private static OCSPReq generateOCSPRequest(X509Certificate issuerCert, BigInteger serialNumber) throws OCSPException, IOException {
//Add provider BC
Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
// Generate the id for the certificate we are looking for
CertificateID id = new CertificateID(CertificateID.HASH_SHA1, issuerCert, serialNumber);
// basic request generation with nonce
OCSPReqGenerator gen = new OCSPReqGenerator();
gen.addRequest(id);