How to make a Bouncy Castle ECPublicKey

Question

I know the curve name (secp256k1) and the X and Y coordinates of the EC public key.

How do I make a org.bouncycastle.jce.int

Answer 1

In the code which follows, encoded contains 0x04 followed by 32 bytes of X, then 32 bytes of Y.

Alternatively, it can contain 0x02 or 0x03 (dependent on the sign of Y) followed by 32 bytes of X.

public static ECPublicKey decodeKey(byte[] encoded) throws InvalidKeySpecException, NoSuchAlgorithmException, NoSuchProviderException{
    ECNamedCurveParameterSpec params = ECNamedCurveTable.getParameterSpec("secp256k1");
    KeyFactory fact = KeyFactory.getInstance("ECDSA", "BC");
    ECCurve curve = params.getCurve();
    java.security.spec.EllipticCurve ellipticCurve = EC5Util.convertCurve(curve, params.getSeed());
    java.security.spec.ECPoint point = ECPointUtil.decodePoint(ellipticCurve, encoded);
    java.security.spec.ECParameterSpec params2 =EC5Util.convertSpec(ellipticCurve, params);
    java.security.spec.ECPublicKeySpec keySpec = new java.security.spec.ECPublicKeySpec(point,params2);
    return (ECPublicKey) fact.generatePublic(keySpec);
}