4step-green-verification.java

 // 4 - create CborObject MAP and retrieve Kid and Signature
CBORObject messageObject = CBORObject.DecodeFromBytes(outputStream.toByteArray());
byte[] coseSignature = messageObject.get(3).GetByteString();
byte[] protectedHeader = messageObject.get(0).GetByteString();
byte[] content = messageObject.get(2).GetByteString();
byte[] dataToBeVerified = getValidationData(protectedHeader, content);
CBORObject unprotectedHeader = messageObject.get(1);
byte[] kid = getKid(protectedHeader, unprotectedHeader);

// ....

private static byte[] getValidationData(byte[] protectedHeader, byte[] content) {
    return CBORObject.NewArray().
            Add("Signature1").
            Add(protectedHeader).
            Add(new byte[0]).
            Add(content).EncodeToBytes();
}

private static byte[] getKid(byte[] protectedHeader, CBORObject unprotectedHeader) {
  CBORObject key = HeaderKeys.KID.AsCBOR();
  CBORObject kid;
  if (protectedHeader.length != 0) {
      try {
          kid = CBORObject.DecodeFromBytes(protectedHeader).get(key);
          if (kid == null) {
              kid = unprotectedHeader.get(key);
          }
      } catch (Exception var8) {
          kid = unprotectedHeader.get(key);
      }
  } else {
      kid = unprotectedHeader.get(key);
  }
  return kid.GetByteString();
}

Related to medium article
https://gae-piaz.medium.com/green-pass-qr-code-signature-verification-java-f742079cc88