GFW主动探测系统研究报告

英文原文来自 https://blog.torproject.org/blog/learning-more-about-gfws-active-probing...

Roya, David, Nick, nweaver, Vern, 和我刚刚完成了关于GFW主动探测系统的研究。这个系统在几年前就被用来探测翻墙工具,比如Tor。我们在之前的博文中介绍过GFW主动探测系统是如何工作的。但有几个问题我们没有回答。比如这个系统的物理结构是怎样的。那些用来主动探测的IP是归GFW所有的么? 有猜测GFW短时间内劫持了部分IP来用来主动探测,但没有证据。这次研究回答了这些问题。

因为这个实验是网络检测,我们从收集数据开始。我们创建了3个数据库,包括了GFW主动探测的小时/月份/年份的数据。这3个不同时段的数据库让我们从不同角度了解GFW主动探测的工作原理。我们公开了其中的两个数据库,你可以重复我们的实验,或者自己分析。

  • 通常来说,如果Tor的某个网桥代理被GFW检测并封锁,它会一直被封锁。但是这意味着网桥代理完全无法访问吗? 我们让中国的VPS一直连接我们控制的网桥代理。我们发现,每25小时,中国的VPS可以短暂的连接到我们的代理网桥。下图显示了这个现象。每个数据点表示中国的VPS试图与网桥代理建立连接。中国联通和中国教育网都有这个周期性现象。有时候,网络安全设备在更新规则时会默认允许所有流量,但我们不知道GFW周期性现象是不是因为这个原因导致的。

  • 我们找到了规律,GFW主动探测的TCP头暗示那几千个IP都来自与同一个地方。下图显示了数据包的初始序号和时间。每个数据点都是一个主动探测连接。如果每个主动探测都是从不同地方发出的,我们应该看到随机的数据点,因为数据包的初始序号是随机选择的。但是下图显示主动探测连接虽然来自不同IP,但是非常有规律。我们认为主动探测的初始序号是按照时间产生的。

 

  • 我们发现GFW主动探测不仅仅针对了Tor。GFW还对 SoftEther 和GoAgent进行了主动探测。这说明主动探测系统是模块化的。GFW工程师能比较简单的对新翻墙软件改进主动探测功能。

  • GFW能(部分的)模拟  vanilla Tor protocol, obfs2, and obfs3 来主动探测网桥代理。有趣的是, node-Tor 因为是使用JavaScript 编写而导致不同的代码实现,从而对主动探测免疫。人为修改了Tor回复能躲避GFW的主动探测,但这应该不是长久之计。

  • 在2012年,主动探测系统每15分钟扫描一次。但现在,主动探测系统能实时扫描。平均来说,中国用户连接Tor网桥代理后半秒内就有主动探测连接。

  • 我们使用 traceroute 发现,GFW的主动探测系统是有状态的,但没有办法重组TCP流。

 

幸运的是,我们有 pluggable transports 来防止主动探测。ScrambleSuitobfs4 能使用预先分享的密钥来防止主动探测。 Meek 使用CDN来代理流量,虽然这不能阻止主动探测,但封锁造成的额外伤害会很大。我们在开发翻墙工具的同时需要注重可用性。大力开发的翻墙工具若很难使用,是没有价值的。这是用户界面的重要性所在。

最后,这是我们的论文数据库和代码,和研究页面。若你有任何问题和反馈,欢迎联系我们

 

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星期四, 11月 30, 2017

关于在中国苹果商店被审查的那674个软件

苹果对中国区的审查行为敞开了大门 - 但这似乎只是冰山一角。

星期二, 5月 23, 2017

Is China establishing cyber sovereignty in the United States?

Last week Twitter came under attack from a DDoS attack orchestrated by the Chinese authorities. While such attacks are not uncommon for websites like Twitter, this one proved unusual. While the Chinese authorities use the Great Firewall to block harmful content from reaching its citizens, it now uses DDoS attacks to take down content that appears on websites beyond its borders. For the Chinese authorities, it is not simply good enough to “protect” the interests of Chinese citizens at home - in their view of cyber sovereignty, any content that might harm China’s interests must be removed, regardless of where the website is located.

And so last week the Chinese authorities determined that Twitter was the target. In particular, the authorities targeted the Twitter account for Guo Wengui (https://twitter.com/KwokMiles), the rebel billionaire who is slowly leaking information about corrupt Chinese government officials via his Twitter account and through his YouTube videos. Guo appeared to ramp up his whistle-blowing efforts last week and the Chinese authorities, in turn, ramped up theirs.

via https://twitter.com/KwokMiles/status/863689935798374401

星期一, 12月 12, 2016

China is the obstacle to Google’s plan to end internet censorship

It’s been three years since Eric Schmidt proclaimed that Google would chart a course to ending online censorship within ten years. Now is a great time to check on Google’s progress, reassess the landscape, benchmark Google’s efforts against others who share the same goal, postulate on the China strategy and offer suggestions on how they might effectively move forward.

flowers on google china plaque

Flowers left outside Google China’s headquarters after its announcement it might leave the country in 2010. Photo: Wikicommons.

What has Google accomplished since November 2013?

The first thing they have accomplished is an entire rebranding of both Google (now Alphabet) and Google Ideas (now Jigsaw). Throughout this blog post, reference is made to both new and old company names.

Google has started to develop two main tools which they believe can help in the fight against censorship. Jigsaw’s DDoS protection service, Project Shield, is effectively preventing censorship-inspired DDoS attacks and recently helped to repel an attack on Brian Krebs’ blog. The service is similar to other anti-DDoS services developed by internet freedom champions and for-profit services like Cloudflare.

星期四, 11月 24, 2016

Facebook: Please, not like this

Facebook is considering launching a censorship tool that would enable the world’s biggest social network to “enter” the China market. Sadly, nobody will be surprised by anything that Mark Zuckerberg decides to do in order to enter the China market. With such low expectations, Facebook is poised to usurp Apple as China’s favorite foreign intelligence gathering partner. If the company launches in China using this strategy they will also successfully erase any bargaining power that other media organizations may hold with the Chinese authorities.

星期二, 7月 05, 2016

GreatFire.org 现在开始测试VPN在中国的速度和稳定性

在中国有一个普遍观念,如果你有一个可以使用的VPN,那么你应该保持沉默。就信息自由而言,这种观念的问题在于获取知识竟成了一种秘密。今天,我们推出一个项目,希望能够摧毁这种模型。

我们最新的网站,翻墙中心,目的在于实时提供那些能够在中国使用的翻墙方案的信息和数据。在2011年以来我们就已经开始收集在中国被屏蔽的网站,现在我们也将增加那些可用的VPN和其他翻墙工具。

我们发布翻墙中心主要有四个目的。

我们的首要目标是助长使用翻墙工具的国人的数量。通过分享我们这些工具的信息和数据,我们希望对更广泛的受众展示那些工具时可以使用的。

我们的第二个目标是通过带来工具性能的透明化来提升中国用户的翻墙体验。我们将会测试工具的速度(流行网站的加载速度)和稳定性(流行网站加载成功的程度)。

我们开发速度测试的目的是要真实反映用户的体验。当用户在网站测速时,浏览器在后台会从10个世界上最流行的网站上下载一些资源文件。根据Alexa排名,这些网站分别是Google, Facebook, YouTube, Baidu, Amazon, Yahoo, Wikipedia, QQ, Twitter and Microsoft Live。速度的结果是简单的计算下载文件文件的大小和下载所需的时间。我们同样也会验证下载的文件是否完整。如果文件的内容是错误的或者在40秒内无法完成下载,我们会标记为失败。这个数据被我们用来生成另一个重要指标-稳定性。

其他的速度测试工具仅仅是通过发送数据到它们自己的服务器来测量上传和下载的速度。这种数据无法反应用户的体验,因为正常的浏览器通常会频繁的发送一系列的请求(而不是上传或下载一个大文件)到许多的服务器,而不止是一个。

我们的第二个指标 - 稳定性 - 是其他的服务通常不会测试的。一个健康的互联网连接应该达到100%的稳定性,除非有人在测试中把网线拔了。但是在中国使用翻墙工具却不是这样。任何时候连接都有可能变得不稳定或十分缓慢。根据请求的大小,最终的地点和代理的方式,一些请求有可能会失败。比较服务的稳定性要比比较速度更加重要。

你可以测试任意的翻墙工具,列表之外的也可以。中国的VPN用户也可以测试他们的工具,测试结果也会添加到数据库中。这些数据都将会对所有人开放。实时的在中国测试是非常重要的,因为VPN随时都可能被封锁或解封。我们欢迎任何的关于测试过程的反馈。有技术能力的用户也可以通过审查我们的javascript代码来获悉我们的测试是如何工作的。

我们郑重的邀请翻墙工具的开发者们向我们提供测试过程的反馈。我们的第三个目标是帮助这些开发人员改进他们的产品,让更多的选择适用于中国的顾客。此外,越多的工具可以工作,就意味着中国当局对翻墙的打击就会越难。

中国的用户都知道,在过去的18个月中当局加紧了对翻墙工具的攻击。而翻墙中心将会吹响反击的号角。反其道而行之,让这不再成为秘密。我们要鼓励人们分享翻墙工具可以工作的信息。

我们的第四个目标就是要为GreatFire.org创造收益。目前GreatFire仍然依靠世界各地的热心人士和组织的捐款。我们希望减少对这些机构的依赖,并探寻GreatFire.org自给自足的道路。用户只需到翻墙中心就能购买任意一款我们目前在测试的付费工具。GreatFire将作为这些工具在中国的经销商,因此VPN供应商会给予我们每个零售的一部分。用户也不必在中国购买这些翻墙服务。

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And I have just completed a GFW Active Detection System. The system in a few years ago was used to detect circumvention tools, such as Tor. We are introduced in a previous blog post how GFW active detection system works. But there are several questions we did not answer. For example, the physical structure of the system is like. Those for active detection of IP is owned by GFW all of it? There is speculation GFW short time hijacked a part of the IP to be used to take the initiative to detect, but there is no evidence. This study answers these questions.

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