在java中生成证书链

通常,我可以为新客户创建RSA密钥：

private KeyPair genRSAKeyPair(){
    // Get RSA key factory:
    KeyPairGenerator kpg = null;
    try {
        kpg = KeyPairGenerator.getInstance("RSA");
    } catch (NoSuchAlgorithmException e) {
        log.error(e.getMessage());
        e.printStackTrace();
        return null;
    }
    // Generate RSA public/private key pair:
    kpg.initialize(RSA_KEY_LEN);
    KeyPair kp = kpg.genKeyPair();
    return kp;

}

我生成相??应的证书：

private X509Certificate generateCertificate(String dn,KeyPair pair,int days,String algorithm)
  throws GeneralSecurityException,IOException  {
    PrivateKey privkey = pair.getPrivate();
    X509CertInfo info = new X509CertInfo();
    Date from = new Date();
    Date to = new Date(from.getTime() + days * 86400000l);
    CertificateValidity interval = new CertificateValidity(from,to);
    BigInteger sn = new BigInteger(64,new SecureRandom());
    X500Name owner = new X500Name(dn);

    info.set(X509CertInfo.VALIDITY,interval);
    info.set(X509CertInfo.SERIAL_NUMBER,new CertificateSerialNumber(sn));
    info.set(X509CertInfo.SUBJECT,new CertificateSubjectName(owner));
    info.set(X509CertInfo.ISSUER,new CertificateIssuerName(owner));
    info.set(X509CertInfo.KEY,new CertificateX509Key(pair.getPublic()));
    info.set(X509CertInfo.VERSION,new CertificateVersion(CertificateVersion.V3));
    AlgorithmId algo = new AlgorithmId(AlgorithmId.md5WithRSAEncryption_oid);
    info.set(X509CertInfo.ALGORITHM_ID,new CertificateAlgorithmId(algo));

    // Sign the cert to identify the algorithm that's used.
    X509CertImpl cert = new X509CertImpl(info);
    cert.sign(privkey,algorithm);

    // Update the algorith,and resign.
    algo = (AlgorithmId)cert.get(X509CertImpl.SIG_ALG);
    info.set(CertificateAlgorithmId.NAME + "." + CertificateAlgorithmId.ALGORITHM,algo);
    cert = new X509CertImpl(info);
    cert.sign(privkey,algorithm);
    return cert;

}

然后我生成证书签名请求,并将其保存到csrFile文件：

public static void writeCertReq(File csrFile,String alias,String keyPass,KeyStore ks) 
        throws KeyStoreException,NoSuchAlgorithmException,InvalidKeyException,IOException,CertificateException,SignatureException,UnrecoverableKeyException {

    Object objs[] = getPrivateKey(ks,alias,keyPass.toCharArray());
    PrivateKey privKey = (PrivateKey) objs[0];

    PKCS10 request = null;

    Certificate cert = ks.getCertificate(alias);
    request = new PKCS10(cert.getPublicKey());
    String sigAlgName = "MD5WithRSA";
    Signature signature = Signature.getInstance(sigAlgName);
    signature.initSign(privKey);
    X500Name subject = new X500Name(((X509Certificate) cert).getSubjectDN().toString());
    X500Signer signer = new X500Signer(signature,subject);
    request.encodeAndSign(signer);
    request.print(System.out);
    FileOutputStream fos = new FileOutputStream(csrFile);
    PrintStream ps = new PrintStream(fos);
    request.print(ps);
    fos.close();
}

哪里

private static Object[] getPrivateKey(KeyStore ks,char keyPass[]) 
        throws UnrecoverableKeyException,KeyStoreException,NoSuchAlgorithmException {
    key = null;        
    key = ks.getKey(alias,keyPass);
    return (new Object[]{ (PrivateKey) key,keyPass });
}

现在我应该使用CA私钥对CSR进行签名,但是我无法看到如何在java中实现这一点.我的jks中有“我自己的”CA私钥.

此外,一旦我设法签署CSR,我应该使用签名的CSR链接CA证书：如何在java中完成？

我宁愿不使用bc或其他外部库,只是“sun.security”类.

谢谢.