SSH兼容私钥

Question

有谁能告诉我如何从Java的RSAPrivateKey生成SSH兼容的私钥？我看了很多帖子但没有为我工作。

KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
        kpg.initialize(2048);
        KeyPair kp = kpg.genKeyPair();

        Writer out = new FileWriter(outfile);
        String encodedPrivateKey = encoder.encodeToString(kp.getPrivate().getEncoded());
        out.write(privKeyPrepend);
        out.write(encodedPrivateKey);
        out.write(privKeyAppend);
        out.close();