From 96342b0771ad3f5a1491ed12cac8afa6222789ab Mon Sep 17 00:00:00 2001
From: Michael Standen <mstan@horizon.io>
Date: Fri, 22 Nov 2024 14:32:34 +1300
Subject: [PATCH] v2 signature decoding validates EIP-6492 signatures

---
 core/v2/v2.go      | 35 +++++++++++++----------------------
 eip6492/eip6492.go | 24 ++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 22 deletions(-)

diff --git a/core/v2/v2.go b/core/v2/v2.go
index 7d84571..5d1c4de 100644
--- a/core/v2/v2.go
+++ b/core/v2/v2.go
@@ -10,14 +10,12 @@ import (
 	"io"
 	"math/big"
 
-	"github.com/0xsequence/ethkit/ethcontract"
 	"github.com/0xsequence/ethkit/ethrpc"
-	"github.com/0xsequence/ethkit/go-ethereum/accounts/abi/bind"
 	"github.com/0xsequence/ethkit/go-ethereum/common"
 	"github.com/0xsequence/ethkit/go-ethereum/common/hexutil"
 	"github.com/0xsequence/ethkit/go-ethereum/crypto"
-	"github.com/0xsequence/go-sequence/contracts"
 	"github.com/0xsequence/go-sequence/core"
+	"github.com/0xsequence/go-sequence/eip6492"
 )
 
 const (
@@ -25,8 +23,6 @@ const (
 	subdigestLeafImageHashPrefix = "Sequence static digest:\n"
 )
 
-var isValidSignatureMagicValue = [4]byte{0x16, 0x26, 0xba, 0x7e}
-
 var Core core.Core[*WalletConfig, core.Signature[*WalletConfig]] = v2Core{}
 
 func init() {
@@ -1055,27 +1051,22 @@ func (l *signatureTreeDynamicSignatureLeaf) recover(ctx context.Context, subdige
 
 	case dynamicSignatureTypeEIP1271:
 		effectiveWeight := l.weight
+		signature := l.signature
 
 		if provider != nil {
-			contract := ethcontract.NewContractCaller(l.address, contracts.IERC1271.ABI, provider)
-
-			var results []any
-			err := contract.Call(&bind.CallOpts{Context: ctx}, &results, "isValidSignature", subdigest.Hash, l.signature)
+			isValid, err := eip6492.ValidateEIP6492Offchain(ctx, provider, l.address, subdigest.Hash, signature, nil)
 			if err != nil {
-				return nil, nil, fmt.Errorf("unable to call isValidSignature on %v: %w", l.address, err)
-			}
-
-			if len(results) != 1 {
-				return nil, nil, fmt.Errorf("expected single return value from isValidSignature, got %v", len(results))
+				return nil, nil, fmt.Errorf("unable to validate signature for %v: %w", l.address, err)
 			}
-
-			magicValue, ok := results[0].([4]byte)
-			if !ok {
-				return nil, nil, fmt.Errorf("expected [4]byte return value from isValidSignature, got %T", results[0])
+			if !isValid {
+				return nil, nil, fmt.Errorf("invalid eip1271 signature for %v", l.address)
 			}
-
-			if magicValue != isValidSignatureMagicValue {
-				return nil, nil, fmt.Errorf("isValidSignature returned %v, expected %v", hexutil.Encode(magicValue[:]), hexutil.Encode(isValidSignatureMagicValue[:]))
+			if eip6492.IsEIP6492Signature(signature) {
+				// Decode the signature and use the nested signature for config recovery
+				_, _, signature, err = eip6492.DecodeEIP6492Signature(signature)
+				if err != nil {
+					return nil, nil, fmt.Errorf("unable to decode eip6492 signature: %w", err)
+				}
 			}
 		} else {
 			// Set the effective weight to 0
@@ -1087,7 +1078,7 @@ func (l *signatureTreeDynamicSignatureLeaf) recover(ctx context.Context, subdige
 		signerSignatures.Insert(l.address, core.SignerSignature{
 			Subdigest: subdigest,
 			Type:      l.type_.signerSignatureType(),
-			Signature: l.signature,
+			Signature: signature,
 		})
 
 		return &WalletConfigTreeAddressLeaf{
diff --git a/eip6492/eip6492.go b/eip6492/eip6492.go
index 864ca15..ab0937c 100644
--- a/eip6492/eip6492.go
+++ b/eip6492/eip6492.go
@@ -3,6 +3,7 @@ package eip6492
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"math/big"
 
 	"github.com/0xsequence/ethkit/ethcoder"
@@ -189,6 +190,29 @@ const EIP_6492_SUFFIX = "0x64926492649264926492649264926492649264926492649264926
 
 var EIP6492MagicBytes = hexutil.MustDecode(EIP_6492_SUFFIX)
 
+func IsEIP6492Signature(signature []byte) bool {
+	return bytes.HasSuffix(signature, EIP6492MagicBytes)
+}
+
+func DecodeEIP6492Signature(signature []byte) (common.Address, []byte, []byte, error) {
+	if !IsEIP6492Signature(signature) {
+		return common.Address{}, nil, nil, fmt.Errorf("not an eip6492 signature")
+	}
+
+	// Strip the magic bytes
+	signature = signature[:len(signature)-32]
+
+	var create2Factory common.Address
+	var factoryCalldata []byte
+	var sigToValidate []byte
+
+	if err := ethcoder.AbiDecoder([]string{"address", "bytes", "bytes"}, signature, []interface{}{&create2Factory, &factoryCalldata, &sigToValidate}); err != nil {
+		return common.Address{}, nil, nil, err
+	}
+
+	return create2Factory, factoryCalldata, sigToValidate, nil
+}
+
 func ValidateEIP6492Offchain(
 	ctx context.Context,
 	provider *ethrpc.Provider,