How to construct PrivateKey if you know the curve name & raw private key/point?

Question

Requirement: For a given named-curve, send as little data as you can, so that receiver can construct EC PrivateKey.

I am currently using BouncyCastle/SpongyCastle on

Answer 1

I was able to figure out how to re-construct EC PrivateKey from BigInteger D & curve name.

 public static PrivateKey getPrivateKeyFromECBigIntAndCurve(BigInteger s, String curveName) {
    X9ECParameters ecCurve = ECNamedCurveTable.getByName(curveName);
    ECParameterSpec ecParameterSpec = new ECNamedCurveSpec(curveName, ecCurve.getCurve(), ecCurve.getG(), ecCurve.getN(), ecCurve.getH(), ecCurve.getSeed());
    ECPrivateKeySpec privateKeySpec = new ECPrivateKeySpec(s, ecParameterSpec);
    try {
        KeyFactory keyFactory = KeyFactory.getInstance("EC");
        return keyFactory.generatePrivate(privateKeySpec);
    } catch (NoSuchAlgorithmException | InvalidKeySpecException e) {
        e.printStackTrace();
        return null;
    }
}