Impl account creation auth endpoints

common/accountcreationauths.go

@@ -4,6 +4,7 @@ import (
 	"time"
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
+	ethCrypto "github.com/ethereum/go-ethereum/crypto"
 	"github.com/iden3/go-iden3-crypto/babyjub"
 )
 
@@ -14,3 +15,36 @@ type AccountCreationAuth struct {
 	Signature []byte             `meddler:"signature"`
 	Timestamp time.Time          `meddler:"timestamp,utctime"`
 }
+
+// HashToSign builds the hash to be signed using BJJ pub key and the constant message
+func (a *AccountCreationAuth) HashToSign() ([]byte, error) {
+	// Calculate message to be signed
+	const msg = "I authorize this babyjubjub key for hermez rollup account creation"
+	comp, err := a.BJJ.Compress().MarshalText()
+	if err != nil {
+		return nil, err
+	}
+	// Hash message (msg || compressed-bjj)
+	return ethCrypto.Keccak256Hash([]byte(msg), comp).Bytes(), nil
+}
+
+// VerifySignature ensures that the Signature is done with the specified EthAddr
+func (a *AccountCreationAuth) VerifySignature() bool {
+	// Calculate hash to be signed
+	msg, err := a.HashToSign()
+	if err != nil {
+		return false
+	}
+	// Get public key from Signature
+	pubKBytes, err := ethCrypto.Ecrecover(msg, a.Signature)
+	if err != nil {
+		return false
+	}
+	pubK, err := ethCrypto.UnmarshalPubkey(pubKBytes)
+	if err != nil {
+		return false
+	}
+	// Get addr from pubK
+	addr := ethCrypto.PubkeyToAddress(*pubK)
+	return addr == a.EthAddr
+}