The certificate in that link is just a self-signed certificate, not something signed by a CA:
Issuer: C=US, ST=Some-State, O=github.com, OU=github.com, CN=github.com
Subject: C=US, ST=Some-State, O=github.com, OU=github.com, CN=github.com
So your browser will warn you that you are not making a secure connection. Firefox users, for instance, will have to make 5 clicks to get through that warning and visit the page.
I think "China turns off SSL access to GitHub" might be a more appropriate title.
If this is real, then the Chinese may have collected some interesting statistics regarding the percentage of developers who don't care about certificate issues.
I didn't see the cert appear over the wire myself, but I'm in China at the moment and spent part of this week in communication with the Gentoo and Debian release engineering teams suggesting they revisit perceived issues in their respective key distribution processes and documentation (issues focused on automated validation of install media; not individual packages). Gentoo was already working on it and Debian got back to me pretty quick. I don't feel I was wasting my time now.
Really, we need a key distribution and trust anchor solution for the masses, as Moxie has spoken about, that includes 'trust agility'. IIRC the latest iteration of his proposed solution there is http://tack.io/
It's worth pointing out that many governments have MITM and warrantless surveillance systems, not only the Chinese. For more background see http://wikileaks.org/spyfiles/ which summarizes "Mass interception of entire populations is not only a reality, it is a secret new industry spanning 25 countries." and Jacob Applebaum's keynote at 29C3, https://www.youtube.com/watch?v=QNsePZj_Yks (Youtube is also banned in China).
(edit: posted beneath this thread as moxie is one of the community's most respected parties in this area and just posted, but had some extra info in here! :)
This seems really sloppy for China. Without further proof, I don't think it was the govt.
It's only "sloppy," though, when conceptualized as a MITM. China does have an extensive history of censoring access to sites, and recently censored access to GitHub entirely IIRC. It could be that they decided to block SSL access, but allow HTTP access, and this is how they implemented that.
I agree that this may be a further extending of the "New Years train ticket" block on Github.
It may also be new toying after the recent "experiment". Leaving Github without SSL inside China still makes trouble - China's insidious corruption at the very top is subtle, incremental small steps, all designed for the "long game".
It may also be raw mercantilism ... as with Google, Twitter, and Facebook long before this.
It should be 中国研究 but you said 中文研究, which means Chinese text research.
The level of sophistication that the GFW seems to be achieving is disturbing. We've had certificate attacks before, perhaps they are testing something out that will be deployed more broadly to solve there "gmail" problem?
Appreciate your insight - thanks for weighing in on this.