Make bdn work with different suites

sign/bdn/bdn.go

@@ -30,7 +30,7 @@ var modulus128 = new(big.Int).Sub(new(big.Int).Lsh(big.NewInt(1), 128), big.NewI
 // other words, find m' where H(m) == H(m')
 // We also use the entire roster so that the coefficient will vary for the same
 // public key used in different roster
-func hashPointToR(pubs []kyber.Point) ([]kyber.Scalar, error) {
+func hashPointToR(g kyber.Group, pubs []kyber.Point) ([]kyber.Scalar, error) {
 	peers := make([][]byte, len(pubs))
 	for i, pub := range pubs {
 		peer, err := pub.MarshalBinary()
@@ -61,12 +61,37 @@ func hashPointToR(pubs []kyber.Point) ([]kyber.Scalar, error) {
 
 	coefs := make([]kyber.Scalar, len(pubs))
 	for i := range coefs {
-		coefs[i] = mod.NewIntBytes(out[i*16:(i+1)*16], modulus128, kyber.LittleEndian)
+		b, err := mod.NewIntBytes(out[i*16:(i+1)*16], modulus128, kyber.LittleEndian).MarshalBinary()
+		if err != nil {
+			return nil, err
+		}
+		if g.Scalar().ByteOrder() == kyber.BigEndian {
+			reverse(b, b)
+		}
+
+		coefs[i] = g.Scalar()
+		coefs[i].SetBytes(b)
 	}
 
 	return coefs, nil
 }
 
+// reverse copies src into dst in byte-reversed order and returns dst,
+// such that src[0] goes into dst[len-1] and vice versa.
+// dst and src may be the same slice but otherwise must not overlap.
+func reverse(dst, src []byte) []byte {
+	if dst == nil {
+		dst = make([]byte, len(src))
+	}
+	l := len(dst)
+	for i, j := 0, l-1; i < (l+1)/2; {
+		dst[i], dst[j] = src[j], src[i]
+		i++
+		j--
+	}
+	return dst
+}
+
 type Scheme struct {
 	blsScheme sign.Scheme
 	sigGroup  kyber.Group
@@ -133,7 +158,7 @@ func (scheme *Scheme) AggregateSignatures(sigs [][]byte, mask *sign.Mask) (kyber
 		return nil, errors.New("length of signatures and public keys must match")
 	}
 
-	coefs, err := hashPointToR(mask.Publics())
+	coefs, err := hashPointToR(scheme.sigGroup, mask.Publics())
 	if err != nil {
 		return nil, err
 	}
@@ -166,7 +191,7 @@ func (scheme *Scheme) AggregateSignatures(sigs [][]byte, mask *sign.Mask) (kyber
 // AggregateSignatures for signatures) using the hash function
 // H: keyGroup -> R with R = {1, ..., 2^128}.
 func (scheme *Scheme) AggregatePublicKeys(mask *sign.Mask) (kyber.Point, error) {
-	coefs, err := hashPointToR(mask.Publics())
+	coefs, err := hashPointToR(scheme.keyGroup, mask.Publics())
 	if err != nil {
 		return nil, err
 	}

sign/bdn/bdn_test.go

@@ -22,7 +22,7 @@ func TestBDN_HashPointToR_BN256(t *testing.T) {
 	p2 := suite.Point().Mul(two, suite.Point().Base())
 	p3 := suite.Point().Mul(three, suite.Point().Base())
 
-	coefs, err := hashPointToR([]kyber.Point{p1, p2, p3})
+	coefs, err := hashPointToR(suite, []kyber.Point{p1, p2, p3})
 
 	require.NoError(t, err)
 	require.Equal(t, "35b5b395f58aba3b192fb7e1e5f2abd3", coefs[0].String())