Resolve #4

constants/constants.go

@@ -1,12 +1,15 @@
 package constants
 
 import (
-	"github.com/iden3/go-iden3-crypto/utils"
+	"fmt"
 	"math/big"
+
+	"github.com/iden3/go-iden3-crypto/ff"
 )
 
 // Q is the order of the integer field (Zq) that fits inside the SNARK.
 var Q *big.Int
+var QE *ff.Element
 
 // Zero is 0.
 var Zero *big.Int
@@ -21,6 +24,11 @@ func init() {
 	Zero = big.NewInt(0)
 	One = big.NewInt(1)
 	MinusOne = big.NewInt(-1)
-	Q = utils.NewIntFromString(
-		"21888242871839275222246405745257275088548364400416034343698204186575808495617")
+
+	qString := "21888242871839275222246405745257275088548364400416034343698204186575808495617"
+	var ok bool
+	Q, ok = new(big.Int).SetString(qString, 10)
+	if !ok {
+		panic(fmt.Sprintf("Bad base 10 string %s", qString))
+	}
 }

mimc7/mimc7.go

@@ -75,7 +75,7 @@ func MIMC7HashGeneric(fqR field.Fq, xIn, k *big.Int, nRounds int) *big.Int {
 
 // HashGeneric performs the MIMC7 hash over a *big.Int array, in a generic way, where it can be specified the Finite Field over R, and the number of rounds
 func HashGeneric(iv *big.Int, arr []*big.Int, fqR field.Fq, nRounds int) (*big.Int, error) {
-	if !utils.CheckBigIntArrayInField(arr, constants.fqR.Q) {
+	if !utils.CheckBigIntArrayInField(arr) {
 		return nil, errors.New("inputs values not inside Finite Field")
 	}
 	r := iv
@@ -108,7 +108,7 @@ func MIMC7Hash(xIn, k *big.Int) *big.Int {
 
 // Hash performs the MIMC7 hash over a *big.Int array
 func Hash(arr []*big.Int, key *big.Int) (*big.Int, error) {
-	if !utils.CheckBigIntArrayInField(arr, constants.fqR.Q) {
+	if !utils.CheckBigIntArrayInField(arr) {
 		return nil, errors.New("inputs values not inside Finite Field")
 	}
 	var r *big.Int

utils/utils.go

@@ -6,6 +6,9 @@ import (
 	"fmt"
 	"math/big"
 	"strings"
+
+	"github.com/iden3/go-iden3-crypto/constants"
+	"github.com/iden3/go-iden3-crypto/ff"
 )
 
 // NewIntFromString creates a new big.Int from a decimal integer encoded as a
@@ -87,20 +90,36 @@ func HexDecodeInto(dst []byte, h []byte) error {
 	return nil
 }
 
-// CheckBigIntInField checks if given big.Int fits in a Field Q element
-func CheckBigIntInField(a *big.Int, q *big.Int) bool {
-	if a.Cmp(q) != -1 {
+// CheckBigIntInField checks if given *big.Int fits in a Field Q element
+func CheckBigIntInField(a *big.Int) bool {
+	if a.Cmp(constants.Q) != -1 {
 		return false
 	}
 	return true
 }
 
-// CheckBigIntArrayInField checks if given big.Int fits in a Field Q element
-func CheckBigIntArrayInField(arr []*big.Int, q *big.Int) bool {
+// CheckBigIntArrayInField checks if given *big.Int fits in a Field Q element
+func CheckBigIntArrayInField(arr []*big.Int) bool {
 	for _, a := range arr {
-		if !CheckBigIntInField(a, q) {
+		if !CheckBigIntInField(a) {
 			return false
 		}
 	}
 	return true
 }
+
+// CheckElementArrayInField checks if given *ff.Element fits in a Field Q element
+func CheckElementArrayInField(arr []*ff.Element) bool {
+	for _, aE := range arr {
+		a := big.NewInt(0)
+		aE.ToBigIntRegular(a)
+		if !CheckBigIntInField(a) {
+			return false
+		}
+	}
+	return true
+}
+
+func NewElement() *ff.Element {
+	return &ff.Element{0, 0, 0, 0}
+}