Adding a test for hashToScalar.

Author: armfazh

hash.go

@@ -1,10 +1,12 @@
 package h2c
 
 import (
+	"fmt"
 	"math/big"
 
 	M "github.com/armfazh/h2c-go-ref/mapping"
 	C "github.com/armfazh/tozan-ecc/curve"
+	"github.com/armfazh/tozan-ecc/field"
 	GF "github.com/armfazh/tozan-ecc/field"
 )
 
@@ -21,7 +23,10 @@ type HashToPoint interface {
 	GetHashToScalar() HashToScalar
 }
 
+// HashToScalar allows to hash string into the field of scalars used for scalar multiplication.
 type HashToScalar interface {
+	// GetScalarField returns the field of scalars.
+	GetScalarField() GF.Field
 	// Hash returns an element of a field given a byte string.
 	Hash(in []byte) GF.Elt
 }
@@ -32,11 +37,11 @@ type fieldEncoding struct {
 	L   uint
 }
 
+func (f *fieldEncoding) GetScalarField() GF.Field { return f.F }
+
 // Hash deterministically hashes a string msg of any length into
 // an element of the given finite field.
-func (f *fieldEncoding) Hash(msg []byte) GF.Elt {
-	return f.hashToField(msg, 1)[0]
-}
+func (f *fieldEncoding) Hash(msg []byte) GF.Elt { return f.hashToField(msg, 1)[0] }
 
 // hashToField is a function that hashes a string msg of any length into an
 // element of a finite field.
@@ -64,16 +69,23 @@ func (f *fieldEncoding) hashToField(
 }
 
 type encoding struct {
-	E           C.EllCurve
-	Mapping     M.MapToCurve
-	Field       *fieldEncoding
-	ScalarField GF.Field
+	E       C.EllCurve
+	Mapping M.MapToCurve
+	Field   *fieldEncoding
 }
 
 func (e *encoding) GetCurve() C.EllCurve { return e.E }
 
 type encodeToCurve struct{ *encoding }
 
+func (e *encoding) GetHashToScalar() HashToScalar {
+	return &fieldEncoding{
+		F:   field.NewFp(fmt.Sprintf("%v", e.E.Order()), e.E.Order()),
+		Exp: e.Field.Exp,
+		L:   e.Field.L,
+	}
+}
+
 func (s *encodeToCurve) IsRandomOracle() bool { return false }
 func (s *encodeToCurve) Hash(in []byte) C.Point {
 	u := s.Field.hashToField(in, 1)
@@ -82,14 +94,6 @@ func (s *encodeToCurve) Hash(in []byte) C.Point {
 	return P
 }
 
-func (e *encoding) GetHashToScalar() HashToScalar {
-	return &fieldEncoding{
-		F:   e.ScalarField,
-		Exp: e.Field.Exp,
-		L:   e.Field.L,
-	}
-}
-
 type hashToCurve struct{ *encoding }
 
 func (s *hashToCurve) IsRandomOracle() bool { return true }

suite_test.go

@@ -55,9 +55,10 @@ func (v vectorSuite) test(t *testing.T) {
 	if err != nil {
 		t.Skipf(err.Error())
 	}
-	//hashToScalar := hashToCurve.GetHashToScalar()
+	hashToScalar := hashToCurve.GetHashToScalar()
 	E := hashToCurve.GetCurve()
 	F := E.Field()
+	maxScalar := hashToScalar.GetScalarField().Order()
 	for i := range v.Vectors {
 		var x, y []interface{}
 		for _, xi := range strings.Split(v.Vectors[i].P.X, ",") {
@@ -73,12 +74,11 @@ func (v vectorSuite) test(t *testing.T) {
 			t.Fatalf("suite: %v\ngot:  %v\nwant: %v", v.SuiteID, got, want)
 		}
 
-		// TODO: test HashToScalar
-		// gotH2S := hashToScalar.Hash([]byte(v.Vectors[i].Msg))
-		// var wantH2S field.Elt // TATIANA: how do I get the "want" value here?
-		// if !F.AreEqual(gotH2S, wantH2S) {
-		// 	t.Fatalf("suite: %v\ngot:  %v\nwant: %v", v.SuiteID, gotH2S, wantH2S)
-		// }
+		kElt := hashToScalar.Hash([]byte(v.Vectors[i].Msg))
+		kInt := kElt.Polynomial()[0]
+		if kInt.Sign() < 0 || kInt.Cmp(maxScalar) >= 0 {
+			t.Fatalf("suite: %v\ngot:  %v", v.SuiteID, kInt)
+		}
 	}
 }
 

suites.go

@@ -8,7 +8,6 @@ import (
 
 	C "github.com/armfazh/h2c-go-ref/curve"
 	M "github.com/armfazh/h2c-go-ref/mapping"
-	"github.com/armfazh/tozan-ecc/field"
 )
 
 // SuiteID is the identifier of supported hash to curve suites.
@@ -54,8 +53,7 @@ func (id SuiteID) Get(dst []byte) (HashToPoint, error) {
 				Exp: exp,
 				L:   s.L,
 			},
-			ScalarField: field.NewFp(fmt.Sprintf("%v", E.Order()), E.Order()),
-			Mapping:     m,
+			Mapping: m,
 		}
 		if s.RO {
 			return &hashToCurve{e}, nil