private long? GetCRLNumber(Org.BouncyCastle.X509.X509Crl crlEntry)
        {
            Asn1OctetString extValue = crlEntry.GetExtensionValue(Org.BouncyCastle.Asn1.X509.X509Extensions.CrlNumber);

            if (extValue != null)
            {
                Asn1Object asn1Value = Org.BouncyCastle.X509.Extension.X509ExtensionUtilities.FromExtensionValue(extValue);

                return DerInteger.GetInstance(asn1Value).PositiveValue.LongValue;
            }

            return null;
        }