Define an abstract type for wallet.Sig

backend/ethereum/channel/adjudicator.go

@@ -27,9 +27,11 @@ import (
 	"perun.network/go-perun/backend/ethereum/bindings"
 	"perun.network/go-perun/backend/ethereum/bindings/adjudicator"
 	cherrors "perun.network/go-perun/backend/ethereum/channel/errors"
+	ethwallet "perun.network/go-perun/backend/ethereum/wallet"
 	"perun.network/go-perun/channel"
 	"perun.network/go-perun/client"
 	"perun.network/go-perun/log"
+	"perun.network/go-perun/wallet"
 	psync "polycry.pt/poly-go/sync"
 )
 
@@ -81,7 +83,11 @@ func (a *Adjudicator) Progress(ctx context.Context, req channel.ProgressReq) err
 		state adjudicator.ChannelState,
 		_ [][]byte,
 	) (*types.Transaction, error) {
-		return a.contract.Progress(opts, params, state, ethNewState, ethActorIndex, req.Sig)
+		sigBytes, err := req.Sig.MarshalBinary()
+		if err != nil {
+			return nil, errors.WithMessage(err, "converting to byte array")
+		}
+		return a.contract.Progress(opts, params, state, ethNewState, ethActorIndex, sigBytes)
 	}
 	return a.call(ctx, req.AdjudicatorReq, progress, Progress)
 }
@@ -105,12 +111,35 @@ func toEthSignedStates(subChannels []channel.SignedState) (ethSubChannels []adju
 		ethSubChannels[i] = adjudicator.AdjudicatorSignedState{
 			Params: ToEthParams(x.Params),
 			State:  ToEthState(x.State),
-			Sigs:   x.Sigs,
+			Sigs:   sigsToByteArrays(x.Sigs),
 		}
 	}
 	return
 }
 
+func sigsToByteArrays(signs []wallet.Sig) [][]byte {
+	byteArrays := make([][]byte, len(signs))
+	var err error
+	for i := range signs {
+		if signs[i] != nil {
+			byteArrays[i], err = signs[i].MarshalBinary()
+			if err != nil {
+				panic("Marshalling to Binary should not error: " + err.Error())
+			}
+		}
+	}
+	return byteArrays
+}
+
+func byteArraysToSigs(byteArrays [][]byte) []wallet.Sig {
+	sigs := make([]wallet.Sig, len(byteArrays))
+	for i := range byteArrays {
+		sig := (ethwallet.Sig)(byteArrays[i])
+		sigs[i] = &sig
+	}
+	return sigs
+}
+
 func (a *Adjudicator) callConclude(ctx context.Context, req channel.AdjudicatorReq, subStates channel.StateMap) error {
 	ethSubStates := toEthSubStates(req.Tx.State, subStates)
 
@@ -153,7 +182,7 @@ func (a *Adjudicator) call(ctx context.Context, req channel.AdjudicatorReq, fn a
 		if err != nil {
 			return nil, errors.WithMessage(err, "creating transactor")
 		}
-		tx, err := fn(trans, ethParams, ethState, req.Tx.Sigs)
+		tx, err := fn(trans, ethParams, ethState, sigsToByteArrays(req.Tx.Sigs))
 		if err != nil {
 			err = cherrors.CheckIsChainNotReachableError(err)
 			return nil, errors.WithMessage(err, "calling adjudicator function")

backend/ethereum/channel/adjudicator_test.go

@@ -30,6 +30,7 @@ import (
 	ethwallettest "perun.network/go-perun/backend/ethereum/wallet/test"
 	"perun.network/go-perun/channel"
 	channeltest "perun.network/go-perun/channel/test"
+	"perun.network/go-perun/wallet"
 	pkgtest "polycry.pt/poly-go/test"
 )
 
@@ -43,7 +44,7 @@ func testSignState(t *testing.T, accounts []*keystore.Account, state *channel.St
 }
 
 func signState(accounts []*keystore.Account, state *channel.State) (channel.Transaction, error) {
-	sigs := make([][]byte, len(accounts))
+	sigs := make([]wallet.Sig, len(accounts))
 	for i := range accounts {
 		sig, err := channel.Sign(accounts[i], state)
 		if err != nil {

backend/ethereum/channel/subscription.go

@@ -193,7 +193,7 @@ func (a *Adjudicator) convertEvent(ctx context.Context, e *adjudicator.Adjudicat
 		return &channel.RegisteredEvent{
 			AdjudicatorEventBase: *base,
 			State:                &state,
-			Sigs:                 ch.Sigs,
+			Sigs:                 byteArraysToSigs(ch.Sigs),
 		}, nil
 
 	case phaseForceExec:

backend/ethereum/channel/test/transactor.go

@@ -27,7 +27,6 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"perun.network/go-perun/backend/ethereum/channel"
-	"perun.network/go-perun/backend/ethereum/wallet"
 )
 
 // TransactorSetup holds the setup for running generic tests on a transactor implementation.
@@ -90,7 +89,7 @@ func sigFromRSV(t *testing.T, r, s, _v *big.Int, chainID int64) []byte {
 		sigVAdd      = 35
 		sigVSubtract = 27
 	)
-	sig := make([]byte, wallet.SigLen)
+	sig := make([]byte, sigLen)
 	copy(sig[elemLen-len(r.Bytes()):elemLen], r.Bytes())
 	copy(sig[elemLen*2-len(s.Bytes()):elemLen*2], s.Bytes())
 	v := byte(_v.Uint64()) // Needed for chain ids > 110.

backend/ethereum/channel/withdraw.go

@@ -168,7 +168,12 @@ func (a *Adjudicator) newWithdrawalAuth(request channel.AdjudicatorReq, asset as
 	}
 
 	sig, err := request.Acc.SignData(enc)
-	return auth, sig, errors.WithMessage(err, "sign data")
+	if err != nil {
+		return assetholder.AssetHolderWithdrawalAuth{}, nil, errors.WithMessage(err, "sign data")
+	}
+	sigBytes, err := sig.MarshalBinary()
+
+	return auth, sigBytes, errors.WithMessage(err, "marshalling signature into bytes")
 }
 
 func encodeAssetHolderWithdrawalAuth(auth assetholder.AssetHolderWithdrawalAuth) ([]byte, error) {

backend/ethereum/wallet/backend.go

@@ -15,27 +15,15 @@
 package wallet
 
 import (
-	"io"
-
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/pkg/errors"
 
 	"perun.network/go-perun/wallet"
-	"perun.network/go-perun/wire/perunio"
 )
 
 // Backend implements the utility interface defined in the wallet package.
 type Backend struct{}
 
-// SigLen length of a signature in byte.
-// ref https://godoc.org/github.com/ethereum/go-ethereum/crypto/secp256k1#Sign
-// ref https://github.com/ethereum/go-ethereum/blob/54b271a86dd748f3b0bcebeaf678dc34e0d6177a/crypto/signature_cgo.go#L66
-const SigLen = 65
-
-// sigVSubtract value that is subtracted from the last byte of a signature if
-// the last bytes exceeds it.
-const sigVSubtract = 27
-
 // compile-time check that the ethereum backend implements the perun backend.
 var _ wallet.Backend = (*Backend)(nil)
 
@@ -46,31 +34,35 @@ func (b *Backend) NewAddress() wallet.Address {
 	return &addr
 }
 
-// DecodeSig reads a []byte with length of an ethereum signature.
-func (*Backend) DecodeSig(r io.Reader) (wallet.Sig, error) {
-	return DecodeSig(r)
+// NewSig returns a variable of type Sig, which can be used for unmarshalling a
+// signature from its binary representation.
+func (*Backend) NewSig() wallet.Sig {
+	sig := Sig(make([]byte, sigLen))
+	return &sig
 }
 
-// VerifySignature verifies a signature.
+// VerifySignature verifies if the signature on the given message was made by
+// this account.
 func (*Backend) VerifySignature(msg []byte, sig wallet.Sig, a wallet.Address) (bool, error) {
 	return VerifySignature(msg, sig, a)
 }
 
-// DecodeSig reads a []byte with length of an ethereum signature.
-func DecodeSig(r io.Reader) (wallet.Sig, error) {
-	buf := make(wallet.Sig, SigLen)
-	return buf, perunio.Decode(r, &buf)
-}
-
-// VerifySignature verifies if a signature was made by this account.
+// VerifySignature verifies if the signature on the given message was made by
+// this account.
 func VerifySignature(msg []byte, sig wallet.Sig, a wallet.Address) (bool, error) {
+	ethSig, ok := sig.(*Sig)
+	if !ok {
+		return false, errors.New("signature was not of the expected type")
+	}
+
 	hash := PrefixedHash(msg)
-	sigCopy := make([]byte, SigLen)
-	copy(sigCopy, sig)
-	if len(sigCopy) == SigLen && (sigCopy[SigLen-1] >= sigVSubtract) {
-		sigCopy[SigLen-1] -= sigVSubtract
+	ethSigCopy := make([]byte, sigLen)
+	copy(ethSigCopy, *ethSig)
+	if ethSigCopy[sigLen-1] >= sigVSubtract {
+		ethSigCopy[sigLen-1] -= sigVSubtract
 	}
-	pk, err := crypto.SigToPub(hash, sigCopy)
+
+	pk, err := crypto.SigToPub(hash, ethSigCopy)
 	if err != nil {
 		return false, errors.WithStack(err)
 	}

backend/ethereum/wallet/hd/account.go

@@ -35,14 +35,15 @@ func (a *Account) Address() wallet.Address {
 }
 
 // SignData is used to sign data with this account.
-func (a *Account) SignData(data []byte) ([]byte, error) {
+func (a *Account) SignData(data []byte) (wallet.Sig, error) {
 	hash := crypto.Keccak256(data)
 	sig, err := a.wallet.SignText(a.Account, hash)
 	if err != nil {
 		return nil, errors.Wrap(err, "SignText")
 	}
 	sig[64] += 27
-	return sig, nil
+	ethSig := (ethwallet.Sig)(sig)
+	return &ethSig, nil
 }
 
 // NewAccountFromEth creates a new perun account from a given ethereum account.

backend/ethereum/wallet/keystore/account.go

@@ -34,14 +34,15 @@ func (a *Account) Address() wallet.Address {
 }
 
 // SignData is used to sign data with this account.
-func (a *Account) SignData(data []byte) ([]byte, error) {
+func (a *Account) SignData(data []byte) (wallet.Sig, error) {
 	hash := ethwallet.PrefixedHash(data)
 	sig, err := a.wallet.Ks.SignHash(a.Account, hash)
 	if err != nil {
 		return nil, errors.Wrap(err, "SignHash")
 	}
 	sig[64] += 27
-	return sig, nil
+	ethSig := (ethwallet.Sig)(sig)
+	return &ethSig, nil
 }
 
 // NewAccountFromEth creates a new perun account from a given ethereum account.

backend/ethereum/wallet/keystore/wallet_test.go

@@ -62,7 +62,6 @@ func TestSignatures(t *testing.T) {
 	acc := ethwallettest.NewTmpWallet().NewAccount()
 	sign, err := acc.SignData(dataToSign)
 	assert.NoError(t, err, "Sign with new account should succeed")
-	assert.Equal(t, len(sign), ethwallet.SigLen, "Ethereum signature has wrong length")
 	valid, err := new(ethwallet.Backend).VerifySignature(dataToSign, sign, acc.Address())
 	assert.True(t, valid, "Verification should succeed")
 	assert.NoError(t, err, "Verification should succeed")
@@ -113,7 +112,8 @@ func TestCurve_SigningAndVerifying(t *testing.T) {
 	sig, err := hex.DecodeString("538da6430f7915832de165f89c69239020461b80861559a00d4f5a2a7705765219eb3969eb7095f8addb6bf9c9f96f6adf44cfd4a8136516f88b337a428bf1bb1b")
 	require.NoError(t, err, "decode sig should not error")
 	addr := ethwallet.Address(common.HexToAddress("f17f52151EbEF6C7334FAD080c5704D77216b732"))
-	b, err := ethwallet.VerifySignature(msg, sig, &addr)
+	ethSig := ethwallet.Sig(sig)
+	b, err := ethwallet.VerifySignature(msg, &ethSig, &addr)
 	assert.NoError(t, err, "VerifySignature should not error")
 	assert.True(t, b, "VerifySignature")
 }

backend/ethereum/wallet/sig.go

@@ -0,0 +1,57 @@
+// Copyright 2019 - See NOTICE file for copyright holders.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package wallet
+
+import (
+	"fmt"
+
+	"perun.network/go-perun/wallet"
+)
+
+const (
+	// sigLen length of a signature in byte.
+	// ref https://godoc.org/github.com/ethereum/go-ethereum/crypto/secp256k1#Sign
+	// ref https://github.com/ethereum/go-ethereum/blob/54b271a86dd748f3b0bcebeaf678dc34e0d6177a/crypto/signature_cgo.go#L66
+	sigLen = 65
+
+	// sigVSubtract value that is subtracted from the last byte of a signature if
+	// the last bytes exceeds it.
+	sigVSubtract = 27
+)
+
+// Sig represents a signature generated using an ethereum account.
+type Sig []byte
+
+// MarshalBinary marshals the signature into its binary representation. Error
+// will always be nil, it is for implementing BinaryMarshaler.
+func (s Sig) MarshalBinary() ([]byte, error) {
+	return s[:], nil
+}
+
+// UnmarshalBinary unmarshals the signature from its binary representation.
+func (s *Sig) UnmarshalBinary(data []byte) error {
+	if len(data) != sigLen {
+		return fmt.Errorf("unexpected signature length %d, want %d", len(data), sigLen) //nolint: goerr113
+	}
+	copy(*s, data)
+	return nil
+}
+
+// Clone returns a deep copy of the signature.
+func (s Sig) Clone() wallet.Sig {
+	clone := Sig(make([]byte, sigLen))
+	copy(clone, s)
+	return &clone
+}

backend/ethereum/wallet/simple/account.go

@@ -37,14 +37,15 @@ func (a *Account) Address() wallet.Address {
 }
 
 // SignData is used to sign data with this account.
-func (a *Account) SignData(data []byte) ([]byte, error) {
+func (a *Account) SignData(data []byte) (wallet.Sig, error) {
 	hash := ethwallet.PrefixedHash(data)
 	sig, err := a.SignHash(hash)
 	if err != nil {
 		return nil, errors.Wrap(err, "SignHash")
 	}
 	sig[64] += 27
-	return sig, nil
+	ethSig := (ethwallet.Sig)(sig)
+	return &ethSig, nil
 }
 
 // SignHash is used to sign an already prefixed hash with this account.

backend/ethereum/wallet/simple/wallet_test.go

@@ -78,7 +78,6 @@ func TestSignatures(t *testing.T) {
 	sig, err := acc.SignData(dataToSign)
 	assert.NoError(t, err, "Sign with new account should succeed")
 	assert.NotNil(t, sig)
-	assert.Equal(t, len(sig), ethwallet.SigLen, "Ethereum signature has wrong length")
 	valid, err := new(ethwallet.Backend).VerifySignature(dataToSign, sig, acc.Address())
 	assert.True(t, valid, "Verification should succeed")
 	assert.NoError(t, err, "Verification should succeed")

backend/sim/channel/backend.go

@@ -54,7 +54,7 @@ func (*backend) CalcID(p *channel.Params) (id channel.ID) {
 }
 
 // Sign signs `state`.
-func (b *backend) Sign(addr wallet.Account, state *channel.State) ([]byte, error) {
+func (b *backend) Sign(addr wallet.Account, state *channel.State) (wallet.Sig, error) {
 	log.WithFields(log.Fields{"channel": state.ID, "version": state.Version}).Tracef("Signing state")
 
 	buff := new(bytes.Buffer)
@@ -65,7 +65,7 @@ func (b *backend) Sign(addr wallet.Account, state *channel.State) ([]byte, error
 }
 
 // Verify verifies the signature for `state`.
-func (b *backend) Verify(addr wallet.Address, state *channel.State, sig []byte) (bool, error) {
+func (b *backend) Verify(addr wallet.Address, state *channel.State, sig wallet.Sig) (bool, error) {
 	buff := new(bytes.Buffer)
 	if err := state.Encode(buff); err != nil {
 		return false, errors.WithMessage(err, "pack state")