fear(eip712): Add EIP-712 encoding for multiple messages of the same type (#1483)

* Add EIP-712 encoding for multiple messages of the same type

* Fix Protobuf encoding bug

* Add ante tests

* Refactor naming and minor implementation details

* Test empty transaction coverage

* Address revisions for code clarity

* Move aminoMessage type definition

app/ante/ante_test.go

@@ -387,7 +387,7 @@ func (suite AnteTestSuite) TestAnteHandler() {
 					from, grantee, &banktypes.SendAuthorization{SpendLimit: gasAmount}, &expiresAt,
 				)
 				suite.Require().NoError(err)
-				return suite.CreateTestEIP712CosmosTxBuilder(from, privKey, "ethermint_9000-1", gas, gasAmount, msg).GetTx()
+				return suite.CreateTestEIP712SingleMessageTxBuilder(from, privKey, "ethermint_9000-1", gas, gasAmount, msg).GetTx()
 			}, false, false, true,
 		},
 
@@ -457,6 +457,28 @@ func (suite AnteTestSuite) TestAnteHandler() {
 				return txBuilder.GetTx()
 			}, false, false, true,
 		},
+		{
+			"success- DeliverTx EIP712 Multiple MsgSend",
+			func() sdk.Tx {
+				from := acc.GetAddress()
+				coinAmount := sdk.NewCoin(evmtypes.DefaultEVMDenom, sdk.NewInt(20))
+				amount := sdk.NewCoins(coinAmount)
+				gas := uint64(200000)
+				txBuilder := suite.CreateTestEIP712MultipleMsgSend(from, privKey, "ethermint_9000-1", gas, amount)
+				return txBuilder.GetTx()
+			}, false, false, true,
+		},
+		{
+			"fails - DeliverTx EIP712 Multiple Signers",
+			func() sdk.Tx {
+				from := acc.GetAddress()
+				coinAmount := sdk.NewCoin(evmtypes.DefaultEVMDenom, sdk.NewInt(20))
+				amount := sdk.NewCoins(coinAmount)
+				gas := uint64(200000)
+				txBuilder := suite.CreateTestEIP712MultipleSignerMsgs(from, privKey, "ethermint_9000-1", gas, amount)
+				return txBuilder.GetTx()
+			}, false, false, false,
+		},
 		{
 			"fails - DeliverTx EIP712 signed Cosmos Tx with wrong Chain ID",
 			func() sdk.Tx {

app/ante/utils_test.go

@@ -272,7 +272,7 @@ func (suite *AnteTestSuite) CreateTestEIP712TxBuilderMsgSend(from sdk.AccAddress
 	// Build MsgSend
 	recipient := sdk.AccAddress(common.Address{}.Bytes())
 	msgSend := types2.NewMsgSend(from, recipient, sdk.NewCoins(sdk.NewCoin(evmtypes.DefaultEVMDenom, sdkmath.NewInt(1))))
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgSend)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgSend)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712TxBuilderMsgDelegate(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
@@ -280,7 +280,7 @@ func (suite *AnteTestSuite) CreateTestEIP712TxBuilderMsgDelegate(from sdk.AccAdd
 	valEthAddr := tests.GenerateAddress()
 	valAddr := sdk.ValAddress(valEthAddr.Bytes())
 	msgSend := types3.NewMsgDelegate(from, valAddr, sdk.NewCoin(evmtypes.DefaultEVMDenom, sdkmath.NewInt(20)))
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgSend)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgSend)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712MsgCreateValidator(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
@@ -296,7 +296,7 @@ func (suite *AnteTestSuite) CreateTestEIP712MsgCreateValidator(from sdk.AccAddre
 		sdk.OneInt(),
 	)
 	suite.Require().NoError(err)
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgCreate)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgCreate)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712MsgCreateValidator2(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
@@ -313,7 +313,7 @@ func (suite *AnteTestSuite) CreateTestEIP712MsgCreateValidator2(from sdk.AccAddr
 		sdk.OneInt(),
 	)
 	suite.Require().NoError(err)
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgCreate)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgCreate)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712SubmitProposal(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins, deposit sdk.Coins) client.TxBuilder {
@@ -321,7 +321,7 @@ func (suite *AnteTestSuite) CreateTestEIP712SubmitProposal(from sdk.AccAddress,
 	suite.Require().True(ok)
 	msgSubmit, err := types5.NewMsgSubmitProposal(proposal, deposit, from)
 	suite.Require().NoError(err)
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgSubmit)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgSubmit)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712GrantAllowance(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
@@ -335,7 +335,7 @@ func (suite *AnteTestSuite) CreateTestEIP712GrantAllowance(from sdk.AccAddress,
 	grantedAddr := suite.app.AccountKeeper.NewAccountWithAddress(suite.ctx, granted.Bytes())
 	msgGrant, err := feegrant.NewMsgGrantAllowance(basic, from, grantedAddr.GetAddress())
 	suite.Require().NoError(err)
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgGrant)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgGrant)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712MsgEditValidator(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
@@ -346,7 +346,7 @@ func (suite *AnteTestSuite) CreateTestEIP712MsgEditValidator(from sdk.AccAddress
 		nil,
 		nil,
 	)
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgEdit)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgEdit)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712MsgSubmitEvidence(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
@@ -359,12 +359,12 @@ func (suite *AnteTestSuite) CreateTestEIP712MsgSubmitEvidence(from sdk.AccAddres
 	})
 	suite.Require().NoError(err)
 
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgEvidence)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgEvidence)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712MsgVoteV1(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
 	msgVote := govtypes.NewMsgVote(from, 1, govtypes.VoteOption_VOTE_OPTION_YES, "")
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgVote)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgVote)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712SubmitProposalV1(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
@@ -403,14 +403,28 @@ func (suite *AnteTestSuite) CreateTestEIP712SubmitProposalV1(from sdk.AccAddress
 
 	suite.Require().NoError(err)
 
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, msgProposal)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, msgProposal)
 }
 
 func (suite *AnteTestSuite) CreateTestEIP712MsgExec(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
 	recipient := sdk.AccAddress(common.Address{}.Bytes())
 	msgSend := types2.NewMsgSend(from, recipient, sdk.NewCoins(sdk.NewCoin(evmtypes.DefaultEVMDenom, sdkmath.NewInt(1))))
 	msgExec := authz.NewMsgExec(from, []sdk.Msg{msgSend})
-	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, &msgExec)
+	return suite.CreateTestEIP712SingleMessageTxBuilder(from, priv, chainId, gas, gasAmount, &msgExec)
+}
+
+func (suite *AnteTestSuite) CreateTestEIP712MultipleMsgSend(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
+	recipient := sdk.AccAddress(common.Address{}.Bytes())
+	msgSend := types2.NewMsgSend(from, recipient, sdk.NewCoins(sdk.NewCoin(evmtypes.DefaultEVMDenom, sdkmath.NewInt(1))))
+	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, []sdk.Msg{msgSend, msgSend, msgSend})
+}
+
+// Fails
+func (suite *AnteTestSuite) CreateTestEIP712MultipleSignerMsgs(from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins) client.TxBuilder {
+	recipient := sdk.AccAddress(common.Address{}.Bytes())
+	msgSend1 := types2.NewMsgSend(from, recipient, sdk.NewCoins(sdk.NewCoin(evmtypes.DefaultEVMDenom, sdkmath.NewInt(1))))
+	msgSend2 := types2.NewMsgSend(recipient, from, sdk.NewCoins(sdk.NewCoin(evmtypes.DefaultEVMDenom, sdkmath.NewInt(1))))
+	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, []sdk.Msg{msgSend1, msgSend2})
 }
 
 // StdSignBytes returns the bytes to sign for a transaction.
@@ -451,8 +465,14 @@ func StdSignBytes(cdc *codec.LegacyAmino, chainID string, accnum uint64, sequenc
 	return sdk.MustSortJSON(bz)
 }
 
-func (suite *AnteTestSuite) CreateTestEIP712CosmosTxBuilder(
+func (suite *AnteTestSuite) CreateTestEIP712SingleMessageTxBuilder(
 	from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins, msg sdk.Msg,
+) client.TxBuilder {
+	return suite.CreateTestEIP712CosmosTxBuilder(from, priv, chainId, gas, gasAmount, []sdk.Msg{msg})
+}
+
+func (suite *AnteTestSuite) CreateTestEIP712CosmosTxBuilder(
+	from sdk.AccAddress, priv cryptotypes.PrivKey, chainId string, gas uint64, gasAmount sdk.Coins, msgs []sdk.Msg,
 ) client.TxBuilder {
 	var err error
 
@@ -473,8 +493,8 @@ func (suite *AnteTestSuite) CreateTestEIP712CosmosTxBuilder(
 	fee := legacytx.NewStdFee(gas, gasAmount)
 	accNumber := suite.app.AccountKeeper.GetAccount(suite.ctx, from).GetAccountNumber()
 
-	data := legacytx.StdSignBytes(chainId, accNumber, nonce, 0, fee, []sdk.Msg{msg}, "", nil)
+	data := legacytx.StdSignBytes(chainId, accNumber, nonce, 0, fee, msgs, "", nil)
-	typedData, err := eip712.WrapTxToTypedData(ethermintCodec, ethChainId, msg, data, &eip712.FeeDelegationOptions{
+	typedData, err := eip712.WrapTxToTypedData(ethermintCodec, ethChainId, msgs[0], data, &eip712.FeeDelegationOptions{
 		FeePayer: from,
 	})
 	suite.Require().NoError(err)
@@ -517,7 +537,7 @@ func (suite *AnteTestSuite) CreateTestEIP712CosmosTxBuilder(
 	err = builder.SetSignatures(sigsV2)
 	suite.Require().NoError(err)
 
-	err = builder.SetMsgs(msg)
+	err = builder.SetMsgs(msgs...)
 	suite.Require().NoError(err)
 
 	return builder

ethereum/eip712/eip712_test.go

@@ -93,6 +93,9 @@ func (suite *EIP712TestSuite) TestEIP712SignatureVerification() {
 		signing.SignMode_SIGN_MODE_LEGACY_AMINO_JSON,
 	}
 
+	// Fixed test address
+	testAddress := suite.createTestAddress()
+
 	testCases := []struct {
 		title         string
 		chainId       string
@@ -176,7 +179,30 @@ func (suite *EIP712TestSuite) TestEIP712SignatureVerification() {
 			expectSuccess: true,
 		},
 		{
-			title: "Fails - Two MsgVotes",
+			title: "Succeeds - Two Single-Signer MsgDelegate",
+			fee: txtypes.Fee{
+				Amount:   suite.makeCoins("aphoton", math.NewInt(2000)),
+				GasLimit: 20000,
+			},
+			memo: "",
+			msgs: []sdk.Msg{
+				stakingtypes.NewMsgDelegate(
+					testAddress,
+					sdk.ValAddress(suite.createTestAddress()),
+					suite.makeCoins("photon", math.NewInt(1))[0],
+				),
+				stakingtypes.NewMsgDelegate(
+					testAddress,
+					sdk.ValAddress(suite.createTestAddress()),
+					suite.makeCoins("photon", math.NewInt(5))[0],
+				),
+			},
+			accountNumber: 25,
+			sequence:      78,
+			expectSuccess: true,
+		},
+		{
+			title: "Fails - Two MsgVotes with Different Signers",
 			fee: txtypes.Fee{
 				Amount:   suite.makeCoins("aphoton", math.NewInt(2000)),
 				GasLimit: 20000,
@@ -196,10 +222,22 @@ func (suite *EIP712TestSuite) TestEIP712SignatureVerification() {
 			},
 			accountNumber: 25,
 			sequence:      78,
-			expectSuccess: false, // Multiple messages are currently not allowed
+			expectSuccess: false,
 		},
 		{
-			title: "Fails - MsgSend + MsgVote",
+			title: "Fails - Empty transaction",
+			fee: txtypes.Fee{
+				Amount:   suite.makeCoins("aphoton", math.NewInt(2000)),
+				GasLimit: 20000,
+			},
+			memo:          "",
+			msgs:          []sdk.Msg{},
+			accountNumber: 25,
+			sequence:      78,
+			expectSuccess: false,
+		},
+		{
+			title: "Fails - Single-Signer MsgSend + MsgVote",
 			fee: txtypes.Fee{
 				Amount:   suite.makeCoins("aphoton", math.NewInt(2000)),
 				GasLimit: 20000,
@@ -207,12 +245,12 @@ func (suite *EIP712TestSuite) TestEIP712SignatureVerification() {
 			memo: "",
 			msgs: []sdk.Msg{
 				govtypes.NewMsgVote(
-					suite.createTestAddress(),
+					testAddress,
 					5,
 					govtypes.OptionNo,
 				),
 				banktypes.NewMsgSend(
-					suite.createTestAddress(),
+					testAddress,
 					suite.createTestAddress(),
 					suite.makeCoins("photon", math.NewInt(50)),
 				),

ethereum/eip712/encoding.go

@@ -1,13 +1,14 @@
 package eip712
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 
 	"github.com/cosmos/cosmos-sdk/simapp/params"
 	"github.com/cosmos/cosmos-sdk/x/auth/migrations/legacytx"
 
-	cosmosTypes "github.com/cosmos/cosmos-sdk/types"
+	sdk "github.com/cosmos/cosmos-sdk/types"
 	txTypes "github.com/cosmos/cosmos-sdk/types/tx"
 
 	apitypes "github.com/ethereum/go-ethereum/signer/core/apitypes"
@@ -16,9 +17,14 @@ import (
 	"github.com/cosmos/cosmos-sdk/codec"
 )
 
+type aminoMessage struct {
+	Type  string      `json:"type"`
+	Value interface{} `json:"value"`
+}
+
 var (
-	ethermintProtoCodec codec.ProtoCodecMarshaler
+	protoCodec codec.ProtoCodecMarshaler
-	ethermintAminoCodec *codec.LegacyAmino
+	aminoCodec *codec.LegacyAmino
 )
 
 // SetEncodingConfig set the encoding config to the singleton codecs (Amino and Protobuf).
@@ -26,8 +32,8 @@ var (
 // populated with all relevant message types. As a result, we must call this method on app
 // initialization with the app's encoding config.
 func SetEncodingConfig(cfg params.EncodingConfig) {
-	ethermintAminoCodec = cfg.Amino
+	aminoCodec = cfg.Amino
-	ethermintProtoCodec = codec.NewProtoCodec(cfg.InterfaceRegistry)
+	protoCodec = codec.NewProtoCodec(cfg.InterfaceRegistry)
 }
 
 // Get the EIP-712 object hash for the given SignDoc bytes by first decoding the bytes into
@@ -59,67 +65,69 @@ func GetEIP712TypedDataForMsg(signDocBytes []byte) (apitypes.TypedData, error) {
 	// Attempt to decode as both Amino and Protobuf since the message format is unknown.
 	// If either decode works, we can move forward with the corresponding typed data.
 	typedDataAmino, errAmino := decodeAminoSignDoc(signDocBytes)
-	if errAmino == nil && verifyEIP712Payload(typedDataAmino) {
+	if errAmino == nil && isValidEIP712Payload(typedDataAmino) {
 		return typedDataAmino, nil
 	}
 	typedDataProtobuf, errProtobuf := decodeProtobufSignDoc(signDocBytes)
-	if errProtobuf == nil && verifyEIP712Payload(typedDataProtobuf) {
+	if errProtobuf == nil && isValidEIP712Payload(typedDataProtobuf) {
 		return typedDataProtobuf, nil
 	}
 
-	return apitypes.TypedData{}, fmt.Errorf("could not decode sign doc as either Amino or Protobuf. amino: %v protobuf: %v", errAmino, errProtobuf)
+	return apitypes.TypedData{}, fmt.Errorf("could not decode sign doc as either Amino or Protobuf.\n amino: %v\n protobuf: %v", errAmino, errProtobuf)
 }
 
-// verifyEIP712Payload ensures that the given TypedData does not contain empty fields from
+// isValidEIP712Payload ensures that the given TypedData does not contain empty fields from
 // an improper initialization.
-func verifyEIP712Payload(typedData apitypes.TypedData) bool {
+func isValidEIP712Payload(typedData apitypes.TypedData) bool {
 	return len(typedData.Message) != 0 && len(typedData.Types) != 0 && typedData.PrimaryType != "" && typedData.Domain != apitypes.TypedDataDomain{}
 }
 
-// Attempt to decode the SignDoc bytes as an Amino SignDoc and return an error on failure
+// decodeAminoSignDoc attempts to decode the provided sign doc (bytes) as an Amino payload
+// and returns a signable EIP-712 TypedData object.
 func decodeAminoSignDoc(signDocBytes []byte) (apitypes.TypedData, error) {
 	var aminoDoc legacytx.StdSignDoc
-
+	if err := aminoCodec.UnmarshalJSON(signDocBytes, &aminoDoc); err != nil {
-	if err := ethermintAminoCodec.UnmarshalJSON(signDocBytes, &aminoDoc); err != nil {
 		return apitypes.TypedData{}, err
 	}
 
-	// Unwrap fees
 	var fees legacytx.StdFee
-	if err := ethermintAminoCodec.UnmarshalJSON(aminoDoc.Fee, &fees); err != nil {
+	if err := aminoCodec.UnmarshalJSON(aminoDoc.Fee, &fees); err != nil {
 		return apitypes.TypedData{}, err
 	}
 
-	if len(aminoDoc.Msgs) != 1 {
+	// Validate payload messages
-		return apitypes.TypedData{}, fmt.Errorf("invalid number of messages in SignDoc, expected 1 but got %v", len(aminoDoc.Msgs))
+	msgs := make([]sdk.Msg, len(aminoDoc.Msgs))
+	for i, jsonMsg := range aminoDoc.Msgs {
+		var m sdk.Msg
+		if err := aminoCodec.UnmarshalJSON(jsonMsg, &m); err != nil {
+			return apitypes.TypedData{}, fmt.Errorf("failed to unmarshal sign doc message: %w", err)
+		}
+		msgs[i] = m
 	}
 
-	var msg cosmosTypes.Msg
+	if err := validatePayloadMessages(msgs); err != nil {
-	if err := ethermintAminoCodec.UnmarshalJSON(aminoDoc.Msgs[0], &msg); err != nil {
+		return apitypes.TypedData{}, err
-		return apitypes.TypedData{}, fmt.Errorf("failed to unmarshal first message: %w", err)
 	}
 
-	// By default, use first address in list of signers to cover fee
+	// Use first message for fee payer and type inference
-	// Currently, support only one signer
+	msg := msgs[0]
-	if len(msg.GetSigners()) != 1 {
+
-		return apitypes.TypedData{}, errors.New("expected exactly one signer for message")
+	// By convention, the fee payer is the first address in the list of signers.
-	}
 	feePayer := msg.GetSigners()[0]
 	feeDelegation := &FeeDelegationOptions{
 		FeePayer: feePayer,
 	}
 
-	// Parse ChainID
 	chainID, err := ethermint.ParseChainID(aminoDoc.ChainID)
 	if err != nil {
 		return apitypes.TypedData{}, errors.New("invalid chain ID passed as argument")
 	}
 
 	typedData, err := WrapTxToTypedData(
-		ethermintProtoCodec,
+		protoCodec,
 		chainID.Uint64(),
 		msg,
-		signDocBytes, // Amino StdSignDocBytes
+		signDocBytes,
 		feeDelegation,
 	)
 	if err != nil {
@@ -129,21 +137,19 @@ func decodeAminoSignDoc(signDocBytes []byte) (apitypes.TypedData, error) {
 	return typedData, nil
 }
 
-// Attempt to decode the SignDoc bytes as a Protobuf SignDoc and return an error on failure
+// decodeProtobufSignDoc attempts to decode the provided sign doc (bytes) as a Protobuf payload
+// and returns a signable EIP-712 TypedData object.
 func decodeProtobufSignDoc(signDocBytes []byte) (apitypes.TypedData, error) {
-	// Decode sign doc
 	signDoc := &txTypes.SignDoc{}
 	if err := signDoc.Unmarshal(signDocBytes); err != nil {
 		return apitypes.TypedData{}, err
 	}
 
-	// Decode auth info
 	authInfo := &txTypes.AuthInfo{}
 	if err := authInfo.Unmarshal(signDoc.AuthInfoBytes); err != nil {
 		return apitypes.TypedData{}, err
 	}
 
-	// Decode body
 	body := &txTypes.TxBody{}
 	if err := body.Unmarshal(signDoc.BodyBytes); err != nil {
 		return apitypes.TypedData{}, err
@@ -154,60 +160,60 @@ func decodeProtobufSignDoc(signDocBytes []byte) (apitypes.TypedData, error) {
 		return apitypes.TypedData{}, errors.New("body contains unsupported fields: TimeoutHeight, ExtensionOptions, or NonCriticalExtensionOptions")
 	}
 
-	// Verify single message
+	if len(authInfo.SignerInfos) != 1 {
-	if len(body.Messages) != 1 {
+		return apitypes.TypedData{}, fmt.Errorf("invalid number of signer infos provided, expected 1 got %v", len(authInfo.SignerInfos))
-		return apitypes.TypedData{}, fmt.Errorf("invalid number of messages, expected 1 got %v", len(body.Messages))
 	}
 
-	// Decode signer info (single signer for now)
+	// Validate payload messages
+	msgs := make([]sdk.Msg, len(body.Messages))
+	for i, protoMsg := range body.Messages {
+		var m sdk.Msg
+		if err := protoCodec.UnpackAny(protoMsg, &m); err != nil {
+			return apitypes.TypedData{}, fmt.Errorf("could not unpack message object with error %w", err)
+		}
+		msgs[i] = m
+	}
+
+	if err := validatePayloadMessages(msgs); err != nil {
+		return apitypes.TypedData{}, err
+	}
+
+	// Use first message for fee payer and type inference
+	msg := msgs[0]
+
 	signerInfo := authInfo.SignerInfos[0]
 
-	// Parse ChainID
 	chainID, err := ethermint.ParseChainID(signDoc.ChainId)
 	if err != nil {
 		return apitypes.TypedData{}, fmt.Errorf("invalid chain ID passed as argument: %w", err)
 	}
 
-	// Create StdFee
 	stdFee := &legacytx.StdFee{
 		Amount: authInfo.Fee.Amount,
 		Gas:    authInfo.Fee.GasLimit,
 	}
 
-	// Parse Message (single message only)
-	var msg cosmosTypes.Msg
-	if err := ethermintProtoCodec.UnpackAny(body.Messages[0], &msg); err != nil {
-		return apitypes.TypedData{}, fmt.Errorf("could not unpack message object with error %w", err)
-	}
-
-	// Verify single signer (single signer for now)
-	if len(msg.GetSigners()) != 1 {
-		return apitypes.TypedData{}, fmt.Errorf("invalid number of signers, expected 1 got %v", len(authInfo.SignerInfos))
-	}
-
-	// Init fee payer
 	feePayer := msg.GetSigners()[0]
 	feeDelegation := &FeeDelegationOptions{
 		FeePayer: feePayer,
 	}
 
-	// Get tip
 	tip := authInfo.Tip
 
-	// Create Legacy SignBytes (expected type for WrapTxToTypedData)
+	// WrapTxToTypedData expects the payload as an Amino Sign Doc
 	signBytes := legacytx.StdSignBytes(
 		signDoc.ChainId,
 		signDoc.AccountNumber,
 		signerInfo.Sequence,
 		body.TimeoutHeight,
 		*stdFee,
-		[]cosmosTypes.Msg{msg},
+		msgs,
 		body.Memo,
 		tip,
 	)
 
 	typedData, err := WrapTxToTypedData(
-		ethermintProtoCodec,
+		protoCodec,
 		chainID.Uint64(),
 		msg,
 		signBytes,
@@ -219,3 +225,61 @@ func decodeProtobufSignDoc(signDocBytes []byte) (apitypes.TypedData, error) {
 
 	return typedData, nil
 }
+
+// validatePayloadMessages ensures that the transaction messages can be represented in an EIP-712
+// encoding by checking that messages exist, are of the same type, and share a single signer.
+func validatePayloadMessages(msgs []sdk.Msg) error {
+	if len(msgs) == 0 {
+		return errors.New("unable to build EIP-712 payload: transaction does contain any messages")
+	}
+
+	var msgType string
+	var msgSigner sdk.AccAddress
+
+	for i, m := range msgs {
+		t, err := getMsgType(m)
+		if err != nil {
+			return err
+		}
+
+		if len(m.GetSigners()) != 1 {
+			return errors.New("unable to build EIP-712 payload: expect exactly 1 signer")
+		}
+
+		if i == 0 {
+			msgType = t
+			msgSigner = m.GetSigners()[0]
+			continue
+		}
+
+		if t != msgType {
+			return errors.New("unable to build EIP-712 payload: different types of messages detected")
+		}
+
+		if !msgSigner.Equals(m.GetSigners()[0]) {
+			return errors.New("unable to build EIP-712 payload: multiple signers detected")
+		}
+	}
+
+	return nil
+}
+
+// getMsgType returns the message type prefix for the given Cosmos SDK Msg
+func getMsgType(msg sdk.Msg) (string, error) {
+	jsonBytes, err := aminoCodec.MarshalJSON(msg)
+	if err != nil {
+		return "", err
+	}
+
+	var jsonMsg aminoMessage
+	if err := json.Unmarshal(jsonBytes, &jsonMsg); err != nil {
+		return "", err
+	}
+
+	// Verify Type was successfully filled in
+	if jsonMsg.Type == "" {
+		return "", errors.New("could not decode message: type is missing")
+	}
+
+	return jsonMsg.Type, nil
+}