.URLEncoding.EncodeToString(signature)))
 
 	return result, nil
 }
diff --git a/internal/cliutil/transaction.go b/internal/cliutil/transaction.go
index f309b6d..09387e2 100644
--- a/internal/cliutil/transaction.go
+++ b/internal/cliutil/transaction.go
@@ -106,3 +106,16 @@ func SignTransaction(key []byte, tx *protocol.Transaction) error {
 
 	return nil
 }
+
+// SignTransactionId signs the transaction ID with the given key
+func SignTransactionId(key []byte, tid []byte) ([]byte, error) {
+	privateKey, _ := btcec.PrivKeyFromBytes(btcec.S256(), key)
+
+	// Decode to multihash ID
+	idBytes, err := multihash.Decode(tid)
+	if err != nil {
+		return nil, err
+	}
+
+	return btcec.SignCompact(btcec.S256(), privateKey, idBytes.Digest, true)
+}