Function RecoverSecret

share/poly.go:174–200

RecoverSecret reconstructs the shared secret p(0) from a list of private shares using Lagrange interpolation.

(g kyber.Group, shares []*PriShare, t, n int)

// RecoverSecret reconstructs the shared secret p(0) from a list of private
// shares using Lagrange interpolation.
func RecoverSecret(g kyber.Group, shares []*PriShare, t, n int) (kyber.Scalar, error) {
	x := xScalar(g, shares, t, n)

	if len(x) < t {
		return nil, errors.New("share: not enough shares to recover secret")
	}

	acc := g.Scalar().Zero()
	num := g.Scalar()
	den := g.Scalar()
	tmp := g.Scalar()

	for i, xi := range x {
		num.Set(shares[i].V)
		den.One()
		for j, xj := range x {
			if i == j {
				continue
			}
			num.Mul(num, xj)
			den.Mul(den, tmp.Sub(xj, xi))
		}
		acc.Add(acc, num.Div(num, den))
	}

	return acc, nil
}

func xScalar(g kyber.Group, shares []*PriShare, t, n int) map[int]kyber.Scalar {
	x := make(map[int]kyber.Scalar)