Add HashGlobalInputs for ZKInputs

Add HashGlobalInputs for ZKInputs compatible with js & circom circuits version.

Compatible with hermeznetwork/commonjs at version: c6a1448db5bae4cda839ce36c1f35d8defccc9cd
(c6a1448db5)

common/utils.go

@@ -1,9 +1,11 @@
 package common
 
 import (
+	"encoding/hex"
 	"math/big"
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
+	"github.com/iden3/go-iden3-crypto/babyjub"
 )
 
 // SwapEndianness swaps the order of the bytes in the slice.
@@ -19,3 +21,18 @@ func SwapEndianness(b []byte) []byte {
 func EthAddrToBigInt(a ethCommon.Address) *big.Int {
 	return new(big.Int).SetBytes(a.Bytes())
 }
+
+// BJJFromStringWithChecksum parses a hex string in Hermez format (which has
+// the Hermez checksum at the last byte, and is encoded in BigEndian) and
+// returns the corresponding *babyjub.PublicKey. This method is not part of the
+// spec, is used for importing javascript test vectors data.
+func BJJFromStringWithChecksum(s string) (*babyjub.PublicKey, error) {
+	b, err := hex.DecodeString(s)
+	if err != nil {
+		return nil, err
+	}
+	pkBytes := SwapEndianness(b)
+	var pkComp babyjub.PublicKeyComp
+	copy(pkComp[:], pkBytes[:])
+	return pkComp.Decompress()
+}