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

A shorter variation on Thomas' answer, which does not use a KeyFactory would be:

public static ECPublicKey decodeKey(byte[] encoded) {
  ECNamedCurveParameterSpec params = ECNamedCurveTable.getParameterSpec("secp256k1");
  ECPublicKeySpec keySpec = new ECPublicKeySpec(params.getCurve().decodePoint(encoded), params);
  return new BCECPublicKey("ECDSA", keySpec, BouncyCastleProvider.CONFIGURATION);
}

I assume that encoded was obtained by BCECPublicKey.getQ().getEncoded(bool), i.e. it is a byte 0x2-0x4 followed by one or two affine coordinates of the public point on secp256k1.