Enforce len assumption in reverse()

sign/bdn/bdn.go

@@ -66,7 +66,8 @@ func hashPointToR(g kyber.Group, pubs []kyber.Point) ([]kyber.Scalar, error) {
 			return nil, err
 		}
 		if g.Scalar().ByteOrder() == kyber.BigEndian {
-			reverse(b, b)
+			// Safely ignore the err as len(b) == len(b)
+			_, _ = reverse(b, b)
 		}
 
 		coefs[i] = g.Scalar()
@@ -79,17 +80,21 @@ func hashPointToR(g kyber.Group, pubs []kyber.Point) ([]kyber.Scalar, error) {
 // 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 {
+func reverse(dst, src []byte) ([]byte, error) {
 	if dst == nil {
 		dst = make([]byte, len(src))
 	}
+
+	if len(dst) != len(src) {
+		return nil, errors.New("destination length doesn't match the source")
+	}
+
 	l := len(dst)
-	for i, j := 0, l-1; i < (l+1)/2; {
-		dst[i], dst[j] = src[j], src[i]
-		i++
-		j--
+	for left, right := 0, l-1; left < (l+1)/2; left, right = left+1, right-1 {
+		dst[left], dst[right] = src[right], src[left]
 	}
-	return dst
+
+	return dst, nil
 }
 
 type Scheme struct {