Update AccountCreationAuth & fix auth.HashToSign

- Fix AccountCreationAuth.HashToSign (was using `[]byte("0x...")`, which
uses the bytes of the string. Now uses the bytearray of the compressed
BJJ public key (compatible with js implementation))
- Update AccountCreationAuth to last specification (add to hash
parameters ChainID & HermezAddress)
- Add missing test to AccountCreationAuth

common/accountcreationauths.go

@@ -1,15 +1,20 @@
 package common
 
 import (
+	"encoding/binary"
 	"time"
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
 	ethCrypto "github.com/ethereum/go-ethereum/crypto"
-	"github.com/hermeznetwork/tracerr"
 	"github.com/iden3/go-iden3-crypto/babyjub"
 )
 
-// AccountCreationAuth authorizations sent by users to the L2DB, to be used for account creations when necessary
+// AccountCreationAuthMsg is the message that is signed to authorize an account
+// creation
+const AccountCreationAuthMsg = "I authorize this babyjubjub key for hermez rollup account creation"
+
+// AccountCreationAuth authorizations sent by users to the L2DB, to be used for
+// account creations when necessary
 type AccountCreationAuth struct {
 	EthAddr   ethCommon.Address     `meddler:"eth_addr"`
 	BJJ       babyjub.PublicKeyComp `meddler:"bjj"`
@@ -18,21 +23,21 @@ type AccountCreationAuth struct {
 }
 
 // HashToSign builds the hash to be signed using BJJ pub key and the constant message
-func (a *AccountCreationAuth) HashToSign() ([]byte, error) {
+func (a *AccountCreationAuth) HashToSign(chainID uint16,
+	hermezContractAddr ethCommon.Address) ([]byte, error) {
 	// Calculate message to be signed
-	const msg = "I authorize this babyjubjub key for hermez rollup account creation"
-	comp, err := a.BJJ.MarshalText()
-	if err != nil {
-		return nil, tracerr.Wrap(err)
-	}
-	// Hash message (msg || compressed-bjj)
-	return ethCrypto.Keccak256Hash([]byte(msg), comp).Bytes(), nil
+	var chainIDBytes [2]byte
+	binary.BigEndian.PutUint16(chainIDBytes[:], chainID)
+	// to hash: [AccountCreationAuthMsg | compressedBJJ | chainID | hermezContractAddr]
+	return ethCrypto.Keccak256Hash([]byte(AccountCreationAuthMsg), a.BJJ[:], chainIDBytes[:],
+		hermezContractAddr[:]).Bytes(), nil
 }
 
 // VerifySignature ensures that the Signature is done with the specified EthAddr
-func (a *AccountCreationAuth) VerifySignature() bool {
+func (a *AccountCreationAuth) VerifySignature(chainID uint16,
+	hermezContractAddr ethCommon.Address) bool {
 	// Calculate hash to be signed
-	msg, err := a.HashToSign()
+	msg, err := a.HashToSign(chainID, hermezContractAddr)
 	if err != nil {
 		return false
 	}

common/accountcreationauths_test.go

@@ -0,0 +1,41 @@
+package common
+
+import (
+	"encoding/hex"
+	"testing"
+
+	ethCommon "github.com/ethereum/go-ethereum/common"
+	ethCrypto "github.com/ethereum/go-ethereum/crypto"
+	"github.com/iden3/go-iden3-crypto/babyjub"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAccountCreationAuth(t *testing.T) {
+	// Ethereum key
+	ethSk, err := ethCrypto.HexToECDSA("fad9c8855b740a0b7ed4c221dbad0f33a83a49cad6b3fe8d5817ac83d38b6a19")
+	require.NoError(t, err)
+	ethAddr := ethCrypto.PubkeyToAddress(ethSk.PublicKey)
+
+	// BabyJubJub key
+	var sk babyjub.PrivateKey
+	_, err = hex.Decode(sk[:], []byte("0001020304050607080900010203040506070809000102030405060708090001"))
+	assert.NoError(t, err)
+
+	chainID := uint16(0)
+	hermezContractAddr := ethCommon.HexToAddress("0xc344E203a046Da13b0B4467EB7B3629D0C99F6E6")
+	a := AccountCreationAuth{
+		EthAddr: ethAddr,
+		BJJ:     sk.Public().Compress(),
+	}
+	msg, err := a.HashToSign(chainID, hermezContractAddr)
+	assert.NoError(t, err)
+	assert.Equal(t, "cb5a7e44329ff430c81fec49fb2ac6741f02d5ec96cbcb618a6991f0a9c80ffd", hex.EncodeToString(msg))
+
+	// sign AccountCreationAuth with eth key
+	sig, err := ethCrypto.Sign(msg, ethSk)
+	assert.NoError(t, err)
+	a.Signature = sig
+
+	assert.True(t, a.VerifySignature(chainID, hermezContractAddr))
+}