无法在Ubuntu 14.04中通过命令行安装Composer？

Question

我无法通过以下方式在Ubuntu 14.04上安装Composer：

sudo curl -sS https://getcomposer.org/installer | 的PHP

我收到错误消息：

#!/usr/bin/env php
Some settings on your machine make Composer unable to work properly.
Make sure that you fix the issues listed below and run this script again:

The json extension is missing.
Install it or recompile php without --disable-json

The openssl extension is missing, which means that secure HTTPS transfers are impossible.
If possible you should enable it or recompile php with --with-openssl

当前的PHP版本：

PHP 5.5.3 (cli) (built: Feb  9 2015 12:47:41) 
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies