// ScalarEncodeTo provides a generic implementation of Scalar.EncodeTo
// based on Scalar.Encode.
func ScalarMarshalTo(s abstract.Scalar, w io.Writer) (int, error) {
buf, err := s.MarshalBinary()
if err != nil {
return 0, err
}
return w.Write(buf)
}
// Simple helper to compute G^{ab-cd} for Theta vector computation.
func thenc(grp abstract.Group, G abstract.Point,
a, b, c, d abstract.Scalar) abstract.Point {
var ab, cd abstract.Scalar
if a != nil {
ab = grp.Scalar().Mul(a, b)
} else {
ab = grp.Scalar().Zero()
}
if c != nil {
if d != nil {
cd = grp.Scalar().Mul(c, d)
} else {
cd = c
}
} else {
cd = grp.Scalar().Zero()
}
return grp.Point().Mul(G, ab.Sub(ab, cd))
}
// ScalarDecodeFrom provides a generic implementation of Scalar.DecodeFrom,
// based on Scalar.Decode, or Scalar.Pick if r is a Cipher or cipher.Stream.
// The returned byte-count is valid only when decoding from a normal Reader,
// not when picking from a pseudorandom source.
func ScalarUnmarshalFrom(s abstract.Scalar, r io.Reader) (int, error) {
if strm, ok := r.(cipher.Stream); ok {
s.Pick(strm)
return -1, nil // no byte-count when picking randomly
}
buf := make([]byte, s.MarshalSize())
n, err := io.ReadFull(r, buf)
if err != nil {
return n, err
}
return n, s.UnmarshalBinary(buf)
}
// Simple helper to verify Theta elements,
// by checking whether A^a*B^-b = T.
// P,Q,s are simply "scratch" abstract.Point/Scalars reused for efficiency.
func thver(A, B, T, P, Q abstract.Point, a, b, s abstract.Scalar) bool {
P.Mul(A, a)
Q.Mul(B, s.Neg(b))
P.Add(P, Q)
return P.Equal(T)
}
// ScalarHex encodes a scalar to hexadecimal
func ScalarHex(suite abstract.Suite, scalar abstract.Scalar) (string, error) {
sbuf, err := scalar.MarshalBinary()
return hex.EncodeToString(sbuf), err
}