class PKCS1Util {

    public static RSAPrivateCrtKeySpec decodePKCS1(byte[] keyBytes) throws IOException {
        DerParser parser = new DerParser(keyBytes);
        Asn1Object sequence = parser.read();
        sequence.validateSequence();
        parser = new DerParser(sequence.getValue());
        parser.read();

        return new RSAPrivateCrtKeySpec(next(parser), next(parser),
                                        next(parser), next(parser),
                                        next(parser), next(parser),
                                        next(parser), next(parser));
    }

    private  PKCS1Util();

}