File file = new File(nomeFich + File.separator + "public.key");
File file2 = new File(nomeFich + File.separator + "private.key");

KeyPair keyPair = KeyPair.createKeyPair();

DataOutputStream dos = new DataOutputStream(new FileOutputStream(file));

dos = new DataOutputStream(new FileOutputStream(file));
dos.write(keyPair.getPublic().exportKey());
dos.close();

dos = new DataOutputStream(new FileOutputStream(file2));
dos.write(keyPair.getPrivate().exportKey());
dos.close();