Add validation to sample remote signer

examples/remote-signing-server/go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/btcsuite/btcd v0.24.0 // indirect
 	github.com/btcsuite/btcd/btcec/v2 v2.2.0 // indirect
 	github.com/btcsuite/btcd/btcutil v1.1.5 // indirect
+	github.com/btcsuite/btcd/btcutil/psbt v1.1.9 // indirect
 	github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0 // indirect
 	github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f // indirect
 	github.com/bytedance/sonic v1.9.1 // indirect

examples/remote-signing-server/go.sum

@@ -12,6 +12,8 @@ github.com/btcsuite/btcd/btcutil v1.0.0/go.mod h1:Uoxwv0pqYWhD//tfTiipkxNfdhG9Ur
 github.com/btcsuite/btcd/btcutil v1.1.0/go.mod h1:5OapHB7A2hBBWLm48mmw4MOHNJCcUBTwmWH/0Jn8VHE=
 github.com/btcsuite/btcd/btcutil v1.1.5 h1:+wER79R5670vs/ZusMTF1yTcRYE5GUsFbdjdisflzM8=
 github.com/btcsuite/btcd/btcutil v1.1.5/go.mod h1:PSZZ4UitpLBWzxGd5VGOrLnmOjtPP/a6HaFo12zMs00=
+github.com/btcsuite/btcd/btcutil/psbt v1.1.9 h1:UmfOIiWMZcVMOLaN+lxbbLSuoINGS1WmK1TZNI0b4yk=
+github.com/btcsuite/btcd/btcutil/psbt v1.1.9/go.mod h1:ehBEvU91lxSlXtA+zZz3iFYx7Yq9eqnKx4/kSrnsvMY=
 github.com/btcsuite/btcd/chaincfg/chainhash v1.0.0/go.mod h1:7SFka0XMvUgj3hfZtydOrQY2mwhPclbT2snogU7SQQc=
 github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1/go.mod h1:7SFka0XMvUgj3hfZtydOrQY2mwhPclbT2snogU7SQQc=
 github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0 h1:59Kx4K6lzOW5w6nFlA0v5+lk/6sjybR934QNHSJZPTQ=

examples/remote-signing-server/server.go

@@ -66,7 +66,7 @@ func main() {
 		case objects.WebhookEventTypeRemoteSigning:
 			if config.RespondDirectly {
 				resp, err := remotesigning.GraphQLResponseForRemoteSigningWebhook(
-					remotesigning.PositiveValidator{}, *event, config.MasterSeed)
+					remotesigning.HashValidator{}, *event, config.MasterSeed)
 				if err != nil {
 					log.Printf("ERROR: Unable to handle remote signing webhook: %s", err)
 					c.AbortWithStatus(http.StatusInternalServerError)
@@ -80,7 +80,7 @@ func main() {
 				}
 			} else {
 				resp, err := remotesigning.HandleRemoteSigningWebhook(
-					lsClient, remotesigning.PositiveValidator{}, *event, config.MasterSeed)
+					lsClient, remotesigning.HashValidator{}, *event, config.MasterSeed)
 				if err != nil {
 					log.Printf("ERROR: Unable to handle remote signing webhook: %s", err)
 					c.AbortWithStatus(http.StatusInternalServerError)

go.mod

@@ -15,7 +15,7 @@ require (
 	github.com/FactomProject/basen v0.0.0-20150613233007-fe3947df716e // indirect
 	github.com/FactomProject/btcutilecc v0.0.0-20130527213604-d3a63a5752ec // indirect
 	github.com/btcsuite/btcd/btcec/v2 v2.2.0 // indirect
-	github.com/btcsuite/btcd/btcutil v1.1.5 // indirect
+	github.com/btcsuite/btcd/btcutil v1.1.5
 	github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0 // indirect
 	github.com/btcsuite/btclog v0.0.0-20170628155309-84c8d2346e9f // indirect
 	github.com/decred/dcrd/crypto/blake256 v1.0.1 // indirect
@@ -27,6 +27,7 @@ require (
 
 require (
 	github.com/btcsuite/btcd v0.24.0
+	github.com/btcsuite/btcd/btcutil/psbt v1.1.9
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect

go.sum

@@ -16,6 +16,8 @@ github.com/btcsuite/btcd/btcutil v1.0.0/go.mod h1:Uoxwv0pqYWhD//tfTiipkxNfdhG9Ur
 github.com/btcsuite/btcd/btcutil v1.1.0/go.mod h1:5OapHB7A2hBBWLm48mmw4MOHNJCcUBTwmWH/0Jn8VHE=
 github.com/btcsuite/btcd/btcutil v1.1.5 h1:+wER79R5670vs/ZusMTF1yTcRYE5GUsFbdjdisflzM8=
 github.com/btcsuite/btcd/btcutil v1.1.5/go.mod h1:PSZZ4UitpLBWzxGd5VGOrLnmOjtPP/a6HaFo12zMs00=
+github.com/btcsuite/btcd/btcutil/psbt v1.1.9 h1:UmfOIiWMZcVMOLaN+lxbbLSuoINGS1WmK1TZNI0b4yk=
+github.com/btcsuite/btcd/btcutil/psbt v1.1.9/go.mod h1:ehBEvU91lxSlXtA+zZz3iFYx7Yq9eqnKx4/kSrnsvMY=
 github.com/btcsuite/btcd/chaincfg/chainhash v1.0.0/go.mod h1:7SFka0XMvUgj3hfZtydOrQY2mwhPclbT2snogU7SQQc=
 github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1/go.mod h1:7SFka0XMvUgj3hfZtydOrQY2mwhPclbT2snogU7SQQc=
 github.com/btcsuite/btcd/chaincfg/chainhash v1.1.0 h1:59Kx4K6lzOW5w6nFlA0v5+lk/6sjybR934QNHSJZPTQ=

remotesigning/validation.go

@@ -1,10 +1,13 @@
 package remotesigning
 
 import (
+	"bytes"
 	"encoding/hex"
 	"errors"
 	"regexp"
 
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/btcsuite/btcd/btcutil/psbt"
 	"github.com/btcsuite/btcd/txscript"
 )
 
@@ -26,6 +29,63 @@ func GetPaymentHashFromScript(scriptHex string) (*string, error) {
     if len(match) > 0 {
 		return &match[1], nil
 	} else {
-		return nil, errors.New("No match found")
+		return nil, errors.New("no match found")
 	}
 }
+
+func CalculateWitnessHash(amount int64, script string, transaction string) (*string, error) {
+	decodedTx, err := hex.DecodeString(transaction)
+	if err != nil {
+		return nil, err
+	}
+
+	tx, err := btcutil.NewTxFromBytes(decodedTx)
+	if err != nil {
+		return nil ,err
+	}
+
+	decodedScript, err := hex.DecodeString(script)
+	if err != nil {
+		return nil ,err
+	}
+
+	prevOutFetcher := txscript.NewCannedPrevOutputFetcher(
+		decodedScript, amount,
+	)
+
+	txhash := txscript.NewTxSigHashes(tx.MsgTx(), prevOutFetcher)
+	hash, err := txscript.CalcWitnessSigHash(decodedScript, txhash, txscript.SigHashAll, tx.MsgTx(), 0, amount)
+	if err != nil {
+		return nil, err
+	}
+
+	result := hex.EncodeToString(hash)
+
+	return &result, nil
+}
+
+func CalculateWitnessHashPSBT(transaction string) (*string, error) {
+	transactionBytes, err := hex.DecodeString(transaction)
+	if err != nil {
+		return nil, err
+	}
+	// Reader for the PSBT.
+	psbtBytes := []byte(transactionBytes)
+	r := bytes.NewReader(psbtBytes)
+
+	// Create instance of a PSBT.
+	p, err := psbt.NewFromRawBytes(r, false)
+	if err != nil {
+		return nil, err
+	}
+	prevOutFetcher := txscript.NewCannedPrevOutputFetcher(
+		p.Inputs[0].WitnessUtxo.PkScript, int64(p.Inputs[0].WitnessUtxo.Value),
+	)
+	sigHashes := txscript.NewTxSigHashes(p.UnsignedTx, prevOutFetcher)
+	hash, err := txscript.CalcWitnessSigHash(p.Inputs[0].WitnessScript, sigHashes, txscript.SigHashAll, p.UnsignedTx, 0, int64(p.Inputs[0].WitnessUtxo.Value))
+	if err != nil {
+		return nil, err
+	}
+	result := hex.EncodeToString(hash)
+	return &result, nil
+}

remotesigning/validator.go

@@ -1,7 +1,11 @@
 // Copyright ©, 2023-present, Lightspark Group, Inc. - All Rights Reserved
 package remotesigning
 
-import "github.com/lightsparkdev/go-sdk/webhooks"
+import (
+	"strings"
+
+	"github.com/lightsparkdev/go-sdk/webhooks"
+)
 
 // Validator an interface which decides whether to sign or reject a remote signing webhook event.
 type Validator interface {
@@ -13,3 +17,35 @@ type PositiveValidator struct{}
 func (v PositiveValidator) ShouldSign(webhooks.WebhookEvent) bool {
 	return true
 }
+
+type HashValidator struct {} 
+
+func (v HashValidator) ShouldSign(webhookEvent webhooks.WebhookEvent) bool {
+	request, err := ParseDeriveAndSignRequest(webhookEvent)	
+	if err != nil {
+		// Only validate DeriveAndSignRequest events
+		return true
+	}
+
+	for _, signing := range request.SigningJobs {
+		if strings.HasSuffix(signing.DerivationPath, "/2") {
+			msg, err := CalculateWitnessHashPSBT(*signing.Transaction)
+			if err != nil {
+				return false
+			}
+			if strings.Compare(*msg, signing.Message) != 0 {
+				return false
+			}
+		} else {
+			msg, err := CalculateWitnessHash(*signing.Amount, *signing.Script, *signing.Transaction)
+			if err != nil {
+				return false
+			}
+			if strings.Compare(*msg, signing.Message) != 0 {
+				return false
+			}
+		}
+	}
+
+	return true
+}