Matthew Green is a well-known cryptography professor, currently teaching in the computer science department of Johns Hopkins University in Baltimore. Last week, Green authored a long and interesting blog post about the recent revelations that the National Security Agency (NSA) has, among much else, subverted crypto standards. In his words, "The TL;DR ['too long; didn't read' version] is that the NSA has been doing some very bad things." And Green went on to speculate at some length about what those "bad things" were and what they might mean.

Today, Green's academic dean contacted him to ask that "all copies" of the blog post be removed from university servers. Green said that the move was not "my Dean's fault," but he did not elaborate. Were cryptology professors at Johns Hopkins not allowed to say, as Green had, things like:

I was totally unprepared for today's bombshell revelations describing the NSA's efforts to defeat encryption. Not only does the worst possible hypothetical I discussed appear to be true, but it's true on a scale I couldn't even imagine. I'm no longer the crank. I wasn't even close to cranky enough.

Was basic academic freedom on the line? Had the request even come initially from Johns Hopkins or from outside the school—perhaps someone at the NSA headquarters just up the road from Baltimore?

I asked John Hopkins, and spokesman Dennis O'Shea responded with the school's side of the story:

The university received information this morning that Matthew Green’s blog contained a link or links to classified material and also used the NSA logo. For that reason, we asked Professor Green to remove the Johns Hopkins-hosted mirror site for his blog. Upon further review, we note that the NSA logo has been removed and that he appears to link to material that has been published in the news media. Interim Dean Andrew Douglas will inform Professor Green that the mirror site may be restored.

The statement raised further questions, including: from whom did the school "receive" its information? Why was the school's top administration getting involved in the use of the NSA logo on one professor's individual blog post? What was the point of the request given that Green had also published the post to a mirror hosted at Blogger? Wasn't the whole episode likely to bring far greater traffic to Green's post once word of the takedown request got out?

Late this afternoon, Green shared his side of the story on Twitter (tweets concatenated below for ease of reading):

So listen, I'm trying not to talk about this much because anything I say will make it worse. What I've been told is that someone on the APL [Johns Hopkins' Applied Physics Laboratory—motto: "Enhancing national security through science and technology"] side of JHU discovered my blog post and determined that it was hosting/linking to classified documents. This requires a human since I don't believe there's any automated scanner for this process. It's not clear to me whether this request originated at APL or if it came from elsewhere. All I know is that I received an e-mail this morning from the Interim Dean of the Engineering school asking me to take down the post and to desist from using the NSA logo. He also suggested I should seek counsel if I continued. In any case I made it clear that I would not shut down my non-JHU blog, but I did shut down a JHU-hosted mirror. I also removed the NSA logo. I did not remove any links or photos of NOW PUBLIC formerly classified material, because that would just be stupid. I'm baffled by this entire thing. I hope to never receive an e-mail like that again and I certainly believe JHU (APL) is on the wrong side of common sense and academic freedom, regardless of their obligations under the law. That said, I have no desire to cause trouble for any of the very good people at JHU so I'll keep my posts off JHU property. I have no idea if this was serious or a tempest in a teapot. What I have learned: Twitter is really a terrible way to give this explanation. Ow, my thumbs...

Update: Johns Hopkins has confirmed to Ars that "we did not receive any inquiry from the federal government about the blog or any request from the government to take down the mirror site. (Or of course, the personal site, though that never was taken down and we never asked that it be taken down). As to where the information came from, we are still tracing the path of this event, which all exploded into our notice over the past couple of hours."

Update 2: Thanks to the wonder of Google's cache, here is the original post, NSA logo included.